Example of radioactive dating
Most of the impact basins---craters measured in hundreds of kilometers---were made during this time.
It is noteworthy that about the time the heavy bombardment ended, life took hold.
Some of them have orbits that cross the orbits of the planets and moons.
When they get close enough to a planet or moon, they will be pulled in by the large body's gravity and strike the surface at a speed of at least the escape velocity of the planet or moon, i.e., faster than a bullet.
The first frame of a 3D movie flyover of Tycho Crater on the Moon as seen by Kaguya. It displays the classic terraced crater walls and central peak of a complex crater.
Select the image to go to the Selene website for a great flyover of the crater.
At such speeds, the projecticle explodes on impact and carves out a round bowl-shaped depression on the surface. How can you distinguish an impact crater from a volcanic crater?