Craig Childs went looking for the first people in the Americas by walking the ground they walked, back when the map looked nothing like it does now. Sea level was 400 feet lower, an ice sheet sat on Canada, and mammoths, short-faced bears, and lions were the neighbors. So he went to Alaska and dragged his family across mudflats where the land bridge used to be. He hauled a weight approximating what somebody would have carried. He dove the Aucilla River in Florida with archaeologists pulling mastodon bones out of the muck. He walked Mojave playas and Wisconsin ice and Baja beaches, and he slept out in all of it. Along the way he laid out the fight over how people got here and when, which keeps getting older every time somebody digs.
Atlas of a Lost World: Travels in Ice Age America