The Geologic Evolution of the Moon

A synthesis of pre- and post-Apollo 11 studies is presented to produce an outline of the moon's geologic evolution from three lines of evidence: (1) relative ages of lunar landforms and rock types, (2) absolute ages of returned lunar samples, and (3) petrography, chemistry, and isotopic ratios of lunar rocks and soils. It is assumed that the ray craters, circular mare basins, and most intermediate circular landforms are primarily of impact origin, although many other landforms are volcanic or of hybrid origin. The moon's evolution is divided into four main stages, each including several distinct but overlapping events or processes.