out fifty miles in thickness. It seems that
the young earth had no atmosphere, and that ages passed before water
began to accumulate on its surface--before, in other words, there was
any hydrosphere. The water came from the earth itself, to begin with,
and it was long before there was any rain dissolving out saline matter
from the exposed rocks and making the sea salt. The weathering of the
high grounds of the ancient crust by air and water furnished the
material which formed the sandstones and mudstones and other sedimentary
rocks, which are said to amount to a thickness of over fifty miles in
all.

Sec. 3

Making a Home for Life

It is interesting to inquire how the callous, rough-and-tumble
conditions of the outer world in early days were replaced by others that
allowed of the germination and growth of that tender plant we call
LIFE. There are very tough living creatures, but the average organism is
ill suited for violence. Most living creatures are adapted to mild
temperatures and gentle reactions. Hence the fundamental importance of
the early atmosphere, heavy with planetesimal dust, in blanketing the
earth against intensities of radiance from without, as Chamberlin says,
and inequalities of radiance from within. This was the first preparation
for life, but it was an atmosphere without free oxygen. Not less
important was the appearance of pools and lakelets, of lakes and seas.
Perhaps the early waters covered the earth. And water was the second
preparation for life--water, that can dissolve a larger variety of
substances in greater concentration than any other liquid; water, that
in summer does not readily evaporate altogether from a pond, nor in
winter freeze throughout its whole extent; water, that is such a mobile
vehicle and such a subtle cleaver of substances; water, that forms over
80 per cent. of living matter itself.

Of great significance was the abundance of carbon, hydrogen, and oxygen
(in the form of carbonic acid and water) in the atmosphere of the
cooling earth, for these three wonderful elements have a unique
_ensemble_ of properties--ready to enter into reactions and relations,
making great diversity and complexity possible, favouring the formation
of the plastic and permeable materials that build up living creatures.
We must not pursue the idea, but it is clear that the stones and mortar
of the inanimate world are such that they built a friendly home for
life.

Origin of Living Creatures