When looking through a telescope at the Moon, you see the cumulative effect of 41/2 billion years of stuff happening. Some big features from long ago ——for example, Montes Apenninus, the towering mountain chain created during the Imbrium basin's excavation 3.8 billion years ago ——are still clearly visible. But other features, even sizeable ones, have vanished from view due to sub-sequent volcanism and impact erosion.
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