Imbrian

The Imbrian is a lunar geologic period divided into two epochs, the Early and Late.

The impact that created the huge Mare Imbrium basin occurred at the start of the epoch.

It was the epoch during which the mantle below the lunar basins partially melted and filled them with basalt.

The melting is thought to have occurred because the impacts of the Early Imbrian thinned the overlying rock – either causing the mantle to rise because of the reduced pressure on it, bringing molten material closer to the surface, or the top melting as heat flowed upwards through the mantle because of reduced overlying thermal insulation.

[citation needed] Since little or no geological evidence on Earth exists from the time spanned by the Early and Late Imbrian epoch of the Moon, the Early and Late Imbrian has been used by at least one notable scientific work[1] as an unofficial subdivision of the terrestrial Hadean eon.