Final answer:
The maria on the Moon are composed of basalt, similar to Earth's oceanic crust and volcanic lavas, while the Moon's highlands are composed of anorthosite.
Step-by-step explanation:
The maria on the Moon are composed mainly of basalt, which is a type of volcanic lava formed during ancient volcanic eruptions. This basalt is not unique to the Moon; it is very similar to that found beneath Earth's oceans and in terrestrial volcanic eruptions. On the other hand, the highlands on the Moon are composed of anorthosite, which is a rock characterized by a high content of the mineral plagioclase feldspar.
The lunar maria are flat plains of basaltic lava, such as what is visible in Mare Imbrium, while the Moon's mountains and highlands were formed through geological processes early in its history, quite different from those that shaped Earth's landscape.