The scale of the battering the Moon received early in its history has been revealed in remarkable new data from two NASA satellites. Ebb and Flow - together known as the Grail mission - have mapped the subtle variations in gravity across the surface of the lunar body. Reds correspond to mass excesses which create areas of higher local gravity, and blues correspond to mass deficits which create areas of lower local gravity.
4.0–3.8 billion years ago, during the Late Heavy Bombardment, Asteroids and comets bombard the Earth in record numbers and with overwhelming violence. As the bombardment tapers off, the Earth resumes cooling, oceans reappear, and a crust again covers the planet. Convection currents swirling in the mantle begin to break up the crust and force the pieces to collide, split, and merge. (pictured: Marília Meteorite, which fell in Marília, São Paulo state, Brazil, on October 5, 1971)
Late Heavy Bombardment (lunar cataclysm): hypothetical event around 4.1 to 3.8 billion years ago; a large number of impact craters on the Moon would have formed & also on Earth, Mercury, Venus & Mars; late in the Solar System's accretion period when Earth & the other rocky planets formed & gained most of their mass; new research casts doubt on this theory