: Human Life by Knight Sherwood Sweet - Human beings; Life

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DEDICATION

This volume is dedicated to my Mother and my Wife--the two women whose influence has most largely shaped my life, and whose companionship has afforded me so much happiness. It was written with the hope that it might be of value to my two children, and may they find as much happiness in life as has the author.

HUMAN LIFE

THE HABITAT OF MAN

In reviewing the facts concerning humanity, which are well authenticated at the present date, with the object of getting a composite view of the greatest of all "world riddles"--"Life"--possibly nothing tends so largely to expand our mental horizon as a study of the earth itself or man's place of abode. The ideas of the educated and cultured mind, at the beginning of the twentieth century, upon cosmogony, are necessarily of such a character that man's heretofore undisputed boast of being the objective and acme of creation or evolution is forced into that great mass of theories which science has proven to be absolutely untenable. Since the relative importance of the factors of heredity and adaptation has become known, the environment, or conditions surrounding man's existence in times past, is of exceptional importance, as, from an understanding of these prehistoric limitations, we are better able to judge what must have been the achievement of the individual and the race than we could be when in ignorance of these facts.

The length of prehistoric time has been the subject of much intelligent labor and thought, as well as the occasion for much dissenting of opinion and more or less designed misstatement. Until very recently, it has been difficult to reconcile the theories, as promulgated by the authorities in the various departments of science; but, notwithstanding this, some light may be obtained by the summarization of the most plausible hypotheses now advocated. We cannot take the space to go into detail concerning these, but will merely touch upon the most salient points.

The constancy of the supply of heat furnished by the sun and the division of the year into definite seasons was one of the first phenomena which attracted the attention of man at the dawn of history, and in the many accounts of the creation which we find in literature we see the feeble attempts of man to account for what he observed. Although the knowledge which we have at the present time is not complete enough to warrant any feeling of pride, yet we do know enough to say, with certainty, some things concerning the solar system. We know that our sun cannot forever radiate away its heat into space without sometime becoming as cold or colder than we are, unless the energy which it is losing in the form of heat be restored to it by some means not at this time known. Sir William Thomson has calculated that at the present rate of solar radiation, which amounts to about twenty-eight calories per minute, per square centimeter, at the distance of the mean radius of the earth's orbit, it would have taken somewhat more than fifteen million years for the heat generated by the contraction of the sun's mass from the orbit of the outer planet, Neptune, to its present size, to have been radiated away into space. This means that gravity, as a source of heat development, at the rate of solar radiation now known, would account for, perhaps, twenty million years' expenditure of energy in reducing the sun's diameter to but one-thirteen-thousandth part of what it once was. Not only does the nebular hypothesis fall short of accounting for the facts, as will subsequently be shown in this one particular of the length of time during which our solar system has existed, but it does not account for the variation in the obliquity of the poles of the planets, which are the attendants upon the sun; nor does gravitative attraction alone enable us to account for the tremendous velocities of some of the stars through space, such as Arcturus,--so that it may be safely assumed that we shall be forced to modify our ideas as to the value of the nebular hypothesis as a working basis, before we can harmonize our deductions from astronomical and geological grounds. Fortunately, the study of the spiral nebulae has done much to elucidate our conceptions of the formation of the planetary systems, and from the discoveries made concerning these highly attenuated bodies of matter, a new hypothesis has been formed which will completely harmonize, perhaps, with these above stated facts, which could not be made to accord with the nebular theory as previously held.

One source of the continued acquisition of energy by our sun, whose value is hard to estimate, is the shooting stars, or meteors, which constantly fall into it. Astronomical records show that, from the earth alone, no less than twenty million shooting stars are daily within the limits of vision, and inasmuch as the solar system is moving with a velocity of some twenty miles per second through space, it will be seen that the number of meteors which would come within the influence of the sun, being as it is about one and one-third million times the volume of the earth, would be practically infinite. What then must be said of the amount of energy acquired by the sun from these, although each meteor may have a mass of but a few grams, and perhaps may be only several hundred miles away from its successor? It is clearly demonstrated that, if no such additions of energy were received by our sun, in about ten million years its diameter would be reduced to one-half of what it is now, and its mass, where now it exists as a gas, would then become a solid, at least upon the surface, and the quantity of heat received by the earth would become so small that life here, as we know of it, would be an impossibility. But if it be granted that the sun annually gathers, by its gravitative attraction, a combined mass of matter equal to the one-hundredth part of our earth, at a distance away from its center equal to the main radius of the earth's orbit, the energy dissipated by its radiation of heat at its present rate would be accounted for, while the sensible heat of the sun would not diminish, and the supply would be kept up indefinitely. That such additions of mass are made, there can be no doubt, but as to their quantity, we cannot, with our present knowledge, even hazard a guess.

In speaking of the solar heat and man's dependence upon it in a constant definite quantity, as one of the conditions of his existence, perhaps it will give us some just appreciation of his place in nature when we consider that the earth receives somewhat less than one two-billionth part of the heat radiated away by the sun, and while this expression makes the quantity which we receive seem rather small, it is, nevertheless, large enough annually to melt a layer of ice one hundred and seventy-five feet thick--all over the surface of the earth, and is a little more than one six-thousandth part of the quantity of heat which would be generated by the burning of a mass of coal as large as the sun.

Turning from the theories of astronomy, which are obviously more or less inaccurate, owing to their very nature and the character and duration of the observations upon which they are based, we come to the nearer and more certain deductions of geology. Here we have the phenomena of denudation and deposition with which to deal, and inasmuch as these are measurable at many places, and under many conditions upon the earth to-day, it is safe to assume that computations made from these measurements cannot be far from the truth. We know that practically all of the great formations of the earth were depositions of material from water which contained them, and that, in many cases, heat caused these strata to be metamorphosed or crystallized ages after they were deposited, and that in this crystallization many of the fossils remaining imbedded in the deposited matter were destroyed. Concerning this deposition we know that it is going on to-day in the Atlantic and Pacific Oceans, where, in the deeper portions the Globigerina ooze is filling in these depressions with a deposit, resembling chalk, at the rate of perhaps an inch per century. We know that the Gulf of Mexico and several other ocean areas are being filled in with silt at the rate of as high as three inches per century. This silt is brought down in the tributary rivers and emptied into the gulfs. We also know that large areas in the Indian Ocean are being covered with coral and the d?bris from the coral reefs. We are absolutely certain that every geological period has had its characteristic fauna and flora, and that, in both the animal and vegetable kingdoms, some persistent types have connected it with both the past and the future, so that the fossils have become the "open sesame" to the geological records. We further know that the strata composing the earth's surface are subject to elevation and subsidence, such as is now going on in the delta of the Nile, on the coast of the Netherlands, and in many other places, and that such movement is a measurable quantity, given only the necessary time.

The total thickness of known strata measures but about one-three hundred and twentieth part of the earth's diameter, or, in round numbers, twenty-five miles. Thirty thousand feet of this is quite readily identified as belonging to the old Archaic or Laurentian period, and constitutes the oldest stratified deposit known. Even in this, we find the remains of the Eozoon Canadense, which is now universally acknowledged to be the petrifaction of a foraminiferous living organism with a chambered shell. This means that, at this time, the earth's atmosphere must have been very similar to what it is at the present, and that the temperature of the sea was somewhere between the boiling and the freezing points of water. What time had elapsed since the earth was thrown off by the sun in an incandescent state can only be faintly imagined. At the rate of deposition given for the deepest of ocean deposits, this Archaic period would have taken perhaps thirty-six million years; but inasmuch as the water may have been far warmer then than now, and the rainfall more abundant, and the forces of denudation in all respects more active, this figure may be excessive. The next eighteen thousand feet of strata are easily identified as Lower Silurian, by the Diatoms which occur imbedded in them, and these formations include some of the largest deposits of limestone known. At our rate of calculation, this deposit would require no less than nine and one-half million years, and, in assuming this figure, no account is made of the intervals of time during which no deposit took place, although such periods of inactivity must necessarily have been. The Upper Silurian strata consists of twenty thousand feet, the fossils of which are the lower fishes, and for which we must assign a period of time equal to no less than twenty-five million years, inasmuch as these deposits are limestones and sandstones, or the remains of water-living animals and plants.

In the Silurian rocks, we find the remains of an air-breathing scorpion, very similar to that found to-day, which shows that the atmosphere at that remote period was practically the same as we have at the present time.

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