Pre-Nectarian
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The Pre-Nectarian Period of the lunar geologic timescale runs from 4550 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. Pre-Nectarian rocks are mostly composed of highlands material, heavily churned by subsequent impacts.

The original article can be found at: http://en.wikipedia.org/wiki/Pre-Nectarian.
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