Beringia is a prehistoric region that includes land and coastal areas. It is located west of the Lena River in Russia, east of the Mackenzie River in Canada, north of 72° north latitude in the Chukchi Sea, and south of the tip of the Kamchatka Peninsula. This area includes the Chukchi Sea, the Bering Sea, the Bering Strait, the Chukchi and Kamchatka peninsulas in Russia, Alaska in the United States, and Yukon in Canada.

The region covers parts of the North American Plate and Siberian land east of the Chersky Range. At times in the past, Beringia formed a land bridge called the Bering land bridge or the Bering Strait land bridge. This bridge was up to 1,000 km (620 mi) wide and as large as the combined areas of British Columbia and Alberta, totaling about 1.6 million km² (620,000 sq mi). It allowed plants and animals to move between Asia and North America. Today, only a few islands, such as the Diomede Islands, the Pribilof Islands (St. Paul and St. George), St. Lawrence Island, St. Matthew Island, and King Island, are visible from the central part of this land bridge.

It is believed that a small group of people, no more than a few thousand, arrived in Beringia from eastern Siberia during the Last Glacial Maximum. They later moved into the Americas before 23,000 and 21,000 years before present (YBP). This migration happened after glaciers blocking the way southward melted but before the land bridge was covered by the sea around 11,000 YBP.

Geography

In the late 1800s, scientists found the remains of large mammals from the Late Pleistocene era on the Aleutian Islands and in the Bering Sea. These discoveries suggested that a land connection might once have existed beneath the shallow waters between Alaska and Chukotka. At first, scientists thought the land connection was caused by the movement of Earth’s tectonic plates. However, by 1930, researchers believed that changes in ice levels, which caused sea levels to rise and fall, were the main reason for the Bering land bridge. In 1937, Eric Hultén proposed that tundra plants near the Aleutians and Bering Strait had spread from a now-submerged area between Alaska and Chukotka. He named this area Beringia after Vitus Bering, who sailed through the Bering Strait in 1728. Plants in the genera Erythranthe and Pinus support this idea, as similar species are found in both Asia and the Americas.

American geologist David Hopkins later expanded the definition of Beringia to include parts of Alaska and Northeast Asia. Eventually, Beringia was described as stretching from the Verkhoyansk Mountains in the west to the Mackenzie River in the east. During the Pleistocene epoch, global cooling caused glaciers to expand and sea levels to drop, creating land connections in many places. Today, the Bering Strait is about 40 to 50 meters (130 to 160 feet) deep. This means the land bridge only appeared when sea levels were more than 50 meters (160 feet) lower than they are now. Studies of sea level changes show that the Bering Strait had a seaway between about 135,000 and 70,000 years ago, a land bridge between about 70,000 and 60,000 years ago, an intermittent connection between about 60,000 and 30,000 years ago, and another land bridge between about 30,000 and 11,000 years ago. After the last ice age, rising sea levels reopened the strait. Since then, post-glacial rebound has caused some coastal areas to rise.

During the last glacial period, enough water froze in ice sheets across North America and Europe to lower global sea levels. For thousands of years, the ocean floors of shallow seas, including the Bering Strait, the Chukchi Sea to the north, and the Bering Sea to the south, were exposed.

Refugium

The last glacial period, often called the "Ice Age," lasted from about 125,000 to 14,500 years before present (YBP). This was the most recent cold period during the current ice age, which happened near the end of the Pleistocene epoch. The Ice Age reached its coldest point, known as the Last Glacial Maximum, when ice sheets began to grow around 33,000 YBP and reached their largest size about 26,500 YBP. Ice sheets started to melt in the Northern Hemisphere around 19,000 YBP and in Antarctica around 14,500 YBP. The land bridge between Asia and North America was finally covered by rising sea levels around 11,000 YBP. These dates match evidence that melting ice caused a sudden rise in sea levels around 14,500 YBP. Fossil remains from many continents show that large animals went extinct near the end of the last glacial period.

During the Ice Age, a cold and dry grassland called the mammoth steppe stretched from the Arctic islands south to China and from the Iberian Peninsula east across Eurasia and over the Bering land bridge into Alaska and the Yukon. This area was blocked by the Wisconsin glaciation. The plants and animals in Beringia were more similar to those in Eurasia than in North America. Beringia received more moisture and clouds from the North Pacific Ocean than other parts of the mammoth steppe, which were drier. This moisture supported a shrub-tundra habitat that acted as a safe place for plants and animals. In eastern Beringia 35,000 YBP, the northern Arctic areas were 1.5°C (2.7°F) warmer than today, but the southern sub-Arctic regions were 2°C (4°F) cooler. During the Last Glacial Maximum 22,000 YBP, summer temperatures were 3–5°C (5–9°F) cooler than today, with some areas being as much as 7.5°C (13.5°F) cooler. In the driest and coldest periods of the Late Pleistocene, moisture levels varied along a north-south gradient, with the south receiving more cloud cover and rain due to air flow from the North Pacific. Beringia, like much of Siberia and North and Northeast China, was not covered by glaciers because there was very little snowfall.

In the Late Pleistocene, Beringia had a mix of different plant and animal communities. Starting around 57,000 YBP, steppe-tundra vegetation covered large parts of Beringia, with many types of grasses and herbs. There were also areas of shrub tundra and small patches of larch and spruce forests with birch and alder trees. Scientists believe that the large number of big animals in Beringia at this time could only have survived in a very diverse and productive environment.

Studies in Chukotka, on the Siberian side of the land bridge, show that from about 57,000 to 15,000 YBP, the environment was wetter and colder than the steppe-tundra to the east and west. Parts of Beringia began to warm around 15,000 YBP. These changes likely helped animals move after 15,000 YBP, as warmer temperatures increased food for certain animals. At the start of the Holocene, some species adapted to moist environments left Beringia and spread west into northern Asia and east into northern North America.

The Bering land bridge first appeared about 70,000 YBP. However, between 24,000 and 13,000 YBP, the Laurentide and Cordilleran ice sheets merged, allowing animals and plants to move between Beringia (and Eurasia) and North America. The Yukon corridor opened around 13,000 YBP, reconnecting Eurasia and North America until rising sea levels closed the land bridge about 10,000 YBP. During the Holocene, many species adapted to moist environments spread east and west, while forest-adapted species moved north from the south. Species adapted to dry conditions became rare or disappeared.

The ecosystem of Beringia changed as the climate shifted, affecting which plants and animals could survive. The land mass acted as both a barrier and a bridge: during colder times, glaciers expanded and rainfall decreased. During warmer periods, clouds, rain, and snow changed soil and water patterns. Fossil evidence shows that spruce, birch, and poplar trees grew farther north than they do today, indicating that the climate was once warmer and wetter. Conditions in Beringia were not the same everywhere. Studies of woolly mammoth bones show that western Beringia (Siberia) was colder and drier than eastern Beringia (Alaska and Yukon), which had more diverse ecosystems.

Around 25,000 YBP, during the Last Glacial Maximum, grey wolves experienced a sharp drop in population. After this, a single group of modern wolves expanded from their Beringia refuge to repopulate areas across Eurasia and North America, replacing older wolf populations. An extinct pine species, Pinus matthewsii, was found in Pliocene sediments in the Yukon area of the refugium.

The presence of animals unique to Siberia and North America in Beringia has led to the "Beringian Gap" hypothesis, which suggests an unconfirmed geographic factor may have blocked migration across the land bridge when it appeared. Most dry steppe-adapted large animals, such as saiga antelope, woolly mammoths, and caballid horses, could move freely across the land bridge. However, some species were limited to specific areas: woolly rhinos in Siberia did not cross east of the Anadyr River, and species like Arctodus simus, American badgers, American kiang-like equids, Bootherium, and Camelops were found only in North America. The presence of Homotherium in Siberia during the Late Pleistocene is uncertain. The absence of mastodons and Megalonyx is linked to their limited presence in Alaska and the Yukon during interglacial periods. Ground sloth DNA has been found in Siberia, though its significance is still being studied.

Human habitation and migration

The Ancient Beringian (AB) lineage is a group of ancient human ancestors identified through the study of the genome of an infant discovered at the Upward Sun River site (called USR1), which is about 11,500 years old. This AB lineage separated from the Ancestral Native American (ANA) lineage around 20,000 years ago. The ANA lineage is thought to have formed between 20,000 and 25,000 years ago through the mixing of East Asian (about 65%) and Ancient North Eurasian (about 35%) groups. This matches the idea that early humans reached the Americas through Beringia during the Last Glacial Maximum.

It is believed that the first people to settle in the Americas were Paleolithic hunter-gatherers (called Paleo-Indians) who moved from the North Asian Mammoth steppe into North America across the Beringia land bridge. This bridge connected northeastern Siberia and western Alaska because sea levels were lower during the Last Glacial Maximum (26,000 to 19,000 years ago). These early groups expanded south of the Laurentide Ice Sheet, either by land or sea, and spread quickly to occupy both North and South America by 14,000 years ago, possibly earlier than 20,000 years ago. The earliest people in the Americas, before about 10,000 years ago, were called Paleo-Indians. Native peoples of the Americas share similarities with Siberian groups, including blood types and genetic traits found in DNA.

Around 3,000 years ago, the ancestors of the Yupik people settled on both sides of the straits. In 2012, the governments of Russia and the United States announced a plan to create a shared area to protect Beringian heritage. This agreement would connect the Bering Land Bridge National Preserve and the Cape Krusenstern National Monument in the United States with Beringia National Park in Russia.

Previous connections

Biogeographical evidence shows that North America and Asia were once connected. Similar dinosaur fossils have been found in both regions. For example, Saurolophus fossils have been discovered in Mongolia and western North America. Relatives of the dinosaurs Troodon, Triceratops, and Tyrannosaurus rex originated in Asia.

The earliest known fossil of Canis lupus, a type of wolf, was a tooth found in Old Crow, Yukon, Canada. This tooth was in sediment dated to 1 million years ago, but scientists are unsure about the exact age of the sediment. A slightly younger Canis lupus fossil was found in Cripple Creek Sump, Alaska, in sediment dated to 810,000 years ago. These discoveries suggest that these wolves first appeared in eastern Beringia during the Middle Pleistocene.

Fossils also show that primates and plants moved between North America and Asia about 55.8 million years ago. Around 20 million years ago, North America had the last natural exchange of mammal species. Some animals, such as ancient saber-toothed cats, lived in Europe, Africa, Asia, and North America. Over the Cenozoic era, more plants, animals, and fungi generally moved from Asia to North America than the other way around.