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Earth & Space Science: Session 7

A Closer Look: Features of the Moon

How can we describe the geology of the Moon?

moon exploration

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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