Proper noun
Late Heavy Bombardment
A prolonged event believed to have occurred around the Hadean-Archean boundary, during which an unusually high number of asteroids hit the terrestrial planets and their moons.
Between approximately 4.1 and main, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon, and by inference, to that of Earth. Source: Internet
Finally, between approximately 4.1 and 3.8 billion years ago, asteroid impacts during the Late Heavy Bombardment caused significant changes to the surface environment of objects in the Solar System. Source: Internet