Scientists have mapped enormous impact craters hidden under the Antarctic ice sheet using satellite technology.
The asteroid may have raised sea levels by up to 60cm
The craters may have either come from an asteroid between 5 and 11km across that broke up in the atmosphere, a swarm of comets or comet fragments.
The space impacts created multiple craters over an area of 2,092km (1,300 miles) by 3,862km (2,400 miles).
The scientists told a conference this week that the impacts occurred roughly 780,000 years ago during an ice age.
When the impacts hit, they would have melted through the ice and through the crust below.
Professor Frans van der Hoeven, from Delft University in the Netherlands, told the International Geographical Union Congress in Glasgow that the biggest single strike seared a hole in the ice sheet roughly 322km (200 miles) by 322km.
This would have melted about 1% of the ice sheet, raising water levels worldwide by 60cm (2ft).
The research suggests that an asteroid the size of the one blamed for killing off the dinosaurs 65 million years ago could have struck Earth relatively recently.
Early humans would have been living in Africa and other parts of the Old World at the time of the strikes.
But the impacts would have occurred during an ice age, so even tidal waves would have been weakened by the stabilising effect of icebergs on the ocean.
The craters were resolved using satellite data to map gravity anomalies under the ice sheet.