Remember back in high school when you learned all those human-history basics, like the fact that we share a common ancestor with the African ape or that the first Americans reached the continent by way of a grassy strip of terrain called the Bering land bridge that emerged as the ice retreated between Russia and Alaska?

Turns out that last bit might be wrong.

According to a new study, published Wednesday in the journal Nature, the first people to reach the Americas most likely never even saw this route.

Instead, they took an alternative, more westward path along the Pacific coastline across lands that are now underwater.

"It definitely challenges what most people learned in high school," Mikkel Winther Pedersen, the paper's lead author and an anthropologist at the University of Copenhagen in Denmark, told Business Insider.

For centuries, people have considered the Bering land bridge to be the main highway that the earliest human travelers used to get to the Americas. Back in the 16th century, Spanish explorer Jose de Acosta posited that those early hikers made their way south while tracking massive herds of animals like deer and elk, whose meaty flesh would sustain them on their treacherous journey.

Here's a GIF showing how the area called Beringia emerged and disappeared over thousands of years:

The gist of this theory has remained pretty widely accepted among archaeologists, though certain parts of it — like what types of animals and plants lived in the region at the time — are still hotly debated.

One recent study, for example, suggested that while the first Americans did indeed travel throughout and even settle in Beringia, they certainly weren't eating any large game, since the landscape would have supported only small animals and perhaps elk. Still, Beringians would have had all the resources they needed to survive there, the authors of that paper argued two years ago in a post for The Conversation.

The new study challenges that assumption, finding instead that the area simply didn't have the resources to support thousands of hungry humans — at least not until thousands of years later.

But there's strong evidence that humans were present in the Americas long before then. In May, a team of archaeologists uncovered a set of 14,550-year-old stone tools and butchered mastodon bones at the bottom of a Florida river — firmly placing the first Americans in those lands 1,000 earlier than scientists once thought.

So the question for the new study's researchers was this: How did these mastodon-hunting Americans get there? Did they somehow manage to eke out a route along the barren terrain of the Bering land bridge? Or did they use another route — perhaps the other ice-free pathway along what's now part of the submerged Pacific coastline?

To find out, the researchers dug ancient ice cores out of lakes in the region where ice once retreated and filled in with water, essentially forming frozen time capsules. It's a new and developing field of research called environmental DNA, or eDNA for short, that involves carefully inspecting all the genetic material hidden inside a sample of soil, sediment, or water.

"It was kind of like time travel," Pedersen said.

Trapped deep inside each ice core, the researchers found layers of sediment, each of which represented a distinct era in ecological time. They used the cores to get a glimpse of what the area looked like from roughly 15,000 years ago — when the ice retreated and the lakes began to fill with liquid water — up until about 12,600 years ago, when animals and plants began to establish themselves there.

"Putting this together we could suddenly see that, well, humans couldn't have used this corridor until 12,600," Pedersen said, "because they couldn't have walked along a thousand-kilometer stretch of land without having something to sustain them."

The finding could change history, Florida State University archaeologist Jessi Halligan, and one of the authors of the study that uncovered the butchered mastodon bones in Florida but who was not involved with this paper, told Business Insider.

"This is a really big and important study," said Halligan. "It shows these first Americans couldn’t have taken this corridor — it simply wasn't viable at the time."