Final answer:
The observed rate of cratering on the lunar highlands shows that they are younger than the maria.
Step-by-step explanation:
The observed rate of cratering on the lunar highlands helps to show that the highlands
are younger than the maria.
When comparing the numbers of craters on the lunar highlands with those on the maria, it is typically found that there are 10 times more craters on the highlands than on a similar area of maria. However, radioactive dating of highland samples shows that they are only a little older than the maria, typically 4.2 billion years rather than 3.8 billion years. This indicates that the cratering rate on the moon has not been constant and that the highlands are younger than the maria.