On Earth, mountain ranges are caused by plate tectonics - two massive chunks of crust pushing against each other. If both of the plates have the same (or very similar) density, everything moves upward and mountain ranges form (such as the Himalayas). On the other hand, if one plate is more dense (sea floor plates are more dense
5 People sometimes refer to the "dark side'' of the Moon. This is a misconception due to a popular song from the late 1960s. There is, in fact, no permanently dark "side" of the Moon, although there are areas in the polar regions that are probably sunless. More on this later.
than continental plates), the oceanic slab will move down and the continental slab will move up, forming ocean trenches with volcanic mountains along the coast.
In contrast with the Earth, the lunar highlands did not result from an active plate tectonic process; instead, they simply represent a lack of destruction by giant meteorite bombardments, such as those that created the lunar basins. Compared with the deepest basins, the highlands regions are as much as 16 km higher in elevation. The lunar highlands are composed mainly of anorthosite, a type of rock also found on Earth, which is made up largely of the mineral feldspar. Samples from some of the Apollo landing sites showed that within the highlands, the surface rocks were often a jumbled mixture of several kinds of rocks - a breccia.6
The highlands cover so much of the Moon that it is not easy to separate them into mountain "ranges" as is done on Earth. However, there are other features that are more similar to mountain ranges. These are the circular and semi-circular basin ring structures.
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