This is a 10 question multiple choice quiz with answers for the PBS video " The Ancient Tribes That Settled the Americas - First Peoples". As early humans spread out across the world, their toughest challenge was colonizing the Americas because a huge ice sheet blocked the route. It has long been thought that the first Americans were Clovis people, who arrived 13,000 years ago. But an underwater discovery in Mexico suggests people arrived earlier — coming by boat, not on foot