Why is Earth Mostly Crater-Free Compared to the Moon?

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All the activity on Earth's surface is akin to a constant makeover.

Much of our planet's geological history was folded back inside long ago. Some of that is regurgitated by volcanoes, but the results are pretty hard to study. Even more recent events evident on the surface -- craters that can by millions of years old -- get overgrown by vegetation, weathered by wind and rain, and modified by earthquakes and landslides.

The Moon, meanwhile, is geologically quiet and has almost no weather; its craters tell a billions-year-long tale of catastrophic collisions. Interestingly, some of the oldest Earth rocks might be awaiting discovery on the Moon, having been blasted there billions of years ago by the very asteroid impacts that rattle both worlds.