Transcript: Cratering affects the evolution of planets. The cratering history of the Earth has varied over its history. Cratering was much stronger in the first half billion years when there was plenty of debris left over from the formation of the solar system. When you look at the Moon we are looking at a mirror for the cosmic environment of the Earth. The Moon shows evidence of many craters. The Earth has apparently very few. The difference is clear. The Moon is not massive enough to have geological activity, so evidence of its craters is not been removed by tectonic motions. The Moon is also too low in mass to retain an atmosphere, so erosion has not eradicated the evidence of cratering. Earth has been subject to impacts from space over its history, and some of these are implicated in major changes in speciation and mass extinctions in the history of life on Earth. But on the Earth because of the large amount of erosion and the large amount of geological activity, impact craters are difficult to discover and relatively rare.