What geological event caused the Beringia land bridge to become exposed thousands of years ago?

A massive earthquake shifted the tectonic plates

Volcanic eruptions created a new landmass

The formation of huge glaciers during an Ice Age locked up ocean water, lowering sea levels

The natural process of continental drift slowly pushed Asia and North America closer together

What was the primary motivation for the first groups of hunter-gatherers to cross the land bridge into North America?

They were following herds of large animals, like mammoths, for food

To establish new trade routes with other groups