The Pleistocene is a time period that lasted from about 2.58 million to 11,700 years ago. It is known as the Ice Age because it was Earth's most recent time of repeated ice cover. Before 2009, scientists believed the Pleistocene started 1.806 million years ago, but this was changed by the International Union of Geological Sciences. Older writings might still use the earlier date. The end of the Pleistocene happened at the same time as the end of the last ice age and the end of the Paleolithic age in archaeology. The name "Pleistocene" comes from Greek words meaning "most" and "new, recent."
During the Pleistocene, Earth continued to become drier and cooler, which had started in the earlier Neogene period. The climate changed a lot depending on ice cycles, with cold ice ages and warmer periods between them. At the coldest times, sea levels dropped as much as 120 meters (390 feet), allowing land to connect Asia and North America through the Beringia land bridge. Large ice sheets, like the Laurentide Ice Sheet, covered much of northern North America.
At the end of the earlier Pliocene, the Isthmus of Panama connected North and South America. This allowed animals to move between the continents and changed ocean currents. Glaciation in the Northern Hemisphere began around 2.7 million years ago. In the Early Pleistocene (2.58–0.8 million years ago), early humans of the genus Homo appeared in Africa and spread across Afro-Eurasia. The end of the Early Pleistocene marked a change in ice cycles, shifting from 41,000-year cycles to longer, more extreme 100,000-year cycles. The Late Pleistocene saw modern humans leave Africa and the extinction of other human species. Humans also reached Australia and the Americas for the first time.
From about 50,000 years ago, most large land animals outside Africa went extinct. This event is unusual in Earth's history because it mainly affected large animals. Most scientists believe climate changes, the spread of modern humans, or both caused these extinctions.
Etymology
In 1839, Charles Lyell created the term "Pleistocene" to describe rock layers in Sicily that contained at least 70% of their mollusk animals still living today. This helped to tell it apart from the older Pliocene Epoch, which Lyell had first believed to be the youngest layer of fossil rock. He made the name "Pleistocene" from the Greek words pleīstos ("most") and kainós ("new"), meaning "most new" or "newest." This contrasts with the earlier Pliocene ("newer," from pleíōn "more" and kainós) and the later Holocene ("wholly new" or "entirely new," from hólos "whole" and kainós). The Holocene Epoch began after the Pleistocene and continues to the present day.
Dating
The Pleistocene epoch began about 2.580 million years ago and ended 11,700 years ago. The end of this period is also recorded as 10,000 carbon-14 years before present. This time includes most of the repeated ice ages, including the Younger Dryas, a cold period that ended around 9700 BCE (11,700 years before present). The end of the Younger Dryas marks the beginning of the Holocene Epoch. Although the Holocene is a new time period, its temperature changes were similar to earlier warm periods in the Pleistocene. However, the start of the Anthropocene, a time marked by human influence, happened much more quickly than any previous changes.
In the ICS timescale, the Pleistocene is divided into four stages: Gelasian, Calabrian, Chibanian (previously called the "Middle Pleistocene"), and Upper Pleistocene (previously called the "Tarantian"). Other regional divisions are also used.
In 2009, the International Union of Geological Sciences (IUGS) updated the start date of the Pleistocene to 2.580 million years before present. This change included the Gelasian stage as the beginning of the Pleistocene, defined by the Monte San Nicola GSSP. The IUGS has not yet approved a GSSP for the boundary between the Pleistocene and Holocene. A proposed location for this boundary is the North Greenland Ice Core Project ice core at coordinates 75° 06' N 42° 18' W. The start of the Pleistocene is officially defined by a specific magnetic pattern in rocks called the Matuyama (C2r) chronozone, isotopic stage 103. After this point, certain tiny marine fossils, such as Discoaster pentaradiatus and Discoaster surculus, disappeared. The Pleistocene includes the most recent repeated ice ages.
In the past, the term "Plio-Pleistocene" was used to describe the last ice age. The boundary between the Pliocene and Pleistocene was once marked by the first appearance of the foraminiferal species Hyalinea baltica in Italy. However, the updated definition of the Quaternary period includes all recent ice ages within the Pleistocene.
Radiocarbon dating works well for the Holocene but is not effective for older dates in the Pleistocene. Instead, scientists use marine isotope stages based on oxygen isotope data to date materials from the Pleistocene.
Deposits
Pleistocene non-marine sediments are mostly found in river deposits, lakebeds, slope areas, loess deposits, and large amounts of material moved by glaciers. Less common are sediments from caves, travertine formations, and volcanic materials such as lava and ash. Pleistocene marine sediments are mostly found in shallow ocean basins, usually near the modern shoreline, though there are some exceptions. In certain areas with geological activity, such as the Southern California coast, Pleistocene marine sediments can be found hundreds of meters above sea level.
Paleogeography and climate
During the Pleistocene, the modern continents were mostly in their current positions, with the plates they sit on moving less than 100 km (62 mi) relative to each other since the period began. In glacial periods, sea levels dropped up to 120 m (390 ft) below today’s levels, exposing large parts of the continental shelf as dry land.
According to Mark Lynas (based on collected data), the Pleistocene climate was similar to a continuous El Niño event. Trade winds in the South Pacific weakened or moved eastward, warm air rose near Peru, and warm water spread from the west Pacific and Indian Ocean toward the east Pacific. These patterns are typical of El Niño.
The Pleistocene was marked by repeated glacial cycles, during which continental glaciers reached as far as the 40th parallel in some areas. At the height of glacial periods, about 30% of Earth’s surface was covered by ice. Permafrost extended southward from the edge of the glaciers, stretching hundreds of kilometers in North America and Eurasia. The average temperature at the edge of the ice was −6 °C (21 °F), and at the edge of permafrost, it was 0 °C (32 °F).
Each glacial advance trapped vast amounts of water in thick ice sheets (1,500 to 3,000 meters or 4,900–9,800 feet thick), causing temporary sea-level drops of 100 meters (300 ft) or more globally. During warmer interglacial periods, like today, many coastlines were underwater, though some areas rose due to isostatic or other movements.
Glaciation affected the entire planet. Antarctica remained ice-covered throughout the Pleistocene and the earlier Pliocene. The Andes were covered by the Patagonian ice cap, and glaciers existed in New Zealand, Tasmania, Ethiopia, and the Atlas Mountains. In Africa, glaciers on Mount Kenya, Mount Kilimanjaro, and the Ruwenzori Range were larger than they are today.
In the Northern Hemisphere, glaciers merged into large ice sheets. The Cordilleran Ice Sheet covered the northwest of North America, while the Laurentide Ice Sheet covered the east. The Fenno-Scandian Ice Sheet covered northern Europe, including much of Great Britain, and the Alpine Ice Sheet covered the Alps. Scattered ice domes formed across Siberia and the Arctic shelf, and northern seas were frozen.
Large lakes formed south of ice sheets because outlets were blocked and cooler air reduced evaporation. When the Laurentide Ice Sheet retreated, Lake Agassiz covered much of north-central North America. Over 100 basins in the western U.S. were once overflowing, such as Lake Bonneville, which existed where the Great Salt Lake is today. In Eurasia, glaciers created large lakes, and rivers were larger and more braided. African lakes were fuller due to less evaporation, while deserts were drier and larger because of reduced rainfall.
During the Pleistocene, the East Antarctic Ice Sheet thinned by at least 500 meters, with thinning since the Last Glacial Maximum being less than 50 meters and likely beginning around 14,000 years ago.
Over 2.5 million years, the Pleistocene experienced cold periods called glacials (part of the Quaternary ice age) every 40,000 to 100,000 years in Europe and North America. These long cold periods were separated by shorter, warmer interglacials lasting 10,000–15,000 years. The last cold period ended about 10,000 years ago. More than 11 major glacial events and many smaller ones have been identified. A "glacial" refers to a major cold period, while a "stadial" is a minor cold phase.
Glacial events vary by region due to differences in latitude, terrain, and climate. Names for glacial events are often region-specific and should not be applied to other areas without evidence. In the 20th century, only a few regions were studied, but today, more research is expanding the number of glacial names. Some glacial events remain unnamed, and evidence for them may be hidden by larger events or studied through climate cycles.
Terms like "pluvial" (a warm, rainy period) and "interpluvial" (a dry period) are used alongside "glacial" and "interglacial." However, pluvials and glacials do not always match globally. For example, the "Riss pluvial" has been used in Egypt, but such matches are due to local factors.
Cyclical changes in climate, ocean currents, wind, and temperature are driven by the Earth’s motion, such as Milankovitch cycles. These cycles caused repeated glaciations. Around 1 million years ago, glacial cycles shifted from 41,000-year patterns to longer 100,000-year patterns. A 2020 study suggested that stronger Northern Hemisphere summers, linked to Earth’s tilt (obliquity), may have influenced ice age endings.
Milankovitch cycles explain variations in solar radiation reaching Earth, but they are not the only factor. Feedbacks like increased carbon dioxide and Earth’s reflectivity (albedo) amplified their effects. However, Milankovitch cycles alone cannot explain long-term cooling trends.
Fauna
During the Pleistocene, both ocean and land animal groups were mostly similar to modern species, but included many more large mammals such as mammoths, mastodons, Diprotodons, Smilodons, tigers, lions, aurochs, short-faced bears, giant sloths, and species from Gigantopithecus. On isolated landmasses like Australia, Madagascar, New Zealand, and Pacific islands, large birds and reptiles evolved, including the elephant bird, moa, Haast's eagle, Quinkana, Megalania, and Meiolania.
The start of the Pleistocene marked a faster decrease in the variety of hoofed animals that had been happening since the Late Miocene, likely because of ice forming at both poles and drier global conditions.
The Ice Age’s harsh climate greatly affected plants and animals. As ice advanced, large areas of land became empty, and species moving south faced extreme stress. The most severe challenges came from sudden climate shifts, less living space, and less food. A major extinction event of large mammals, including mammoths, mastodons, saber-toothed cats, glyptodons, woolly rhinoceroses, giraffids like Sivatherium, ground sloths, Irish elk, cave lions, cave bears, Gomphotheres, American lions, dire wolves, and short-faced bears, began late in the Pleistocene and continued into the Holocene. Neanderthals also went extinct during this time. At the end of the last ice age, cold-blooded animals, small mammals like wood mice, migratory birds, and fast animals like whitetail deer replaced the large mammals and moved north. Late Pleistocene bighorn sheep were slimmer and had longer legs than their modern descendants. Scientists believe that changes in predator species after the extinctions led to body shape changes as animals adapted for strength instead of speed.
The extinctions had little effect in Africa but were especially severe in North America, where native horses and camels disappeared.
Asian land mammal ages (ALMA) include Zhoukoudianian, Nihewanian, and Yushean.
European land mammal ages (ELMA) include Villafranchian, Galerian, and Aurelian.
North American land mammal ages (NALMA) include Blancan (4.75–1.8), Irvingtonian (1.8–0.24), and Rancholabrean (0.24–0.01) in millions of years. The Blancan extends into the Pliocene.
South American land mammal ages (SALMA) include Uquian (2.5–1.5), Ensenadan (1.5–0.3), and Lujanian (0.3–0.01) in millions of years. The Uquian was previously part of the Pliocene but is now fully within the Pleistocene.
In July 2018, Russian scientists working with Princeton University announced they revived two female nematodes frozen in permafrost from about 42,000 years ago. These nematodes were the oldest confirmed living animals at the time.
Pleistocene of Northern Spain included woolly mammoths, cave lions eating reindeer, horses, and woolly rhinoceroses.
Pleistocene of South America included Megatherium and two Glyptodon.
Anatomically modern humans evolved during the Pleistocene. At the start of the Pleistocene, Paranthropus species and early human ancestors were present, but by the lower Paleolithic, Paranthropus disappeared, and Homo erectus was the only hominin found in fossils for much of the Pleistocene. Acheulean tools appeared with Homo erectus around 1.8 million years ago, replacing older Oldowan tools used by Australopithecus garhi and early Homo species. The Middle Paleolithic saw more variety in Homo species, including the appearance of Homo sapiens about 300,000 years ago. Artifacts showing modern human behavior are clearly recorded from 40,000–50,000 years ago.
According to mitochondrial timing methods, modern humans migrated from Africa after the Riss glaciation during the Eemian Stage in the Middle Paleolithic, spreading worldwide during the late Pleistocene. A 2005 study suggests that humans in this migration interbred with non-African archaic humans by the late Pleistocene, adding their genetic material to the modern human gene pool.