The document summarizes key facts about the Moon learned from Apollo missions between 1969-1972. It describes the Moon's density and lack of an atmosphere. Craters are common due to meteorite impacts, while erosion has erased most craters on Earth. Craters form when meteoroids compress surface material, some of which is ejected to form crater rims. The Moon also features highlands and dark maria (plural of mare) formed by ancient lava flows. The lunar surface is covered by a regolith layer composed of debris from meteorite bombardment.