Final answer:
An old crater can be distinguished from a new one by counting the number of impact craters on a planetary surface. The more heavily cratered terrain is generally older, indicating that more time has elapsed since the surface was 'swept clean'. This method is used to estimate the age of surfaces on worlds with little erosion or internal activity, such as the Moon.
Step-by-step explanation:
The age of a crater can be determined by counting the number of impact craters on a planetary surface. The more heavily cratered terrain is generally older, indicating that more time has elapsed since the surface was 'swept clean' by ongoing lava flows or molten materials from a large impact. This method is used to estimate the age of surfaces on worlds with little erosion or internal activity, such as the Moon. By estimating the rate of crater formation and counting the number of craters, scientists can determine the surface age.
For example, on the Moon, where there has been little erosion or internal activity in the past 3 billion years, the number of impact craters can be used to estimate the age of the surface. The rate of impacts has been roughly constant for several billion years, so the number of craters is proportional to the length of time the surface has been exposed. This technique has been successfully applied to many solid planets and moons.
It is important to note, however, that crater counts can only provide an estimation of how long it has been since a major change occurred on the surface. Factors like volcanic eruptions or ongoing lava flows can modify or erase preexisting craters, so the age estimation is not always precise.