In the
lunar geologic timescale, the
Early Imbrian epoch occurred between 3850 million years ago to about 3800 million years ago. It overlaps the end of the
Late Heavy Bombardment of the
Inner Solar System. The
impact that created the huge
Mare Imbrium basin occurred at the start of the epoch. The other large basins that dominate the lunar nearside (such as Crisium, Tranquilitatis, Serenitatis, Fecunditatis, and Procellarum) were also formed in this period. These basins filled with
basalt mostly during the subsequent
Late Imbrian epoch. The Early Imbrian was preceded by the
Nectarian.