High Quality Content by WIKIPEDIA articles! The Pre-Nectarian Period of the lunar geologic timescale runs from 4533 million years ago (the time of the initial formation of the Moon) to 3920 million years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period. Pre-Nectarian rocks are rare in the lunar sample suite; they are mostly composed of lunar highlands material which have been heavily churned, brecciated, and thermally affected by subsequent impacts, particularly during the Late Heavy Bombardment that marks the approximate beginning of the Nectarian Period. The primary Pre-Nectarian lunar highland material is dominated by the rock type anorthosite, which suggests that the early stage of lunar crustal formation occurred via mineral crystallization of a global magma ocean.