That's actually how it is with the earth too, but rivers, mountains and vegetation gradually wipe out traces. All the geological layers in and under a submarine meteor crater function as solid documentation on the earth's development over millions of years. The crater and the sediment, therefore, carry unique information about the process and consequences of such an impact. A meteor is a relatively large fragment from the asteroid belt. A meteor consists of minerals and metals and are different from comets which come from outer space and mainly consist of ice.
Meteorites fall on the earth daily.
In all, man knows of 160 craters on the globe, but just seven of these are submarine.