Much of the action on Mars occurred during a period known as the Late Heavy Bombardment about 3.9 billion years ago. Large comets and asteroids raining down on the planet would have produced enough heat to melt subsurface ice, likely enhancing climate conditions enough to make Mars more conducive to life — at least for a time.
Phenomenally durable crystals called zircons are used to date some of the earliest and most dramatic cataclysms of the solar system, such as the late heavy bombardment that created hellish surface conditions on the young Earth and Moon about 4 billion years ago. Now a study of zircons from a gigantic meteorite impact in South Africa casts doubt on the methods used to date lunar impacts.
Scientists at MIT and elsewhere have identified regions on the far side of the Moon, called the lunar highlands, that may have been so heavily pelted by small asteroids during a period called the Late Heavy Bombardment 4 billion years ago that the impacts completely shattered the upper crust, leaving these regions essentially as fractured and porous as they could be.