TOEFL Reading Comprehension

1. Methodology & Mathematics

1.1. In science, a theory is a reasonable explanation of observed events that are related. A theory often involves an imaginary model that helps scientists picture the way an obseved event could be produced. A good example of this is found in the kinetic molecular theory, in which gases are pictured as being made up of many small particles that are in constant motion.

A useful theory, in ad***ion to explaining past observations, helps to predict events that have not as yet been observed. After a theory has been publicized, scientists design experiments to test the theory. If observations confirm the scientists'' predictions, the theory is supported. If observations do not confirm the predictions, the scientists must search further. There may be a fault in the experiment, or the theory may have to be revised or rejected.

Science involves imagination and creative thinking as well as collecting information and performing experiments. Facts by themselves are not science. As the mathematician Jules Henri Poincare said: "Science is built with facts just as a house is built with bricks, But a collection of facts cannot be called science any more than a pile of bricks can be called a house. "

Most scientists start an investigation by finding out what other scientists have learned about a particular problem. After known facts have been gathered, the scientist comes to the part of the investigation that requires considerable imagination. Possible solutions to the problem are formulated. these possible solutions are called hypotheses.

In a way, any hypothesis is a leap into the unknown. It extents the scientist''s thinking beyond the known facts. The scientist plans experiments, performs calculations and makes observations to test hypotheses. For without hypotheses, further investigation lacks purpose and direction. When hypotheses are confirmed, they are incorporated into theories.


1.2. It is said that mathematics is the base of all other sciences, and that arithmetic, the science of numbers, is the base of mathematics. Numbers consist of whole number (integers) which are formed by the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 and by the combinations of them. For example, 247 õ?" two hundred and forty seven õ?" is a number formed by three digits. Parts of numbers smaller than 1 are sometimes expressed in terms of fractions, but in scientific usage they are given as decimals. This is because it is easier to perform the various mathematical operations if decimals are used instead of fractions. The main operations are: to add, subtract, multiply, and divide; to square, cube, or raise to any other power; to take a square, cube, or raise to any other roots, and to find a ratio or proportion between pairs of numbers or a series of numbers. Thus, the decimal, or ten-scale, system is used for scientific purposes throughout the world, even in countries whose national system of weights and measurements are based upon other scales. The other scale in general use nowadays in the binary, or two-scale, in which numbers are expressed by combinations of only two digits, 0 and 1. Thus, in the binary scale, 2 is expressed as 010, 3 is given as 011, 4 is represented as 100, etc. This scale is perfectly adapted to the õ?ooff-onõ? pulses of electricity, so it is widely used in electronic computers. Because of its simplicity it is often called õ?othe lazy schoolboyõ?Ts dream!õ?.


1.3. Marjorie Rice was an unlikely candidate for the role of mathematical innovator. She had no formal education in mathematics save a single course required for graduation from high school in 1939. Nonetheless, in 1975 she took up a problem that professional mathematicians had twice left for dead, and showed how much life as in it still.

The problem was tessellation, or tiling of the plane, involves taking a single closed figure a triangle, for example, or a rectangle and fitting it together with copies of itself so that a plane is covered without any gaps or overlap. A region of this plane would look rather like a jigsaw puzzle whose pieces are all identical. Rice worked primarily with polygons, which consist only of straight lines. More specifically, she worked with convex polygons, in which the line joining any two points on the polygon lies entirely within the polygon itself or on one of its edges (A five-pointed star, for example, does not qualify as a convex polygon. )

By the time Rice took up tiling, its basic properties had been established. Obviously, any square can tile the plane, as many kitchen floors have demonstrated. Equilateral triangles are also a fairly clear-cut case. There is one other regular polygon(a polygon whose angles, and sides, are equal) that can tile the plane: the hexagon. This fact was established by the ancient Greeks but had long before been exploited by honeybees in building their honeycombs.

And what of irregular polygons? As it turns out any triangle or quadrilateral, no matter how devoid of regularity, will tile the plane. On the other hand, no convex polygon with more than six sides can do so, and the three classes of convex hexagons that can were uncovered by the end of the First World War. So the only real question left by the time Marjorie Rice began her work was which convex pentagons tile the plane.

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2. Physics.

2.1. When a ray of light hits the surface of an object, one or a combination of the following three things happens: the light may be thrown back towards the source of the light (reflection), it may be passed through the object (refraction), or it may be absorbed into the object. Different materials and substances have unique patterns in the way light behaves when it falls upon them. This pattern gives objects their special appearance and color. If an object allows light to pass directly through it, as does a totally clear sheet of glass, it is said to be transparent. If it scatters and diffuses the light, in a manner similar to a frosted pane of glass, it is translucent. Finally, if it obstructs the passage of the light it is deem opaque.

When light is shined upon a reflecting object, it makes a certain angle with an imaginary line that is a right anglers, or õ?onormal,õ? with that object. This angle is called the angle of incidence. The ray that is reflected from the object also makes an angle with the normal line. This is termed the angle of reflection. The law of reflection dictates that the angle of incident is always equal to the angle of reflection. In a reflecting object with a smooth surface, like a mirror; the light reflects back without spreading out; however, if the object is rough, the light does spread out. This explains why light reflected from a mirror form such as a sharp image while that form a piece of cloth forms no image at all. The law of refection holds true in any case.

When light is refractedá it slows down as it passes through the substance. If it enters the object at an angle other than a right angle, this slowing down causes the light to bend at the surface of the substance. This accounts for the well-known example of a pencil appearing to bend if it is placed in a glass of water.

When a material absorbs light, the light either raised the energy level of the materialõ?Ts atoms, or the light may be converted into heat energy. The most common example of the latter is that objects left in sunshine tend to heat up form the absorption of life.


2.2. The modern age is an age of electricity. People are so used to electric lights, radio, televisions, and telephones that it is hard to imagine what life would be like without them. When there is a power failure, people grope about in flickering candlelight, cars hesitate in the streets because there are no traffic lights to guide them, and food spoils in silent refrigerators.

Yet, people began to understand how electricity works only a little more than two centuries ago. Nature has apparently been experimenting in this field for millions of years. Scientists are discovering more and more that the living won may hold many interesting secrets of electricity that could benefit humanity.

All living cells send out tiny pulses of electricity. As the heart beats, it set out pulses of recorded, they form an electrocardiogram, which a doctor can study to determine how well the heart is working. The brain, too, sends out brain waves of electricity, which can be recorded in an electroenephalogram. The electric currents generated by most living cells are extremely smalloften so small that sensitive instruments are needed to record them. But in some animals, certain muscle cells have become so specialized as electrical generators that they do not work as muscle cells at all. When large numbers of these cells are linked together, the effects can be astonishing.

The electric eel is an amazing storage battery It send a jolt of as much as eight hundred volts of electricity through the water in which it lives (An electric house current is only one hundred twenty volts. ). As many as four-fifths of all the cells in the electric eel''s body are specialized for generating electricity, and the strength of the shock it can deliver corresponds roughly to the length of its body.


2.3. The word laser was coined as an acronym for Light Amplification by the Stimulated Emission of Radiation. Ordinary light, from the Sun or a light bulb, is emitted spontaneously, when atoms or molecules get rid of excess energy by themselves, without any outside intervention. Stimulated emission is different because it occurs when an atom or molecule holding onto excess energy has been stimulated to emit it as light.

Albert Einstein was the first *****ggest the existence of stimulated emission in a paper published in 1917. How ever, for many years physicists thought that atoms and molecules always were much more likely to emit light spontaneously and that stimulated emission thus always would be much weaker. It was not until after the Second World War that physicists began trying to make stimulated emission dominate. They sought ways by which one atom or molecule could stimulate many others to emit light, amplifying it to much higher powers.

The first *****cceed was Charles H. Townes, then at Columbia University in New York. Instead of working with light, however, he worked with microwaves, which have a much longer wavelength, and built a device he called a õ?omaster,õ? for Microwave Amplification by the Stimulated Emission of Radiation. Although he thought of the key idea in 1951, the first master was not completed until a couple of years later. Before long, many other physicists were building masers and trying to discover how to produce stimulated emission at even shorter wavelengths.

The key concepts emerged about 1957. Townes and Arthur Schawlow, then at Bell Telephone Laboratories, wrote a long paper outlining the con***ions need to amplify stimulated emission of visible light waves. At about the same time, similar ideas crystallized in the mid of Gordon Gould, then a 37-year-old graduate student at Columbia, who wrote them down in a series of notebooks. Towners and Schawlow published their ideas in a scientific journal, Physical Review Letters, but Gould filed a patent application. Three decades later, people still argue about who deserves the cre*** for the concept of the laser.


2.4. The semiconductor laser changes electric signals to optical signals and is extensively used in the making Computer Discs (CDs) and fiber optic communications. The recording of computer data and music on a disc is done through a laser beam that makes small pits on the disc. Computer discs with gigantic storage space are referred to as CD-ROM (Compact Disc Read-Only Memory)

Semiconductors are the most frequently used lasers because of their small size, light weight, and limited demand for energy. The semiconductor in the laser is constructed of two different pieces of semiconductor material having unlike electric characteristics. After these two pieces are connected and stimulated by using electric current, the laser emits coherent light which moves in a parallel path, divergent from incoherent light.

Gas lasers are glass tubes filled by a gas or a combination of gases, for instance, neon, helium, carbon dioxide, and krypton. Through stimulating electrical current and using different gases, various light beams can be produced. Carbon dioxide, used as a medium, emits infrared light and it works in the 1 to 1 million watt range. Gas laser are desirable for welding and cutting metals. The low-powered lasers, no more than a few hundred watts, on the other hand, are widely used for cutting wood, fabric, ceramics, and plastic.

In recent years, the uses of the laser have constantly increased. Overall, lasers have several advantages over conventional methods of production. First, they are compact, therefore, they require little space. Second, they need not bee fastened to the work area since they do not jar while operating. Third, the heat energy produced is directed to the exact location they are working on, consequently, they do not warm up or possibly destroy the other parts of the object that is being worked on.

Laser beam programmable controls include information storage retrieval, laser surgery, holography, high-speed scanner, land laser printing.


2.5. In this era of increased global warming and diminishing fossil fuel supplies, we must begin to put a greater priority of harnessing alternative energy sources. Fortunately, there are a number of readily available, renewable resources that are both cost-effective and earth-friendly. Two such resources are solar power and geothermal power.

Solar energy, which reaches the earth through sunlight, is so abundant that it could meet the needs of worldwide energy consumption 6,000 times over. And solar energy is easily harnessed through the use of photovoltaic cells that convert sunlight into electricity. In the United States alone, more than 100,000 homes are equipped with solar electric systems in the form of solar panels or solar roof tiles. And in other parts of the world, including many developing countries, the use of solar systems is growing steadily.

Another alternative energy source, which is abundant in specific geographical areas, is geothermal power, which creates energy by tapping heat from below the surface of the earth. Hot water and steam that are trapped in underground pools are pumped to the surface and used to run a generator, which produces electricity. Geothermal energy is 50,000 times more abundant than the entire known supply of fossil fuel resources. And as with solar power, the technology needed to utilize geothermal energy is fairly simple. A prime example of effective geothermal use is in Iceland, a region of high geothermal activity, where over 80 percent of private homes are heated by geothermal power.

Solar and geothermal energy are just two of a number of promising renewable alternatives to conventional energy sources. The time is long overdue to invest in the development and use of alternative energy on a global scale.


2.7. Almon Strowger, an American engineer, constructed the first automatic telephone switching system, which had a horizontal, bladelike contact arms, in 1891. The first commercial switchboard based on his invention opened in La Porte, Indiana, a year later and was an instant success with business users. To access the system, the caller pressed buttons to reach the desired number and turned the handle to activate the telephone ringer. During the same year, Stowgerõ?Ts step-by-step call advancement technology was implemented in the long-distance service between New York and Chicago when it proved to have the capacity of carrying signals through cable-joint extensions.

The first actual dial telephones, patented by Lee De Forest in 1907, were installed in Milwaukee in 1896. In 1912, their sound transmittal apparatus adapted an electronic tube to function as an amplifier. Transatlantic radio-telephone service linked New York and London in 1927. However, the long distance coaxial cable, which was hailed as unprecedented, came on the scene in 1936 connecting New York and Philadelphia. The Bell Laboratories research facility came up with the transistor to replace the cumbersome vacuum tube, thus diminishing the size of the electronic switch system to about 10 percent of that of the original. Crossbar switching, installed in terminals in 1938, operated on the principle of an electromagnetic force, which rotated horizontal and vertical bars within a rectangular frame and brought contacts together in a split second. A technological breakthrough in the form of underseas cables between the United States and Hawaii was implemented almost twenty years later. An extension was connected to Japan in 1964.

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Được nguyenthanhchuong sửa chữa / chuyển vào 19:18 ngày 20/07/2003

3.Chemistry
3.1. Hydrogen, the lightest and simplest of the elements, has several properties that make it valuable for many industries. It releases more heat per unit of weight than any other fuel. In rocket engines, tons of hydrogen and oxygen are burned, and hydrogen is used with oxygen for welding torches that produce temperatures as high as 4,000 degrees F and can be used in cutting steel. Fuel cells to generate electricity operate on hydrogen and oxygen.
Hydrogen also serves to prevent metals from tarnishing during heat treatments by removing the oxygen from them. Although it would be difficult to remove the oxygen by itself, hydrogen readily combines with oxygen to form water, which can be heated to steam and easily removed.
Hydrogen is also useful in the food industry for a process known as hydrogenation. Products such as margarine and cooking oils are changed from liquids to semisolids by adding hydrogen to their molecules. Soap manufactures also use hydrogen for this purpose.
Hydrogen is also one of the coolest refrigerants. It does not become a liquid until it reaches temperatures of -425 degrees F. Pure hydrogen gas is used in large electric generators to cool the coils. In ad***ion, in the chemical industry, hydrogen is used to produce ammonia, gasoline, methyl alcohol, and many other important products.
3.2. The elements other than hydrogen and helium exist in such small quantities that it is accurate to say that the universe is somewhat more than 25 percent helium by weight and somewhat less than 75 percent hydrogen.
Astronomers have measured the abundance of helium throughout our galaxy and in other galaxies as well. Helium has been found in old stars, in relatively young ones, in interstellar gas, and in the distant objects known as quasars. Helium nuclei have also been found to be constituents of cosmic rays that fall on the earth (cosmic "rays"are not really a form of radiation; they consist of rapidly moving particles of numerous different kinds). It doesn''t seem to make very much difference where the helium is found. Its relative abundance never seems to vary much. In some places, there may be slightly more of it: in others, slightly less, but the ratio of helium to hydrogen nuclei always remains about the same.
Helium is created in stars. In fact, nuclear reactions that convert hydrogen to helium are responsible for most of the energy that stars produce. However, the amount of helium that could have been produced in this manner can be calculated, and it turns out to be no more than a few percent. The universe has not existed long enough for this figure to be significantly greater. Consequently, if the universe is somewhat more than 25 percent helium now, then it must have been about 25 percent helium at a time near the beginning.
However, when the universe was less than one minute old, no helium could have existed. Calculations indicate that before this time temperatures were too high and particles of matter were moving around much too rapidly. It was only after the one- minute point that helium could exist. By this time, the universe had cooled sufficiently that neutrons and protons could stick together. But the nuclear reactions that led to the formation of helium went on for only a relatively short time. By the time the universe was a few minutes old, helium production had effectively ceased.
3.3. By long-standing convention all meteorites are assigned to three broad divisions on the basis of two kinds of material that they contain: metallic nickel-iron(metal)and silicates, which are compounds of other chemical elements with silicon and oxygen. As their name suggests, the iron meteorites consist almost entirely of metal. At the opposite extreme, the stony meteorites consist chiefly of silicates and contain little or no metal. A third category, stony-irons, includes those meteorites that contain similar amounts of metal and silicates. Since meteoritic metal weighs more than twice as much as the same volume of meteoritic silicates, these three kinds of meteorites can usually be distinguished by density, without more elaborate tests.
The stony meteorites can also be subdivided into two categories by using nothing more complicated than a magnifying glass. The great majority of such meteorites are chondrites, which take their name from tiny, rounded objects -chondrules -that occur in most of them and are among their most puzzling features. The rest of the stony meteorites lack chondritic texture and are therefore called achondrites. Achondrites vary widely in texture, composition, and history.
Irons, stony-irons, chondrites, and achondrites are by no means equally abundant among observed meteorites: chondrites are much more common than all other kinds of meteorites put together. The irons, which are usually prominent in museum displays, are really quite uncommon. Curators like to highlight iron meteorites because many of them are large and their internal structure is spectacular in polished, etched slices. A stony meteorite has a beauty of its own, but it only appears under the microscope: to the unaided eye, stony meteorites appear to be-indeed they are-rather homely black or gray rocks.
To go further with meteorite classification, it is necessary to be more specific about the minerals that make up a meteorite: which silicates are present, and what kind of metal? To answer these questions, one needs to see more detail than is visible to the unaided human eye.
3.4. Nitinol is one of the most extraordinary metals to be discovered this century. A simple alloy of nickel and titanium, nitinol has some perplexing properties. A metal with a memory, it can be made to remember any shape into which it is fashioned, returning to shape whenever it is heated.
For example, a piece of nitinol wire bent to form a circle that is then heated and quenched will remember this shape. It may then be bent or crumpled, but on reheating, will violently untwist, reforming its original shape. This remarkable ability is called Shape Memory Effect (SME): other alloys, such as brasses, are known to posses it to a limited extent. No one fully understands SME, and nitinol remains particularly perplexing, for, whenever it performs this peculiar feat, it appears to be breaking the laws of thermodynamics by springing back into shape with greater force than was used to deform it in the first place.
But not only is nitinol capable of remembering. It also has the ability to "learn". If the heating -cooling -crumpling -reheating process is carried out sufficiently often, and the metal is always crumpled in exactly the same way, the nitinol will not only remember its original shape, but gradually it learns to remember its crumpled form as well, and will begin to return to the same crumpled shape every time it is cooled. Eventually, the metal will crumple and uncrumple, totally unaided, in response to changes in temperature and without any sign of metal fatigue.
Engineers have produced prototype engines that are driven by the force of nitinol springing from one shape to another as it alternately encounters hot and cold water. The energy from these remarkable engines is, however, not entirely free: heat energy is required to produce the temperature differences needed to run the engine. But the optimum temperatures at which the metal reacts can be controlled by altering the proportions of nickel to titanium: some alloys will even perform at room temperature. The necessary temperature range between the warm and the cold can be as little as twelve degrees centigrade.
Technique is of no use unless it is combined with musical knowledge and understanding. Great artists are those who are so thoroughly at home in the language of music that they can enjoy performing works written in any century.
3.5. Glass is a remarkable substance made from the simplest raw materials. It can be colored or colorless, monochrome or polychrome, transparent, translucent, or opaque. It is lightweight impermeable to liquids, readily cleaned and reused, durable yet fragile, and often very beautiful Glass can be decorated in multiple ways and its optical properties are exceptional. In all its myriad forms ăC as table ware, containers, in architecture and design ăC glass represents a major achievement in the history of technological developments.
Since the Bronze Age about 3, 000 B. C. , glass lias been used for making various kinds of objects. It was first made from a mixture of silica, line and an alkali such as soda or potash, and these remained the basic ingredients of glass until the development of lead glass in the seventeenth century. When heated, the mixture becomes soft and malleable and can be formed by various techniques into a vast array of shapes and sizes. The homogeneous mass thus formed by melting then cools to create glass, but in contrast to most materials formed in this way (metals, for instance), glass lacks the crystalline structure normally associated with solids, and instead retains the random molecular structure of a liquid. In effect, as molten glass cools, it progressively stiffens until rigid, but does so without setting up a network of interlocking crystals customarily associated with that process. This is why glass shatters so easily when dealt a blow. Why glass deteriorates over time, especially when exposed to moisture, and why glassware must be slowly reheated and uniformly cooled after manufacture to release internal stresses Induced by uneven cooling.
3.6. Combustion is the scientific name for burning. Although there are many types of combustion, the basic process is the same: Oxygen from the air combines with a material that can burn. Heat is then produced from this reaction. If the process occurs very quickly, flames or an explosion can result. When combustion occurs under controlled con***ions, it can produce useful energy. Such controlled combustion is what drives the engines that power out cars.
Gasoline is burned within each cylinder of an engine in a controlled fashion. The role of the engine is to convert chemical energy stored in the gasoline into work. This controlled combustion results in a great force which acts on a piston. The piston then turns a crankshaft which, using a rotary motion, is then used to propel the car. The combustion process in the piston occurs over a four-stroke cycle. This cycle include two up and two down movements of the piston during the combustion of a single introduction of fuel. These four strokes are: intake, compression, power, and exhaust.
As the intake stroke begins, a valve opens at the top of the cylinder, which allows an air-fuel mixture to fill the expanding chamber. When the piston reaches the bottom of the intake stroke, the valve closes, trapping the air-fuel mixture inside. The upward stroke that immediately follows compresses the mixture to about ten percent of its original volume. The downward power stroke is the result of the explosion that occur when spark plug releases up to 30,000 volts of electricity. The force which drives the piston downward can equal up to three tons. Finally, the cycle in completed with the upward exhaust stroke. When the piston has reached the bottom during the power stroke, the exhaust valve opens. As the piston rises in the chamber, it forces out the remaining combustion gases. When the piston again reaches the top of the chamber, it is ready to start the four-stroke cycle all over again.
The ideal air-to-fuel ration for gasoline engines in automobiles is 15:1 (fifteen parts of air to one part of fuel). A õ?orichõ? mixture has less air and more fuel, and thus a lower ratio (10:1). A õ?oleanõ? mixture has a higher ratio (20:1). The only time a mixture richer than 15:1 is required is when starring a cold engine. When the engine is cold, the gasoline is not vaporizing readily. By manipulating the choke, air intake is reduced. At such times, closing the choke on the carburetor provides the necessary rich mixture. To help a cold engine start easily, gasoline manufacturers also produce a blend of gasoline that contains special hydrocarbons that vaporize at low temperatures. But at normal operating fouls the spark plugs, and causes pollution. A lean mixture can lead to even higher costs in the long run, since it can cause the valves and pistons to burn, warp, and even crack.
3.7. A seventeenth-century theory of burning proposed that anything that burns must contain material that the theorists called "phlogiston. " Burning was explained as the release of phlogiston from the combustible material to the air. Air was thought essential, since it had to provide a home for the released phlogiston. There would be a limit to the phlogiston transfer, since a given volume of air could absorb only so much phlogiston. When the air had become saturated, no ad***ional amounts of phlogiston could leave the combustible substance, and the burning would stop. Burning would also stop when the combustible substance was emptied of all its phlogiston.
Although the phlogiston theory was self-consistent, it was awkward because it required that imaginative, even mysterious, properties be ascribed to phlogiston. Phlogiston was elusive. No one had ever isolated it and experimentally determined its properties. At times it seemed to show a negative weight: the residue left after burning weighed more than the material before burning. This was true, for example, when magnesium burned. Sometimes phlogiston seemed to show a positive weight, when, for example, wood burned, the ash weighed less than the starting material. And since so little residue was left when alcohol, kerosene, or high-grade coal burned, these obviously different materials were thought to be pure or nearly pure phlogiston.
In the eighteenth century, Antoine Lavoisier, on the basis of careful experimentation, was led to propose a different theory of burning, one that required a constituent of air- later shown to be oxygen- for combustion. Since the weight of the oxygen is always added, the weight of the products of combustion, including the evolved gases, would always be greater than the weight of the starting material.
Lavoisier''s interpretation was more reasonable and straightforward than that of the phlogiston theorists. The phlogiston theory, always clumsy, became suspect, eventually fell into scientific disrepute, and was replaced by new ideas.
3.8. Evaporation and recondensation of water entail an important step in purification called distillation. During evaporation, water molecules rise from the surface of a solution, but the salts and other minerals that had been dissolved in it crystallize and precipitate from the solution, forming sediment. As water is heated, its molecules acquire sufficient energy to break the weak pull between them and rise in the form of vapor. As the vapor temperature falls, the attractive force between molecules grows to hold the molecules together, resulting in condensation. When water vapor recondenses, it consists only of water. Pure water used in chemical laboratories is obtained by this process. Water from the ocean and other sources is perpetually evaporated, purified, and eventually recondensed in the atmosphere.
Water can be purified by distillation or other methods. The hydrological cycle of the earth consists of water vapor entering the atmosphere through evaporation and coming back via condensation and precipitation. Since oceans occupy approximately 70 percent of the planetõ?Ts surface, the largest amount of water in the cycle is derived from the evaporation of water from the ocean surfaces. A secondary source of water vapor lies in rivers, lakes, and soil. Plant transpiration occurs in areas with heavily vegetated land and adds to the vapor in the cycle.
3.9. The art or science of alchemy is of great antiquity, for it has been practiced for over two thousand years. It also has along history, for there are still alchemists to be found in continents as far apart as America, Europe, and Asia. Its heyday was from about 800 A.D. to the middle of the seventeenth century, and its practioners ranged from kings, popes, and emperors to minor clergy, merchants, doctors, and clerks.
Alchemy is of a twofold nature, outward or exoteric, and hidden or esoteric. Exoteric alchemy is concerned with attempts to prepare a substance, the philosophersõ?T stone, or simply the Stone, endowed with the power of transmuting the base metals lead, tin copper, iron, and mercury into the precious metals gold and silver. The Stone was cre***ed not only with the power of transmutation but with being able to prolong human life indefinitely. In esoteric alchemy, the transmutation of metals became symbolic of the transformation of men into perfect beings.
Two kinds of alchemy became inextricably mixed with the search for the Stone and mystical belief intertwined.
It has to be remembered that the practical alchemists were well aware that if they succeeded in making gold artificially, their lives might be in great danger from avaricious people.
Even the suspicion that they had discovered the secret was often sufficient to endanger them. One alchemist complained that falling under suspicion, he had to disguise himself, shave off his beard, and put on a wig before he was able to escape, under a false name. He added that he know of people who had been found strangled in their beds simply because they were thought to have found the Stone, though in reality they know no more about it than their murderers.

3.9. The art or science of alchemy is of great antiquity, for it has been practiced for over two thousand years. It also has along history, for there are still alchemists to be found in continents as far apart as America, Europe, and Asia. Its heyday was from about 800 A.D. to the middle of the seventeenth century, and its practioners ranged from kings, popes, and emperors to minor clergy, merchants, doctors, and clerks.
Alchemy is of a twofold nature, outward or exoteric, and hidden or esoteric. Exoteric alchemy is concerned with attempts to prepare a substance, the philosophers?T stone, or simply the Stone, endowed with the power of transmuting the base metals lead, tin copper, iron, and mercury into the precious metals gold and silver. The Stone was cre***ed not only with the power of transmutation but with being able to prolong human life indefinitely. In esoteric alchemy, the transmutation of metals became symbolic of the transformation of men into perfect beings.
Two kinds of alchemy became inextricably mixed with the search for the Stone and mystical belief intertwined.
It has to be remembered that the practical alchemists were well aware that if they succeeded in making gold artificially, their lives might be in great danger from avaricious people.
Even the suspicion that they had discovered the secret was often sufficient to endanger them. One alchemist complained that falling under suspicion, he had to disguise himself, shave off his beard, and put on a wig before he was able to escape, under a false name. He added that he know of people who had been found strangled in their beds simply because they were thought to have found the Stone, though in reality they know no more about it than their murderers.
3.10. Although its purpose and techniques were often magical, alchemy was, in many ways, the predecessor of modern science, especially the science of chemistry. The fundamental premise of alchemy derived from the best philosophical dogma and scientific practice of the time, and the majority of educated persons in the period from 1400 to 1600 believed that alchemy had great merit.
The earliest authentic works on European alchemy are those of the English monk Roger Bacon and the German philosopher St. Albertus Magnus. In their treatises they maintained that gold was the perfect metal and that inferior metals such as lead and mercury were removed by various degrees of imperfection from gold. They further asserted that these base metal could be transmuted to gold by blending them with a substance even more perfect than gold. This elusive substance was referred to as the ?ophilosopher?Ts stonê?. The process was called transmutation.
Most of the early alchemists were early alchemists were artisans who were accustomed to keeping trade secrets and often resorted to cryptic terminology to record the progress of their work. The term sun was used for gold, moon for silver, and the five known planets for base metals. This convention of substituting symbolic language attracted a group of mystical philosophers began to use the artisan?Ts terms in the mystical literature that they produced. Thus, by the fourteenth century, alchemy had developed two distinct groups of practitioners ?" the laboratory alchemist and the literary alchemist. Both groups of alchemists continued to work throughout the history of alchemy, but, of course, it was the literary alchemist who was most like to produce a written record; therefore, much of what is known about the science of alchemy is derived from philosophers rather than from the alchemists who labored in laboratories.
Despite centuries of experimentation, laboratory alchemists failed to produce gold from other materials. However, they did gain wide knowledge of chemical substances, discovered chemical properties, and invented many of the tools and the techniques that are still used by the chemists today. Many of the laboratory alchemists earnestly devoted themselves to the scientific discovery of new compounds and reactions and, therefore, must be considered the legitimate forefathers of modern chemistry. They continued to call themselves alchemists, but they were becoming true chemists.
3.11. Diamond value is based on four characteristics: carat, color, clarity, and cut. A diamond?Ts size is measured by carat weight. There are 100 points in a carat and 142 carats in an ounce. Each point above 1 carat is more valuable than each point below 1 carat. Thus, a stone that weighs more than 1 carats is more valuable per point than a stone that is smaller than 1 carat.
The scale used for rating a diamond?Ts color begins with ?oD,? which means the stone is absolutely colorless and therefore most valuable. ?oE? and ?oF? are almost colorless. All three are good for investments. A stone rated between ?oG? and ?oJ? is good for jewelry. After that the stone take on a slightly yellowish color, which gets deeper as the grade declines.
The clarity of a stone is determined by its lack of carbon spots, inner flaws, and surface blemishes. While most of these are invisible to the unaided eye, they do affect the diamond?Ts brilliance. For jewelry, a diamond rated VVS1 (very very slight imperfections) is as close to flawless as one will find. After that the scale goes to VVS2, VS1, VS2, SI1, SI2, I1, I2, and so on.
The final characteristic is cut. When shaped (round, oval, emerald, marquise, pear, or heart), the diamond should be faceted so that light is directed into the depths of the prism and then reflected outward again. A well-cut diamond will separate the light into different colors when the light is reflected. Only stones of separate the light into different colors when the light is reflected. Only stones of similar shape should have their reflective qualities compared, as some shapes are more reflective than others. For example, the round shape is the most reflective.
3.12. Petroleum products, such as gasoline, kerosene, home heating oil, residual fuel oil, and lubricating oils, come from one source ?" crude oil found below the earth?Ts surface, as well as under large bodies of water, from a few hundred feet below the surface to as deep as 25,000 feet into the earth?Ts interior. Sometimes crude oil is secured by drilling a hole into the earth, but more dry holes are drilled that those producing oil. Either pressure at the source of pumping forces crude oil to the surface.
Crude oil wells flow at varying rates, from about ten to thousands of barrels per hour. Petroleum products are always measured in forty-two-gallon barrels.
Petroleum products vary greatly in physical appearance: thin, thick, transparent, or opaque, but regardless, their chemical composition is made up only two elements: carbon and hydrogen, which form compounds called hydro-carbons. Other chemical elements found in union with the hydrocarbons are few and are classified as impurities. Trace elements are also found, but in such minute quantities that they are disregarded. The combination of carbon and hydrogen forms many thousands of compounds which are possible because of the various positions and unions of these two atoms in the hydrocarbon molecule.
The various petroleum products are refined by heating crude oil and then condensing the vapors. These products are the so-called light oils, such as gasoline, kerosene, and distillate oil. The residue remaining after the light oils are distilled is known as heavy or residual fuel oil and is used mostly for burning under boilers. Ad***ional complicated refining processes rearrange the chemical structure of the hydrocarbons to produce other products, some of which are used to upgrade and increase the octane rating of various types of gasoline.
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4. Astronomy
4.1. A popular theory explaining the evolution of the universe is known as the Big Bang Model. According to the model, at some time between ten and twenty billion years ago, all present matter and energy were compressed into a small ball only a few kilometers in diameter. It was, in effect, an atom that contained in the form of pure energy the fundamental components of the entire universe. Then, at a moment in time that astronomers refer to as T = O, the ball exploded, hurling the energy into space. Expansion occurred. As the energy cooled, most of it became matter in the form of protons, neutrons, and electrons. These basic particles combined to form hydrogen and helium, and continued to expand. Matter formed into galaxies with stars and planets.
4.2. The best-known theory of galactic evolution is the one originated in the 1920s by Edwin P. Hubble. According to this theory, a galaxy begins as a vast accumulation of gases, chiefly hydrogen and helium, rotating about a central point. Thanks to the mutual gravitational attraction of matter, this ?oprotogalaxy? slowly condenses into millions or, more often, billions of stars, collected in a gigantic, roughly spherical cloud. This is what Hubble called an ?oellipsoidal? galaxy.
Over many more millions of years, gravity slowly causes such a galaxy to contract, flatten, and become increasingly congested near its center. Due to the law of the conservation of angular momentum, it also begins to rotate more and more rapidly. The centrifugal force thus generated finally scatters much of the material from the galaxy?Ts outer edges may thousands of light years in*****rrounding space. This is how the familiar ?ospiral? galaxy, with its characteristic compact nucleus and its widely dispersed, spiraling outer arms, is formed.
4.3. In the late 1920?Ts, after examining the photographs of the structural appearance of galaxies, Edwin P. Hubble, the American astronomer, classified the galaxies into three distinct groups. These galaxies are compromised of stars that have diverse structure, unequal degree of brightness, and definitely varied sizes. One group, spirals, is highly luminous and has either a normal or a barred structure. Normal spirals have two arms which radiate from the center of the galaxy to the exterior edges. The two contrasting arms are enclosed in a disk structure made up of stars; however, in the barred structure the arms radiate from the top and the bottom of a bright bar that goes through the nucleus of the galaxy. Barred spirals account for nearly 25 percent of all spirals. Over two-thirds of eminent, highly luminous galaxies are Spirals. The Milky Way and The Andromeda are examples of spiral galaxies. Another group referred to as elliptical galaxies exhibit soft, but dim brightness has tow subgroups: The giant and the dwarf. While the giant elliptical galaxies have countless large luminous stars, the dwarf ellipticals have a smaller number of less luminous stars. Together they make up less than one-third of the galaxies. The last group is the irregularly ?" shaped galaxies, which are non-symmetric, and their pattern is rather chaotic. They account for about 3% of the galaxies and their luminosity is quite grainy. The Magellanic Cloud is an example of an irregularly-shaped galaxy.
4.4. Galaxies are not evenly distributed throughout the universe. A few are found alone, but almost all are grouped in formations termed galactic clusters. These formations should not be confused with stellar clusters, globular clusters of stars that exist within a galaxy. The size of galactic clusters varies enormously, with some clusters containing only a dozen or so members and others containing as many as 10,000. Moreover, galactic clusters themselves are part of larger clusters of clusters, termed superclusters. It is surmised that even clusters of superclusters are possible.
Our galaxy, the Milky Way, is part of a galactic cluster called the Local Group, which has twenty members and is typical in terms of the types of galaxies it contains. There are three large spiral galaxies: Andromeda, the largest galaxy in the group; the Milky Way, the second-largest galaxy; and the Large Cloud of Magellan and the Small Cloud of Magellan. There are four regular elliptical galaxies; the reminders are dwarf ellipticals. Other than our own galaxy, only Andromeda and the Clouds of Magellan can be seen with the naked eye, and the Clouds are visible only from the Southern Hemisphere.
In the vicinity of the Local Group are several clusters, each containing around twelve members. The nearest cluster rich in members is the Virgo Cluster, which contains thousands of galaxies of all types. Like most large clusters, it emits X rays. The Local Group, the small neighboring clusters, and the Virgo Cluster form part of a much larger cluster of clusters ?" the Local Supercluster.
The existence of galactic clusters presented and riddle to scientists for many years ?" the ?omissing mass? problem. Clusters are presumably held together by the gravity generated by their members. However, measurements showed that the galaxies did not have enough mass to explain their apparent stability. Why didn?Tt these clusters disintegrate ? Is it now thought that galaxies contain great amounts of ?odark matter,? which cannot be directly observed but which generates gravitational pull. This matter includes gas, dust, burnt-out stars, and even black holes.
4.5. Until recently, it has been merely an unexplained observation that, in disk-shaped galaxies, certain bright, intensely hot, young stars known to astronomers as O-stars are concentrated along spiral arms radiating from the galactic center. The recent discovery of vast clouds of interstellar gas in our own galaxy, and their subsequent study, indicate both a solution for this puzzle and a mechanism that may, in part, explain how stars are generated out of interstellar gas and dust.
The spiral arms are now thought to have been formed from density waves in the galaxy, induced by gravitational fluctuations that arise at the galactic center. These waves appear to cause scattered clouds of interstellar gas to collect and coalesce into clumps of relatively high concentration.
These gas concentrations, or molecular-cloud complexes, are now thought to consist of about 99 percent molecular, or diatomic, hydrogen, and have been mapped by radio telescope. Molecular hydrogen itself is invisible to radio telescope. But astronomers have been able to use carbon monoxide as a reliable tracer of hydrogen, since the asymmetric molecule of that gas emits specific electromagnetic wave bands as it rotates.
Extensive mapping has established a clear correlation between the cloud complexes and the O-stars on the spiral arms ?" a coincidence too striking, in view of the expanse of ?ounpopulated spacê? even within galaxies, to be the result of change. It is now theorized that pressure waves generated by the O-stars themselves may condense the gas of these clouds to initiate the formation of new stars.
4.6. The old view that every point of light in the sky represented a possible home for life is very foreign to modern astronomy. The stars have surface temperatures of anything from 1,650 degrees to 60,000 degrees or more and are at far higher temperatures inside. A large part of the matter of the universe consists of stellar mater at a temperature of millions of degrees. Its molecules are broken up into atoms, and the atoms broken up, partially or wholly, into their constituent parts. The rest consists, for the most part, of nebular gas or dust. Now the very concept of life implies duration in time. There can be no life ?" or at least no life similar to that we know on earth ?" where atoms change their makeup millions of times a second and no pair of atoms can every stay joined together. It also implies a certain mobility in space, and these tow implications restrict life to the small range of physical con***ions in which the liquid-state is possible. A survey of the universe has shown how small this range is in comparison with that exhibited by the universe as a whole. It is not to be found in the stars, nor in the nebulae out of which the stars are born. Indeed, probably only an infinitesimal fraction of the matter of the universe is in the liquid state.
Actually, we know of no type of astronomical body in which con***ions can be favorable to life except planets like our own revolving around a sun. Even these may be too hot or too cold for life to obtain a footing. In the solar system, for instance, it is hard to imagine life existing on Mercury or Neptune since liquids boil on the former and freeze hard on the latter.

4.7. For 150 years scientists have tried to determine the solar constant, the amount of solar energy that reaches the Earth. Yet, even in the most cloud-free regions of the planet, the solar constant cannot be measured precisely. Gas molecules and dust particles in the atmosphere absorb and scatter sunlight and prevent some wavelengths of the light from ever reaching the ground.
With the advent of satellites, however, scientists have finally been able to measure the Sun?Ts output without being impeded by the Earth?Ts atmosphere. Solar Max, a satellite from the National Aeronautics and Space Administration (NASA), has been measuring the Sun?Ts output since February 1980. Although a malfunction in the satellitê?Ts control system limited its observation for a few years, the satellite was repaired in orbit by astronauts from the space shuttle in 1984. Max?Ts observations indicate that the solar constant is not really constant after all.
The satellitê?Ts instruments have detected frequent, small variations in the Sun?Ts energy output, generally amounting to no more than 0.05 percent of the Sun?Ts mean energy output and lasting from a few days to a few weeks. Scientists believe these fluctuations coincide with the appearance and disappearance of large groups of sunspots on the Sun?Ts disk. Sunspots are relatively dark regions on the Sun?Ts surface that have strong magnetic fields and a temperature about 2,000 degrees Fahrenheit cooler than the rest of the Sun?Ts surface. Particularly large fluctuations in the solar constant have coincided with sightings of large sunspot groups. In 1980, for example, Solar Max?Ts instruments registered a 0.3 percent drop in the solar energy reaching the Earth. At that time a sunspot group covered about 0.6 percent of the solar disk, an area 20 times larger than the Earth?Ts surface.
Long-term variations in the solar constant are more difficult to determine. Although Solar Max?Ts data have indicated a slow and steady decline in the Sun?Ts output, some scientists have thought that the satellitê?Ts aging detectors might have become less sensitive over the years, thus falsely indicating a drop in the solar constant. This possibility was dismissed, however, by comparing Solar Max?Ts observations with data from a similar instrument operating on NASA?Ts Nimbus 7 weather satellite since 1978.
4.8. The Sun today is a yellow dwarf star. It is fueled by thermonuclear reactions near its center that convert hydrogen to helium. The Sun has existed in its present state for about 4 billion, 600 million years and is thousands of times larger than the Earth.
By studying other stars, astronomers can predict what the rest of the Sun?Ts life will be like. About 5 billion years from now, the core of the Sun will shrink and become hotter. The surface temperature will fall. The higher temperature of the center will increase the rate of thermonuclear reactions. The outer regions of the Sun will expand approximately 35 million miles, about the distance to Mercury, which is the closet planet to the Sun. The Sun will then be a red giant star. Temperatures on the Earth will become too hot for life to exist.
Once the Sun has used up its thermonuclear energy as a red giant, it will begin to shrink. After it shrinks to the size of the Earth, it will become a white draft star. The Sun may throw off huge amounts of gases in violent eruptions called nova explosions as it changes from a red giant to a white dwarf.
After billions of years as a white draft, the Sun will have used up all its fuel and will have lost its heat. Such a star is called a black dwarf. After the Sun has become a black dwarf, the Earth will be dark and cold. If any atmosphere remains there, it will have frozen onto the Earth?Ts surface.
4.9. The temperature of the Sun is over 10,000 degrees Fahrenheit at the surface, but it rises to perhaps more than 27,000,000o at the center. The Sun is so much hotter than the Earth that matter can exist only as a gas, except perhaps at the core. In the core of the Sun, the pressures are so great that, despite the high temperature, there may be a small solid core. However, on one really knows, since the center of the Sun can never be directly observed.
Solar astronomers do know that the Sun is divided into five general layers or zones. Starting at the outside and going down into the Sun, the zones are the corona, chromosphere, photosphere, convection zone, and finally the core. The first three zones are regarded as the Sun?Ts atmosphere. But since the Sun has no solid surface, it is hard to tell when the atmosphere ends and the main body of the Sun begins.
The Sun?Ts outermost layer begins about 10,000 miles above the visible surface and goes outward for millions of miles. This is the only part of the Sun that can be seen during an eclipse such as the one in February 1979. At any other time, the corona can be seen only when special instruments are used on cameras and telescopes to block the light from the photosphere.
The corona is a brilliant, pearly white, filmy light, about as bright as the full Moon. Its beautiful rays are a sensational sight during an eclipse. The coronâ?Ts ray flash out in a brilliant fan that has wispy spikelike rays near the Sun?Ts north and south poles. The corona is generally thickest at the Sun?Ts equator.
The corona is made up of gases streaming outward at tremendous speeds that reach a temperature of more than 2 million degree Fahrenheit. The gas thins out as it reaches the space around the planets. By the time the gas of the corona reaches the Earth it has a relative low density.
4.10. According to the controversial sunspot theory, great storms on the surface of the sun hurl streams of solar particles into the atmosphere, causing a shift in the weather on earth.
A typical sunspot consists of a dark center like the spokes of a wheel. Actually, the sunspots are cooler than the rest of the photosphere, which may account for their color. Typically, the temperature in a sunspot umbra is about 4000 K, whereas the temperature in a penumbra resisters 5500 K, and the granules outside the spot are 6000 K.
Sunspots range in size form tiny granules to complex structures with areas stretching for billions of square miles. About 5 percent of the spots are large enough so that they can be seen without instruments; consequently, observations of sunspots have been recorded for several thousand years.
Sunspots have been observed in arrangements of one to more then one hundred spots, but they tend to occur in pairs. There is also a marked tendency for the two spots of a pair to have opposite magnetic polarities. Furthermore, the strength of the magnetic field associated with any given sunspot is closely related to the spot?Ts size.
Although there is no theory that completely explains the nature and function of sunspots, several models attempt to relate the phenomenon to magnetic fields along the lines of longitude from the north and south poles of the sun.
4.11. The question of lunar formation has long puzzled astronomers. It was once theorized that the moon formed alongside the earth as material in a swirling disk coalesced to form both bodies. However, if both bodies formed simultaneously out of the same substance, we would expect the mean densities to be more or less identical. In fact, this is not the case at all. One of the most curious characteristics of the moon is that it is far less dense than the earth. Compared to the earth?Ts mean density, which is 5.5 times that of water, the density of the moon is a mere 3.3 times that of water. Most of the earth?Ts mass is located in its dense iron core, while the mantle and crust are composed primarily of lighter silicates. The moon, on the other hand, is composed entirely of lighter substances.
An alternative explanation, the ?ocapture theory,:? suggested that the moon formed far away and was later captured by the earth. The moon was once wandering in space, like an asteroid, unattached to a planet. The rogue satellite veered too close to the earth and has since been tethered by the earth?Ts gravitational field. However, comparison of lunar and terrestrial isotopes has undermined this theory. Isotopes are atomic indicators that leave a sort of geological fingerprint. The isotopes from lunar rock samples indicate that both earth and moon came from the same source.
A more recent theory, the ?oimpact theory? of lunar formation postulates that a large planet-like object, perhaps twice the mass of Mars, struck the earth at a shallow angle. The object disintegrated a portion of the earth?Ts crust and mantle, sending a cloud of silicate vapor into orbit around the earth. In time, most of the material fell back to the earth, while the rest coalesced into our moon.
Computer simulations (1997) by Robin Canup and Glen Stewart of the University of Colorado and by Shigeru Ida of the Tokyo Institute of Technology demonstrated that such a scenario is at least theoretically possible. While the impact theory is attractive in that it explains both why the moon is less dense than the earth and how both bodies could have originated from the same source, it is not without problems. Impact from a Mars-sized body would produce an earth-moon system with twice as much angular momentum as that which is actually observed. Therefore, although we are closer to resolving the question of lunar formation, the origin of the moon is still shrouded in mystery.
4.12. For centuries, sky watchers have reported seeing mysterious flashes of light on the surface of the Moon. Modern astronomers have observed the same phenomenon, but no one has been able to satisfactorily explain how or why the Moon sporadically sparks. However, researches now believe they have found the cause.
Researchers have examined the chemical content of Moon rocks retrieved by astronauts during the Apollo missions and have found that they contain volatile gases such as helium, hydrogen, and argon. The researchers suggest that stray electrons, freed when the rock cracks, may ignite these gases. Indeed, lunar rock samples, when fractured in the lab, throw off sparks.
What causes these rocks to crack on the lunar surface ? The flashes are most often seen at the borders between sunlight and shade on the Moon, where the surface is being either intensely heated or cooled. A sudden change in temperature may cause thermal cracking. Another possibility is that meteors may strike the rocks and cause them to crack. Finally, lunar rocks may be fractured by seismic events ?" in other words, by tiny moonquakes.
4.13. Of the six outer planets, Mars, commonly called the Red Planet, is the closet to Earth. Mars, 4,200 miles in diameter and 55 percent of the size of Earth, is 34,600,000 miles from Earth, and 141,000,000 miles from the Sun. It takes this planet, along with its two moons, Phobos and Deimos, 1.88 years to circle the Sun, compared to 365 days for the Earth.
For many years, Mars had been thought of as the planet with the man-made canals, supposedly discovered by an Italian astronomer, Schiaparelli, in 1877. With the United States spacecraft Viking I?Ts landing on Mars in 1976, the man-made canal theory was proven to be only a myth.
Viking I, after landing on the soil of Mars, performed many scientific experiments and took numerous pictures. The pictures showed that the red color of the planet is due to the reddish, rocky Martian soil. No biological life was found, though it had been speculated by many scientists. The Viking also monitored many weather changes including violent dust storms. Some water vapor, polar ice, and permafrost (frost below the surface) were found, indicating that at one time there were significant quantities of water on this distant planet. Evidence collected by the spacecraft shows some present volcanic action, though the volcanoes are believed to be dormant, if not extinct.
4.14. According to the best evidence gathered by space probes and astronomers, Mars is an inhospitable planet, more similar to Earth?Ts Moon than to Earth itself ?" a dry, stark, seemingly lifeless world. Mars?T air pressure is equal to Earth?Ts at an altitude of 100,000 feet. The air there is 95 percent carbon dioxide.
Mars has no ozone layer to screen out the sun?Ts lethal radiation. Daytime temperatures may reach above freezing, but because the planet is blanketed by the more wisp of an atmosphere, the heat radiates back into space. Even at the equator, the temperature drops to -50oC (-60oF) at night. Today there is no liquid water, although valleys and channels on the surface show evidence of having been carved by running water. The polar ice caps are made of frozen water and carbon dioxide, and water may be frozen in the ground as permafrost.
Despite these difficult con***ions, certain scientists believe that there is a possibility of transforming Mar into a more Earth-like planet. Nuclear reactors might be used to melt frozen gases and eventually build up the atmosphere. This in turn could create a ?ogreenhouse effect? that would stop heat from radiating back into space. Liquid water could be thawed to form a polar ocean. Once enough ice has melted, suitable plants could be introduced to build up the level of oxygen in the human colonies. ?othis was once thought to be so far in the future as to be irrelevant,? said Christopher McKay, a research scientist at the National Aeronautics and Space Administration. ?oBut now it?Ts starting to look practical. We could begin work in four or five decades.?
The idea of ?oterra-forming? Mars as enthusiasts call it, has its roots in science fiction. But as researchers develop a more profound understanding of how Earth?Ts ecology support life, they have begun to see how it may be possible to create similar con***ions of Mars. Don?Tt plan on homesteading on Mars any time soon, though. The process could take hundreds or even thousands of years to complete and the cost would be staggering.
4.15. Asteroids are rocky, metallic objects that orbit the Sun but are too small to be considered planets. The largest known asteroid, Ceres, has a diameter about 1,000 kilometers. The smallest asteroids are the size of pebbles. Millions are the size of boulders. Most are irregularly shaped ?" only a few are large enough for gravity to have made them into spheres. About 250 asteroids in the solar system are 100 kilometers in diameter, and at least sixteen have diameter of 240 kilometers or greater. They orbits lie in an area that stretches form Earth?Ts orbit to beyond Saturn?Ts orbit. Tens of thousands of asteroids exist in a belt between the orbits of Mars and Jupiter. An asteroid that hits Earth?Ts atmosphere is called a meteor or shooting star, because it burns and gives off a bright flash of light, What ever does not completely burn falls to Earth as meteorite. Between 1,000 and 10,000 tons of this material fall to Earth daily. Much is in the form of small grains of dust, but about 1,000 metallic or rocky bits fall to Earth each year.
There has been much speculation about large meteors hitting Earth. A large asteroid or comet is thought to have landed in Mexico about 65 million years ago. The impact may have led to the extinction of may species, including the dinosaurs, by throwing dust into the atmosphere, blocking the sunlight, and causing a climate change. The period of time between such large meteor impact is probably in the millions of years, but smaller meteors, such as the one caused the Meteor Crater in Arizona (about 1.2 kilometers in diameter), may hit the earth every 50,000 to 100,000 years. Therê?Ts no historical record of a person being killed by a meteorite. The only reported injury occurred on November 30, 1954, when an Alabama woman was bruised by an eight-pound meteorite that fell through her roof.
4.16. The most easily recognizable meteorites are the iron variety, although they only represent about 5 percent of all meteorite falls. They are composed of iron and nickel along with sulfur, carbon, and traces of other elements. Their composition is thought to he similar to that of Earth''s iron core 3 and indeed they might have once made up the core of a large planetoid that disintegrated long ago. Due to their dense structure, iron meteorites have the best chance of surviving an impact, and most are found by farmers plowing their fields.
One of the best hunting grounds for meteorites is on the glaciers of Antarctica1 where the dark stones stand out in stark contrast to the white snow and ice. When meteorites fall on the continent) they are embedded in the moving ice sheets. At places where the glaciers move upward against mountain ranges, meteorites are left exposed on the surface. Some of the meteorites that have landed in Antarctica are believed to have conic from the Moon and even as far away as Mars, when large impacts blasted out chunks of material and hurled them toward Earth.
Perhaps the world''s largest source of meteorites is the Nullarbor Plain, an area of limestone that stretches for 400 miles along the southern coast of Western and South Australia. The pale, smooth desert plain provides a perfect backdrop for spotting meteorites, which are usually dark brown of black. Since very little erosion takes place, the meteorites are well preserved and are found just where they landed. Over 1, 000. fragments from 150 meteorites that fell during the last 20, 000 years have been recovered. One large iron meteorite, called the Mundrabilla meteorite, weighed more than 11 tons.
Stony meteorites, called chordates, are the most common type and make up more than 90 percent of all falls. But because they are similar to Earth materials and therefore erode easily, they are often difficult to find. Among the most ancient bodies in the solar system are the carbonaceous chondrites that also contain carbon compounds that might have been the precursors of life on Earth.

4.17. According to recent scientific theory, it is probable that life will develop on planets that have a favorable environment ?" planets similar to ours, that orbit stars like our suns. Since there are 400 billion stars in our galaxy alone, that means there are a huge number of planets like ours that could sustain life. Planets with advanced civilizations are likely to be widely scattered throughout the universe. In the past four decades, humans on Earth have begun to search for these civilizations. This search is called SETI, the Search for the Extra-Terrestrial Intelligence, and it has been conducted largely by searching for radio waves emitted from civilizations on other planets.
In 1960, Dr. Frank Drake made the first attempt at SETI, by conducting a radio search using an 85-foot antenna of the National Radio Astronomy Observatory in West Virginia. This search, called Project Ozma, observed two stars about 12 light years away. Since that time, more than 60 searches have been conducted by dozens of astronomers in at least eight countries.
All searches, thus far, have faced many limitations: they used equipment that lacked sensitivity, they did not search frequently, they covered little of the sky, or they could search for only a few types of signals or in a few directions. The searches did turn up signals of unknown origin, but data collected in these searches were often processed long after the observation. In order to be sure that a signal is from another civilization, it has to be independently verified and shown to originate from a point beyond the solar system. Later searches for the unknown signals turned up nothing.
Project Phoenix, the latest SETI effort, consists of orders of magnitude more comprehensive than any of those previous experiments, and uses the world?Ts largest antennas. It will scrutinize the regions around 1,000 nearby Sun-like stars, and immediately test candidate signals to see if they are extraterrestrial in origin. It is important that Project Phoenix continue to operate, because radio interference from Earth sources is growing, and may soon interfere with our ability to detect possible extraterrestrial signals. In order to over come this growing interference, ever-better antenna systems are being developed.
4.18. Edwin Hubble was an American astronomer whose research lead to discovery about galaxies and the nature of universe. He settled a long debate by demonstrating that the Andromeda nebula was located outside our galaxy, establishing the islands universe theory, which states that galaxies exist outside of our own. His study of the distribution of galaxies resulted in Hubblê?Ts Constant, a standard relationship between a galaxy?Ts distance from the earth and its speed of recession.
By 1925, Hubble had devised a classification system for the structure of galaxies and provided conclusive observational evidence for the expansion of the universe. His work pushed the one-hundred-inch Mount Wilson telescope beyond its capability and provided strong impetus for the construction of an instrument twice its size at Mount Palomar, which Hubble used during his last years of research. The telescope that bears his name was launched on a space shuttle in 1990 and orbits the earth, collecting data about the size and age of the universe.
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5. Earth Science
5.1. Modern geology has for its aim the deciphering of the whole evolution of the earth, from the time of the earliest records that can be recognized in the rocks, to the present day. So ambitious a program requires much subdivision of effort, and in practice it is convenient to divide the subject into a number of branches. The key words of the three main branches are the materials of the earth?Ts rocky framework (mineralogy and petrology); the geological processes of machinery of the earth, by means of which changes of all kinds are brought about (physical geology); and finally the succession of these changes, or the history of the earth (historical geology)
Geology is by no means without practical importance in relation to the needs and industries of mankind. Thousands of geologists are actively engaged in locating and exploring the mineral resources of the earth. The whole world is being searched for oil and coal and for the ores of useful metals. Geologists are also directly concerned with the vital subject of water supply. Many engineering projects, such as tunnels, canals, docks, and reservoirs, call for geological advice in the selection of sites and materials. In these and in many other ways, geology is appeal to the service of mankind.
Although geology has its own laboratory methods for studying minerals, rocks, and fossils, it is essentially an open-air science. It attracts its followers to mountains and waterfalls, glaciers and volcanoes, beaches and coral reefs in search of information about the earth and its often puzzling behavior. Wherever rocks are to be seen in cliffs and quarries, their arrangement and sequence can be observed and their story deciphered. With hammer and maps, the geologist in the field leads a healthy and exhilarating life. His powers of observation become sharpened, his love of nature is deepened, and the thrill of discovery is always at hand.
5.2. One of the major achievements of modern science is the determination of the approximate age of the earth, now reckoned at 4.6 billion years. This makes the Earth far older than was formerly imagined. Indeed, one eighteenth-century religious and scientific authority circulate the widely accepted view that the planet was only some four thousand years old. To modern scientists, however, geologic time begins with the formation of the Earth solid crust sometime earlier than the age of the oldest known rock. Geologists divide this vast expanse of time into four eras ?" the Precambrian, the Paleozic, the Mesozoic, and the Cenozoic which takes us to the present. Thus, the almost five billion years of planetary history and the 100,000 or so years of human existence are encapsulated in a mere four categories. Obviously, to aid in the discussion of such vast periods of time, further division and specification becomes necessary. Accordingly, the last three eras are further divided into 12 periods and more than 40 epochs, each division being determined by characteristic types of rock and plant and animal fossils. Since the Precambrian era alone is more than four billion years long, is structurally complex, and has few fossils, it has been divided roughly in half for convenience of discussion. Scientists are working hard to discover clues about the earth?Ts most distant past, but there still is a startling lack of detail about both portions of the planet?Ts Precambrian era.
5.3. The hard, rigid plates that form the outermost portion of the Earth are about 100 kilometer thick. These plates include both the Earth?Ts crust and the upper mantle.
The rocks of the crust are composed mostly of minerals with light elements, like aluminum and sodium, while the mantle contains some heavier elements, like iron and magnesium. Together, the crust and upper mantle that form the surface plates are called the lithosphere. This rigid layer floats on the denser material of the lower mantle the way a wooden raft floats on a pond. The plates are supported by a weak, plastic layer lithospheric plates are carried along by slow currents in this more fluid layer beneath them.
With an understanding of plate tectonics, geologists have put together a new history for the Earth?Ts surface. About 200 million years ago, the plates at the Earth?Ts surface formed a ?osupercontinent? called Pangaea. When this supercontinent started to tear apart because of plate movement, Pangaea first broke into two large continental masses with a newly formed sea that grow between the land areas as the depression filled with water. The southern one ?" which included the modern continents of South America, Africa, Australia, and Antarctica ?" is called Gondwanaland. The northern one ?" with North America, Europe, and Asia ?" is called Laurasia. North America tore away form Europe about 180 million years ago, forming the northern Atlantic Ocean.
Some of the lithospheric plates carry ocean floor and others carry land masses or a combination of the two types. The movement of the lithospheric plates is responsible for earthquakes, volcanoes, and the Earth?Ts largest mountain ranges. Current understanding of the interaction between different plates explains why these occur where they do. For example, the edge of the Pacific Ocean has been called the ?oRing of Firê? because so many volcanic eruptions and earthquakes happen there. Before the 1960?Ts, geologists could not explain why active volcanoes and strong earthquakes were concentrated in that region. The theory of plate tectonics gave them an answer.
5.4. The magnetosphere consists of two stronger belts of radiation that lie within a band of weaker radiation surrounding most of the earth. It extends outward for tens of thousands of miles. The magnetosphere is comprised of slow-moving electrons, trapped by the earth?Ts magnetic lines of force. The shape of the magnetosphere is determined by the earth?Ts magnetic field, but it is distorted by electrically charged particles that emanate from the sun to the earth. These charged particles are often referred to as the solar wind, pushing nearer the earth on the sunlit side and away from the earth on the dark side. Thus, the higher end of the magnetosphere extends up to forty thousand miles on the sunlit side, and the lower end hovers within a few hundred miles of the earth on the dark side.
There is very little radiation near the earth?Ts north and south poles because the magnetic lines of force enter the earth near the poles. Conversely, the same lines of forces are far above the earth near the equator.
5.5. Most of our planet is covered by water. There is so much of it that if all the mountains of the world were leveled and their debris dumped into the oceans, the surface of the globe would be entirely submerged beneath water to a depth of several thousand meters. The great basins between the continents, in which all this water lies, are themselves more varied, topographically than the surface of the land. The highest terrestrial mountain, Mount Everest, would fit into the deepest part of the ocean, the Mariana Trench, with its peak a kilometer beneath the surface. On the other hand, the biggest mountains of the sea are so huge that they rise above the surface of water to form chains of islands. Mauna Kea, the highest of the Hawaiian volcano, measured from its base on the ocean floor is more than 10, 000 meters high and so can claim to be highest mountain on the planet.
The sea first formed when the Earth began to cool soon after and its birth and hot water vapor condensed on its surface. They were further fed by water gushing through volcanic vents from the interior of the Earth. The water of these young seas was not pure, like rainwater, but contained significant quantities of chlorine, bromine, iodine, boron, and nitrogen, as well as traces of many rarer substances. Since then, other ingredients have been added. As continental rocks weather and erode, they produce salts that are carried in solution down to the sea by rivers. So, over millennia, the sea has been getting saltier and saltier.
Life first appeared in this chemically rich water some 3. 5 billion years ago. We know from fossils that the first organisms were simple single-celled bacteria and algae. Organisms very like them still exist in the sea today. They are the basis of all marine life, indeed, were it not for these algae, the seas would still be completely sterile and the land uninhabited.
5.6. The ocean bottom ------a region nearly 2.5 times greater than the total land area of the Earth ---- is a vast frontier that even today is largely unexplored and uncharted. Until about a century ago, the deep-ocean floor was completely inaccessible, hidden beneath waters averaging over 3,600 meters deep. Totally without light and subjected to intense pressures hundreds of times greater than at the Earth''s surface, the deep-ocean bottom is a hostile environment to humans, in some ways as forbidding and remote as the void of outer space.
Although researchers have taken samples of deep-ocean rocks and sediments for over a century, the first detailed global investigation of the ocean bottom did not actually start until 1968, with the beginning of the National Science Foundation''s Deep Sea Drilling Project (DSDP).Using techniques first developed for the offshore oil and gas industry, the DSDP''s drill ship, theGlomar Challenger, was able to maintain a steady position on the ocean''s surface and drill in very deep waters, extracting samples of sediments and rock from the ocean floor.
The Glomar Challenger completed 96 voyages in a 15-year research program that ended in November 1983. During this time, the vessel logged 600,000 kilometers and took almost 20,000 core samples of seabed sediments and rocks at 624 drilling sites around the world. The Glomar Challenger''s core samples have allowed geologists to reconstruct what the planet looked like hundred of millions of years ago and to calculate what it will probably look like millions of years in the future. Today, largely on the strength of evidence gathered during the Glomar Challenger''s voyages, nearly all earth scientists agree on the theories of plate tectonics and continental drift that explain many of the geological processes that shape the Earth.
The cores of sediment drilled by the Glomar Challenger have also yielded information critical to understanding the world''s past climates. Deep-ocean sediments provide a climatic record stretching back hundreds of millions of years, because they are largely isolated from the mechanical erosion and the intense chemical and biological activity that rapidly destroy much land-based evidence of past climates. This record has already provided insights into the patterns and causes of past climatic change --- information that may be used to predict future climates.
5.7. Seismologists have devised two scales of measurement to enable them to describe earthquakes in quantitative terms. On is the Richter scale, a numerical logarithmic scale developed and introduced by American seismologist Charles R. Richter in 1935. The purpose of the scale is to measure the amplitude of the larges trace recorded by a standard seismography one hundred kilometers from the epicenter of an earthquake. Tables have been formulated to demonstrate the magnitude of any earthquake from any seismography. For example, for a one-unit increase in magnitude, there is an increase of times thirty in released energy. To put that another way, each number on the Richter scale represents an earthquake ten times as strong as one of the next lower magnitude. Specifically, an earthquake of magnitude 6 is ten times as strong as an earthquake of magnitude 5.
The Richter scale considers earthquakes of 6.75 as great and 7.0 to 7.75 as major. As earthquake that reads 4 to 5.5 would be expected to cause localized damage, and those of magnitude 2 may be felt.
The other scale, introduced by the Italian seismologists Giuseppe Mercalli, measures the intensity of shaking, using gradations from 1 to 12. Because the effects of such shaking dissipate with distance from the epicenter of the earthquake, the Mercalli rating depends on the site of the measurement. Earthquakes of Mercalli 2 or 3 are basically the same as those of Richter 3 or 4; measurement of 11 or 12 on the Mercalli scale can be roughly correlated with magnitudes of 8 or 9 on the Richter scale.
It is estimated that almost one million earthquakes occur each year, but most of them are so minor that they pass undetected. In fact, more than one thousand earthquakes of a magnitude of 2 or less on the Richter scale occur every day.
5.8. In ad***ion to the great ridges and volcanic chains, the oceans conceal another form of undersea mountains: the strange guyot, or flat-stopped seamount. No marine geologists even suspected the existence of these isolated mountains until they were discovered by geologist Harry H. Hess in 1946. He was serving at the time as a naval officer on a ship equipped with a fathometer. Hess named these truncated peaks for the nineteenth-century Swiss-born geologist. Arnold Guyot, who had served on the faculty of Princeton University for thirty years. Since then, hundreds of guyots have been discovered in every ocean but the Artic. Like offshore canyons, guyots present a challenge to oceanographic theory. They are believed to be extinct volcanoes. Their flat tops indicate that they once stood above or just below the surface, where the action of waves leveled off their peaks. Yet today, by definition, their summits are at least 600 feet below the surface, and some are as deep as 8,200 feet. Most lie between 3,200 feet and 6,500 feet. Their tops are not really flat but slope upward to a low pinnacle at the center. Dredging from the tops of guyots has recovered basalt and coral rubble, and that would be expected from the eroded tops of what were once islands. Some of this material is over 80 million years old. Geologists think the drowning of the guyots involved two processes: The great weight of the volcanic mountains depressed the sea floor beneath them, and the level of the sea rose a number of times, especially when the last Ice Age ended, some 8,000 to 11,000 years ago.
5.9. Most volcanoes are found along an imaginary belt, called the Ring of Fire, that encircles the Pacific Ocean. However, volcanic activity takes place in many far-flung regions of the world, such as Hawaii, Iceland, Europe, and even the floor of the earth?Ts oceans. The leading theory as to why volcanic activity, as well as earthquakes, takes place when and where it does is called the theory of ?olate tectonics.? The theory holds that the outer shell of the earth is divided into many different rigid sections of rock, call plates. These plates are not static; they are in continuous motion over a layer of partly melted rock. While their movement may appear insignificant, at only several inches per year, it is not. Indeed, the collisions between the plates caused by this almost imperceptible movement can have catastrophic consequences. Volcanic activity and earthquakes are concentrated near the boundaries of the giant, moving plates.
The majority of volcanoes are formed at the point where two plates collide. One of the plates is forced underneath the other. As the plate sinks, the earth?Ts heat and the friction of the movement cause a portion of the sinking plate to melt. This melted portion of plate is called magma, and when it reaches the earth?Ts heat and the friction of the movement cause a portion of the sinking plate to melt. This melted portion of plate is called magma, and when it reaches the earth?Ts surface it becomes a volcano. Volcanoes can also be created when two plates begin to diverge. Then, magma from below the earth?Ts crust moves up to fill the void between the two plates. Large quantities of lava spill out from the void. Volcanoes of this type usually are found not on land, but on the ocean floor. In extreme instances this can lead to the formation of gigantic, sunken mountain ranges like the Mid-Atlantic Ridge that spans nearly the entire length of the Atlantic Ocean. The theory of plate tectonics also explains why some volcanic activity takes place so far form any known plate boundaries. Basically, these volcanoes are the result of huge columns of magma, or plumes, that rise up and break through the surface of the earth.

5.10. Volcanic fire and glacial ice are natural enemies. Eruptions at glaciated volcanoes typically destroy ice fields, as they did in 1980 when 70 percent of Mount Saint Helens ice cover was demolished. During long dormant intervals, glaciers gain the upper hand cutting deeply into volcanic cones and eventually reducing them to rubble. Only rarely do these competing forces of heat and cold operate in perfect balance to create a phenomenon such as the steam ****s at Mount Rainier National Park.
Located inside Rainier''s two ice-filled summit craters, these ****s form a labyrinth of tunnels and vaulted chambers about one and one-half miles in total length. Their creation depends on an unusual combination of factors that nature almost never brings together in one place. The ****-making recipe calls for a steady emission of volcanic gas and heat, a heavy annual snowfall at an elevation high enough to keep it from melting during the summer, and a bowl-shaped crater to hold the snow.
Snow accumulating yearly in Rainier''s summit craters is compacted and compressed into a dense form of ice called firn, a substance midway between ordinary ice and the denser crystalline ice that makes up glaciers. Heat rising from numerous openings (called fumaroles) along the inner crater walls melts out chambers between the rocky walls and the overlying ice pack. Circulating currents of warm air then melt ad***ional opening in the firn ice, eventually connecting the individual chambers and, in the larger of Rainier''s two craters, forming a continuous passageway that extends two- thirds of the way around the crater''s interior.
To maintain the **** system, the elements of fire under ice must remain in equilibrium. Enough snow must fill the crater each year to replace that melted from below. If too much volcanic heat is discharged, the crater''s ice pack will melt away entirely and the ****s will vanish along with the snow of yesteryear. If too little heat is produced, the ice, replenished annually by winter snowstorms, will expand, pushing against the enclosing crater walls and smothering the present ****rns in solid firn ice.
5.11. Clays and muds and rocks are made of tiny crystals. They are abundant on Earth and probably always have been. When you look at the surface of some types of clay and other minerals with scanning electron microscope, you see an amazing and beautiful sight. Crystals grow like rows of flowers or cactuses, gardens of inorganic rose petals, tiny spirals like cross-sections of succulent plants, bristling organ pipes, complicated angular shapes folded as if in miniature crystalline origami, writhing growths like worm casts or squeezed toothpaste. The ordered patterns become even more striking at greater levels of magnification. At levels that betray the actual position of atoms, the surface of a crystal is seen to have all the regularity of a machine-woven piece of herringbone tweed. But ?" and here is the vital point ?" there are flaws. Right in the middle of an expanse of orderly herringbone there can be a patch, identical to the rest except that it is twisted round at a different angle so that the ?oweavê? goes off in another direction. Or the weave may lie in the same direction, but each row has ?ospilled? half a row to one side. Nearly all naturally occurring crystals have flaws. And once a flaw has appeared, it tends to be copied as subsequent layers of crystal encrust themselves on top of it.
5.12. The appearance and character of a hardened lava field depend on numerous factors. Among the key variables are the chemical nature of the magma and the degree of viscosity of the liquid rock once it beings to flow.
Since the ultimate nature of lava is influenced by chemical composition, it is possible to predict certain aspects of the final appearance of the field from a sample of the molten fluid. The main components of lava are silica and various oxides, including those potassium, iron, calcium, magnesium, sodium, and aluminum. Magnesium and iron oxides are found in high concentrations in the dark-colored basic basalt, while silica, soda, and potash preponderate in the lighter-colored, acidic felsite rocks.
The viscosity of the liquid rock helps to determine the appearance of the hardened field?Ts surface. When it issues, the lava is red - or even white-hot. It soon begins to cool, and the surface darkens and crusts over. In extremely viscous flows, the underpart may yet be in motion as the surface solidifies. The curst breaks up into a mass of jagged blocks of rock that are carried as a tumbling, jostling ass on the surface of the slowly moving stream. When the stream eventually stops and hardens, the field is extremely rough and difficult to traverse. On the other hand, highly liquid lava may harden with much smoother surface that exhibit ropy, curved, wrinkled, and wavelike forms.
5.13. A geyser is the result of underground water under the combined con***ions of high temperatures and increased pressure beneath the surface of the earth. Since temperature rises about 1oF for every sixty feet under the earth?Ts surface, and pressure increases with depth, water that seeps down in cracks and fissures until it reaches very hot rocks in the earth?Ts interior becomes heated to a temperature of approximately 290oF.
Water under pressure can remain liquid at temperatures above its normal boiling point, but in a geyser, the weight of the water nearer the surface exerts so much pressure on the deeper water that the water at the bottom of the geyser reaches much higher temperatures than does the water at the top of the geyser. As the deep water becomes hotter, and consequently, lighter, it suddenly rises to the surface and shoots out of the surface in the form of steam and hot water, in turn, the explosion agitates all the water in the geyser reservoir, creating further explosions, immediately afterward, the water again flows into the underground reservoir, heating begins, and the process repeats itself.
In order to function, then, a geyser must have a source of heat, a reservoir where water can be stored until the temperature rises to an unstable point, an opening through which the hot water and steam can escape, and underground channels for resupplying water and an eruption.
Favorable con***ions for geysers exist in regions of geologically recent volcanic activity, especially in areas of more than average precipitation. For the most part, geysers are located in three regions of the world: New Zealand, Iceland, and the Yellowstone National Park area of the United Stats. The most famous geyser in the world is Old Faithful in Yellowstone Park, Old Faithful erupts almost every hour, rising to a height of 125 to 170 feet and expelling more than ten thousand gallons during each eruption. Old Faithful earned its name because, unlike most geysers, it has never failed to erupt on schedule even once in eighty years of observation.
5.14. The aurora is an atmospheric phenomenon occurring near the earth?Ts poles. Known as aurora borealis or ?onorthern lights? in the northern hemisphere, and as aurora australis or ?osouthern lights? in the southern hemisphere, it is a kind of cosmic light show.
Although their causes are not precisely known, auroras seem to result from solar activity. The sun?Ts outer atmosphere, or corona, can be extremely hot, up to several million degrees. Such heat causes atoms to dissolve, and changes hydrogen into plasma ?" free electrons and protons. Holes in the sun?Ts magnetic field allow this plasma to escape. As the sun rotates, it throws plasma outward in a spiral. The plasma moves further and further away from the sun, eventually reaching Earth?Ts orbit. When the plasma particles get caught in the earth?Ts magnetic field, they travel to the magnetic poles, where, at heights of several hundred kilometers, they collide with oxygen and nitrogen atoms. This energetic activity knocks away electrons to leave ions in excited states. The ions emit radiation and create color. Then the light show begins.
The longest lasting aurora from is the arc, which may remain in the sky for several hours. An aurora can also appear as a curtain, ray, or band. In the dazzling auroral substorm, an aurorâ?Ts shape may change dramatically. Green lights can fill the sky towards the pole, and end in a shimmering, folded arc with a red border at the bottom. The bottom of the arc or fold often takes a sharper from than the top part. Towards the end of the display, the shapes pale and gradually drift towards the pole.
5.15. Precipitation, commonly referred to as rainfall, is a measure of the quantity of water in the form of either rain, hail, or snow which reaches the ground. The average annual precipitation over the whole of the United States is thirty-six inches. It should be understood however, that a foot of snow is not equal to a foot of precipitation. A general formula for computing the precipitation of snowfall is that ten inches of snow is equal to one inch of precipitation. Forty inches of rain would be recorded as forty inches of precipitation. The total annual precipitation would be recorded as forty-two inches.
The amount of precipitation is a combined result of several factors, including location, altitude, proximity to the sea, and the direction of prevailing winds. Most of the precipitation in the United States is brought originally by prevailing winds from the Pacific Ocean, the Gulf of Mexico, the Atlantic Ocean, and the Great Lakes. Because these prevailing winds generally come from the West, the Pacific Coast receives more annual precipitation than the Atlantic Coast. Along the Pacific Coast itself, however, altitude causes some diversity in rainfall. The mountain ranges of the United States, especially the Rocky Mountain Range and the Appalachian Mountain Range, influence the amount of precipitation in their areas. East of the Rocky Mountains, the annual precipitation decreases substantially from that west of the Rocky Mountains. The precipitation north of the Appalachian Mountains is about 40 percent less than that south of the Appalachian Mountains.
5.16. The first scientific attempt at coaxing moisture from a cloud was in 1946, when scientists Vincent Schaefer dropped 3 pounds of dry ice from an airplane into a cloud and, to his delight, produced snow. The success of the experiment was modest, but it spawned optimism among farmers and ranchers around the country. It seemed to them that science had triumphed over weather.
Unfortunately, it didn?Tt work out that way. Although there were many cloud-seeding operations during the late 1940s and 1950s, no one could say whether they had any effect on precipitation. Cloud seeding, or weather modification as it came to be called, was clearly more complicated than had been thought. It was not until the early 1970s that enough experiments had been done to understand the processes involved. What these studies indicated was that only certain types of clouds are amenable to seeding. One of the most responsive is the winter orographic cloud, formed when air currents encounter a mountain slope and rise. If the temperature in such a cloud is right, seeding can increase snow yield by 10 to 20 percent.
There are two major methods of weather modification. In one method, silver iodide is burned in propane-fired ground generators. The smoke rises into the clouds where the tiny silver-lodide particles act an nuclei for the formation of ice crystals. The alternate system uses airplanes to deliver dry-ice pellets. Dry ice does not provide ice-forming nuclei. Instead, it lowers the temperature near the water droplets in the clouds so that they freeze instantly ?" a process called spontaneous nucleation. Seeding from aircraft is more efficient but also more expensive.
About 75 percent of all weather modification in the United States takes place in the Western states. With the population of the West growing rapidly, few regions of the world require more water. About 85 percent of the waters in the rivers of the West comes from melted snow. As one expert put it, the water problems of the future may make the energy problems of the 70s seem like child?Ts play to solve. That?Ts why the U.S. Bureau of Reclamation, along with state governments, municipal water districts, and private interests such as ski areas and agricultural cooperatives, is putting increased effort into cloud-seeding efforts. Without consistent and heavy snowfalls in the Rockies and Sierras, the West would literally dry up. The most intensive efforts to produce precipitation was during the West?Ts disastrous snow drought of 1976-77. It is impossible to judge the efficiency of weather modification based on one crash program, but most experts think that such hurry-up programs are not very effective.
5.17. Recent technological advances in manned and unmanned undersea vehicles along with breakthroughs in satellite technology and computer equipment have overcome some of the limitations of divers and diving equipment. Without a vehicle, divers often became sluggish and their mental concentration was limited. Because of undersea pressure that affected their speech organs, communication among divers was difficult or impossible. But today, most oceanographers make direct observations by means of instruments that are lowered into the ocean, from samples taken from the water, or from photographs made by orbiting satellites. Direct observations of the ocean floor are made not only by divers but also by deep-diving submarines and aerial photography. Some of the submarines can dive to depths of more than seven miles and cruise at depths of fifteen thousand feet. In ad***ion, radio-equipped buoys can be operated by remote control in order to transmit information back to land-based laboratories, often via satellite. particularly important are data about water temperature, currents and weather. Satellite photographs can show the distribution of sea ice, oil slicks, and cloud formations over the oceans. Maps created from satellite pictures can represent the temperature and the color of the ocean?Ts surface, enabling researches to study the ocean currents. Further more, computers help oceanographers to collect and analyze data from submarines and satellites. By creating a model of the ocean?Ts movement and characteristics, scientists can predict the patterns and possible effects of the ocean on the environment.
Recently, may oceanographer have been relying more on satellites and computers than on research ships or even submarine vehicles because they can supply a greater range of information more quickly and more efficiently. Some of mankind?Ts most serious problems, especially those concerning energy and food, may be solved with the help with the help of observations made possible by this new technology.
5.18. Ambient divers are, unlike divers who go underwater in submersible vehicles or pressure resistant suits, exposed to the pressure and temperature of the surrounding (ambient) water. Of all types of diving, the oldest and simplest is free diving. Free divers may use no equipment at all, but most use a face mask, foot fins, and a snorkel. Under the surface, free divers must hold their breath. Most free divers can only descend 30 to 40 feet, but some skilled divers can go as deep as 100 feet.
Scuba diving provides greater range than free diving. The word scuba stands for self-contained underwater breathing apparatus. Scuba divers wear metal tanks with compressed air or other breathing gases. When using open-circuit equipment, a scuba diver simply breathes air from the tank through a hose and releases the exhaled air into the water. A closed-circuit breathing device, also called a rebreather, filters out carbon dioxide and other harmful gases and automatically adds oxygen. This enables the diver to breathe the same air over and over.
In surface-supplied diving, divers wear helmets and waterproof canvas sits. Today, sophisticated plastic helmets have replaced the heavy copper helmets used in the past. These divers get their air from a hose connected to compressors on a boat. Surface-supplied divers can go deeper than any other type of ambient diver.
5.19. Fog is a cloud in contact with or just above the surface of land or sea. It can bee a major environmental hazard. Fog on highways can cause chain-reaction accidents involving dozens of cars. Delays and shutdowns at airports ca cause economic losses to airlines and inconvenience to thousands of travelers. Fog at sea has always been a danger to navigation. Today, with supertankers carrying vast quantities of oil, fog increases the possibility of catastrophic oil spills.
The most common type of fog, radiation fog, forms at night, when moist air near the ground loses warmth through radiation on a clear night. This type of fog often occurs in valleys, such as Californiâ?Ts San Joaquin valley. Another common type, advection fog, results from the movement of warm, wet air over cold ground. The air loses temperature to the ground and condensation sets in. This type of fog often occurs along the California coast and the shores of the Great Lakes. Advection fog also forms when air associated with a warm ocean current blows across the surface of a cold current. The thick fogs of the Grand Banks off Newfoundland, Canada, are largely of this origin, because here the Labrador Current comes in contact with the warm Gulf Stream.
Two other types of fog are somewhat more unusual. Frontal fog occurs when two fronts of different temperatures meet, and rain from the warm front falls into the colder one, saturating the air. Steam fog appears when cold air picks up moisture by moving over warmer water.
5.20. A snowflake originates from countless water molecules that initially come together in small groups as a result of a weak attractive force between oxygen and hydrogen atoms. The same forces subsequently organize the groups into a frozen molecular crystal, a perfectly organized lattice of molecules. Finally, several molecular crystals join to form a snowflake. Scientists have realized for some time that the forces that assemble molecules into natural crystals can be utilized to produce a variety of important materials. They have determined the structure of more than 90,000 different molecular crystals, the most common examples of which are aspirin and mothballs.
5.21. When glaciers covered large areas of the United States, their movement cut deep, sharp valleys into the landscape. When the climate warmed, the melting water of a glacier often remained to fill a valley. This is the most common vehicle of lake formation in the United States, and it explains why there are more lakes in the northern stats than in the southern ones. Lakes can also before because of the presence of underlying bed of limestone, as in may of the over on thousand lakes in Lake County, Florida. This foundation of limestone gradually disloves as it comes into contact with slightly acidic rainwater. Eventually, this erosion results in the formation of a number of underground streams that function to carry off the rainwater. When the top of one of these subterranean passages collapses, a sink-hole is formed. With the proper climatic con***ions this sinkhole may fill with subsequent rainfall and become a lake. The long-term collection of rainwater in the craters of extinct volcanoes can also form lakes, as can a naturally occurring deposit of silt that backs up a river at its natural outlet to the sea. Finally, the construction of dams in the United States and worldwide has resulted in the creation of great artificial lakes.

5.22. The ice sheet that blanketed much of North America during the last glaciation was in the areas of maximum accumulation more than a mile thick. Everywhere the glacier lay, its work is evident today. Valleys were scooped out and rounded by the moving ices; speaks were scraped clean. Huge quantities of rock were torn from the northern lands and carried south. Long, high east-west ridges of this eroded debris were deposited by the ice at its melting southern margin. Furthermore, the weight of the huge mass of ice depressed the crust of the Earth in some parts of Canada by over a thousand feet. The crust is still rebounding from that depression.
In North American, perhaps the most conspicuous features of the postglacial landscape are the Great Lakes on the border between the United States and Canada. No other large freshwater body lies at such favorable latitudes. The history of the making of these lakes is long and complex.
As the continental ice sheet pushed down from its primary centers of accumulation in Canada, it moved forward in lobes of ice that followed the existing lowlands. Before the coming of the ice, the basins of the present Great Lakes were simply the lowest-lying regions of a gently undulating plain. The moving tongues of ice soured and deepened these lowlands as the glacier made its way toward its eventual terminus near the present Ohio and Missouri rivers.
About 16,000 years ago the ice sheet stood for a long time with its edge just to the south of the present great Lakes. Erosional debris carried by the moving ice was dumped at the melting southern edge of the glacier and built up long ridges called terminal moraines. When the ice began to melt back from this position about 14,000 years ago, meltwater collected behind the dams formed by the moraines. The crust behind the moraines was still depressed form the weight of the ice it had borne, and this too helped create the Great Lakes. The first of these lakes drained southward across Illinois and Indiana, along the channels of the present Illinois and Wabash river.
5.23. The San Andreas Fault is a fracture at the congruence of two major plates of the earth?Ts crust, one of which supports most of the North American continent, and the other of which underlies the coast of California and the ocean floor of the Pacific. The fault originates about six hundred miles from the Gulf of California and runs north in an irregular line along the west coast to San Francisco, where it continues north for about two hundred more miles before angling into the ocean. In places, the trace of the fault is marked by a trench, or, in geological terms, a rift, and small ponds called sag ponds that dot the landscape. Its western side always moves north in relation to its eastern side. The total net slip along the San Andreas Fault and the length of time it has been active are matters of conjecture, but it has been estimated that, during the past fifteen million years, coastal California along the San Andreas Fault has moved about 190 miles in a northwesterly direction with respect to North America. Although the movement along the fault averages only a few inches a year, it is intermittent and variable. Some segments of the fault do not move at all for long periods of time, building up tremendous pressure that must be related. For this reason, tremors are not unusual along the San Andreas Fault, and some of them are classified as major earthquakes.
It is worth noting that the San Andres Fault passes uncomfortably close to several major metropolitan areas, including Los Angeles and San Francisco. In ad***ion, the San Andreas Fault has created smaller fault system, many of which underlie the smaller towns and cities along the California coast. For this reason, Californians have long anticipated the recurrence of what they refer to as the ?oBig Onê?, a destructive earth quarter that would measure near 8 on the Richter scale, similar in intensity to those occurred in 1857 and 1906. The effects of such a quake would wreak devastating effects on the life and property in the region. Unfortunately, as pressure continues to build along the fault, the likelihood of such an earthquake increases substantially.
5.24. The spectacular eruptions of Old Faithful geyser in Yellowstone National Park do not occur like clockwork. Before earthquake of 1959, eruptions came every 60 to 65 minutes; today they are as little as 30 minutes or as much as 90 minutes apart. The geyser usually gives a warning: a short burst of steam. Then a graceful column rises up to 150 feet in the air. The water unfurls in the sunlight with the colors of the rainbow playing across it.
This eruption is only the visible part of the spectacle. The geyser is linked by an intricate plumbing network to some extremely hot rocks. As water seeps into the underground system, it is heated at the bottom like water in a tea kettle. But while water in a kettle rises because of convection, the narrow tubes of the geyser system prevent free circulation of the water. Thus, the water in the upper tubes is far cooler than the water at the bottom. The weight of the water puts pressure on the column, and this raises the boiling point of the water near the bottom. Finally, the water in the upper part of the column warms and expands, some of it welling out of the mouth the geyser. This decreases the pressure on the superheated water, which abruptly turns to steam. This in turn forces all the water and vapor out of the geyser.
5.25. Deep within the Earth there seethes a vast cauldron called Hot Dry Rock, or HDR, that observers believe could make the United States and other nations practically energy independent. HDR is a virtually limitless source of energy that generates neither pollution nor dangerous waste.
The concept, now being tested at the Los Alamos National Laboratory in New Mexico, is quite simple, at least in theory. Two adjacent wells are punched several miles into the Earth to reach this subterranean furnace. Water is pumped down one well to collect inside the Hot Dry Rock, creating a pressurized reservoir of superheated liquid. This is then drawn through the other well to the surface and there the water?Ts accumulated load of heat energy is transferred to a volatile liquid that, in turn, drives an electric power-producing turbine.
David Duchane, HDR program manager at Los Alamos, believes that an economically competitive, 1-megawatt plant of this type will be up and running in around two decades. A small prototype station will be built in half that time. But Duchane dreams an even grander dream. ?oWe could build an HDR plant near the seacoast,? he says. ?oCould you imagine pumping seawater down to where it heats up well above its boiling point ? Then you bring it to the surface to make electrical energy, and your turn some into vapor to get as much pure water as you need.?
5.26. Visitors to Prince Edward Island, Canada, delight in the ?ounspoiled? scenery ?" the well-kept farms and peaceful hamlets of the island?Ts central core and the rougher terrain of the east and west. In reality, the Island ecosystems are almost entirely artificial.
Islanders have been tampering with the natural environment since the eighteenth century and long ago broke down the Island?Ts natural forest cover to exploit its timber and clear land for agriculture. By 1900, 80 percent of the forest had been cut down and much f what remained had been destroyed by disease. Since then, however, some farmland has been abandoned and has returned to forest through the invasion of opportunist species, notably spruce. Few examples of the original climax forest, which consisted mostly of broadleaved trees such as maple, birch, and oak, survive today.
Apart from a few stands of native forest, the only authentic habitats on Prince Edward Island are its sand dunes and salt marshes. The dunes are formed from sand washed ashore by waves and then dried and blown by the wind to the land beyond the beach. The sand is prevented from spreading farther by marram grass, a tall, long-tooted species that grows with the dunes and keeps them remarkably stable. Marram grass acts as a windbreak and allows other plants such as beach pea and bayberry to take hold. On dunes where marram grass is broken down ?" for instance, where it is trampled ?" the dunes may spread inland and inundate agricultural lands or silt up fishing harbors. The white dunes of the north coast are the most impressive. There are also white dunes on the east and west coasts. Only in the south are there red dunes, created when the soft sandstone cliffs crumble into the sea and subsequently wash ashore as red sand. The dunes were once used as cattle pasture but were abandoned as the early settlers moved inland.
Salt marshes are the second remaining authentic habitat. These bogs are the result of the flooding of low coastal areas during unusually high tides. In the intervals between tides, a marsh area remains and plants take root, notably cord grass, the ?omarsh hay? used by the early settlers as winter forage for their livestock. Like the dunes, though, the marshes were soon dismissed as wasteland and escaped development.
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6. General Biology
6.1. In recent years, scientific and technological developments have drastically changed human life on our planet, as well as our views both of ourselves as individuals in society and of the universe as a whole. Perhaps one of the most profound developments of the 1970s was the discovery of recombinant DNA technology, which allows scientists to introduce genetic material (or genes) from one organism into another. In its simplest form, the technology requires the isolation of a piece of DNA, either directly from the DNA of the organism under study or artificially synthesized from an RNA template by using a viral enzyme called reverse transcriptase. This piece of DNA is then ligated to a fragment of bacterial DNA which has the capacity to replicate itself independently. The recombinant molecule thus produced can be introduced into the common intestinal bacterium Eschrichia coli, which can be grown in very large amounts in synthetic media. Under proper con***ions, the foreign gene will not only replicate in the bacteria, but also express itself, through the process of transcription and translation, to give rise to large amounts of the specific protein coded by the foreign gene.
The technology has already been successfully applied to the production of several therapeutically important biomolecules, such as insulin, interferon, and growth hormones. Many other important applications are under detailed investigation in laboratories throughout the world.
6.2. The reasons for the extinction of a species and for the rapid rates of change in our environment are currently the focus of much scientific research. An individual species?T susceptibility to extinction depends on at least two things: the taxon (the biological group ?" kingdom, phylum, class, order, family, or genus) to which a species belongs, and the overall rate of environmental change. Fossil evidence shows that more mammals and birds become extinct than do mollusk or insects. Studies of the extinction of the dinosaurs and other reptiles during the Cretaceous Period show that a changing environment affects different taxa in different ways. Some may be dramatically affected, others less so.
The best way to answer the question of what causes an extinction is to combine fields on inquiry and a variety of viewpoints. Using the fossil record and historical documentation, the different rates of the extinction of various taxa and different responses to environmental change can be detected. The evolutionary development of the different species can be compared, and traits that may be disadvantageous can be singled out. Finally, the researchers can use mathematical formulae to determine whether a population is likely to adapt itself to the changing environment or disappear. Hopefully, as more of this information is collected, specialists in different fields ?" e.g. physiological and behavioral ecology, population ecology, community ecology, evolutionary biology and systematics, biogeography, and paleobiology ?" will work together to make predictions about the broader changes that might occur in the ecosystem.
6.3. It has long been known that when exposed to light under suitable con***ions of temperature ad moisture, the green parts of plants use carbon dioxide from the atmosphere and release oxygen to it. The exchanges are the opposite of those that occur in respiration. The process is called photosynthesis. In photosynthesis, carbohydrates are synthesized from carbon dioxide and water by the chloroplast of plant cells in the presence of light. In most plants, the water used in photosynthesis is absorbed from the soil by the roots and translocated through the xylem of the root and stem to leaves. Except for the usually small percentage used in respiration, the oxygen released in the process diffuses out of the leaf into the atmosphere through the stomates. Oxygen is the product of the reaction. For each molecule of carbon dioxide used, one molecule of oxygen is released. A summary chemical equation for photosynthesis is
6C02 + 6H20 ?' C6H12O6 + 602
As a result of this process, radiant energy form the sun is stored as chemical energy. In turn, the chemical energy is used to decompose carbon dioxide and water. The products if their decomposition are recombined into a new compound, which is successively built up into more and more complex substances. After many intermediate steps, sugar is produced. At the same time, a balance of gases is preserved in the atmosphere.
6.4. Deciding whether a given population constitutes a species can be difficult in part because there is no single accepted definition of the term. Years ago, evolutionary biologist Ernst W. Mayr, propounding what is called the biological species concept, proposed that the definition be base on reproductive compatibility. Specifically, he considered a species to be a group of animals that can mate which one another to produce fertile offspring but cannot mate successfully with members of a different group.
Yet this idea can be too restrictive. First, mating between species (hybridization), as often occurs in the canine family, is quite common in nature. Second, in some instances, the differences between two populations might not prevent them from interbreeding, even though they are rather dissimilar in traits unrelated to reproduction: one might question whether such disparate groups should be considered a single species. A third problem with the biological species concept is that investigators cannot always determine whether two groups that live in different places are capable of interbreeding.
When the biological species concept is difficult to apply, some investigators use phenotype, an organism?Ts observable characteristics, as a surrogate. Two groups that have evolved separately are likely to display measurable differences in many of their traits, such as the size of the skull or the width of the teeth. If the distribution of measurements from one group does overlap those of the other group, the two groups might be considered distinct species. Another widely discussed idea designates a species based on the presence of some unique characteristic not found in the another closely related organism ?" for example, the upright posture of humans ?" or a distinguishing sequence of nucleotides (DNA building blocks) in a gene.
Proving that the red world fits any of these descriptions has been extremely challenging. For instance, the red wolf is not a species by Mayr?Ts definition, because it can breed extensively with the coyote and the gray wolf (C. lupus). And efforts to classify the red wolf based on its phenotypic traits have yielded ambiguous results. John James Audubon and John Bachman, who described the red wolf in their classic 1851 book, Viviparcus Quadrupeds of North America, had difficulty distinguishing the red wolf from the physically similar coyote and gray wolf. Modern researchers looking at phenotypic traits have variously concluded that the red wolf is a subspecies of the gray wolf, a hybrid of the coyote and the gray wolf, and a full-fledged species.
6.5. The biological community changes again as one moves from the city to the suburbs. Around all cities is a biome called the ?osuburban forest?. The trees of this forest are species that are favored by man, and most of them have been deliberately planted. Mammals such as rabbits, skunks, and opossums have moved in from the surrounding countryside. Raccoons have become experts at opening garbage cans, and in some places even deer wander suburban throughfares. Several species of squirrel get along nicely in suburbia, but usually only one species is predominant in any given suburb ?" fox squirrels in one place, red squirrels in another, gray squirrels in a third ?" for reasons that are little understood. The diversity of birds in the suburbs is great, and in the south, lizards thrive in gardens and even houses. Of course, insects are always present.
There is an odd biological sameness in these suburban communities. True, the palms of Los Angeles are missing from the suburbs of Boston, and there are species of insects in Miami not found in Seattle. But over wide stretches of the United States, ecological con***ions in suburban biomes vary much less than do those of natural biomes. Ad unlike the natural biomes, the urban and suburban communities exist in spite of, not because of, the climate.

6.6. Biological diversity has become widely recognized as a critical conservation issue only in the past two decades. The rapid destruction of the tropical rain forests, which are the ecosystems with the highest known species diversity on Earth, has awakened people to the importance and fragility of biological diversity. The high rate of species extinctions in these environments is jolting, but it is important to recognize the significance of biological diversity in all ecosystems. As the human population continues to expand, it will negatively affect one after another of Earth''s ecosystems. In terrestrial ecosystems and in fringe marine ecosystems (such as wetlands), the most common problem is habitat destruction. in most situations, the result is irreversible. Now humans are beginning to destroy marine ecosystems through other types of activities, such as disposal and run off of poisonous waste; in less than two centuries, by significantly reducing the variety of species on Earth, they have unraveled cons of evolution and irrevocably redirected its course.
Certainly, there have been periods in Earth''s history when mass extinctions have occurred. The extinction of the dinosaurs was caused by some physical event, either climatic or cosmic. There have also been less dramatic extinctions, as when natural competition between species reached an extreme conclusion. Only. 01 percent of the species that have lived on Earth have survived to the present, and it was largely chance that determined which species survived and which died out.
However, nothing has ever equaled the magnitude and speed with which the human species is altering the physical and chemical world and demolishing the environment. In fact, there is wide agreement that it is the rate of change humans are inflicting, even more than the changes themselves, that will lead to biological devastation. Life on Earth has continually been in flux as slow physical and chemical changes have occurred on Earth, but life needs time to adapt-time for migration and genetic adaptation within existing species and time for the proliferation of new genetic material and new species that may be able *****rvive in new environments.
6.7. Rachel Carson was born in 1907 in Springsdale, Pennsylvania. She studied biology at college and zoology at Johns Hopkins University, where she received her master?Ts degree in 1933. In 1936, she was hired by the U.S. fish and Wildlife Service, where she worked most of her life.
Carson?Ts first book, Under the Sea Wind, was published in 1941. It received excellent reviews, but sales were poor until it was reissued in 1952. In that year she published The Sea Around Us, which provided a fascinating look beneath the ocean?Ts surface, emphasizing human history as well as geology and marine biology. Her imagery and language had a poetic quality. Carson consulted no less experts in the field. However, she had voluminous correspondence and frequent discussions with experts in the field. However, she always realized the limitations of her nontechnical readers.
In 1962, Carson published Silent Spring, a book that sparked considerable controversy. It proved how much harm was done by the uncontrolled, reckless use of insecticides. She detailed how they poison the food supply of animals, kill birds and fish, and contaminate human food. At the time, spokesmen for the chemical industry mounted personal attacks against Carson and issued propaganda to indicate that her findings were flawed. However, her work was vindicated by a 1963 report of the President?Ts Science advisory Committee.
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7. Botany
7.1. Fifty years ago, plan physiologists set out to grow roots by themselves in solutions in laboratory flasks. The scientists found that the nutrition of isolated roots was quite simple. They required sugar and the unusual minerals and vitamins. However, they did not require organic nitrogen compounds. These roots got along fine on mineral inorganic nitrogen. Roots are capable of making their own proteins and other organic compounds. These activities by roots require energy, of course. The process of respiration uses sugar to make the high energy compound ATP, which drives the biochemical reactions. Respiration also requires oxygen. Highly active roots require a good deaf of oxygen.
The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants. The leaves of the shoots provide the roots with sugar and vitamins, and the roots provide the shoots with water and minerals. In ad***ion, roots can provide the shoots with organic nitrogen compounds. This comes in handy for the growth of buds in early spring when leaves are not yet functioning. Once leaves begin photosynthesizing, they produce protein, but only mature leaves can ?oexport? protein to the rest of the plant in the form of amino acids.
7.2. Many flowering plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue tells the pollinator that the flower is full of far more pollen than are neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flower. Plants do not have to spend precious resources maintaining reservoirs of nectar in all their flowers. Thus, the color-coded communication system benefits both plant and insect.
For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-unidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. By the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiments with papers flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scent of the nectar.
In other type of plants, blossoms change from with to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.
7.3. Light from a living plant or animals is called bioluminescence, or cold light, to distinguish it from incandescence, or heat-generating light. Life forms could not produce incandescent light without being burned. Their light is produced by chemicals combining in such a way that little or no measurable heat is produced. Although bioluminescence is a relatively complicated process, it can be reduced to simple terms. Living light occurs when luciferin and oxygen combine in the presence of luciferase. Fireflies require an ad***ional compound call ATP.
Much remains unknown, but many scientists who study bioluminescence believe that the origin of the phenomenon goes back to a time when there was no oxygen in the earth?Ts atmosphere. When oxygen was gradually introduced into the atmosphere, it was poisonous to life forms. Plants and animals produced light to use up the oxygen. Millions of years ago, all life produced light *****rvive. As the millennia passed, life forms on earth became tolerant of, and finally dependent on oxygen, and the adaptation that produced bioluminescence was no longer necessary, but some primitive plants and animals continued to use the light for new functions such as mating or attracting prey.
7.4. Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher, the sequoia tree can pump water to its very top, more than 100 meters above the ground. Until the end of the nineteenth century , the movement of water''s in trees and other talls plants was a mystery. Some botanists hypothesized that the living cells of plants acted as pumps, but many experiments demonstrated that the stems of plants in which all the cells are killed can still move water to appreciable heights. Other explanations for the movement of water in plants have been based on root pressure, a push on the water from the roots at the bottom of the plant. But root pressure is not nearly great enough to push water to the tops of tall trees, Furthermore, the conifers, which are among the tallest trees have unusually low root pressures.
If water is not pumped to the top of a tall tree, .and if it is not pushed, to the top of a tall tree, then we may ask. How does it get there? According to the currently accepted cohesion-tension theory, water is pulled there. The pull on a rising column of water in a plant results from the evaporation of water at the top of the plant. As water is lost from the surface of the leaves,a negative pressure or tension is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water .are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore, the forces of cohestion (the attraction between water molecules) arc so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to be pulled to great heights without being broken.
7.5. Water scarcity is fast becoming one of the major limiting factors in world crop production. In many areas, poor agricultural practices have led to increasing desertification and the loss of formerly arable lands. Consequently, those plant species that are well adapted *****rvival in dry climates are being looked at for an answer in developing more efficient crops to grow on marginally arable lands.
Plants use several mechanisms to ensure their survival in desert environment. Some involve purely mechanical and physical adaptations, such as the shape of the plant?Ts surface, smaller leaf size, and extensive root systems. Some of the adaptations are related to chemical mechanisms. Many plants, such as cacti, have internal gums and mucilages which give them water-retaining properties. Another chemical mechanism is that of the epicuticular wax layer. This wax layer acts as an impervious cover to protect the plant. It prevents excessive loss of internal moisture. It also protects the plant from external aggression, which can come from inorganic agents such as gases, or organic agents which include bacteria and plant pests.
Researchers have proposed that synthetic waxes with similar protective abilities could be prepared based on knowledge of desert plants. If successfully developed, such a compound could be used to greatly increase a plant?Ts ability to maintain health in such adverse situations as inadequate water supply, limited fertilizer availability, attack by pests, and poor storage after harvesting.
7.6. Plants are subject to attack and infection by a remarkable variety of symbiotic species and have evolved a diverse array of mechanisms designed to frustrate the potential colonists. These can be divided into preformed or passive defense mechanisms and inducible or active systems. Passive plant defense comprises physical and chemical barriers that prevent entry of pathogens, such as bacteria, or render tissues unpalatable or toxic to the invader. The external surfaces of plants, in ad***ion to being covered by an epidermis and a waxy cuticle, often carry spiky hairs known as trichomes, which either prevent feeding by insects or may even puncture and kill insect larvae. Other trichomes are sticky and glandular and effectively trap and immobilize insects.
If the physical barriers of the plant are breached, then preformed chemicals may inhibit or kill the intruder, and plant tissues contain a diverse array of toxic or potentially toxic substances, such as resins, tannins, glycosides, and alkaloids, many of which are highly effective deterrents to insects that feed on plants. The success of the Colorado beetle in infesting potatoes, for example, seems to be correlated with its high tolerance to alkaloids that normally repel potential pests. Other possible chemical defenses, while not directly toxic to the parasite, may inhibit some essential step in the establishment of a parasitic relationship. For example, glycoproteins in plant cell walls may inactivate enzymes that degrade cell walls. These enzymes are often produced by bacteria and fungi.
Active plant defense mechanisms are comparable to the immune system of vertebrate animals, although the cellular and molecular bases are fundamentally different. Both, however, are triggered in reaction to intrusion, implying that the host has some means of recognizing the presence of a foreign organism. The most dramatic example of an inducible plant defense reaction is the hypersensitive response. In the hypersensitive response, cells undergo rapid necrosis--that is, they become diseased and die--after being penetrated by a parasite; the parasite itself subsequently ceases to grow and is therefore restricted to one or a few cells around the entry site. Several theories have been put forward to explain the basis of hypersensitive resistance.
7.7. It?Ts a sound you will probably never hear, a sickened tree sending out a distress signal. But a group of scientists has heard the cries, and they think some insects also hear the trees and are draw to them like vultures to a dying animal.
Researchers with the U.S. Department of Agriculturê?Ts Forest Service fastened sensors to the bark of drought-stricken trees and clearly heard distress calls. According to one of the scientists, most parched trees transmit their plight in the 50- to 500-kilohertz range. The unaided human ear can detect no more than 20 kilohertz.) Red oak, maple, white pine, and birch all make slightly different sounds in the form of vibrations at the surface of the wood.
The scientists think that the vibrations are created when the water columns inside tubes that run the length of the tree break, a result of too little water flowing through them. These fractured columns send out distinctive vibration patterns. Because some insects communicate at ultrasonic frequencies, they many pick up the trees?T vibrations and attack the weakened trees. Researchers are now running tests with potted trees that have been deprived of water to see if the sound is what attracts the insects. ?oWater-stressed trees also smell differently from other trees, and they experience thermal changes, so insects could be responding to something other than sound,? one scientist said.
7.8. A division of the bryophytes, liverworts are relatively small plants which have adapted to different habitats. Two species of liverworts, Riella and Ricciocarpus, thrive in aquatic habitats. Some a found in the company of other vegetation such as mosses, lichens, and sedges in the tundra in Antarctica, while most others prefer moist, shady floors and tree trunks of tropical forests. Leafy liverworts, with two or three rows of lobe-shaped leaves which overlap incompletely, are discovered plentifully in the tropical forests. These plants develop water storage pockets which become home to a host of very small animals. They have a prostrate growth, and single-cell rhizoids ?" hairlike projections ?" anchor the plant but are incapable of transporting nutrients to the plant. The absence of a midrib is quite common in bryophytes. Sphaerocarpo, a Thallus liverwort, sometimes produces round rosettes or extended, flattened lobes.
The bryophytes not only aid soil formation on rocky and unproductive land but balance the moisture content of the soil. Their epidermal cells ?" outer cells of the plant ?" fused with significant air pores enclose the photosynthetic cells. These pores play a major role in the photosynthetic process in which carbon dioxide is take in and oxygen is given off.
7.9. Lichens, of which more than twenty thousand species have been named, are complex associations between certain fungi and certain algae. The lichen itself is not an organism; rather it is the morphological and biochemical product of the association. Neither a fungus nor an alga alone can produce a lichen.
The intimate relationship between these two living components of a lichen was once erroneously thought to represent mutualism. In mutualistic relationships, both participants benefit. With lichens, however, it appears the fungus actually parasitizes the algae. This is one of the conclusions drawn from experiments in which the two components of lichens were separated and grown apart.
In nature, lichen fungi may encounter and grow around several kinds of algae. Some types of algae the fungi may kill; other types it may reject. Lichen algae are autotropic, meaning they make their own food through photosynthesis. Lichen fungi are heterotrophic, meaning they depend upon the algae within the lichen *****pply their food. Up to ninety percent of the food made by the green algal cell is transferred to the fungus. What, if anything, the fungus contributes to the association is not well understood.
Lichens are hardy. They grow in many habitats and are often pioneers in hostile environments where few other organisms can flourish. They have been known to grow endolithically, having been discovered thriving inside of rocks in Antarctica. Lichens help reduce erosion by stabilizing soil. Several kinds of insects glue lichens to their exoskeletons for camouflage. Many species of birds use lichens as building materials for nests. Humans have used lichens for dyes and antibiotics.

6.6. Biological diversity has become widely recognized as a critical conservation issue only in the past two decades. The rapid destruction of the tropical rain forests, which are the ecosystems with the highest known species diversity on Earth, has awakened people to the importance and fragility of biological diversity. The high rate of species extinctions in these environments is jolting, but it is important to recognize the significance of biological diversity in all ecosystems. As the human population continues to expand, it will negatively affect one after another of Earth''s ecosystems. In terrestrial ecosystems and in fringe marine ecosystems (such as wetlands), the most common problem is habitat destruction. in most situations, the result is irreversible. Now humans are beginning to destroy marine ecosystems through other types of activities, such as disposal and run off of poisonous waste; in less than two centuries, by significantly reducing the variety of species on Earth, they have unraveled cons of evolution and irrevocably redirected its course.
Certainly, there have been periods in Earth''s history when mass extinctions have occurred. The extinction of the dinosaurs was caused by some physical event, either climatic or cosmic. There have also been less dramatic extinctions, as when natural competition between species reached an extreme conclusion. Only. 01 percent of the species that have lived on Earth have survived to the present, and it was largely chance that determined which species survived and which died out.
However, nothing has ever equaled the magnitude and speed with which the human species is altering the physical and chemical world and demolishing the environment. In fact, there is wide agreement that it is the rate of change humans are inflicting, even more than the changes themselves, that will lead to biological devastation. Life on Earth has continually been in flux as slow physical and chemical changes have occurred on Earth, but life needs time to adapt-time for migration and genetic adaptation within existing species and time for the proliferation of new genetic material and new species that may be able *****rvive in new environments.
6.7. Rachel Carson was born in 1907 in Springsdale, Pennsylvania. She studied biology at college and zoology at Johns Hopkins University, where she received her master?Ts degree in 1933. In 1936, she was hired by the U.S. fish and Wildlife Service, where she worked most of her life.
Carson?Ts first book, Under the Sea Wind, was published in 1941. It received excellent reviews, but sales were poor until it was reissued in 1952. In that year she published The Sea Around Us, which provided a fascinating look beneath the ocean?Ts surface, emphasizing human history as well as geology and marine biology. Her imagery and language had a poetic quality. Carson consulted no less experts in the field. However, she had voluminous correspondence and frequent discussions with experts in the field. However, she always realized the limitations of her nontechnical readers.
In 1962, Carson published Silent Spring, a book that sparked considerable controversy. It proved how much harm was done by the uncontrolled, reckless use of insecticides. She detailed how they poison the food supply of animals, kill birds and fish, and contaminate human food. At the time, spokesmen for the chemical industry mounted personal attacks against Carson and issued propaganda to indicate that her findings were flawed. However, her work was vindicated by a 1963 report of the President?Ts Science advisory Committee.
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7. Botany
7.1. Fifty years ago, plan physiologists set out to grow roots by themselves in solutions in laboratory flasks. The scientists found that the nutrition of isolated roots was quite simple. They required sugar and the unusual minerals and vitamins. However, they did not require organic nitrogen compounds. These roots got along fine on mineral inorganic nitrogen. Roots are capable of making their own proteins and other organic compounds. These activities by roots require energy, of course. The process of respiration uses sugar to make the high energy compound ATP, which drives the biochemical reactions. Respiration also requires oxygen. Highly active roots require a good deaf of oxygen.
The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants. The leaves of the shoots provide the roots with sugar and vitamins, and the roots provide the shoots with water and minerals. In ad***ion, roots can provide the shoots with organic nitrogen compounds. This comes in handy for the growth of buds in early spring when leaves are not yet functioning. Once leaves begin photosynthesizing, they produce protein, but only mature leaves can ?oexport? protein to the rest of the plant in the form of amino acids.
7.2. Many flowering plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue tells the pollinator that the flower is full of far more pollen than are neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flower. Plants do not have to spend precious resources maintaining reservoirs of nectar in all their flowers. Thus, the color-coded communication system benefits both plant and insect.
For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-unidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. By the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiments with papers flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scent of the nectar.
In other type of plants, blossoms change from with to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.
7.3. Light from a living plant or animals is called bioluminescence, or cold light, to distinguish it from incandescence, or heat-generating light. Life forms could not produce incandescent light without being burned. Their light is produced by chemicals combining in such a way that little or no measurable heat is produced. Although bioluminescence is a relatively complicated process, it can be reduced to simple terms. Living light occurs when luciferin and oxygen combine in the presence of luciferase. Fireflies require an ad***ional compound call ATP.
Much remains unknown, but many scientists who study bioluminescence believe that the origin of the phenomenon goes back to a time when there was no oxygen in the earth?Ts atmosphere. When oxygen was gradually introduced into the atmosphere, it was poisonous to life forms. Plants and animals produced light to use up the oxygen. Millions of years ago, all life produced light *****rvive. As the millennia passed, life forms on earth became tolerant of, and finally dependent on oxygen, and the adaptation that produced bioluminescence was no longer necessary, but some primitive plants and animals continued to use the light for new functions such as mating or attracting prey.
7.4. Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher, the sequoia tree can pump water to its very top, more than 100 meters above the ground. Until the end of the nineteenth century , the movement of water''s in trees and other talls plants was a mystery. Some botanists hypothesized that the living cells of plants acted as pumps, but many experiments demonstrated that the stems of plants in which all the cells are killed can still move water to appreciable heights. Other explanations for the movement of water in plants have been based on root pressure, a push on the water from the roots at the bottom of the plant. But root pressure is not nearly great enough to push water to the tops of tall trees, Furthermore, the conifers, which are among the tallest trees have unusually low root pressures.
If water is not pumped to the top of a tall tree, .and if it is not pushed, to the top of a tall tree, then we may ask. How does it get there? According to the currently accepted cohesion-tension theory, water is pulled there. The pull on a rising column of water in a plant results from the evaporation of water at the top of the plant. As water is lost from the surface of the leaves,a negative pressure or tension is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water .are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore, the forces of cohestion (the attraction between water molecules) arc so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to be pulled to great heights without being broken.
7.5. Water scarcity is fast becoming one of the major limiting factors in world crop production. In many areas, poor agricultural practices have led to increasing desertification and the loss of formerly arable lands. Consequently, those plant species that are well adapted *****rvival in dry climates are being looked at for an answer in developing more efficient crops to grow on marginally arable lands.
Plants use several mechanisms to ensure their survival in desert environment. Some involve purely mechanical and physical adaptations, such as the shape of the plant?Ts surface, smaller leaf size, and extensive root systems. Some of the adaptations are related to chemical mechanisms. Many plants, such as cacti, have internal gums and mucilages which give them water-retaining properties. Another chemical mechanism is that of the epicuticular wax layer. This wax layer acts as an impervious cover to protect the plant. It prevents excessive loss of internal moisture. It also protects the plant from external aggression, which can come from inorganic agents such as gases, or organic agents which include bacteria and plant pests.
Researchers have proposed that synthetic waxes with similar protective abilities could be prepared based on knowledge of desert plants. If successfully developed, such a compound could be used to greatly increase a plant?Ts ability to maintain health in such adverse situations as inadequate water supply, limited fertilizer availability, attack by pests, and poor storage after harvesting.
7.6. Plants are subject to attack and infection by a remarkable variety of symbiotic species and have evolved a diverse array of mechanisms designed to frustrate the potential colonists. These can be divided into preformed or passive defense mechanisms and inducible or active systems. Passive plant defense comprises physical and chemical barriers that prevent entry of pathogens, such as bacteria, or render tissues unpalatable or toxic to the invader. The external surfaces of plants, in ad***ion to being covered by an epidermis and a waxy cuticle, often carry spiky hairs known as trichomes, which either prevent feeding by insects or may even puncture and kill insect larvae. Other trichomes are sticky and glandular and effectively trap and immobilize insects.
If the physical barriers of the plant are breached, then preformed chemicals may inhibit or kill the intruder, and plant tissues contain a diverse array of toxic or potentially toxic substances, such as resins, tannins, glycosides, and alkaloids, many of which are highly effective deterrents to insects that feed on plants. The success of the Colorado beetle in infesting potatoes, for example, seems to be correlated with its high tolerance to alkaloids that normally repel potential pests. Other possible chemical defenses, while not directly toxic to the parasite, may inhibit some essential step in the establishment of a parasitic relationship. For example, glycoproteins in plant cell walls may inactivate enzymes that degrade cell walls. These enzymes are often produced by bacteria and fungi.
Active plant defense mechanisms are comparable to the immune system of vertebrate animals, although the cellular and molecular bases are fundamentally different. Both, however, are triggered in reaction to intrusion, implying that the host has some means of recognizing the presence of a foreign organism. The most dramatic example of an inducible plant defense reaction is the hypersensitive response. In the hypersensitive response, cells undergo rapid necrosis--that is, they become diseased and die--after being penetrated by a parasite; the parasite itself subsequently ceases to grow and is therefore restricted to one or a few cells around the entry site. Several theories have been put forward to explain the basis of hypersensitive resistance.
7.7. It?Ts a sound you will probably never hear, a sickened tree sending out a distress signal. But a group of scientists has heard the cries, and they think some insects also hear the trees and are draw to them like vultures to a dying animal.
Researchers with the U.S. Department of Agriculturê?Ts Forest Service fastened sensors to the bark of drought-stricken trees and clearly heard distress calls. According to one of the scientists, most parched trees transmit their plight in the 50- to 500-kilohertz range. The unaided human ear can detect no more than 20 kilohertz.) Red oak, maple, white pine, and birch all make slightly different sounds in the form of vibrations at the surface of the wood.
The scientists think that the vibrations are created when the water columns inside tubes that run the length of the tree break, a result of too little water flowing through them. These fractured columns send out distinctive vibration patterns. Because some insects communicate at ultrasonic frequencies, they many pick up the trees?T vibrations and attack the weakened trees. Researchers are now running tests with potted trees that have been deprived of water to see if the sound is what attracts the insects. ?oWater-stressed trees also smell differently from other trees, and they experience thermal changes, so insects could be responding to something other than sound,? one scientist said.
7.8. A division of the bryophytes, liverworts are relatively small plants which have adapted to different habitats. Two species of liverworts, Riella and Ricciocarpus, thrive in aquatic habitats. Some a found in the company of other vegetation such as mosses, lichens, and sedges in the tundra in Antarctica, while most others prefer moist, shady floors and tree trunks of tropical forests. Leafy liverworts, with two or three rows of lobe-shaped leaves which overlap incompletely, are discovered plentifully in the tropical forests. These plants develop water storage pockets which become home to a host of very small animals. They have a prostrate growth, and single-cell rhizoids ?" hairlike projections ?" anchor the plant but are incapable of transporting nutrients to the plant. The absence of a midrib is quite common in bryophytes. Sphaerocarpo, a Thallus liverwort, sometimes produces round rosettes or extended, flattened lobes.
The bryophytes not only aid soil formation on rocky and unproductive land but balance the moisture content of the soil. Their epidermal cells ?" outer cells of the plant ?" fused with significant air pores enclose the photosynthetic cells. These pores play a major role in the photosynthetic process in which carbon dioxide is take in and oxygen is given off.
7.9. Lichens, of which more than twenty thousand species have been named, are complex associations between certain fungi and certain algae. The lichen itself is not an organism; rather it is the morphological and biochemical product of the association. Neither a fungus nor an alga alone can produce a lichen.
The intimate relationship between these two living components of a lichen was once erroneously thought to represent mutualism. In mutualistic relationships, both participants benefit. With lichens, however, it appears the fungus actually parasitizes the algae. This is one of the conclusions drawn from experiments in which the two components of lichens were separated and grown apart.
In nature, lichen fungi may encounter and grow around several kinds of algae. Some types of algae the fungi may kill; other types it may reject. Lichen algae are autotropic, meaning they make their own food through photosynthesis. Lichen fungi are heterotrophic, meaning they depend upon the algae within the lichen *****pply their food. Up to ninety percent of the food made by the green algal cell is transferred to the fungus. What, if anything, the fungus contributes to the association is not well understood.
Lichens are hardy. They grow in many habitats and are often pioneers in hostile environments where few other organisms can flourish. They have been known to grow endolithically, having been discovered thriving inside of rocks in Antarctica. Lichens help reduce erosion by stabilizing soil. Several kinds of insects glue lichens to their exoskeletons for camouflage. Many species of birds use lichens as building materials for nests. Humans have used lichens for dyes and antibiotics.

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