| | L11 The selenologic column and time scale |
 | | A consequence of micrometeorite gardening is that from Earth based observations, large Moon craters can be sorted into two broad age-categories: young craters (such as Copernicus, with high albedo ejector aprons and associated secondary-impact ejecta craters and rays); and, old partly obliterated craters (such as Eratosthenes, with slumped rims and no clearly visible rays). |
 | | Also, as Moon craters are impact craters (no longer an assumption, since analysis of Apollo returned materials), the younger age of the maria formation is corroborated by the terrae formation being fifteen times more cratered (counting craters 10 kilometers or larger in diameter). |
 | | Crater counting the relative age of the Copernican and the Eratosthenian craters, and knowing the age of the maria and the terra and establishes that the flux and size range of infalling material (meteorites, planetesimals) has exponentially decreased since Moon's rock record began. |
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