Large impacts and climatic catastrophes on the early Earth

Abstract

Radiometric data of cratered lunar surfaces suggest that the cratering rate on the ancient Moon was substantially larger than the present rate before about 3.2 Gyr. Since the cratering rate was higher than present on the Moon, it seems likely that is was similarly higher on the Earth. Recently the occurrence of beds of spherules up to 2m thick was reported in 3.2 to 3.5 Gyr old Archean rocks. These spherule beds closely resemble the 3 mm thick spherule beds associated with the K/T boundary (including elevated iridium abundances), widely believed to have been deposited in association of a 10 km diameter comet or asteroid