During the early chapters of the earth's history, no living creature
that we can imagine could possibly have lived there. The temperature was
too high; there was neither atmosphere nor surface water. Therefore it
follows that at some uncertain, but inconceivably distant date, living
creatures appeared upon the earth. No one knows how, but it is
interesting to consider possibilities.
[Illustration: _Reproduced from the Smithsonian Report, 1915._