It may surprise you to know that there are more than 180 confirmed impact craters on our planet. It is likely that many more have been erased by the actions of wind and water. An asteroid smashing into a water rich world like Earth or Mars can generate reservoirs of hot water which may be a good place for early life to start. It could also preserve ancient life forms in impact glass. Perhaps impact craters are the places to search for evidence that life has existed on Mars.