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A Closer Look: Features of the Moon
How can we describe the geology of the Moon?
 The face of the Moon — its “near
side” to us — is
divided into light areas called the lunar highlands and darker
areas called maria. The maria are lower in altitude than the
highlands and their appearance
comes from the dark lava flows from earlier periods of lunar
volcanism. Both the maria and the highlands have many craters,
which are the result
of meteor impacts. The impact destroys the meteor and displaces
part of the moon's surface. A bowl is created, with the edges
higher than the
surrounding surface, the interior much lower than the surrounding
surface, and sometimes a raised bump in the center. During impact,
rock is often
ejected outward, and the material is scattered across the Moon's
surface in streaks radiating from the crater. There are many
more impact craters
in the highlands than in the maria.
Satellite pictures show that
the far side of the Moon — the side
that we can’t see — is almost completely covered by craters
with virtually no maria. Why might this be? Scientists believe
that the near side of the Moon has been “shielded” by its
interaction with the Earth. The far side is thought to have been
impacted much more
frequently by meteors.
What do we know about the Moon’s geological
history?
Scientists believe that when the Moon formed and its
surface cooled, its interior was still mostly liquid. The energy
from continual bombardment by meteors kept the Moon's interior liquefied.
When very large
meteors struck the Moon, the Moon's surface would crack. The
lava from the Moon's molten mantle was able to escape through
the holes created
by the meteor. The lava filled in the crater, creating the
dark,
smooth maria. When more lava escaped than could be contained
in the crater, it
would overflow, and cover more of the Moon's surface. Because
there are more craters in the highlands than in the maria,
the highlands are thought
to be significantly older than the maria.
Are there other landforms on the Moon?
Unlike the Earth, the Moon
does not have active erosion by water or wind. Similarly, there
is no shifting of tectonic plates to
create mountains or subduct existing features into a mantle.
Because of this,
there are few landforms compared to those on Earth. However,
the accumulation of volcanic processes and impact cratering
is
readily visible, and one
can learn a lot about the Moon's history by studying its surface.
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