What science had yet to discover in Galileo’s time, was that
the depressions he observed through his scope were in fact craters that were
caused by the impact of explosions from meteors hitting the Moon’s surface,
utterly un-impeded by an atmosphere (the Moon has none). Earth’s far stronger gravity attracts many more
times the number of meteors than does the Moon.
That doesn’t mean that the Moon never gets hit at all. But the atmosphere on Earth burns up the vast
majority of them before they could ever reach its surface. Consequently Earth has few such depressions
(“Meteor Crater” in Arizona is one example) to show for its entire bombardment
history.
So the real question
of how the meteors aimed at the Moon make it all the way to its surface, has a simple and obvious answer: it has
no atmosphere in place that will cause them to burn up and disinte-grate. Nevertheless,
from our vantage point as Earthlings this answer ought to amaze and fill us
with gratitude for our own living arrangements.
The entire range of benefits that result from the possession of an
atmosphere of the kind that we happen to enjoy on Earth, is too lengthy to
describe in this essay. But this exhaustive
list of benefits must surely include the protective
aspect of our atmosphere which prevents such harmful objects from otherwise making
their way to the surface, thereby bringing damage to such a degree that life
here on Earth would be impossible.
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