THE RECORD OF THE ROCKS

The Outline of History: Being a Plain History of Life and Mankind by H. G. Wells, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. THE RECORD OF THE ROCKS

THE RECORD OF THE ROCKS

§ 1 The first living things

We do not know how life began upon the earth.

Biologists, that is to say, students of life, have made guesses about these beginnings, but we will not discuss them here. Let us only note that they all agree that life began where the tides of those swift days spread and receded over the steaming beaches of mud and sand.

The atmosphere was much denser then, usually great cloud masses obscured the sun, frequent storms darkened the heavens. The land of those days, upheaved by violent volcanic forces, was a barren land, without vegetation, without soil. The almost incessant rain-storms swept down upon it, and rivers and torrents carried great loads of sediment out to sea, to become muds that hardened later into slates and shales, and sands that became sandstones. The geologists have studied the whole accumulation of these sediments as it remains to-day, from those of the earliest ages to the most recent. Of course the oldest deposits are the most distorted and changed and worn, and in them there is now no certain trace to be found of life at all. Probably the earliest{v1-8} forms of life were small and soft, leaving no evidence of their existence behind them. It was only when some of these living things developed skeletons and shells of lime and such-like hard material that they left fossil vestiges after they died, and so put themselves on record for examination.

The literature of geology is very largely an account of the fossils that are found in the rocks, and of the order in which layers after layers of rocks lie one on another. The very oldest rocks must have been formed before there was any sea at all, when the earth was too hot for a sea to exist, and when the water that is now sea was an atmosphere of steam mixed with the air. Its higher levels were dense with clouds, from which a hot rain fell towards the rocks below, to be converted again into steam long before it reached their incandescence. Below this steam atmosphere the molten world-stuff solidified as the first rocks. These first rocks must have solidified as a cake over glowing liquid material beneath, much as cooling lava does. They must have appeared first as crusts and clinkers. They must have been constantly remelted and recrystallized before any thickness of them became permanently solid. The name of Fundamental Gneiss is given to a great underlying system of crystalline rocks which probably formed age by age as this hot youth of the world drew to its close. The scenery of the world in the days when the Fundamental Gneiss was formed must have been more like the interior of a furnace than anything else to be found upon earth at the present time.

After long ages the steam in the atmosphere began also to condense and fall right down to earth, pouring at last over these warm primordial rocks in rivulets of hot water and gathering in depressions as pools and lakes and the first seas. Into those seas the streams that poured over the rocks brought with them dust and particles to form a sediment, and this sediment accumulated in layers, or as geologists call them, strata, and formed the first Sedimentary Rocks. Those earliest sedimentary rocks sank into depressions and were covered by others; they were bent, tilted up, and torn by great volcanic disturbances and by tidal strains that swept through the rocky crust of the earth. We find these first sedimentary rocks still coming to the surface of the{v1-9} land here and there, either not covered by later strata or exposed after vast ages of concealment by the wearing off of the rock that covered them later—there are great surfaces of them in Canada especially; they are cleft and bent, partially remelted, recrystallized, hardened and compressed, but recognizable for what they are. And they contain no single certain trace of life at all. They are frequently called Azoic (lifeless) Rocks. But since in some of these earliest sedimentary rocks a substance called graphite (black lead) occurs, and also red and black oxide of iron, and since it is asserted that these substances need the activity of living things for their production, which may or may not be the case, some geologists prefer to call these earliest sedimentary rocks Archæozoic (primordial life). They suppose that the first life was soft living matter that had no shells or skeletons or any such structure that could remain as a recognizable fossil after its death, and that its chemical influence caused the deposition of graphite and iron oxide. This is pure guessing, of course, and there is at least an equal probability that in the time of formation of the Azoic Rocks, life had not yet begun.

Long ago there were found in certain of these ancient first-formed rocks in Canada, curious striped masses, and thin layers of white and green mineral substance which Sir William Dawson considered were fossil vestiges, the walls or coverings of some very simple sort of living thing which has now vanished from the earth. He called these markings Eozoon Canadense (the Canadian dawn-animal). There has been much discussion and controversy over this Eozoon, but to-day it is agreed that Eozoon is nothing more than a crystalline marking. Mixed minerals will often intercrystallize in blobs or branching shapes that are very suggestive of simple plant or animal forms. Any one who has made a lead tree in his schooldays, or lit those queer indoor fireworks known as serpents’ eggs, which unfold like a long snake, or who has seen the curious markings often found in quartz crystals, or noted the tree-like pattern on old stone-ware beer mugs, will realize how closely non-living matter can sometimes mock the shapes of living things.

Overlying or overlapping these Azoic or Archæozoic rocks come others, manifestly also very ancient and worn, which do{v1-10} contain traces of life. These first remains are of the simplest description; they are the vestiges of simple plants, called algæ, or marks like the tracks made by worms in the sea mud. There are also the skeletons of the microscopic creatures called Radiolaria. This second series of rocks is called the Proterozoic (beginning of life) series, and marks a long age in the world’s history. Lying over and above the Proterozoic rocks is a third series, which is found to contain a considerable number and variety of traces of living things. First comes the evidence of a diversity of shellfish, crabs, and such-like crawling things, worms, seaweeds, and the like; then of a multitude of fishes and of the beginnings of land plants and land creatures. These rocks are called the Palæozoic (ancient life) rocks. They mark a vast era, during which life was slowly spreading, increasing, and developing in the seas of our world. Through long ages, through the earliest Palæozoic time, it was no more than a proliferation of such swimming and creeping things in the water. There were creatures called trilobites; they were crawling things like big sea woodlice that were probably related to the American king-crab of to-day. There were also sea-scorpions, the prefects of that early world. The individuals of certain species of these were nine feet long. These were the very highest sorts of life. There were abundant different sorts of an order of shellfish called brachiopods. There were plant animals, rooted and joined together like plants, and loose weeds that waved in the waters.

It was not a display of life to excite our imaginations. There was nothing that ran or flew or even swam swiftly or skilfully. Except for the size of some of the creatures, it was not very different from, and rather less various than, the kind of life a student would gather from any summer-time ditch nowadays for microscopic examination. Such was the life of the shallow seas through a hundred million years or more in the early Palæozoic period. The land during that time was apparently absolutely barren. We find no trace nor hint of land life. Everything that lived in those days lived under water for most or all of its life.

Life in the Early Palæozoic

Note its general resemblance, except for size, to the microscopic summer ditch-water life of to-day.

Between the formation of these Lower Palæozoic rocks in which the sea scorpion and trilobite ruled, and our own time, there have intervened almost immeasurable ages, represented by layers{v1-12} and masses of sedimentary rocks. There are first the Upper Palæozoic Rocks, and above these the geologists distinguish two great divisions. Next above the Palæozoic come the Mesozoic (middle life) rocks, a second vast system of fossil-bearing rocks, representing perhaps a hundred millions of swift years, and containing a wonderful array of fossil remains, bones of giant reptiles and the like, which we will presently describe; and above these again are the Cainozoic (recent life) rocks, a third great volume in the history of life, an unfinished volume of which the sand and mud that was carried out to sea yesterday by the rivers of the world, to bury the bones and scales and bodies and tracks that will become at last fossils of the things of to-day, constitute the last written leaf.

(It is, we may note, the practice of many geologists to make a break between the rest of the Cainozoic system of rocks and those which contain traces of humanity, which latter are cut off as a separate system under the name of Quaternary. But that, as we shall see, is rather like taking the last page of a book, which is really the conclusion of the last chapter, and making a separate chapter of it and calling it the last chapter.)

These markings and fossils in the rocks and the rocks themselves are our first historical documents. The history of life that men have puzzled out and are still puzzling out from them is called the Record of the Rocks. By studying this record men are slowly piecing together a story of life’s beginnings, and of the beginnings of our kind, of which our ancestors a century or so ago had no suspicion. But when we call these rocks and the fossils a record and a history, it must not be supposed that there is any sign of an orderly keeping of a record. It is merely that whatever happens leaves some trace, if only we are intelligent enough to detect the meaning of that trace. Nor are the rocks of the world in orderly layers one above the other, convenient for men to read. They are not like the books and pages of a library. They are torn, disrupted, interrupted, flung about, defaced, like a carelessly arranged office after it has experienced in succession a bombardment, a hostile military occupation, looting, an earthquake, riots, and a fire. And so it is that for countless generations this Record of the Rocks lay unsuspected beneath the{v1-13} feet of men. Fossils were known to the Ionian Greeks in the sixth century B.C., they were discussed at Alexandria by Eratosthenes and others in the third century B.C., a discussion which is summarized in Strabo’s Geography (?20-10 B.C.). They were known to the Latin poet Ovid, but he did not understand their nature. He thought they were the first rude efforts of creative power. They were noted by Arabic writers in the tenth century. Leonardo da Vinci, who lived so recently as the opening of the sixteenth century (1452-1519), was one of the first Europeans to grasp the real significance of fossils,and it has been only within the last century and a half that man has begun the serious and sustained deciphering of these long-neglected early pages of his world’s history.

§ 2 How old is the world?

Speculations about geological time vary enormously. Estimates of the age of the oldest rocks by geologists and astronomers starting from different standpoints have varied between 1,600,000,000, and 25,000,000. The lowest estimate was made by Lord Kelvin in 1867. Professor Huxley guessed at 400,000,000 years. There is a summary of views and the grounds upon which the estimates have been made in Osborn’s Origin and Evolution of Life; he inclines to the moderate total of 100,000,000. It must be clearly understood by the reader how sketchy and provisional all these time estimates are. They rest nearly always upon theoretical assumptions of the slenderest kind. That the period of time has been vast, that it is to be counted by scores and possibly by hundreds of millions of years, is the utmost that can be said with certainty in the matter. It is quite open to the reader to divide every number in the appended time diagram by ten or multiply it by two; no one can gainsay him. Of the relative amount of time as between one age and another we have, however, stronger evidence; if the reader cuts{v1-14} down the 800,000,000 we have given here to 400,000,000, then he must reduce the 40,000,000 of the Cainozoic to 20,000,000. And be it noted that whatever the total sum may be, most geologists are in agreement that half or more than half of the whole of geological time had passed before life had developed to the Later Palæozoic level. The reader reading quickly through these opening chapters may be apt to think of them as a mere swift prelude{v1-15} of preparation to the apparently much longer history that follows, but in reality that subsequent history is longer only because it is more detailed and more interesting to us. It looms larger in perspective. For ages that stagger the imagination this earth spun hot and lifeless, and again for ages of equal vastness it held no life above the level of the animalculæ in a drop of ditch-water.

Not only is Space from the point of view of life and humanity empty, but Time is empty also. Life is like a little glow, scarcely kindled yet, in these void immensities.

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