It seems that between about 3.2 and 3.5 billion years ago, Earth got whacked at least three times by *big* impactors. Keep in mind that the rock that killed the dinosaurs was on the order of 10 kilometers in diameter; these earlier impactors were on the order of 50 to 100 kilometers in diameter (or up to 1000 times the impact energy). There was life on Earth at the time in the form of primitive single cell organisms, but these impacts would have played hell with them. Estiamtes are that the impact would have driven the planetary air temperature to over 500 Celcius for weeks, and above the boiling point of water for over a year. Sea levels would have dropped by up to 100 meters as the upper levels of the oceans boiled away.

Rocks this old are fairly rare, but examination of some examples show showers of BB-sized “droplets” of molten rock kicked up by the impacts.

Ancient Asteroid Impacts Boiled the Oceans and Made Life on Earth Hell

A 100-kilometer impactor is *exactly* the sort of thing that mankind would not be able to do diddly-squat about, other than to send a small remnant of terrestrial life to, say, Mars. Certainly wouldn’t want to go to the moon; the moon would almost certainly get pummeled by chunks of Earth blasted into space.