Beringia: The Bering Land Bridge Between Asia and America

Beringia is the name scientists give to the region that linked north-east Asia and North America during the Ice Ages, when sea levels fell and a wide plain of land emerged where the Bering Strait lies today. At the height of the last Ice Age, roughly 26,000 to 19,000 years ago, this land bridge connected Siberia and Alaska. It was the route by which the ancestors of Native Americans reached the New World, and it may have been their home for thousands of years before they did.

How the land bridge formed

During the Ice Ages vast amounts of water were locked up in ice sheets on land, and global sea levels fell. At the Last Glacial Maximum, about 26,000 to 19,000 years ago, sea level was roughly 120 metres lower than today. Because the seafloor beneath the Bering and Chukchi Seas is shallow, mostly less than 50 metres deep, a broad stretch of land was exposed.

At its greatest extent this land stretched as much as about 1,000 kilometres from north to south. It was not a narrow bridge but a subcontinent, joined to the unglaciated lowlands of eastern Siberia and to Alaska and the Yukon. Similar land connections had appeared during earlier glacial periods too.

The term Beringia was coined in 1937 by the Swedish botanist Eric Hultén, who studied how plants were shared between Siberia and Alaska. The idea that people had reached the Americas from Asia by land is much older: the Spanish Jesuit José de Acosta suggested it as early as 1590.

A land without ice sheets

Despite the cold, much of Beringia was not covered by glaciers. The climate was too dry for large ice sheets to build up. Instead, the land was covered by a cold, dry grassland and tundra often called the mammoth steppe. It supported woolly mammoths, horses, bison, caribou, musk oxen, saiga antelope and predators such as lions and short-faced bears.

Animals moved across Beringia in both directions over hundreds of thousands of years. Horses and camels, which first evolved in North America, crossed into Asia, while mammoths, bison and others crossed into America. Some sheltered pockets of shrub and woodland in southern Beringia may have offered refuges for plants and animals during the coldest periods.

People in Beringia

Human presence in the region is old. The Yana Rhinoceros Horn Site in Arctic Siberia, well north of the Arctic Circle, shows that people were living in western Beringia by about 32,000 years ago. Claims of human activity at Bluefish Caves in the Yukon around 24,000 years ago, based on cut marks on animal bones, are intriguing but debated.

Firm evidence of people in eastern Beringia, in Alaska and the Yukon, appears by about 14,000 years ago at sites such as Swan Point. At Upward Sun River in central Alaska, archaeologists found the remains of an infant who died about 11,500 years ago. Her genome, published in 2018, revealed a previously unknown population, now called Ancient Beringians, related to but distinct from the ancestors of other Native Americans.

The Beringian standstill

Genetic studies of Native Americans have revealed a puzzle. Their ancestors appear to have separated from East Asian populations considerably earlier than people are thought to have entered the Americas. In 2007 a team led by Erika Tamm proposed the Beringian standstill hypothesis: that the ancestral population lived in isolation in or near Beringia for several thousand years before spreading south.

Estimates of how long the standstill lasted have varied widely, from a few thousand years to as long as 15,000 years in early versions; many recent studies favour a few thousand years, from perhaps around 25,000 to 20,000 years ago or somewhat later. Where the population lived is also debated. Some researchers favour the shrub refuges of central Beringia, now underwater; others suggest north-east Asia. The hypothesis helps explain the distinctive genetic variants found in Native Americans but not in Asia.

Crossing into the Americas

From Beringia, people could move south only when routes past the great North American ice sheets were open. Two main routes have been proposed: along the Pacific coast, which became free of ice from about 17,000 to 16,000 years ago, and through an ice-free corridor east of the Rocky Mountains, which opened later. The debate over these routes is central to the peopling of the Americas.

As the ice melted, sea levels rose. Beringia was gradually flooded, and by around 11,000 years ago the Bering Strait had reopened, separating Asia and America. Later peoples, including the ancestors of the Inuit and other Arctic groups, crossed by boat and over winter sea ice. In 1728 the Danish-born navigator Vitus Bering sailed through the strait that now bears his name, and he later reached Alaska during the Great Northern Expedition.

How scientists reconstruct Beringia

Because most of the land bridge now lies under the sea, researchers reconstruct it from indirect evidence. Cores drilled from the floor of the Bering and Chukchi Seas contain ancient soils, peat and pollen that show what grew there and when the sea returned. Mapping of the seafloor, known as bathymetry, combined with models of past sea levels, shows which areas were dry land at different times.

On land, frozen sediments in Alaska, the Yukon and Siberia preserve bones, plant remains and insects. Mammoth, horse and bison bones, some still bearing hair or soft tissue, have been dated by radiocarbon to track how animal populations changed. Fossil beetles are particularly useful, because different species live in narrow temperature ranges and so record past climate. Increasingly, DNA extracted directly from ancient sediments reveals which plants and animals were present even where no visible fossils survive.

These lines of evidence show that Beringia was not uniform. The interior was cold and dry, but the southern margins, closer to the Pacific, were milder and wetter, with shrubs such as birch and willow and perhaps scattered trees. Such places may have been where people and animals sheltered during the coldest centuries of the Last Glacial Maximum.

Myths and facts

A common picture shows a narrow causeway that people crossed in a single journey. In reality Beringia was a vast region, and the people who lived there were not trying to reach a new continent; they were following game and resources across a landscape that, to them, was simply home. Their descendants moved south over many generations.

Another misconception is that the first Americans must have walked through a gap in the ice sheets straight after leaving Beringia. Current evidence suggests that the coastal route opened first, and that the inland corridor became usable only later, after people were already living further south.

Timeline

• c. 32,000 years ago: People live at the Yana site in western Beringia.
• c. 26,000–19,000 years ago: The Last Glacial Maximum; the land bridge is at its widest.
• c. 17,000–16,000 years ago: The Pacific coastal route begins to open.
• c. 14,000 years ago: People are living at Swan Point in Alaska.
• c. 11,500 years ago: An infant is buried at Upward Sun River, Alaska.
• c. 11,000 years ago: Rising seas flood the land bridge and the Bering Strait reopens.
• 1590: José de Acosta suggests that the first Americans came from Asia over land.
• 1937: Eric Hultén coins the term Beringia.

Why it matters

Beringia was the gateway between the Old World and the New. Without the land bridge and the conditions it created, the first people could not have walked into the Americas when they did. The region also shaped the genetic history of Native Americans, whose ancestors may have spent thousands of years there before beginning one of the great migrations of human history.