Rocks in space collide with things—Earth included—all the time, but in human history these collisions have mostly been small events that make little lasting impact. Go back long enough, and massive impacts start to appear in the geological record. And the solar system’s youth was downright barbaric: momentous impacts left, right, and center. While the scars of impacts on Mercury, the Moon, and Mars have more or less been preserved over billions of years in their pockmarked surfaces, Earth has plate tectonics and weather and oceans and life. Our planet…
