HOW WAS THE EARTH MADE?
IN referring to the reputed works of Hercules, one of the Latin writers expressed skepticism concerning them, and stated that it is difficult to believe what the poets have said. In like manner some of the current beliefs are questioned. Some modern thinkers have found difficulty in believing what other thinkers have said.
Nebular and Planetesimal Theories
Those who question the foundation of theories make themselves as unpopular in certain quarters as Socrates was with the ancient Greeks when he pointed out to them the absurdity of their beliefs. Recently a speaker who mentioned the fact that serious doubt had been thrown on the nebular theory was accused of being a mental anarchist. "Why," the objector asked, "should things that we have accepted all our life be turned upside down?"
Since the nebular theory was formulated, more than a century ago, great progress has been made in the accumulation of facts relating to the heavenly bodies, and particularly to the earth as one of these bodies. In the light of these facts, this theory has been weighed in the balance and, in the opinion of some, found wanting. The planetesimal theory, founded on modern knowledge, formulated to take its place, is accepted by some and rejected by others.
Behold, now, the working of the conservative mind! We were brought up to believe that the nebular theory presents a true picture of the origin of the earth, and we were quite content in this belief as long as no one said it was wrong. Why isn't it true? Therefore, by implication, of course it is true! How foolish to argue against it! Has it not been law for a hundred years? Volumes have been written about it; universities teach it; textbooks are full of it; and even the children of the kindergarten rush home to tell mother that the world was once nothing but steam like that from the kettle. Almost everyone knows, or thinks he knows, that the solar system was once a mass of diffused gas and that on cooling, this mass formed the sun and the planets.
Whatever else may have resulted from the diffusion of gas, many a nebulous tale has resulted. The comparison of Genesis and geology is a favorite theme, especially with some who seem to know little about either.
I recall the stirring eloquence of an orator well known many years ago, as he painted in lurid hues the picture of the cooling earth receiving the torrential downpour of water to form the oceans, and of a thick atmosphere, too murky for the rays of the sun to penetrate. He had learned, perhaps, that the great beds of coal of the Carboniferous period are formed of vegetable matter, and that plants cannot grow without light. Therefore, he called on the thick clouds which shut out the light of the sun to illuminate the earth by electric flashes. How we closed our eyes as the lightnings of that far-off time flashed (in the fertile imagination of the speaker) so constantly that they furnished the light necessary for the growth of forests. And how the thunder (mostly of oratory) roared!
The picture was worked out in great wealth of detail, and really served a good purpose, for it gave the theory a ludicrous aspect and caused some to wonder whether there was really any truth in it.
Such word painting is in the class of an address periodically delivered by an acquaintance of mine who is fond of preaching in support of the story of Jonah and his accommodating whale. He reaches a grand climax with the statement that an all-powerful Being would be able, if necessary, to "prepare for Jonah's accommodation a whale with up-to-date apartments including steam heat and electric light."
Unfortunately, such statements sometimes reach large audiences, for fancy runs through many editions while fact is searching for a publisher. And sometimes fancy even creeps into science, the acknowledged realm of facts. Too often unsupported assertions carry the weight of conviction where demonstrated law makes little impression. Witness the theories of the origin of the earth!
Recently a well known publication conveyed to nearly half a million readers the unqualified assertion that the earth was once
a great, fiery ball, so hot that water can not rest tranquilly upon its surface. . . . All of the carbonic acid that is to supply the carbon to form the immense coal fields and to combine with calcium to form the great beds of limestone is in the atmosphere, and all the water of all the modern seas and oceans, lakes and rivers, is held in a great thundercloud that envelops the entire earth.
There is no light except that from the glow of volcanic fires, and from the almost incessant flashes of lightning . . . rain falls actually in rivers. The roar of the thunder and the crashes of volcanic explosions are deafening. As the rivers of rain strike the hot surface of the earth, they are converted again into steam and thrown into the sky.
The weight of the atmosphere under the ocean of steam and cloud and carbonic acid gas is so great that water must be heated red-hot before it will boil.
Such a word picture has a certain uncanny fascination and recalls the tales told by Baron Munchausen. Yet it is a fair deduction from the nebular theory of the origin of the earth. Years ago such statements might have passed unchallenged, but now scholars qualified to speak with authority say that such extreme conceptions must be abandoned. Few up-to-date geologists would undertake to defend the statements quoted. We should at least be told that they express only possibilities and that many leading scientists treat the subject differently.
A Cherished Belief
The origin of the earth is a fascinating subject. The belief in the nebular theory is cherished by those who grew up under it, and some of these show a tendency to regard modern thinkers who reject it as agitators trying to overturn an established order of thought.
According to this theory the original nebula, consisting of gas, extended from the sun as a center outward beyond the orbits of the planets. This nebula, which had in some way acquired a rotary motion, slowly contracted as it cooled. Its rotation increased correspondingly until the centrifugal force which tended to throw off the outer portions equaled the gravitative force which tended to hold them to the central mass. Then a ring was formed like the rings of Saturn, which in time became a planet. This process was repeated for each planet, each ring being left behind as the central mass continued to shrink into the sun.
As enunciated by the great French scholar Laplace this theory seemed ample and satisfying. Its very boldness and splendor gave it a dignity which seems to have overcome all opposition. It set forth so clearly the march of events in the creation of the world that it swept aside obstacles to its progress. It seemed to be in harmony with the fundamental relations of the solar system as they were understood at the time it was announced. It was in general agreement with the learning of a century ago. Above all, it offered a clear, easily comprehended answer to the question of universal interest, How was the earth made? Few suspected that the answer which the nebular theory gave might be wrong, and, later the theory became so popular that opposition to it was unpleasant to maintain. Even at the present time an attempt to discredit it in certain quarters seems useless. There is hope for a blind man who wants to see, but none for those who have eyes but will not see!
Difficulty of Changing Established Opinion
As long as there was no great number of well-established facts opposing the nebular theory it ran its course without let or hindrance, and many still hold to the opinion that it is good enough to be let alone. Others not so easily satisfied contend that theories, however beautiful, should not obstruct progress. The false must perish and the true survive!
The opposition to any radical change in established belief is well expressed by the following satirical verse by Charlotte Perkins Stetson:1
There was once a Neolithic Man,
The nebular theory was a magnificent conception, worthy of the great mind that formulated it. Through its influence on the thoughts of men it accomplished immense results. But beautiful as it is, it may not be correct. The limelight of mathematics, astrophysics, and modern geology has been turned upon it and has discovered facts that it cannot explain. Many of these facts have been pointed out. One illustration may suffice.
Errors in Application
According to the older theory the earth at one time consisted wholly of melted rock like the boiling slag of some immense blast furnace. As the earth cooled a crust was formed and gradually thickened until a stable surface allowed water to remain on it. At first the water was boiling hot, but later in the earth's history the surface became cool enough to permit plants and animals to live on it. The cooling continued, according to this conception, through geologic ages, and in relatively recent timethat is, during the Great Ice Agethe surface of the earth became so cold that glaciers formed over large parts of it.
At this point the prophets take up the refrain and predict dire catastrophes. They point out the terrible consequences of the inexorable law of cooling worlds. Soon the earth will freeze and die. Is not the moon already dead?
The picture seemed plausible enough as long as only one glacial epoch was known. But in course of time the discovery was made that glaciers covered parts of the earth long ages before the Great Ice Age, at times when, according to the nebular theory, the earth was sweltering under a hot, murky atmosphere. (Why will scientific men persist in spoiling perfectly good theories by damaging discoveries!) The evidence of still older ice ages was discovered, one so old that its records are found in rocks laid down during one of the first of the geologic periods.
Origin of the Planetesimal Theory
The planetesimal theory was formulated several years ago by Prof. T. C. Chamberlin, of Chicago University. It has been slow in finding its way into nonscientific circles, but it is worthy of consideration. It is fundamentally different from the old theory. The problems are approached from a different point of view. No attempt is made to expand the new theory into a universal law. It seeks to explain our solar system and nothing more.
Unlike the old theory, the new one is based on numerous physical laws which have been discovered in the course of modern research. It may not now be expressed as clearly as was the old theory, for some of the newly discovered laws are not yet widely known outside of scientific circles. Many of the new words and some combinations of words necessary to express the new ideas are unfamiliar. Until one understands what is meant by kinetic view of gases, earth-knots, planetesimals, krenal atmospheres, and vestiges of cosmogonic states, one can scarcely be expected to understand a theory in which these terms are used. However, difficulty in understanding the nomenclature of a theory is no argument against its truth.
A Collision of Worlds
In place of the concept of a solar system evolved or derived from an evenly diffused gas, this system, under the planetesimal theory, is evolved from irregularly scattered matter of various kinds, some of it solid and some gaseous. This material is supposed to have been derived from a heavenly body already in existence, called the ancestral sun, because it contained the material now distributed among the several planets and satellites. Like every theory that deals with the origin of worlds, it starts with matter already in existence. But it contrasts sharply with the nebular theory in assuming that this matter was in a physical state such as we are familiar with.
The ancestral sun, according to the theory, was disrupted or was partly torn to pieces by near collision with another heavenly body that passed near it. As stars move in different directions and at varying velocities, it would seem strange if in past ages no two heavenly bodies had approached near enough together to interfere with each other. The sudden increase in brilliancy of some stars noted by astronomers is supposed to be due to collision. Hence the postulated interference of a star with the ancestral sun is not only possible but reasonable. The star need not actually strike the sun in order to tear it to pieces and scatter the fractured material; in fact, a head-on collision probably would not produce the rotary motion possessed by the solar system.
Under the laws of body-tides, a star passing near the sunthat is, within a few hundred millions of mileswould interfere with the sun's internal equilibrium and cause it to shoot out a part of its substance toward the passing star and another part in the opposite direction, for the same reasons that tides of the ocean are formed on opposite sides of the globe. The attractive force of the passing star, aided by the internal expansive forces of the sun, is supposed to have caused gigantic eruptions similar in character to those taking place on a relatively small scale in the sun at the present time. During times of solar eclipse eruptions are observed through the telescope, in which great masses of matter are shot far out from the surface of the sun. A more familiar illustration is found in volcanoes of the explosive type. But instead of a cubic mile or two of rock blown from a volcano, the matter supposed to have been ejected from the ancestral sun at the time of disruption contained the substance of future worlds and was shot out millions of miles into space. Under the influence of the passing star material thus thrown out from the ancestral sun may have been given a rotary motion around the parent mass, forming a spiral nebula similar to those revealed by the telescope in many parts of the heavens.
A Nebula Formed
In this way, according to the new theory, was produced the diffusion of matter from which our solar system was evolved. Chamberlin states the case thus:
The term solar nebula is not here used in the inherited sense of a nebula that condensed into the sun and its attendants, but as a nebula evoked from the sun to form its attendants. As here interpreted the solar nebula was little more than a streaming knotty pair of arms of nebulous matter shot out from the sun and curved into spiral appendages about it by the joint pull of itself and a passing star.
The larger aggregates or knots may have retained a high temperature, but much of the widely diffused matter must have been cooled to the temperature of interstellar spacethat is, to a temperature commonly known as absolute zero.
The derivation of world matter from the ancestral sun by this disruptive process may not tax too greatly the credulity of the reader if he reflects that only 1/745 of the sun's substance was required to form our whole planetary system; and that the substance of the earth is about one three-thousandth of 1 per cent of that of the sun.
It is clear that, with this fundamental departure from the former conception of a nebula, the new story of the development of the solar system must be very different from the old. The task of writing it naturally fell to the lot of the man who had questioned the validity of the nebular theory. It is an unwritten law in science that an accepted theory may not be destroyed until it can be replaced by something better. In harmony with this law the author of the planetesimal theory has shown how the solar system, as it exists, could be built up from cold matter, irregularly scattered in space. That he has succeeded in forming a reasonable explanation is attested by the number of scientific men who look favorably on his conclusions.
A New System
According to the new theory, the "knots" or relatively dense parts of the disrupted matter which was shot out from the sun served as nuclei for gathering the more widely scattered particles and finally grew to be planets and satellites. It is estimated that the earth knot originally may have contained 30 or 40 per cent of the earth's adult mass. Whether it was composed in whole or in part of hot gas or of particles of solid matter held together loosely does not affect the theory. The scattered fragments, large and small, solid and gaseous, ranging in size from infinitesimal particles to great masses, are called planetesimals; hence the name planetesimal theory.
The earth knot, composed of material originally somewhat closely aggregated, gathered into a compact mass under gravitative force, thus forming a young earth, perhaps less than half its present size. At this early stage the growing earth developed a character that greatly affected its later history, for when less than half grown its gravitational force was strong enough to hold an atmosphere. Previous to this time the unprotected infant earth may have been continually bombarded by falling planetesimals, but the material of its outer half thereafter was brought in from surrounding space through an enveloping layer of gas, which acted as a cushion to ease the force of the bombardment.
So great is the importance of an atmosphere on the growth and character of the earth that we may stop for a moment to consider this subject.
Under the kinetic view of gases the molecules are "fidgety midgets," always apparently in a whirl or a quiver, flying to and fro with marvelous velocity, colliding and rebounding with extraordinary frequency. Their rate of movement depends on many circumstances. Light molecules, such as those of hydrogen, are likely to move rapidly; heavy molecules, like those of carbon dioxide, move more slowly. Molecules of a hot gas move more rapidly than those of a cold gas.
Gases, like other forms of matter, are controlled within certain limits by gravity; hence the molecules of the atmosphere, although in rapid motion, are held close to earth. But there is a limit to this control. If the resistance of the atmosphere could be removed a bullet shot directly upward with a velocity about seven miles per second would never return to earth. It might be captured by the sun or by some other body of strong attraction; or it might wander through space like a meteorite.
The molecules of the atmospheric gases may be thought of as minute bullets. If a molecule starts on an unobstructed path directly away from the earth, with a velocity of 6.9 miles per second, it will escape. The earth's attraction is not strong enough to hold it. A larger body, such as Jupiter or the sun, can control the swifter molecules of light gases, but a small body like the moon cannot control even the slower molecules of the heavy gases. This may explain why such light gases as hydrogen and helium occur in the sun's atmosphere but not in that of the earth and why such heavier gases as oxygen and nitrogen are held under control by the earth but not by the moon.
Atmosphere and Ocean
Under the planetesimal theory the earth was once too small to hold an atmosphere. In its early life it may have been as cold and barren and spectral as the moon. But as it grew, by gathering up the solid planetesimals near by, it became strong enough in time to gather in and control the gaseous matter. At this critical stage in its history, as already stated, the manner of its growth changed. Planetesimals falling to the earth had to penetrate an atmosphere in the same manner as meteorites now penetrate it. Probably then, as now, the smaller ones were oxidized and reached the earth as meteoric dust.
In the presence of an atmosphere captured water vapor was condensed and the circulation of water was established. The importance of water as an active geologic agent can scarcely be overemphasized. A body like the earth which grew in the presence of freely circulating water would be very different from a body formed of molten rock and essentially completed before water began to accumulate on it. It may be said in passing that the constitution of the earth's crust, as observed, harmonizes with this theory of accumulation of matter in the presence of water.
In brief, the planetesimal theory pictures the earth as growing from a modest beginning chiefly by gathering in cold particles of scattered matter near it. This growth has not yet entirely ceased, for meteorites are still coming to the earth in great numbers. It may never have been molten throughout and may never have been too hot for the existence of organic matter. At first the young earth had no atmosphere and no oceans. It may have been as cold and dry as the moon is at the present time. An atmosphere began to gather when the earth was less than half grown and oceans began to form somewhat later. In the beginning the oceans were small and contained fresh water. Their present salinity is an acquired character; their salt was derived from the rocks. In place of the postulated hot, murky darkness of early ages, the planetesimal theory pictures the atmosphere as dry, cool, and bright.
The new theory explains many things that seemed inexplicable under the old. It is not my purpose here to attempt to apply the theory in detail. Such application would require volumes. But the following examples may illustrate the possibilities of application.
Good, orderly, well-behaved moons like our own revolve about their planets in the same direction that the planets rotate. The discovery that two of the moons of Jupiter and one of Saturn revolve in the opposite direction was puzzling and disconcerting under the old theory. Under the new, this retrograde motion is regarded as normal.
Under the old theory it was difficult to explain the high development of the oldest known forms of life found fossilized in the rocks. Biology demanded longer periods for development than geology could supply. But under the new theory, conditions suitable for life on the the earth may extend back indefinitely in time. Biology may now have all the time necessary.
Glaciology called for several cold periods, some dating back to a time when the earth was young. The new theory accommodatingly allows as many as are needed, and sets no limit to their antiquity. In brief, the planetesimal theory seems to meet some of the demands of the progressive age in which we live.
Before leaving this subject, it may be frankly admitted that the planetesimal theory has made slow progress toward general acceptance. It has gained many powerful friends, but enemies have arisen against it.
The opposition to this theory may be due to a variety of causes. The theory may have fundamental defects. On this question there seem to be differences of opinion. Some are naturally reluctant to cast aside the cherished belief of a lifetime. "An old dog does not readily learn new tricks."
Many are indifferent. They care little which theory prevails. Apathy is a difficult enemy to combat.
Among those who are without knowledge of the merits and demerits of the opposing theories, the one which is understood with the least effort is the one most likely to gain acceptance. The argument that a thing is true because it is simple is as curious as it is fallacious. The fact that the nebular theory is more easily understood than the planetesimal theory is no argument in its favor.
Unfortunately the planetesimal theory is cumbered with a great number of unusual terms. Those who are unfamiliar with these terms find difficulty in comprehending discussions in which these terms are used. Unhappily, some valuable suggestions perish because millstones of unfortunate expression are attached to them.
Last Updated: 31-Dec-2009