How did they get south?
After journeying from Siberia to Alaska across the ancient Bering land bridge that emerged toward the end of the last ice age, the first humans to reach the Americas still had a ways to go.
At the time, Canada was blanketed in ice sheets, so it was previously believed that these people waited until receding glaciers gave way to an ice-free corridor just east of the Rocky Mountains, which provided a direct route south.
A new study published in the journal Nature pinpoints when the corridor became viable for human migration, based on ancient DNA from lake sediment, fossils, pollen, and radiocarbon dating.
The evidence suggests that this particular north-south route wouldn’t have been suitable for travel until around 12,600 years ago. It was around this time that the corridor went from being a frozen wasteland to a place where steppe plants grew, bison and woolly mammoths roamed, and importantly, the resources needed to survive a long journey became available.
Yet traces of human habitation began to pop up south of the ice sheets well before this time. For instance, the Clovis culture is believed to have set up shop, in what is today the contiguous US, more than 13,000 years ago. If the corridor was impassable at that time, how did those early settlers get there?
The most likely scenario is now that the entry route for the first New World settlers was actually along the Pacific coast, while the ice-free corridor would become available for people arriving in subsequent waves.