For most of the past 50 years, archaeologists thought they knew how humans arrived in the New World. At the end of the last ice age, sea levels dropped and big-game hunters living in eastern Siberia followed their prey across the Bering land bridge and into Alaska. Then they swept across the unpopulated continent. Archaeologists called these presumed pioneers the Clovis culture, after distinctive stone tools were found at sites near Clovis, New Mexico, in the 1920s and 1930s.

Any evidence of humans in the New World before the Clovis time was dismissed, sometimes harshly. That was the case with a Washington-state mastodon kill first described around 30 years ago but then largely ignored.

Intense criticism also rained down on competing theories of how people arrived, such as the idea that early Americans might have skirted the coastline in boats, avoiding the Bering land bridge entirely. “I was once warned not to write about coastal migration in my dissertation. My adviser said I would ruin my career,” says Jon Erlandson, an archaeologist at the University of Oregon in Eugene.

Read more about the rise and fall of the Clovis hypothesis: Ancient migration: Coming to America by Andrew Curry, Nature