It is believed that people first arrived in the Americas when ancient hunter-gatherers, called Paleo-Indians, crossed from North Asia into North America. This happened through a land bridge called Beringia, which connected northeastern Siberia to western Alaska. This land bridge formed because sea levels dropped during the Last Glacial Maximum, which occurred between 26,000 and 19,000 years ago. These early groups moved south of the Laurentide Ice Sheet, either by land or by sea, and spread quickly to both North and South America by about 14,000 years ago. Some evidence suggests they may have arrived even earlier, possibly before 20,000 years ago. Before about 10,000 years ago, the earliest people in the Americas were known as Paleo-Indians. Scientists have found connections between Indigenous peoples of the Americas and Siberian populations through shared blood types and genetic similarities, as shown by DNA studies.
Although most experts agree that the Americas were first settled by people from Asia, the exact paths they took and the specific places in Eurasia where they originated are still unclear. The most widely accepted idea is that a group called Ancient Beringians moved to the Americas when sea levels were much lower due to ice ages. They followed herds of large, now-extinct animals along ice-free paths between the Laurentide and Cordilleran ice sheets. Another possible route suggests they traveled along the Pacific coast to South America, as far as Chile, either by walking or using boats. Evidence of early coastal settlements from the last Ice Age is likely hidden under the ocean, as sea levels have risen by up to 100 meters since then.
The exact time when the first people arrived in the Americas remains a topic of study. Progress in archaeology, studies of ancient Earth layers, physical anthropology, and DNA analysis have provided more information, but many questions remain. The Clovis First theory suggests that the Clovis culture, known for its unique tools, represents the earliest human presence in the Americas around 13,000 years ago. However, evidence of earlier cultures, called pre-Clovis, has been found, which suggests humans may have arrived earlier. Most scientists believe people reached North America south of the Laurentide Ice Sheet between 15,000 and 20,000 years ago. Current research focuses on four possible paths into North America during the Ice Age: coastal routes around 24,000 and 15,000 years ago, an inland route around 14,000 years ago, and another coastal route around 12,000 years ago. The Swan Point Archaeological Site in Alaska has produced the oldest undisputed evidence of human activity, with artifacts dated to about 14,000 years ago, or around 12,000 BCE.
Scholarly debate
Historically, scientists believed one theory explained how people first arrived in the Americas. This theory focused on findings from Blackwater Draw, New Mexico, where human tools and bones of extinct animals were discovered in the 1930s. This led to the "Clovis-first model," which suggested that the first people in the Americas came from Asia across the Beringia land bridge during the last ice age. This model connected the earliest people to special spear points called Clovis points, which are about 13,250 to 12,800 years old.
In the 1990s, many discoveries challenged the Clovis-first model. For example, Monte Verde in Chile has evidence of human activity dating back 14,500 years. In Oregon's Paisley Caves, human feces are 14,300 years old. In Texas, stone tools at the Buttermilk Creek complex are 15,500 years old. In Argentina, butchered animal bones at Arroyo Seco 2 are 14,000 years old. At Meadowcroft Rockshelter in Pennsylvania, signs of human presence may be as old as 16,000 years. However, scientists still debate the exact dates for some sites. The Swan Point Archaeological Site in Alaska has undisputed evidence of human habitation, with artifacts and hearths dated to 14,000 years ago, or about 12,000 BCE.
By the 2000s, research suggested that people arrived in the Americas in multiple waves, not just one group. This means humans may have lived in North and South America as early as 15,000 to 20,000 years ago. Some evidence supports a migration route along the coast.
Genetic studies of Indigenous peoples show that their ancestors adapted over thousands of years. Scientists found that a group in Beringia split from Siberian populations about 36,000 years ago. Around 25,000 years ago, this group became isolated and formed a new genetic group linked to today’s Indigenous populations. This group later split into two main groups between 14,500 and 17,000 years ago, matching the early spread of people across the Americas.
Chiquihuite Cave in Mexico may be an ancient site in the Astillero Mountains. Stones found there, possibly tools, are dated to 26,000 years ago based on animal bones and charcoal. However, scientists debate whether these stones are human-made or natural. No human DNA or hearths have been found there.
The oldest known human footprints in North America were discovered at White Sands National Park in New Mexico. These footprints, buried in gypsum soil, are between 21,000 and 23,000 years old. Some scientists questioned the dates at first because the plants used for dating might have absorbed carbon from water instead of air. However, later tests using pollen and other methods supported the original dates.
Some researchers claim human activity near San Diego, California, dates back 130,000 years at the Cerutti Mastodon site. However, most scientists reject this claim. Scholars like David J. Meltzer note that no sites in the Americas older than 16,000 years are widely accepted, casting doubt on claims of sites being 20,000, 25,000, or 130,000 years old.
Environment during the latest glaciation
During the Wisconsin glaciation, Earth's ocean water was stored in glacier ice at different times. As more water froze into glaciers, the amount of water in the oceans decreased, causing global sea levels to drop. Scientists have studied changes in sea level over time using methods like analyzing oxygen in ocean sediments, dating coastal landforms, and examining ice samples from the ocean and modern glaciers. A drop in sea level by about 60 to 120 meters (200 to 390 feet) around 30,000 years ago created Beringia, a large land area connecting Siberia and Alaska. As sea levels rose after the Last Glacial Maximum (LGM), this land bridge was submerged again. Studies suggest the land bridge was fully underwater about 11,000 years ago, though new research may change this date. Understanding how Beringia changed during this time could help scientists learn more about how humans moved into North America.
After 30,000 years ago, large glaciers and ice sheets expanded, blocking paths out of Beringia. By 21,000 years ago, ice sheets in the Rocky Mountains and eastern Canada came together, closing a route into the center of North America. Glaciers in coastal areas and Alaska separated Beringia from the Pacific Ocean. Along the coast, glaciers merged into large ice formations that covered regions as far south as Vancouver Island and blocked the Strait of Juan de Fuca by 18,000 years ago. Coastal glaciers began to shrink around 19,000 years ago, while ice in the Puget lowlands continued to grow until 16,800 years ago. Even at the height of the ice, some islands remained ice-free and supported animals. As glaciers melted, these areas expanded, and the coast became ice-free by 15,000 years ago. By about 17,000 years ago, melting glaciers on the Alaskan Peninsula opened a path from Beringia to the Pacific. The ice barrier between Alaska and the Pacific broke down around 16,200 years ago. A path to the center of North America opened between 13,000 and 12,000 years ago. In eastern Siberia, glaciers were limited to mountain areas and did not block movement between Siberia and Beringia.
Scientists have studied past climates and plant life in Siberia and Alaska using oxygen in ice and pollen in soil layers. Before the LGM, Siberia’s climate varied between conditions similar to today and colder periods. Warm periods before the LGM allowed large animals to thrive. Oxygen data from Greenland suggests these warm cycles lasted hundreds to two thousand years, with colder periods becoming longer after 32,000 years ago. Pollen from lakes in Siberia shows that shrubs and trees were replaced by grasses and herbs before 30,000 years ago, as forests gave way to tundra. Similar changes occurred in Arctic Siberia. The lack of human remains in northern Siberia during the LGM may be due to rapid cooling or the loss of animal species. In Alaska, pollen records show shifts between grasses and shrubs, suggesting less warming than in Siberia. Large animals lived in these environments, but cold and dry conditions led to herb tundra dominating during the LGM.
Coastal areas during the LGM were complex. Lower sea levels and rising land exposed the ocean floor, creating a coastal plain. While much of this plain was covered by glaciers, some islands remained ice-free and supported animals. These areas may have had more ice-free regions than discovered so far. Pollen data show grasses and shrubs dominated ice-free areas, with some forests near the southern edge of glaciers. The ocean remained productive, as shown by fossils of seals. Kelp forests near the shore may have attracted early humans. Studies of the Beringian coast suggest it had a rich marine environment.
Pollen data show a warm period between 17,000 and 13,000 years ago, followed by cooling until 11,500 years ago. Coastal glaciers and ice retreated quickly as sea levels rose. By 16,000 to 15,000 years ago, the coast was mostly free of ice. Marine life replaced ice meltwater as oceans covered the land. Coniferous forests began growing north of Haida Gwaii by 15,000 years ago. Rising sea levels caused flooding to increase.
Inland ice sheets retreated more slowly than coastal glaciers. A path through the ice-free area opened after 13,000 to 12,000 years ago. Early conditions in this path included melting ice and lakes formed by blocked water. Life grew slowly in these areas. Scientists think the path became suitable for humans around 11,500 years ago.
Birch trees started growing in Beringia by 17,000 years ago, showing the land became more productive as the climate improved.
Studies of sediments from northern Alaska suggest humans may have burned Beringian landscapes as early as 34,000 years ago. Scientists think fire was used to hunt large animals.
Chronology, reasons for, and sources of migration
The Indigenous peoples of the Americas have been present in the region for at least 15,000 years. Recent research suggests that humans may have arrived even earlier, between 18,000 and 26,000 years ago, during a time when the Earth was very cold. Scientists are still working to determine the exact dates of some sites and the conclusions from studies of Native American genetics.
In the early 2000s, researchers proposed two main theories about when people first arrived in the Americas. The first, called the short chronology theory, suggests that the first people arrived after the last ice age, then left the area around 19,000 years ago, followed by later groups. The second, called the long chronology theory, suggests that people may have entered a land bridge called Beringia as early as 40,000 years ago, with a second wave arriving much later.
The Clovis First theory, which was widely accepted for much of the 20th century, was challenged in the 2000s when archaeologists found sites in the Americas that were dated to be older than 13,000 years. The oldest sites that are widely accepted are about 15,000 years old. These include the Buttermilk Creek Complex in Texas, the Meadowcroft Rockshelter in Pennsylvania, and the Monte Verde site in southern Chile. Some evidence, like the Topper Site in South Carolina, suggests human activity as early as 16,000 years ago, during a time when sea levels were lower.
Some scientists believed that a path through a region now in western Canada allowed people to move into North America before the ice age ended. However, a 2016 study suggested that this path was unlikely to be used much earlier than the Clovis sites. Instead, the study proposed that Clovis people may have come from the south, following animals like bison. Another idea is that people traveled along the coast of the Pacific Northwest, where the shoreline was exposed due to lower sea levels.
Evidence of humans in Beringia, the land bridge between Asia and North America, before the last ice age is debated. Sites like Bluefish Caves and Old Crow Flats in the Yukon Territory, and Meadowcroft Rockshelter in Pennsylvania, have been dated to around 14,000 years ago. Some studies of sediment in northern Alaska suggest humans may have lived there as early as 34,000 years ago. However, these findings are still being studied.
At Old Crow Flats, broken mammoth bones and stone tools have been found, but some scientists question whether the bones were processed by humans. No human remains have been found at these sites. In 2020, a site in Mexico called Chiquihuite Cave was dated to 26,000 years ago, but some researchers debate whether the artifacts there were made by humans.
In South America, evidence of humans before the last ice age includes sites like Pedra Furada in Brazil and others in the Midwest and Southeast of Brazil. A 2003 study suggested that humans may have used fire before 40,000 years ago. DNA analysis of a fossil called Luzia Woman showed her ancestry was Native American, not Australo-Melanesian as previously thought.
In southern California, tools found near a mastodon skeleton were dated to about 130,000 years ago, but some experts doubted the evidence. In Siberia, a site called Yana River Rhino Horn shows human activity 31,300 years ago, but this may have happened just before the last ice age.
In 2021, human footprints found in New Mexico were dated to between 18,000 and 26,000 years ago. Later studies confirmed the footprints were up to 23,000 years old. Some scientists who support the Clovis First theory remain skeptical of these findings, arguing that the oldest well-documented sites in the Americas are between 13,000 and 14,200 years old.
Migration routes
Historically, theories about how people moved into the Americas have focused on travel from a region called Beringia through the center of North America. In the 1930s, artifacts found near Clovis, New Mexico, along with remains of animals from the Ice Age, showed that humans arrived in North America earlier than previously thought, when large glaciers still covered much of the continent. This led to the idea that people may have traveled between two large ice sheets to reach North America. The Clovis site is known for stone tools with a special shape, called a flute, used to attach spear points to shafts. This type of tool was later found across much of North America and in South America. Because these tools were linked to Ice Age animal remains, scientists proposed the Clovis First theory, suggesting that people who hunted large animals migrated from Beringia and spread throughout the Americas.
Recent studies using radiocarbon dating found that Clovis sites are between 13,000 and 12,600 years old, which is later than earlier estimates. Some older dates from Clovis sites, including the original site in New Mexico, are now considered unreliable. Comparing Clovis dates with other archaeological sites and the timing of ice-free areas has raised questions about the Clovis First theory. For example, the Monte Verde site in southern Chile is dated to 14,800 years ago, and the Paisley Cave site in Oregon has evidence of human activity from 14,500 years ago. Other sites in North America show tools and remains that are older than Clovis, though their exact ages are not always clear.
New research suggests that the ice-free corridor, a path through glaciers, opened around 13,800 years ago, later than the earliest known human sites in the Americas. This timing makes it unlikely that the corridor was the main route for early people. An alternative idea, called the "stepping stones" hypothesis, suggests that people moved across islands in the Bering Transitory Archipelago before reaching the mainland.
Geological studies show that the ice-free corridor may have been closed as early as 30,000 years ago and became usable for humans around 11,500 years ago, after many Clovis and older sites were already occupied. Some theories propose that people moved into the interior of the Americas before the last Ice Age, but sites like Meadowcroft Rock Shelter, Monte Verde, and Paisley Cave have not yet provided clear evidence of this.
In the American Southwest, especially in the Mojave Desert, stone tools from the Pleistocene era, such as those found in Lake Mojave quarries, suggest people may have moved into the region as early as 13,800 years ago.
A connection between the Na-Dené languages of North America (like Navajo and Apache) and the Yeniseian languages of Siberia was first suggested in 1923. A detailed study by Edward Vajda in 2010 supported this idea, which has also been backed by archaeological and genetic research.
The Arctic Small Tool tradition, found in Alaska and the Canadian Arctic, may have originated in East Siberia about 5,000 years ago. This is linked to the ancient Paleo-Eskimo peoples of the Arctic. The tradition may have come from the Syalakh-Bel'kachi-Ymyakhtakh culture in East Siberia, dated to 6,500–2,800 years ago.
The interior route is thought to explain how the Na-Dene language group and a genetic group called subhaplogroup X2a spread into the Americas after the first migrations. Some scholars suggest that the ancestors of Western North Americans speaking Na-Dene languages may have traveled by boat along the coast.
It is possible that humans reached the Americas through interior routes that existed before the last Ice Age. A method called cosmogenic exposure dating, used by Mark Swisher, suggests an ice-free corridor in North America existed 25,000 years ago. Swisher links sites like Monte Verde, Meadowcroft Rockshelter, Manis Mastodon, and Paisley Caves to this corridor.
The Pacific coastal migration theory, proposed in 1979 by Knute Fladmark, suggests people first reached the Americas by traveling along coastlines from northeast Asia. This model explains how people quickly spread to distant coastal sites, such as Monte Verde in Chile and Taima-Taima in Venezuela. A similar idea, the marine migration hypothesis, suggests people used boats to bypass ice barriers and settle in coastal areas before glaciers melted completely. This theory requires a population in coastal East Asia skilled in maritime travel.
A 2007 study proposed the "kelp highway hypothesis," a coastal migration idea based on using kelp forests along the Pacific Rim from Japan to Beringia, the Pacific Northwest, and South America. When glaciers in Alaska and British Columbia melted about 16,000 years ago, these kelp forests, along with other coastal habitats, may have created a continuous migration route. A 2016 DNA study supports the feasibility of this coastal route.
A specific genetic group, mitochondrial subhaplogroup D4h3a, found along the west coast of the Americas, is linked to coastal migration. This group was identified in a skeleton called Anzick-1, found in Montana with Clovis artifacts dated to 12,500 years ago.
Coastal migration theories offer a new view of how people arrived in the Americas, but they also face challenges. For example, rising sea levels since the last Ice Age have submerged ancient coastlines, making it harder to find early sites linked to maritime travel.