THE WORLD BEFORE MAN
Man is of recent introduction on the earth. For millions of years the
slow process of world-making had been going on, with reference to
physical structure and to the lower grades of living creatures. Only
within a few thousand years does our globe seem to have been fitted for
its highest tenant. The evidence of this is to be found in any text-book
of geology. I propose here merely to present the history of the earth in
a series of word-pictures, introductory to our special subject.
Our first picture may be that of a nebula, vast and vaporous, containing
the mixed and unconsolidated materials of the sun and planets--a void
and desolate mass, slowly aggregating itself under the influence of
gravitation.
Our next may be that of an incandescent globe, molten and glowing, and
surrounded by a vast vaporous envelope, but tending by degrees to a
condition in which it shall have a solid crust, on which the greater
part of the watery vapour suspended in its atmosphere is to be condensed
into a heated ocean.
Our third picture may represent the world of what geologists call the
archæan, or eozoic period, when the crust had been furrowed up into
ridges of land, and corresponding but wider depressions occupied by the
sea. Into the latter the rains falling on the land are carrying sediment
derived from the wasting rocks, though the waters are still warm and the
thinner parts of the crust are still welling out rocky material, either
molten or dissolved in heated water. In this period there were probably
low forms of animal life in the waters and plants on the land, though we
know little of their exact nature.
A fourth picture may represent that great and long-continued palæozoic
period in which the waters swarmed with many forms of life, when fishes
were introduced into the sea, and when the land became covered with
dense forests of plants allied to the modern club-mosses, ferns,
mares'-tails and pines; while insects, scorpions and snails, and some
of the humbler forms of reptiles, found place on the land.
Returning after an interval, we should see a fifth picture, that of the
mesozoic world. This was the age of reptiles, when animals of that class
attained their highest and most gigantic forms, and occupied in the sea,
on the land, and in the air the places now held by the mammals and the
birds; while the continents were covered with a flora distinct alike
from that of the previous and succeeding periods, replaced, however, as
time went on by forests very like those of the modern world. In this age
the earliest mammals or ordinary quadrupeds were introduced, few at
first, small and of low rank in their class. Birds also made their
appearance, and toward the close of the period fishes of modern types
swarmed for the first time in the sea.
Lastly, we might see in the cenozoic, or tertiary age, the newest of
all, quadrupeds dominant on the land and modern types of animal life in
the sea. In this period our continents finally assumed their present
forms. Toward its close and after many vicissitudes of geography and
climate, and several successive dynasties of mammalian life, man and the
land animals now his contemporaries occupied the world, and thus the
cenozoic passes into the _anthropic_, or modern period, called by some,
but without good reason, 'quaternary,' since it is in all respects a
proper continuation of the tertiary, or cenozoic.[3]
[3] It will be seen that our six pictures are in some degree parallel
with the 'days' of creation. This is not an intentional reconciliation.
It merely expresses the fact of the case, whatever its significance.
This last age of the world is so intimately connected with man that it
will be necessary to consider it more in detail. More particularly we
may endeavour to answer, if we can, the questions of order and time
involved in man's late appearance.
No geologist would expect to find any remains of man or his works in the
periods represented by our five earlier pictures, because in these
periods the physical conditions necessary to man and the animals nearest
to him in structure do not appear to have existed, and their places in
nature were occupied by lower types.
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.
In the course of the pliocene the previously high temperature of the
northern hemisphere was sensibly lowered, and at its close the
pleistocene period introduced a cold and wintry climate, along with
gradual and unequal subsidence of the land, the whole producing that
most dismal of the geological ages, known as the 'glacial period.' At
this time much of the lower land of the continents was submerged and the
mountains became covered with snow and ice, leaving space for vegetable
and animal life only toward the south and in a few favoured spots in the
higher latitudes. There is much difference of opinion among geologists
as to the extent, duration and vicissitudes of this reign of ice, but
there can be no doubt that it destroyed much of the animal and vegetable
life of the pliocene, or obliged it to migrate to the southward. In this
period great deposits of mud, sand and gravel were laid down, which
prepared the world for a new departure in the succeeding age. This we
may name the post-glacial, or early modern period, and in it we have the
most certain evidence of the existence of man, though the geographical
arrangement of our continents and their animal inhabitants were in many
respects different from what they now are. If geologists are right in
the conclusion already stated, that the close of the glacial period is
as recent as 7,000 years ago, this will give us a narrow limit in time
for the age of man, at least under his present conditions.
While, however, there is an absolute consensus of opinion among
geologists as to the existence of man at or about the close of the
glacial age, in the northern temperate regions at least, there are some
facts which have been supposed to indicate a pre-glacial human period,
or the advent of man even as early as the middle of the cenozoic time.
These merit a short consideration.