The land bridge between Alaska and Russia, known as Beringia, was drowned by rising seas as the last ice age ended. At its peak roughly 20,000 years ago, it was a vast, walkable landscape stretching over 1,000 miles from north to south. Today, only a shallow strait about 85 kilometers wide and 50 meters deep separates the two continents, along with a handful of islands that mark the highest points of the old land mass still poking above the waterline.
How the Land Bridge Formed
During the Last Glacial Maximum, so much of Earth’s water was locked in massive ice sheets that global sea levels dropped roughly 130 meters below where they sit today. The Bering Strait is only about 53 meters deep at its deepest point, so even a fraction of that drop was enough to expose a wide plain of dry land connecting Siberia to Alaska. This wasn’t a narrow footbridge. At its widest, Beringia stretched roughly 1,600 kilometers from north to south, making it larger than many modern countries. It persisted for thousands of years, long enough for entire ecosystems and human populations to establish themselves on it.
What the Land Bridge Looked Like
Beringia was not a frozen wasteland. Scientists once called its ecosystem the “mammoth steppe,” imagining something like a vast prairie, but more recent evidence from ancient DNA preserved in sediments and plant fossils paints a different picture. The vegetation was a patchwork of grasses, herbs, and low shrubs better described as “steppe-tundra,” a landscape that could support large grazing animals but looked nothing like the Great Plains.
Woolly mammoths, steppe bison, horses, muskoxen, caribou, lions, brown bears, and wolves all roamed this terrain. The land bridge served as a two-way highway. Most of the traffic moved east: mammoths, bison, and brown bears crossed from Asia into North America. Horses went the other direction, originating in North America and dispersing westward into Asia. Interestingly, genetic analysis shows that once mammoths colonized North America, very few bred back with their Asian relatives. Bison show a similar pattern, with DNA from eastern and western Beringia populations remaining surprisingly distinct, suggesting that even on this enormous land mass, animals didn’t freely wander back and forth as much as you might expect.
When and How It Flooded
The flooding of Beringia wasn’t a single dramatic event. As the planet warmed and ice sheets melted, sea levels rose gradually over thousands of years. The exact timing is still debated, with two main lines of evidence pointing to slightly different dates.
Sediment cores drilled from the seafloor near the strait show a sharp transition from land-like to open marine conditions around 11,000 to 12,000 years ago. But biological evidence tells an earlier story. Fossils of Pacific mollusk species have turned up on raised beaches in the Canadian Arctic dating to roughly 13,000 to 13,500 years ago. For those mollusks to reach Canada from the Pacific, water had to be flowing through an open or partially open strait well before the sediment cores register full marine flooding.
The most likely explanation is that the strait began to flood as a shallow, brackish channel around 13,000 years ago, then widened and deepened over the next 1,500 to 2,000 years until it became the open ocean passage that exists today. By roughly 11,000 years ago, Asia and North America were fully separated.
People Who Crossed It
Humans were among the species that used Beringia. Archaeological sites in interior Alaska’s Tanana Valley, including Swan Point, Broken Mammoth, and Healy Lake, contain evidence of human occupation dating between roughly 11,000 and 14,000 years ago. These early Alaskans left behind stone tools, microblades, and distinctive biface points. Some of these sites sit only about 20 kilometers apart and appear to represent related groups of people occupying the same landscape during the late Pleistocene.
Whether these people walked directly across the land bridge or took coastal routes remains an active question. But the timing is clear: humans were living in Alaska while the land bridge still existed or had only recently flooded, and their ancestors almost certainly traveled through Beringia at some point during its long exposure.
What’s Left of It Today
Beringia didn’t vanish completely. Several islands in the Bering and Chukchi Seas are the surviving high points of the old land mass. The Diomede Islands sit almost exactly in the middle of the strait, with Big Diomede belonging to Russia and Little Diomede to the United States, separated by less than four kilometers. St. Lawrence Island, King Island, and the Pribilof Islands of St. Paul and St. George are also remnants of the submerged landscape. These islands still support wildlife populations whose ancestors roamed a much larger, connected territory.
The Bering Land Bridge National Preserve on Alaska’s Seward Peninsula protects part of the coastline that once bordered this vanished land. Beneath the shallow waters of the strait, the old terrain is remarkably flat, a reminder that this was gently rolling lowland, not mountainous country.
How the Flooding Changed Global Climate
The opening and closing of the Bering Strait had consequences far beyond the Arctic. Research using computer climate simulations found that when the strait was closed during ice ages, it cut off the flow of relatively fresh Pacific water into the saltier Atlantic Ocean. Without that dilution, the Atlantic grew more saline, and heavier salt water intensified a major ocean current called the meridional overturning circulation, essentially a giant conveyor belt that pulls warm tropical water northward.
This warmed Greenland and parts of North America by about 1.5 degrees Celsius, enough to reverse the advance of ice sheets and shrink them by nearly 112 meters in height every thousand years. As those ice sheets melted, sea levels rose, eventually reopening the strait. Once fresh Pacific water poured back through, it weakened the same Atlantic current, allowing the north to cool again. This feedback loop, the strait closing, the Atlantic warming, ice sheets melting, the strait reopening, repeated multiple times over hundreds of thousands of years, influencing ice sheet cycles and climate patterns across the globe.
The Bering Strait today remains one of the most consequential geographic features on Earth. A channel barely 50 meters deep controls the exchange of water between two oceans and continues to play a role in Arctic Ocean circulation, sea ice formation, and the marine ecosystems that depend on both.