The pre-Nectarian period of the lunar geologic timescale runs from 4.533 billion years ago (the time of the initial formation of the Moon ) to 3.920 billion years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period.
5-613: 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 Heavy Bombardment Eon (HBE; a period of 0.6-1 Gy from the formation of the Moon until at least the formation of the Imbrium Basin ~3.9 Ga, or even later with the formation of Orientale Basin) that marks
10-622: The Cryptic era , Basin Groups 1-9, Nectarian and Lower Imbrian , though the first two of these lunar divisions are informal and collectively make up the pre-Nectarian. Nectarian The Nectarian Period of the lunar geologic timescale was from 3.920 billion years ago to 3.850 billion years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events . Ejecta from Nectaris form
15-599: 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. This geologic period has been informally subdivided into the Cryptic Era (4.533 - 4.172 Ga ago) and Basin Groups 1-9 (4.172 - 3.92 Ga ago), but these divisions are not used on any geologic maps. Similarly
20-515: The later period has also been called the Aitkenian period. Since little or no geological evidence on Earth exists from the time spanned by the pre-Nectarian period of the Moon, the pre-Nectarian has been used as a guide by at least one notable scientific work to subdivide the unofficial terrestrial Hadean eon . In particular, it is sometimes found that the Hadean eon is subdivided into
25-516: The upper part of the densely cratered terrain found in lunar highlands. The period ended with the formation of the Imbrium basin , which initiated the Imbrian Period. Magnetic anomalies found in some Nectarian Period basins suggest that the Moon possessed a core dynamo magnetic field at that time. Since little or no geological evidence on Earth exists from the time spanned by
#652347