The Moon probably formed early in the formation of the Solar System when a planet perhaps as large as Mars hit the newly-formed Earth which threw out a cloud of gas and dust which eventually formed the Moon. As it formed it became hot and molten. As it cooled the crust formed.
The Moon is not big enough to hold on to an atmosphere. Its gravity is too weak to stop molecules of gas escaping. Without an atmosphere any small meteorites which hit the surface do not burn up, but instead form small craters. Large ones form large craters. Large meteorite impacts created the mare basins (people originally thought they were seas, which is the meaning of mare). Volcanoes then filled these basins with dark basaltic lavas. Other areas of the Moon are higher than the basins. They are heavily cratered and lighter in color than the mare. They are called terrae, meaning land. Most volcanic activity then stopped, at least 2,000 mya. Most of these lava-flooded mare occurred on one side of the Moon. This made the Moon heavier on one side than the other. This heavy side is attracted to the Earth and always faces it. This was one reason why the Greeks believed that things in the sky did not change, which helped them to believe that the changeable Earth was the center of the Universe. Water has been discovered on the Moon
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