The Pleistocene (/ˈplaɪstəˌsiːn, -stoʊ-/ PLY-stə-seen, -⁠stoh-;[4][5] referred to colloquially as the Ice Age) is the geological epoch that lasted from c. 2.58 million 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).

At the end of the preceding Pliocene, the previously isolated North and South American continents were joined by the Isthmus of Panama, causing a faunal interchange between the two regions and changing ocean circulation patterns, with the onset of glaciation in the Northern Hemisphere occurring around 2.7 million years ago.

During the Early Pleistocene (2.58–0.8 Ma), archaic humans of the genus Homo originated in Africa and spread throughout Afro-Eurasia.

Humans also spread to the Australian continent and the Americas for the first time, co-incident with the extinction of most large-bodied animals in these regions.

The climate was strongly variable depending on the glacial cycle, with the sea levels being up to 120 metres (390 ft) lower than present at peak glaciation, allowing the connection of Asia and North America via Beringia and the covering of most of northern North America by the Laurentide Ice Sheet.

Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today.

This distinguished it from the older Pliocene Epoch, which Lyell had originally thought to be the youngest fossil rock layer.

He constructed the name "Pleistocene" ('most new' or 'newest') from the Greek πλεῖστος (pleīstos) 'most' and καινός (kainós (Latinized as cænus) 'new').

[11] It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell.

Formerly, the boundary between the two epochs was drawn at the time when the foraminiferal species Hyalinea baltica first appeared in the marine section at La Castella, Calabria, Italy.

In a few geologically active areas such as the Southern California coast, Pleistocene marine deposits may be found at elevations of several hundred metres.

The modern continents were essentially at their present positions during the Pleistocene, the plates upon which they sit probably having moved no more than 100 km (62 mi) relative to each other since the beginning of the period.

In glacial periods, the sea level would drop by up to 120 m (390 ft) lower than today[21] during peak glaciation, exposing large areas of the present continental shelf as dry land.

[22] Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places.

During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.

South of the ice sheets large lakes accumulated because outlets were blocked and the cooler air slowed evaporation.

When the Laurentide Ice Sheet retreated, north-central North America was completely covered by Lake Agassiz.

The glacials in the following tables show historical usages, are a simplification of a much more complex cycle of variation in climate and terrain, and are generally no longer used.

These names have been abandoned in favour of numeric data because many of the correlations were found to be either inexact or incorrect and more than four major glacials have been recognised since the historical terminology was established.

[28] However, a 2020 study concluded that ice age terminations might have been influenced by obliquity since the Mid-Pleistocene Transition, which caused stronger summers in the Northern Hemisphere.

[29] Glaciation in the Pleistocene was a series of glacials and interglacials, stadials and interstadials, mirroring periodic climate changes.

The effects of Milankovitch cycles were enhanced by various positive feedbacks related to increases in atmospheric carbon dioxide concentrations and Earth's albedo.

In oxygen isotope ratio analysis, variations in the ratio of 18O to 16O (two isotopes of oxygen) by mass (measured by a mass spectrometer) present in the calcite of oceanic core samples is used as a diagnostic of ancient ocean temperature change and therefore of climate change.

According to this evidence, Earth experienced 102 MIS stages beginning at about 2.588 Ma BP in the Early Pleistocene Gelasian.

Both marine and continental faunas were essentially modern but with many more large land mammals such as Mammoths, Mastodons, Diprotodons, Smilodons, tigers, lions, Aurochs, short-faced bears, giant sloths, species within Gigantopithecus and others.

The most severe stress resulted from drastic climatic changes, reduced living space, and curtailed food supply.

A major extinction event of large mammals (megafauna), which included mammoths, mastodons, saber-toothed cats, glyptodons, the woolly rhinoceros, various giraffids, such as the 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.

In July 2018, a team of Russian scientists in collaboration with Princeton University announced that they had brought two female nematodes frozen in permafrost, from around 42,000 years ago, back to life.

[37] According to mitochondrial timing techniques, modern humans migrated from Africa after the Riss glaciation in the Middle Palaeolithic during the Eemian Stage, spreading all over the ice-free world during the late Pleistocene.