Scattered patches of rough, blistered ground carry so few craters that they look less than 100 million years old, which is a blink in lunar terms.

The Moon was supposed to have finished erupting around a billion years ago. These irregular mare patches — about seventy of them, mostly small — suggest something was still going on when dinosaurs were. Counting craters is the only dating method available without samples, and it is not decisive, so this is a live argument rather than a settled fact.