Original: The Late Heavy Bombardment ( commonly referred to as the lunar cataclysm , or LHB ) is a period of time approximately 4.1 to 3.8 billion years ago ( Ga ) during which a large number of impact craters are believed to have formed on the Moon , and by inference on Earth , Mercury , Venus , and Mars as well .
Simplified: The Late Heavy Bombardment ( LHB ) or lunar cataclysm , is a period of time approximately 4.1 to 3.8 billion years ago ( Ga ) during which a large number of impact craters are believed to have formed on the Moon , and by inference on Earth , Mercury , Venus , and Mars as well .