Final answer:
Lunar highlands have a high crater density due to their early formation in lunar history, with a great number of impacts over billions of years, having about ten times more craters than the maria.
Step-by-step explanation:
The lunar highlands are the lighter, heavily cratered regions of the Moon and have a high crater density. These highland areas are characterized by a significant number of craters due to the Moon's long history of impacts by interplanetary debris. The highlands are composed of low-density rock that solidified early in lunar history, approximately between 4.1 and 4.4 billion years ago, which explains their extensive cratering. Notably, the highlands are much older compared to the lunar maria, which are the dark, less cratered, and younger volcanic plains located primarily in the northern hemisphere of the Moon.
Analysis of the lunar surface reveals that the highlands have about ten times more craters per given area than the maria. However, this does not mean the highlands are ten times older than the maria. The difference in crater density is attributed to a period of heavier bombardment earlier in the Moon's history, particularly before 3.8 billion years ago, when the impact rate was higher.