How do scientists believe that ancient peoples first arrived in the Americas?

Scientists believe that ancient peoples first arrived in the Americas by crossing a land bridge known as Beringia, which connected Siberia to Alaska during the last Ice Age. These early migrations are thought to have taken place around 15,000-20,000 years ago, as nomadic hunter-gatherer groups followed animal herds into the region. Over time, these populations spread and diversified across the continents.