Mars, Moon and the Earth share a common planetary history. At about 4 billion years ago they were all bombarded by meteorites during a time known as the Late Heavy Bombardment period. Because of tectonic movements the traces of Late Heavy Bombardment is almost completely erased from the face of the Earth. However craters are still intact on Moon and Mars.
There are about 30 very large impact craters on Mars that are larger than 1000 km in diameter and probably contributed to the partial loss of its global magnetic field which weakly shows activity in its southern hemisphere. Studies now show that Late Heavy Bombardment is responsible for the crustal dichotomy on Mars where the Northern hemisphere largely consists of lowlands due to a mega impact by an asteroid about 2000 km in diameter which predated all of the large impacts
The most distinct geological feature on Mars is its hemispheric dichotomy: the difference in crater density, elevation (~4 km), and crustal thickness (~30 km) between the Northern Lowlands and the Southern Highlands. Recent impact cratering simulations show that the ~10,000 km diameter Lowlands can be formed by a single large impact. This impact size was common at the end of planetary accretion and falls in the planetary-scale impact size regime, in which the curvature and radial gravity of the planet are important. Dr. Marinova discusses the implications of her research into the puzzling Martian hemispheric dichotomy:
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