Relative dating cratering distribution
The impactor is shattered into small pieces and may melt or vaporize.
Sometimes the force of the impact is great enough to melt some of the local rock.
How can craters be used to determine the age of a planet or moon?
Scientists record the size and number of impact craters — and how eroded they are — to determine the ages and histories of different planetary surfaces.
The largest impact basin on the Moon is 2500 kilometers (1550 miles) in diameter and more than 12 kilometers (7 miles) deep.
Its features, such as the ejecta blanket beyond its rim, are well preserved because of the crater's youth; it has not experienced extensive erosion. The Vredefort impact crater, about 100 kilometers (60 miles) from Johannesburg, South Africa, was formed just a little over 2 billion years ago.Therefore, older surfaces have more impact craters.Mercury and the Moon are covered with impact craters; their surfaces are very old.Geologic processes have not erased the craters with time. The shock wave fractures the rock and excavates a large cavity (much larger than the impactor).The impact sprays material — ejecta — out in all directions.