The Meeting-Place of Geology and History

by Sir John William Dawson

Nor for similar reasons would we expect to meet with man in the earlier part of that last, or cenozoic, period in which we still live; and in point of fact it is only in superficial deposits of the later part of this last great period of the earth's history that we actually meet with evidence of the existence of the human species.

If there is based on this fact a question as to the actual date of man's first appearance, the physical considerations indicate about twenty millions of years for the whole duration of the earth. Setting apart, say, a fourth of this time for the early pre-geologic condition of the world, the remainder may be roughly estimated as five millions for the archæan, or eozoic, six for the palæozoic, three for the mesozoic, and one for the cenozoic. [4] Of the last, the later part, in which there is a possibility of the existence of man, will be limited to less than a quarter of a million; and within this the certainly known remains of man, whether attributed as by some to the latest inter-glacial period, or to the post-glacial—a mere question of terms, and not of facts—cannot be older, according to the best geological estimates, than from seven thousand to ten thousand years. This, according to our present knowledge, is the maximum date of the oldest traces of man, and probably these are nearer in age to the smaller than to the larger number.

[4] The absolute length of these periods is, of course, a matter of estimation; but the relative lengths of the different ages may be regarded as a fair approximation, based on facts.

If the reader will take the trouble to draw on paper a scale of twenty inches, each of these will represent a million of years of the earth's history, and the known duration of the human period may be indicated by a thickish line at one end of the scale. We may thus represent to the eye the recency of man's appearance, so far as at present known to science.

It may be said that all this is mere assertion. It fairly represents, however, the conclusions reached on the latest geological evidence, though this evidence would demand for its full detail a larger space than the whole of this little volume. References are given below to works in which this evidence will be found. [5]

[5] Lyell's Students' Manual; Dana's Manual; Prestwich's Geology; The Story of the Earth, by the author.

It may also be objected that if, as held by some evolutionists, man was slowly developed from lower animals, and if his earliest known remains are still human in their characters, he must have had a vastly longer history covering the periods of his gradual change from, say, ape-like forms. This is admitted; but then we have as yet no good evidence that man was so developed, and no remains of intermediate forms are yet known to science. Even should some animal, either recent or fossil, be discovered intermediate in structure between man and the highest apes, we should still require proof that it was the ancestor of man, by the occurrence of connecting forms, or otherwise. As the facts now stand, the earliest known remains of man are still human, and tell us nothing as to previous stages of development.

We must now glance a little more particularly at what may be termed the more immediate antecedents of man. The latest great period of the earth's geological history (the cenozoic) was ingeniously subdivided by Lyell, on the ground of the percentages of extinct and surviving species of marine shells contained in its several beds. According to this method, which, with some modifications in detail, is still accepted, the eocene age, or that of the dawn of the recent, includes those formations in which the percentage of modern or still living species of marine animals does not exceed three and a half, all the other species found being extinct. The miocene (less recent) includes beds in which the percentage of living species does not exceed thirty-five. The pliocene (more recent) includes beds in which the living forms of marine life exceed thirty-five per cent, but there is still a considerable proportion of extinct species. Newer than this we have the pleistocene (most recent), in which there are scarcely as many extinct species as there are of recent in the eocene. Lastly, the modern, of course, includes only the living species of the modern seas. Other geologists, notably Dawkins and Gandry, have arrived at similar results from a consideration of the vertebrate animals of the land. In the eocene we find numerous remains of mammals, or ordinary land quadrupeds, but all are extinct, and nearly all belong to extinct genera. In the miocene there are many living genera, but no species that survive to the present time. The pliocene begins to show a few living species, and these are dominant in the succeeding pleistocene.

These several stages of the cenozoic were also characterised by great vicissitudes of geography and climate. In the early and middle portions of the eocene, much of the land of the northern hemisphere was under the sea or in the state of swamps and marshes, and there seems to have been a very mild and equable climate, insomuch that plants now limited to warm temperate regions could flourish in Greenland. It is further to be observed that regions such as Mesopotamia, Syria and Egypt, which are known to us historically as among the earliest abodes of man, were at this time under the ocean, as were also rocks that now appear at great elevations in the highest mountains of Europe and Asia. For example, the limestones through which the Nile has cut its valley are marine beds of eocene age, and beds of the same period holding marine remains occur at an elevation of 16,000 feet in the Himalayan region.

In the miocene the amount of land was somewhat greater, though large areas of the continents were still under the sea, and the climate was still mild, but for reasons to be stated in the sequel it is not likely that man inhabited the warm continents of this age. The pliocene inaugurates what has been termed a continental period, when the land of the northern hemisphere was higher and more extensive than at present. It was also a time of great physical change, when much erosion of valleys and sculpturing of the surface of the land occurred, and when extensive earth movements and ejections of igneous rock increased the irregularity of the surface and gave greater variety and beauty to the land. The pliocene was altogether a most important period for giving the finishing touches of physical geography, and in it several modern species of land animals were introduced; but we have as yet, as we shall find in the sequel, no certain evidence that man was a witness of the movements and sculpturing of the earth's crust, so important in the preparation of his future home, though statements to this effect have been made on grounds which we shall have to consider.