The site of Monte Verde in Chile today. Credit: (Geología Valdivia/Wikimedia Commons)

As the Ice Age began to wane, people from northeastern Asia spread to the Americas, some of the last uninhabited continents on Earth. The pioneers traveled south of mile-high ice sheets covering Canada and found vast lands, abounding with mammoth, giant sloth and other now-extinct megafauna.

This much has been known for decades. But when it comes to the details, debates have raged over precisely when and