This time line of the geologic history of the United States chronologically lists important events occurring within the present political boundaries of United States (including territories) before 12,000 years ago. This time line segment may include some events that occurred outside these borders that profoundly influenced later American life and its present landscape. It also includes evidence of Native American communities predating the Clovis culture.
Because of the inaccuracies inherent in radiocarbon dating and other methods of interpreting the geologic (and archaeological) record, most dates in this time line represent approximations that may vary considerably from source to source. The assumptions implicit in geologic dating methods also may yield a general bias in the dating in this time line.
The Pleistocene is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in 2009 by the International Union of Geological Sciences, the cutoff of the Pleistocene and the preceding Pliocene was regarded as being 1.806 million years Before Present (BP). Publications from earlier years may use either definition of the period. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology. The name is a combination of Ancient Greek πλεῖστος, pleīstos, 'most' and καινός, kainós, 'new'.
The Last Glacial Period (LGP), also known colloquially as the last ice age or simply ice age, occurred from the end of the Eemian to the end of the Younger Dryas, encompassing the period c. 115,000 – c. 11,700 years ago. The LGP is part of a larger sequence of glacial and interglacial periods known as the Quaternary glaciation which started around 2,588,000 years ago and is ongoing. The definition of the Quaternary as beginning 2.58 million years ago (Mya) is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Mya, in the mid-Cenozoic. The term Late Cenozoic Ice Age is used to include this early phase. The previous ice age, the Saalian glaciation, which ended about 128,000 years ago, was more severe than the Last Glacial Period in some areas such as Britain, but less severe in others.
The Solutrean industry is a relatively advanced flint tool-making style of the Upper Paleolithic of the Final Gravettian, from around 22,000 to 17,000 BP. Solutrean sites have been found in modern-day France, Spain and Portugal.
The Clovis culture is a prehistoric Paleoamerican culture, named for distinct stone and bone tools found in close association with Pleistocene fauna, particularly two mammoths, at Blackwater Locality No. 1 near Clovis, New Mexico, in 1936 and 1937. It existed from roughly 11,500 to 10,800 years Before Present at the end of the last glacial period and is characterized by the manufacture of "Clovis points" and distinctive bone and ivory tools.
Monte Verde is an archaeological site in the Llanquihue Province in southern Chile, located near Puerto Montt, Southern Chile, which has been dated to as early as 18,500 cal BP. Previously, the widely accepted date for early occupation at Monte Verde was about 14,500 years cal BP. This dating added to the evidence showing that the human settlement of the Americas pre-dates the Clovis culture by roughly 1,000 years. This contradicts the previously accepted "Clovis first" model which holds that settlement of the Americas began after 13,500 cal BP. The Monte Verde findings were initially dismissed by most of the scientific community, but the evidence then became more accepted in archaeological circles.
The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Ice sheets covered much of Northern North America, Northern Europe, and Asia and profoundly affected Earth's climate by causing drought, desertification, and a large drop in sea levels. Based on changes in position of ice sheet margins dated via terrestrial cosmogenic nuclides and radiocarbon dating, growth of ice sheets commenced 33,000 years ago and maximum coverage was between 26,500 years and 19–20,000 years ago, when deglaciation commenced in the Northern Hemisphere, causing an abrupt rise in sea level. Decline of the West Antarctica ice sheet occurred between 14,000 and 15,000 years ago, consistent with evidence for another abrupt rise in the sea level about 14,500 years ago. Glacier fluctuations around the Strait of Magellan suggest the peak in glacial surface area was constrained to between 25,200 and 23,100 years ago. Continental ice sheets never reached their isostatic equilibrium during the LGM, as evidenced by high variability in ice volume over short spans of time.
Topper is an archaeological site located along the Savannah River in Allendale County, South Carolina, United States. It is noted as a location of artifacts which some archaeologists believe to indicate human habitation of the New World earlier than the Clovis culture. The latter were previously believed to be the first people in North America.
Paleo-Indians, Paleoindians or Paleo-Americans were the first peoples who entered, and subsequently inhabited, the Americas during the final glacial episodes of the late Pleistocene period. The prefix paleo- comes from the Greek adjective palaios (παλαιός) 'old; ancient'. The term Paleo-Indians applies specifically to the lithic period in the Western Hemisphere and is distinct from the term Paleolithic.
In the sequence of cultural stages first proposed for the archaeology of the Americas by Gordon Willey and Philip Phillips in 1958, the Lithic stage was the earliest period of human occupation in the Americas, as post-glacial hunter gatherers spread through the Americas. The stage derived its name from the first appearance of Lithic flaked stone tools. The term Paleo-Indian is an alternative, generally indicating much the same period.
The Late Pleistocene is an unofficial age in the international geologic timescale in chronostratigraphy, also known as Upper Pleistocene from a stratigraphic perspective. It is intended to be the fourth division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently defined as the time between c. 129,000 and c. 11,700 years ago. The Late Pleistocene equates to the proposed Tarantian Age of the geologic time scale, preceded by the officially ratified Chibanian and succeeded by the officially ratified Greenlandian. The estimated beginning of the Tarantian is the start of the Eemian interglacial period. It is held to end with the termination of the Younger Dryas, some 11,700 years ago when the Holocene Epoch began.
Meadowcroft Rockshelter is an archaeological site located near Avella in Jefferson Township, Pennsylvania. The site is a rock shelter in a bluff overlooking Cross Creek, and contains evidence that the area may have been continually inhabited for more than 19,000 years. If accurately dated, it would be one of the earliest known sites with evidence of a human presence and continuous human occupation in the New World.
The Page–Ladson archaeological and paleontological site (8JE591) is a deep sinkhole in the bed of the karstic Aucilla River that has stratified deposits of late Pleistocene and early Holocene animal bones and human artifacts. The site was the first pre-Clovis site discovered in southeastern North America; radiocarbon evidence suggest that the site date from 14,200 to 14,550 BP. These dates are roughly 1,000 to 1,500 years before the advent of the Clovis culture. Early dates for Page–Ladson challenge theories that humans quickly decimated large game populations in the area once they arrived.
The Solutrean hypothesis on the peopling of the Americas claims that the earliest human migration to the Americas took place from Europe, with Solutreans traveling along pack ice in the Atlantic Ocean. This hypothesis contrasts with the mainstream academic narrative that the Americas were first populated by people crossing the Bering Strait to Alaska by foot on what was land during the Last Glacial Period or by following the Pacific coastline from Asia to America by boat.
The Late Glacial Interstadial (LGI) c. 14,670 to c. 12,890 BP, also called the Bølling–Allerød interstadial, represents the first pronounced warming since the end of the Last Glacial Maximum (LGM). Human populations, which had previously been forced into refuge areas, gradually begin to repopulate the Northern Hemisphere's Eurasian landmass.
The Paisley Caves or the Paisley Five Mile Point Caves complex is a system of eight caves in an arid, desolate region of south-central Oregon, United States north of the present-day city of Paisley, Oregon. The caves are located in the Summer Lake basin at 4,520 feet (1,380 m) elevation and face west, carved into a ridge of Miocene and Pliocene era basalts mixed with soft volcanic tuffs and breccias by Pleistocene-era waves from Summer Lake. One of the caves may contain archaeological evidence of the oldest definitively-dated human presence in North America. The site was first studied by Luther Cressman in the 1930s.
Hidden Falls is an archaeological site that contains evidence for the earliest occupation in Southern Alaska along with evidence of marine resource usage. It is dated to the Archaic and Pacific period, between 9,500 and 1800 B.C.
Anzick-1 is a Paleo-Indian male infant whose remains were found in south central Montana, United States, in 1968, and date to 13,000–12,850 years BP. The child was found with more than 115 tools made of stone and antlers and dusted with red ocher, suggesting an honorary burial. Anzick-1 is the only human who has been discovered from the Clovis Complex, and is the first ancient Native American genome to be fully sequenced.
The settlement of the Americas began when Paleolithic hunter-gatherers entered North America from the North Asian Mammoth steppe via the Beringia land bridge, which had formed between northeastern Siberia and western Alaska due to the lowering of sea level during the Last Glacial Maximum. These populations expanded south of the Laurentide Ice Sheet and spread rapidly southward, occupying both North and South America, by 12,000 to 14,000 years ago. The earliest populations in the Americas, before roughly 10,000 years ago, are known as Paleo-Indians. Indigenous peoples of the Americas have been linked to Siberian populations by linguistic factors, the distribution of blood types, and in genetic composition as reflected by molecular data, such as DNA.
The coastal migration hypothesis is one of two leading hypotheses about the settlement of the Americas at the time of the Last Glacial Maximum. It proposes one or more migration routes involving watercraft, via the Kurile island chain, along the coast of Beringia and the archipelagos off the Alaskan-British Columbian coast, continuing down the coast to Central and South America. The alternative is the hypothesis solely by interior routes, which assumes migration along an ice-free corridor between the Laurentide and Cordilleran ice sheets during the Last Glacial Maximum.
The similar cultures of peoples across the Bering Strait in both Siberia and Alaska suggest human travel between the two places ever since the strait was formed. After Paleo-Indians arrived during the Last Glacial Period and began the settlement of the Americas, a second wave of people from Asia came to Alaska around 8000 BCE. These "Na-Dene" peoples, who share many linguistic and genetic similarities not found in other parts of the Americas, populated the far north of the Americas and only made it as far south as Oasisamerica. It is suggested that by 4000–3000 BCE Eskimo peoples began coming to the Americas from Siberia. Eskimo tribes live today in both Asia and North America and there is much evidence that they lived in Asia even in prehistory.