The Bering Land Bridge theory proposes that during the last ice age, a massive strip of land connected present-day Siberia and Alaska, allowing humans, animals, and plants to cross between Asia and North America. This wasn’t a narrow walkway. At its widest point, roughly 21,000 years ago, the land bridge stretched more than 1,000 miles from north to south, making it a vast, inhabitable landscape rather than a simple corridor between continents.
How the Land Bridge Formed
During the last ice age, enormous volumes of ocean water became locked in glaciers and ice sheets. Global sea levels dropped roughly 125 meters (about 410 feet) below where they are today, exposing the shallow continental shelf beneath the Bering Strait. The shallow seabed between Siberia and Alaska rose above the waterline, creating a continuous landmass scientists call Beringia.
For decades, researchers assumed the land bridge first appeared around 70,000 years ago based on estimated sea level and temperature records. But a Princeton University study significantly revised that timeline, finding that the Bering Strait remained flooded until about 35,700 years ago. The bridge reached its maximum extent around 21,000 years ago during the coldest phase of the last ice age, known as the Last Glacial Maximum. As temperatures warmed and ice sheets melted, rising seas gradually swallowed the bridge. Today the Bering Strait is only about 55 miles wide and 100 to 160 feet deep, a reminder of just how little sea level change was needed to create or destroy this crossing.
What Beringia Looked Like
The land bridge wasn’t barren ice or featureless tundra. Fossil and sediment evidence paints a picture of a cold, dry landscape covered in what scientists call “steppe-tundra,” a mix of low shrubs (mostly willow and birch), grasses, herbs, and other hardy plants. Earlier researchers described it as a grassland similar to modern prairies, but DNA extracted from ancient sediments shows the vegetation was more varied and shrubby than that.
This landscape supported large animal populations. Woolly mammoths, steppe bison, and horses grazed across Beringia alongside muskoxen and caribou. Predators like lions, brown bears, and wolves followed the herds. The climate was consistently cooler and drier than today, with strong winds that moved dust and sediment across the open terrain. Permafrost lay beneath the surface, and scattered wetlands and shallow lakes dotted the lowlands. For the animals and people living there, Beringia was not a bridge to be crossed quickly. It was a place to live.
Animals That Crossed Between Continents
The land bridge served as a two-way highway for wildlife over hundreds of thousands of years across multiple ice ages. Mammoths, bison, muskoxen, caribou, lions, brown bears, and wolves all moved from Asia into North America through Beringia. Traffic also went the other direction: horses, which evolved in North America, dispersed westward across the bridge into Asia. These exchanges reshaped the ecosystems of both continents and explain why species like bison and brown bears are found on both sides of the Pacific today.
When Humans Arrived
The question of exactly when people first crossed into the Americas remains one of the most actively debated topics in archaeology. The traditional version of the land bridge theory held that humans walked from Siberia to Alaska and then traveled south through an ice-free corridor between two massive ice sheets (the Laurentide and Cordilleran) that covered most of Canada. This route, linked to the Clovis culture and its distinctive stone tools, was long considered the first entry point, dating to roughly 13,000 years ago.
That picture has changed dramatically. Archaeological sites in western Beringia (the Siberian side) show human activity as far back as 32,000 years ago. On the North American side, the Bluefish Caves in Canada’s Yukon Territory contain cut-marked animal bones, clear signs of human butchering, dating to at least 24,000 years ago. This makes Bluefish Caves the oldest confirmed archaeological site in North America and places humans in eastern Beringia thousands of years before anyone moved further south.
The Beringian Standstill Hypothesis
If people reached eastern Beringia by 24,000 years ago but didn’t spread across the Americas until after about 16,000 years ago, what were they doing in between? The Beringian Standstill Hypothesis offers an answer: a population of early Americans migrated from eastern Asia into Beringia and then stayed there, isolated, for thousands of years.
The strongest evidence comes from genetics. Mitochondrial DNA analysis shows that the founding population of the Americas split from East Asian populations and evolved in genetic isolation for up to 15,000 years before dispersing south. During this long pause, they developed the unique genetic signatures that distinguish Indigenous peoples of the Americas from their Asian ancestors. The Bluefish Caves findings provide archaeological support for exactly this kind of prolonged habitation. People weren’t simply passing through Beringia. They were living there, hunting horses and caribou, through some of the coldest millennia of the ice age.
The Coastal Migration Alternative
The traditional land bridge model assumed people walked south through an inland ice-free corridor between the two great ice sheets covering Canada. But research on ancient bison DNA and geological dating shows that corridor was completely blocked from about 23,000 until 13,400 years ago. It wasn’t fully habitable until around 13,000 years ago, with enough plant and animal life to sustain human travelers. By that time, humans were already living well south of the ice sheets. Multiple archaeological sites south of the glaciers predate 15,000 years ago, making it impossible for those people to have come through the inland corridor.
This timing has led most researchers to conclude that the first wave of migration from Beringia into the Americas followed the Pacific coastline rather than an inland path. This coastal migration theory proposes that people moved south along the shore, using boats or traveling on foot along exposed coastline, following productive marine environments rich in kelp, fish, and shellfish. The earliest archaeological sites in the Americas share tool-making technologies with Upper Pleistocene peoples of northern Japan, suggesting a coastal population accustomed to maritime resources. The land bridge still played its role in getting people from Asia to the Americas, but the route south was along the coast, not through the interior.
What Scientists Are Looking for Now
The biggest challenge in studying Beringia is that the land bridge itself is now underwater. Any campsites, tools, or remains left by people who lived there sit beneath the Bering Sea. In 2023, a team of scientists from the USGS, the University of Alaska Fairbanks, and UC Santa Cruz collected sediment cores from the Bering Sea floor, targeting small submerged basins on the shallow continental shelf. Their cores revealed marine sediments sitting on top of ancient lake sediments, a clear record of the transition from dry land to ocean.
By analyzing DNA preserved in these sediments, the team aims to identify the specific plants and animals that lived on the land bridge and the types of wetlands that existed there. This kind of evidence helps reconstruct what conditions were actually like for the people and animals that lived in Beringia, filling in a picture that, for now, mostly comes from sites on the edges of the bridge rather than its submerged center.