Maria are sites of immense meteoric strikes early in lunar history that later were filled by molten lava seeping up from the interior. These maria are also the sites of gravity anomalies, or mascons, which are caused by the concentration of very dense material beneath the surface of the Moon. Mascons are found only on the near side of the Moon (the side of the Moon that faces Earth), suggesting that the influence of Earth's gravitation altered the trajectories of the impacting objects that produced these features