 The process that led to the formation of the Moon approximately 4 @.@ 53 billion years ago is the subject of ongoing research . The working hypothesis is that it formed by accretion from material loosed from Earth after a Mars @-@ sized object , named Theia , impacted Earth . In this scenario , the mass of Theia was approximately 10 % of that of Earth , it impacted Earth with a glancing blow , and some of its mass merged with Earth . Between approximately 4 @.@ 1 and 3 @.@ 8 Gya , 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 . 
