Final answer:
We know the moon has different rock compositions through analysis of moon rocks, radioactive dating that indicates ages of rocks, and observations of crater density. The moon's composition differs from Earth's, mainly consisting of silicate rocks without much iron or metals.
Step-by-step explanation:
We know that different areas of the moon are composed of different rock types by studying moon rocks. When Apollo astronauts brought back lunar samples, scientists were able to apply radioactive dating techniques developed for Earth to these samples. The ages of these rocks ranged from about 3.3 to 4.4 billion years old, which is substantial evidence of the moon's geologic history.
Further examination of moon rocks shows that most of the moon's crust consists of silicate rocks called anorthosites. The composition and structure of the Moon are distinct from Earth's, with an average density of only 3.3 g/cm³, indicating that the Moon is composed mostly of these silicate rocks and is depleted in iron and other metals. These findings contribute to our understanding of the Moon's composition and origin.
Additional evidence comes from observations of craters. The number of craters on different parts of the Moon's surface can give clues about how the regions evolved; more heavily cratered areas are typically older.