Two stones fuel debate over when America’s first settlers arrived
Microscopic bone residue on rocks possibly used to smash mastodon remains draws new scrutiny
![stone with microscopic bone residue](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2020/12/113020_bb_stones_feat.jpg?fit=1030%2C580&ssl=1)
Microscopic bone residue found on this stone supports a disputed claim that the rock was used to break apart mastodon bones at a southern California site around 130,000 years ago, researchers say.
James Berrian/San Diego Natural History Museum