As a result, the moon drew
further and further away from the earth until it reached its
present position, about 240,000 miles away. At the same time the
tidal influence of the earth was lessening the rotational
movement of the moon. This went on until it turned on its axis in
the same period in which it revolves round the earth, and on this
account it always presents the same face to the earth.
Through what chapters of life the moon may have passed in the
meantime it is impossible to say. Its relatively small mass may
have been unable to keep the lighter gases at its surface, or its
air and water may, as some think, have been absorbed. It is
to-day practically an airless and waterless desert, alternating
between the heat of its long day and the intense cold of its long
night. Careful observers, such as Professor Pickering, think that
it may still have a shallow layer of heavy gases at its surface,
and that this may permit the growth of some stunted vegetation
during the day. Certain changes of colour, which are observed on
its surface, have been interpreted in that sense. We can hardly
conceive any other kind of life on it. In the dark even the gases
will freeze on its surface, as there is no atmosphere to retain
the heat.
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