The prehistory of North America spans from the continent’s deep geological past to the threshold of European contact around the 16th century. This immense timeline is defined by dramatic shifts in climate, geography, and ecology that fundamentally shaped human settlement and development. The narrative is a story of continual transformation, beginning with a frozen world dominated by colossal ice sheets and ending with complex, settled agricultural civilizations. Understanding this prehistory requires appreciating the diverse, localized adaptations that allowed various societies to thrive across a massive and varied continent.
The Ice Age Setting and Megafauna
The environment of North America during the Pleistocene epoch was dominated by continental glaciers that locked up vast amounts of the planet’s water. The most expansive was the Laurentide Ice Sheet, which centered over the Hudson Bay region and spread across eastern Canada and the north-central United States. In the west, the Cordilleran Ice Sheet covered the Rocky Mountains and the Pacific Northwest, with the two ice masses meeting in places, creating a barrier across the continent.
The enormous volume of frozen water lowered global sea levels by as much as 120 meters, exposing Beringia, the broad landmass connecting Siberia and Alaska. This vast, unglaciated steppe-tundra provided a continuous route for the movement of flora and fauna between Asia and North America. Beyond the ice sheets, the environment was characterized by cold, arid conditions and a unique ecosystem that supported a spectacular array of megafauna.
This landscape was home to creatures far larger than those found on the continent today, with many weighing over 45 kilograms. Iconic species included the woolly mammoth and the American mastodon, alongside giant ground sloths, short-faced bears, and the saber-toothed cat. The disappearance of these 38 genera of large mammals around 10,000 years ago, coinciding with the end of the Pleistocene, marked a profound shift in the continent’s ecology.
Arrival of the First Peoples
The question of when and how the first humans, known as Paleo-Indians, entered North America has long been a central debate in archaeology. The traditional model proposed that people migrated from Siberia across the exposed Beringia land bridge, moving south through an “Ice-Free Corridor” that opened between the Cordilleran and Laurentide ice sheets around 13,000 years ago. This timing aligned with the widespread evidence of the Clovis culture, characterized by its fluted projectile points dating from about 13,250 to 12,800 years ago.
However, the “Clovis First” model has been challenged by accumulating evidence from pre-Clovis sites suggesting a much earlier arrival. Sites like Monte Verde in Chile (dated around 14,500 years ago) and the Paisley Caves in Oregon (yielding human DNA evidence predating Clovis) indicate humans were south of the ice sheets before the inland corridor opened. This strengthened the Coastal Migration theory, suggesting that early populations traveled along the Pacific coast, potentially using watercraft, before the interior ice sheets fully retreated.
The earliest secure evidence now points to widespread human expansion south of the ice sheets occurring after 16,000 years ago, establishing a timeline that accommodates multiple entry waves and routes. The discovery of human footprints at White Sands, New Mexico, dating back 21,000 to 23,000 years ago, suggests the possibility of an even deeper human presence. The archaeological record suggests a complex scenario of movement, with groups adapting to Beringia’s environment and then rapidly expanding into the Americas through both inland and coastal pathways.
Adapting to a Post-Glacial World
The end of the Ice Age, around 10,000 years ago, ushered in the Holocene epoch and the beginning of the Archaic period, prompting a behavioral shift among human populations. As ice sheets retreated and the climate warmed, most megafauna, including the mammoth and mastodon, became extinct. This loss of specialized big-game prey forced Paleo-Indian descendants to transition from a highly mobile hunting lifestyle to broad-spectrum foraging.
Foraging focused on exploiting a diverse range of local resources, including smaller game like deer, elk, and bison, along with fishing and the gathering of plant foods. The Archaic period, which lasted until about 3,000 years ago, shows a proliferation of new tools adapted for these activities, such as grinding stones (manos and metates) used for processing seeds and nuts. This reliance on plant materials required a decentralized food strategy tailored to specific regional ecologies, such as deserts, forests, and coasts.
The Archaic period is defined by growing regional diversification, as different groups developed unique traditions specific to their local environments. This led to the earliest forms of sedentism, where groups occupied sites for longer periods to take advantage of seasonally abundant resources, such as coastal shellfish or concentrated nut harvests. This reduction in mobility and increased focus on local resource management laid the groundwork for the development of agriculture and permanent settlements.
Emergence of Agricultural Societies
Following the Archaic period, the Woodland and later Mississippian cultures in eastern North America began to establish complex, sedentary societies supported by agriculture. Early cultivation of local plants like squash, sunflower, and various seed crops began during the late Archaic and Early Woodland periods (starting around 1000 BCE). The major transformation came with the widespread adoption of maize, beans, and squash. This “three sisters” agricultural complex provided a reliable food base, enabling population growth and the formation of permanent villages.
The stability afforded by agriculture allowed for the development of sophisticated social structures, long-distance trade networks, and monumental architecture. The Hopewell tradition (Middle Woodland, 200 BCE – 500 CE) is known for its elaborate earthworks, including conical burial mounds and geometric enclosures. These served as ceremonial centers connected by an exchange network for exotic goods like copper and mica. This tradition was followed by the Mississippian period (800 CE – 1600 CE), which saw the creation of hierarchical chiefdoms and massive urban centers.
The largest and most prominent of these centers was Cahokia, located near modern-day St. Louis, featuring dozens of platform mounds used as bases for temples and elite residences. The scale of Monks Mound, the largest prehistoric earthwork in North America, illustrates the organizational complexity and labor mobilization capabilities of the Mississippian people. These late prehistoric societies represent the culmination of adaptation, transitioning from mobile hunter-gatherers to established civilizations capable of constructing large public works and managing extensive agricultural economies.