With almost twice as much solar heat
and light as we have, and with a deeper and denser atmosphere than ours,
it is evident, without seeking other causes of variation, that the
conditions of life upon Venus are notably different from those with
which we are acquainted. At first sight it would seem that a dense
atmosphere, together with a more copious supply of heat, might render
the surface temperature of Venus unsuitable for organic life as we
understand it. But so much depends upon the precise composition of the
atmosphere and upon the relative quantities of its constituents, that it
will not do to pronounce a positive judgment in such a case, because we
lack information on too many essential points.
Experiment has shown that the temperature of the air varies with changes
in the amount of carbonic acid and of water vapor that it contains. It
has been suggested that in past geologic ages the earth's atmosphere was
denser and more heavily charged with vapors than it is at present; yet
even then forms of life suited to their environment existed, and from
those forms the present inhabitants of our globe have been developed.
There are several lines of reasoning which may be followed to the
conclusion that Venus, as a life-bearing world, is younger than the
earth, and, according to that view, we are at liberty to imagine our
beautiful sister planet as now passing through some such period in its
history as that at which the earth had arrived in the age of the
carboniferous forests, or the age of the gigantic reptiles who ruled
both land and sea.
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