The ancestors of Native Americans walked from Siberia to North America across a vast land bridge that connected the two continents during the last ice age. That crossing, which began at least 20,000 years ago, was made possible by sea levels dropping roughly 130 meters (425 feet) below today’s levels, exposing a wide stretch of land between modern-day Russia and Alaska. But the story is more complex than a single trek across a frozen plain. Multiple waves of people likely used different routes over thousands of years, and recent discoveries keep pushing the timeline of arrival further back.
The Bering Land Bridge
During the Last Glacial Maximum, roughly 26,000 to 19,000 years ago, so much of Earth’s water was locked in glaciers that the shallow sea floor between Siberia and Alaska became dry land. This exposed region, known as Beringia, wasn’t a narrow strip. It was a landmass roughly the width of Alaska itself, stretching over a thousand kilometers from north to south. People didn’t “cross a bridge” in any dramatic sense. They lived on it.
Beringia was cold and dry during the peak of the ice age, covered mostly in grasses and low-growing plants, with scattered willow and birch shrubs. Between about 14,600 and 14,000 years ago, a short warm period brought wetter conditions and expanded wetlands across the southern portion of the land bridge, boosting plant growth and likely supporting more wildlife. The land didn’t vanish overnight once the ice age ended. The greatest loss of land area from rising seas happened between about 10,000 and 8,500 years ago, at least 4,500 years after the earliest solid evidence of humans in Alaska.
Some researchers think people didn’t just pass through Beringia quickly. They may have lived there for generations in a kind of holding pattern, a concept sometimes called the Beringian Standstill. Genetic evidence suggests the ancestors of today’s Native Americans split from their closest Siberian relatives around 24,000 years ago. But confirmed archaeological sites in the Americas don’t appear until several thousand years later, leaving a gap that a long stay in Beringia could explain.
Roots in Siberia
DNA studies have firmly traced Native American ancestry to Siberian populations. One striking piece of evidence comes from the skeleton of a boy who lived near Lake Baikal in south-central Siberia around 24,000 years ago, at a site called Mal’ta. His DNA shows close genetic ties to modern Native Americans, with roughly 30 percent of Native American ancestry traceable to his gene pool. He also had connections to western Eurasian groups in central Asia, South Asia, and Europe, which helps explain why some ancient skeletons in the Americas, like Kennewick Man, were initially interpreted as having European-like features. This doesn’t mean people came from Europe. It means the Siberian population that gave rise to Native Americans already carried some of that genetic diversity before they ever left Asia.
Two Possible Routes South
Once people reached Alaska, two massive ice sheets blocked the way into the rest of the continent: the Cordilleran ice sheet along the Pacific coast and the Laurentide ice sheet covering most of Canada. Getting past them required one of two routes.
The Pacific Coast
The route with the strongest support for the earliest arrivals runs along the Pacific coastline. By about 16,000 years ago, the North Pacific coast offered a continuous, sea-level path from northeast Asia into the Americas. Rising seas had actually created a highly fragmented, island-rich coastline along Beringia’s southern edge, conditions well suited to people who lived by the sea.
A continuous chain of kelp forests stretched from Japan to Baja California, forming one of the most productive ecosystems on Earth. These underwater forests supported dense populations of shellfish, fish, seabirds, and marine mammals. For coastal peoples skilled at harvesting these resources, the entire Pacific Rim offered a familiar, reliable food supply that required little adaptation as they moved south. Researchers call this the “kelp highway” hypothesis. The kelp forests even reduced wave energy and provided natural anchor points for boats, making travel by watercraft practical.
The major challenge with proving this route is that the coastline people would have traveled is now submerged under rising seas, making archaeological sites extremely difficult to find.
The Ice-Free Corridor
The other route ran between the two great ice sheets through what is now interior western Canada. For decades, this ice-free corridor was considered the primary entry point. But recent dating work has undermined that idea for the earliest arrivals. Cosmogenic exposure dating shows the corridor didn’t fully open until about 13,800 years ago, and the landscape didn’t support enough plant and animal life for human travel until around 12,600 years ago, when steppe vegetation and animals first appeared near the corridor’s midpoint. By that time, people were already living thousands of kilometers to the south. The corridor almost certainly served as a route for later migrations, but it wasn’t the first one.
The Oldest Evidence in the Americas
The timeline of when people arrived keeps getting pushed back as new sites are discovered and older ones are re-examined with better technology.
The most dramatic recent find is a set of fossilized human footprints at White Sands National Park in New Mexico. First reported in 2021, the footprints were dated to between 23,000 and 20,000 years ago. The dating was initially controversial, but two independent methods, radiocarbon dating of terrestrial pollen grains and a technique that measures when sediment was last exposed to light, both confirmed the original age range. These footprints place humans well south of the ice sheets during the Last Glacial Maximum itself, far earlier than most previous estimates.
In the Yukon, Canada’s Bluefish Caves contain animal bones with cut marks made by stone tools. The oldest of these, a horse jawbone, dates to about 24,000 years ago. A caribou pelvis with filleting marks dates to around 22,000 years ago. These aren’t campsites with hearths and abundant tools. They’re traces of people passing through and butchering game, but they’re enough to confirm a human presence in northwestern North America during the coldest stretch of the ice age.
Meadowcroft Rockshelter in southwestern Pennsylvania preserves signs of human habitation dating back 19,000 years, making it one of the oldest known sites in the eastern part of the continent. And in southern Chile, the site of Monte Verde has yielded burned features, stone tools, and animal remains dating between 18,500 and 14,500 years ago. The fact that people had reached the southern tip of South America by that time suggests the initial entry into the Americas happened considerably earlier.
Not One Migration, but Many
The emerging picture is that the peopling of the Americas wasn’t a single event. The earliest arrivals may have come along the Pacific coast more than 20,000 years ago, likely in small numbers. Later groups followed the same coastal path or eventually used the ice-free corridor once it opened. Each wave brought slightly different genetic signatures that can still be detected in modern Native American populations across North and South America.
The speed of southward expansion was remarkable. If people were in the Yukon by 24,000 years ago and in Chile by 18,500 years ago, some groups covered the full length of two continents in just a few thousand years. Coastal travel by boat, hopping between kelp forest ecosystems that provided consistent food, could account for that pace in a way that overland trekking through unfamiliar terrain cannot.