The first is based on crater density and has three ages: Noachian, Hesperian, and Amazonian.

Absolute ages determined by crater density should therefore be taken with some skepticism.

In fact, the crater density is close to saturation: any new crater will tend to erase an older one.

The higher the crater density, the older the surface.

During this late stage, smooth plains materials were deposited in basins, craters, and localized low areas and have low crater density.

The intercrater plains material is probably about the same age as the ejecta blanket around Beethoven basin: both units have a high crater density.

The crater density is same on the ejecta covered plains outside the basin.

An analysis of crater densities over the surface indicates that the areas with lower crater density are within 9 kilometers of the impact point.

One of the areas of low crater density is around this crater.

The seismic shaking also explains the second area of low crater density, which is on the opposite side of the asteroid from Shoemaker.