If you want to know what happened on Earth 500 years ago, you might ask a historian. But if you want to know what happened on Earth 3.26 billion years ago, nobody was there to write it down; you’d be better off asking a geologist. Quite often they can forensically examine our durable old planet’s remains for evidence of past events—especially the loud and messy kind.
And it doesn’t get much louder or much messier than the asteroid that collided with an area we would now identify with northeastern South Africa towards the end of the Archean Eon. Roughly the size of Luxembourg and traveling 43,000 miles per hour (or about a hundred times faster than an average bullet), it punched a hole in our planet, generated a 10.8 earthquake lasting thirty seconds or more, boiling the oceans, and generally making a mess of things. io9’s George Dvorsky maps out the gory details. Nobody especially minded any of this because life on Earth was strictly microbial at that point, and as far as we know microbes don’t especially mind anything. But the impact did help to generate the modern system of tectonic plates that created the continents as we’ve come to know them, and—being the largest asteroid collision we can find traces of, so far—it probably contributed in some indirect way to the evolution of our species.
Could an asteroid of this size and magnitude hit us again? Probably not—it’s been a few billion years, and there aren’t as many massive near-earth asteroids as there once were. But the risk of an asteroid collision of some kind is still greater than zero, and the consequences greater than we can bear, which is why scientists at LINEAR are hard at work cataloging the damn things:
You might note that the video mentions there are only a couple of hundred visible impact craters on Earth, the rest having been eroded over time. This asteroid’s crater, desire its considerable size, appears to have fallen into the latter category. For a geologically active planet like ours, time heals all wounds.