Scientists Find Signs Big Meteor Hit Earth 3.5 Billion Years Ago:

‘The heat would have killed all single-cell microbes, the only life on Earth at the time, on land and in the upper ocean, which would have boiled into steam. The impact appears to have sent giant tsunamis coursing around the world’s oceans, scouring the early continents.

“The only thing that would have survived would have been bacteria in the deep ocean,” said Dr. Gary R. Byerly, a professor of geology at Louisiana State and the lead author of the article.’ NY Times