Formation & Geology of the Moon: Structures & Vocabulary

The leading model for the Moon's origin is a giant impact early in Solar-System history, followed by accretion of orbiting debris around Earth. The Moon then differentiated internally, formed an early crust, experienced intense impact cratering, and later underwent large basaltic eruptions that filled giant impact basins to create the dark maria.

A giant collision can eject mantle-rich material into Earth orbit while leaving much of the colliding bodies' metal in their cores. As lunar material cooled, lower-density crustal minerals rose while denser material sank. Later impacts excavated basins, and heat-driven volcanism flooded some basins with basalt before the Moon's interior cooled enough for major volcanism to fade.

Apollo samples reveal ancient ages, silicate-rich composition, and isotopic similarities between Earth and Moon material. Crater counts distinguish older heavily cratered highlands from younger maria, while radiometric dating of returned rocks calibrates the crater record. Gravity and seismic measurements constrain the Moon's internal structure.

Lunar structure includes crust, mantle, small metallic core, impact basins, highlands, maria, regolith, and permanently shadowed polar regions. The bright highlands are generally older and more heavily cratered than the darker basaltic maria. Regolith records continuous impact gardening, solar-wind exposure, and space-weathering processes.