A land bridge between Alaska and Siberia flooded to make the Bering Strait 11,000 years ago, more than 1,000 years earlier than previously thought, US researchers reported on Wednesday.

This would have closed off human migration by foot across the bridge 1,000 years earlier, too, the researchers said.

A team at the Woods Hole Oceanographic Institution in Massachusetts, the Scripps Institution of Oceanography in San Diego and the University of Massachusetts found places on the ocean floor where sediment deposits were deep enough to act as a kind of geologic clock.