THE EARTH’S CRUST.
Were earth’s crust no thicker in comparison than the skin of an apple
or peach, or 1/100 of its radius even, still man has never penetrated
to one-twentieth of that depth; for I know of no place where he has
as yet reached one mile below earth’s general level, unless it be in
ocean-soundings. In most places the mines or gorges have been in the
mountains high above the valleys, consequently we know little of what
is far beneath the earth’s surface. How could we judge of the inside
of nuts, fruits, grains, or vegetables if we had penetrated to but
one-twentieth of their coverings?
Take, for instance, a chestnut that all boys are familiar with, and see
what we may learn from it. We find that it is covered with a tough,
brown shell which in turn is enclosed in a large prickly burr ten times
the size of the nut. This protects it until ripened and then opens to
let the nut fall. The burr is fastened to a large forest tree whose
roots are deep in the ground; a tree that had been growing for years
before the chestnut was produced, and first started from another nut
of its kind. From the time its growth began there was nothing in root,
trunk, limb, or leaves for years that in any way resembled a chestnut;
nor in the blossom or burr even, until the nut ripened and fell to the
ground. Could one think, who had never before seen the nut, that from
such a tree a chestnut could be produced?
The same is true of all manner of nuts, fruits, and vegetables. It is
even true of animals, for they are enclosed in such varied coverings
that their nature is often quite concealed from us. We may as well
believe there is something in earth’s interior, away from winds and
cold, as precious over and above its crust as the chestnut is better
than the burr that encloses it; the fruit better than its rind; or
fish, birds, and animals better than their skins. Knowing this, man,
while he would grasp the greatness of the universe, may somewhat
under-rate the contents of his own earth.
Dr. Winchell in speaking of cold has said; “It has been demonstrated
that an ice-cap resting several thousand years over any considerable
portion of the surface would so reduce the subjacent temperature of
the earth that for many centuries after the disappearance of the ice,
a decrease of temperature would be discovered in penetrating downward.
Even centuries later, so much cold would still remain within the earth,
that the rate of increase of temperature would be less than if the
ice-cap had not existed; and after 3,600 years, that rate would be only
half the normal rate.”[12]
Now if the earth’s crust will thus retain the cold why may it not as
well retain the heat? In that case any excess of heat escaping from
earth, over and above the heat it constantly receives from the sun,
may be readily accounted for. It is claimed that the earth has large
quantities of sunlight and heat stored in a liquid state, as petroleum;
in a gaseous state, as natural gas; and in a solidified form, as coal;
some of which are found at a depth of 1600 or more feet, although coal
is sometimes found near the surface, and even upon the mountains. If
these are all stored sunlight, why do they not accumulate over earth’s
entire surface as well as in certain localities,—especially in the
torrid zone where great heat exists,—and accumulate to-day as well as
in former ages?
When we remember that the Mesozoic aeon was preceded by the long
Palæozoic, and earlier by the Eozoic,—whose aeon has been laid down
at eleven million years, with a strata at least 50,000 feet thick of
hardest rock,—what could have been the cause of the submerging of the
lands where these gases and coal lay? For millions of years the Eozoic
strata had upheld the oceans that were two or more miles in depth, and
of enormous weight. If the earth was cooling all those years the crust
must have been hardening, and what added weight could have been at
so late a period to cause the submerging of those lands? It has been
thought that in the glacial period when the accumulation of ice over a
portion of earth’s surface lay 5,000 feet thick that its weight might
have depressed the terrestrial crust.[13] But ice being lighter than
water, even though it were of that thickness, would not have had the
weight of water a mile in depth; whereas more than twice that depth of
water rested upon three-fourths of the globe. Moreover the ice-period
was many millions of years later than the Palæozoic and Eozoic ages,
and had the earth all this time been growing colder its crust must have
been thickening, making it capable of enduring almost any pressure. Any
crust, as ice upon water or the shell upon an egg, will bear more than
its whole weight before it will sink into the substance upon which it
rests.
It might be thought that earth, while cooling, would shrink beneath its
crust and leave a vacuum, as ice sometimes does upon a small surface.
This could not happen as the vast surface of extended crust, by the
enormous pressure of air upon it, would be held closely pressed to
whatever was beneath. For, although earth’s surface is convex, it is
still 25,000 miles around it, a distance so great that its crust would
have almost the same pressure as if the surface were level.
FOOTNOTES:
[12] Winchell, “Walks and Talks in the Geological Field,” p. 99.
[13] Winchell, “Walks and Talks in the Geological Field,” p. 275.