Who were the first Americans?

This will shake things up: A stone knife that is still sharp places Stone Age Europeans in America 20,000 years ago.

Archaeologists have long held that North America remained unpopulated until about 15,000 years ago, when Siberian people walked or boated into Alaska and then moved down the West Coast.
But the mastodon relic found near the mouth of the Chesapeake Bay turned out to be 22,000 years old, suggesting that the blade was just as ancient.
Whoever fashioned that blade was not supposed to be here.

Notice how archaeologists' careers become wedded to a single view of events. You can see the conflict in the review of Across Atlantic Ice. The essence of science is to think like no one has thought before.