The Pleistocene ( /ˈplaɪstəˌsiːn, -toʊ-/, often colloquially referred to as the Ice Age) is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations. 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 Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. In the ICS timescale, the Pleistocene is divided into four stages or ages, the Gelasian, Calabrian, Middle Pleistocene (unofficially the 'Chibanian') and Upper Pleistocene (unofficially the 'Tarantian').[note 1] In addition to this international subdivision, various regional subdivisions are often used.
Before a change finally confirmed in 2009 by the International Union of Geological Sciences, the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years Before Present (BP), as opposed to the currently accepted 2.588 million years BP: publications from the preceding years may use either definition of the period.
|Subdivisions of the Quaternary System|
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"; this contrasting with the immediately preceding Pliocene ("More New" or "Newer", from πλείων, pleíōn, "more", and kainós; usual spelling: Pliocene), and the immediately subsequent Holocene ("wholly new" or "entirely new", from ὅλος, hólos, "whole", and kainós) epoch, which extends to the present time.
The Pleistocene has been dated from 2.588 million (±0.005) to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell. The end of the Younger Dryas has been dated to about 9640 BC (11,654 calendar years BP). The end of the Younger Dryas is the official start of the current Holocene Epoch. Although it is considered an epoch, the Holocene is not significantly different from previous interglacial intervals within the Pleistocene.
It was not until after the development of radiocarbon dating, however, that Pleistocene archaeological excavations shifted to stratified caves and rock-shelters as opposed to open-air river-terrace sites.
In 2009 the International Union of Geological Sciences (IUGS) confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, and accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP. The IUGS has yet to approve a type section, Global Boundary Stratotype Section and Point (GSSP), for the upper Pleistocene/Holocene boundary (i.e. the upper boundary). The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W. The lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: Discoaster pentaradiatus and Discoaster surculus.
The Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age. The revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene.
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 relative to each other since the beginning of the period.
According to Mark Lynas (through collected data), the Pleistocene's overall climate could be characterized as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, and other El Niño markers.
Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places. It is estimated that, at maximum glacial extent, 30% of the Earth's surface was covered by ice. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America, and several hundred in Eurasia. The mean annual temperature at the edge of the ice was −6 °C (21 °F); at the edge of the permafrost, 0 °C (32 °F).
Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres (4,900–9,800 ft) thick, resulting in temporary sea-level drops of 100 metres (300 ft) or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.
The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene. The Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Zealand and Tasmania. The current decaying glaciers of Mount Kenya, Mount Kilimanjaro, and the Ruwenzori Range in east and central Africa were larger. Glaciers existed in the mountains of Ethiopia and to the west in the Atlas mountains.
In the northern hemisphere, many glaciers fused into one. The Cordilleran ice sheet covered the North American northwest; the east was covered by the Laurentide. The Fenno-Scandian ice sheet rested on northern Europe, including much of Great Britain; the Alpine ice sheet on the Alps. Scattered domes stretched across Siberia and the Arctic shelf. The northern seas were ice-covered.
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 totally covered by Lake Agassiz. Over a hundred basins, now dry or nearly so, were overflowing in the North American west. Lake Bonneville, for example, stood where Great Salt Lake now does. In Eurasia, large lakes developed as a result of the runoff from the glaciers. Rivers were larger, had a more copious flow, and were braided. African lakes were fuller, apparently from decreased evaporation. Deserts, on the other hand, were drier and more extensive. Rainfall was lower because of the decreases in oceanic and other evaporation.
It has been estimated that during the Pleistocene, the East Antarctic Ice Sheet thinned by at least 500 meters, and that thinning since the Last Glacial Maximum is less than 50 meters and probably started after ca 14 ka.
Over 11 major glacial events have been identified, as well as many minor glacial events. A major glacial event is a general glacial excursion, termed a "glacial." Glacials are separated by "interglacials". During a glacial, the glacier experiences minor advances and retreats. The minor excursion is a "stadial"; times between stadials are "interstadials".
These events are defined differently in different regions of the glacial range, which have their own glacial history depending on latitude, terrain and climate. There is a general correspondence between glacials in different regions. Investigators often interchange the names if the glacial geology of a region is in the process of being defined. However, it is generally incorrect to apply the name of a glacial in one region to another.
For most of the 20th century only a few regions had been studied and the names were relatively few. Today the geologists of different nations are taking more of an interest in Pleistocene glaciology. As a consequence, the number of names is expanding rapidly and will continue to expand. Many of the advances and stadials remain unnamed. Also, the terrestrial evidence for some of them has been erased or obscured by larger ones, but evidence remains from the study of cyclical climate changes.
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 favor of numeric data because many of the correlations were found to be either inexact or incorrect and more than four major glacials have been recognized since the historical terminology was established.
|Region||Glacial 1||Glacial 2||Glacial 3||Glacial 4|
|Region||Interglacial 1||Interglacial 2||Interglacial 3|
Corresponding to the terms glacial and interglacial, the terms pluvial and interpluvial are in use (Latin: pluvia, rain). A pluvial is a warmer period of increased rainfall; an interpluvial, of decreased rainfall. Formerly a pluvial was thought to correspond to a glacial in regions not iced, and in some cases it does. Rainfall is cyclical also. Pluvials and interpluvials are widespread.
There is no systematic correspondence of pluvials to glacials, however. Moreover, regional pluvials do not correspond to each other globally. For example, some have used the term "Riss pluvial" in Egyptian contexts. Any coincidence is an accident of regional factors. Only a few of the names for pluvials in restricted regions have been stratigraphically defined.
The sum of transient factors acting at the Earth's surface is cyclical: climate, ocean currents and other movements, wind currents, temperature, etc. The waveform response comes from the underlying cyclical motions of the planet, which eventually drag all the transients into harmony with them. The repeated glaciations of the Pleistocene were caused by the same factors.
Glaciation in the Pleistocene was a series of glacials and interglacials, stadials and interstadials, mirroring periodic changes in climate. The main factor at work in climate cycling is now believed to be Milankovitch cycles. These are periodic variations in regional and planetary solar radiation reaching the Earth caused by several repeating changes in the Earth's motion.
Milankovitch cycles cannot be the sole factor responsible for the variations in climate since they explain neither the long term cooling trend over the Plio-Pleistocene, nor the millennial variations in the Greenland Ice Cores. Milankovitch pacing seems to best explain glaciation events with periodicity of 100,000, 40,000, and 20,000 years. Such a pattern seems to fit the information on climate change found in oxygen isotope cores.
In oxygen isotope ratio analysis, variations in the ratio of 18
O to 16
O (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. Cold oceans are richer in 18
O, which is included in the tests of the microorganisms (foraminifera) contributing the calcite.
A more recent version of the sampling process makes use of modern glacial ice cores. Although less rich in 18
O than sea water, the snow that fell on the glacier year by year nevertheless contained 18
O and 16
O in a ratio that depended on the mean annual temperature.
Temperature and climate change are cyclical when plotted on a graph of temperature versus time. Temperature coordinates are given in the form of a deviation from today's annual mean temperature, taken as zero. This sort of graph is based on another of isotope ratio versus time. Ratios are converted to a percentage difference from the ratio found in standard mean ocean water (SMOW).
The graph in either form appears as a waveform with overtones. One half of a period is a Marine isotopic stage (MIS). It indicates a glacial (below zero) or an interglacial (above zero). Overtones are stadials or interstadials.
According to this evidence, Earth experienced 102 MIS stages beginning at about 2.588 Ma BP in the Early Pleistocene Gelasian. Early Pleistocene stages were shallow and frequent. The latest were the most intense and most widely spaced.
By convention, stages are numbered from the Holocene, which is MIS1. Glacials receive an even number; interglacials, odd. The first major glacial was MIS2-4 at about 85–11 ka BP. The largest glacials were 2, 6, 12, and 16; the warmest interglacials, 1, 5, 9 and 11. For matching of MIS numbers to named stages, see under the articles for those names.
Both marine and continental faunas were essentially modern but with many more large land mammals such as Mammoths, Mastodons, Diprotodon, Smilodon, tiger, lion, Aurochs, short-faced bears, giant sloths, Gigantopithecus and others. Isolated places such as Australia, Madagascar, New Zealand and islands in the Pacific saw the evolution of large birds and even reptiles such as the Elephant bird, moa, Haast's eagle, Quinkana, Megalania and Meiolania.
The severe climatic changes during the ice age had major impacts on the fauna and flora. With each advance of the ice, large areas of the continents became totally depopulated, and plants and animals retreating southwards in front of the advancing glacier faced tremendous stress. 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 bears, Gomphothere, dire wolves, and short-faced bears, began late in the Pleistocene and continued into the Holocene. Neanderthals also became extinct during this period. At the end of the last ice age, cold-blooded animals, smaller mammals like wood mice, migratory birds, and swifter animals like whitetail deer had replaced the megafauna and migrated north.
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. The two nematodes, at the time, were the oldest confirmed living animals on the planet.
The evolution of anatomically modern humans took place during the Pleistocene. In the beginning of the Pleistocene Paranthropus species were still present, as well as early human ancestors, but during the lower Palaeolithic they disappeared, and the only hominin species found in fossilic records is Homo erectus for much of the Pleistocene. Acheulean lithics appear along with Homo erectus, some 1.8 million years ago, replacing the more primitive Oldowan industry used by A. garhi and by the earliest species of Homo. The Middle Paleolithic saw more varied speciation within Homo, including the appearance of Homo sapiens about 200,000 years ago.
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. A 2005 study posits that humans in this migration interbred with archaic human forms already outside of Africa by the late Pleistocene, incorporating archaic human genetic material into the modern human gene pool.
Pleistocene non-marine sediments are found primarily in fluvial deposits, lakebeds, slope and loess deposits as well as in the large amounts of material moved about by glaciers. Less common are cave deposits, travertines and volcanic deposits (lavas, ashes). Pleistocene marine deposits are found primarily in shallow marine basins mostly (but with important exceptions) in areas within a few tens of kilometers of the modern shoreline. In a few geologically active areas such as the Southern California coast, Pleistocene marine deposits may be found at elevations of several hundred meters.
Anomalomyidae is a family of extinct muroid rodents from Europe.Baboon
Baboons are monkeys.Baboons are animals.Baboons are Old World monkeys belonging to the genus Papio, part of the subfamily Cercopithecinae which are found natively in very specific areas of Africa and the Arabian Peninsula. The five species are some of the largest non-hominoid members of the primate order; only the mandrill and the drill are larger. Previously, the closely related gelada (genus Theropithecus) and the two species (mandrill and drill) of genus Mandrillus were grouped in the same genus, and these Old World monkeys are still often referred to as baboons in everyday speech. They range in size and weight depending on species. The Guinea baboon is 50 cm (20 in) and weighs only 14 kg (31 lb), while the largest chacma baboon can be 120 cm (47 in) and weigh 40 kg (88 lb).Diluvium
Historically, diluvium was a term in geology for superficial deposits formed by flood-like operations of water, and so contrasted with alluvium or alluvial deposits formed by slow and steady aqueous agencies. The term was formerly given to the boulder clay deposits, supposed to have been caused by the Noachian deluge.
In the late 20th century Russian geologist Alexei Rudoy proposed the term "diluvium" for description of deposits created as a result of catastrophic outbursts of Pleistocene giant glacier-dammed lakes in intermontane basins of the Altai. The largest of these lakes, Chuya and Kuray, had volumes of water in hundreds of cubic kilometers, and their discharge in peak hydrograph flow rate exceeded the maximum rates of the well-known Pleistocene Lake Missoula floods in North America. The term "diluvium" in the meaning of A. N. Rudoy has become accepted, and the process of diluvial morpholithogenesis can be found in modern textbooks.Dire wolf
The dire wolf (Canis dirus, "fearsome dog") is an extinct species of the genus Canis. It is one of the most famous prehistoric carnivores in North America, along with its extinct competitor, the sabre-toothed cat Smilodon fatalis. The dire wolf lived in the Americas during the Late Pleistocene and Early Holocene epochs (125,000–9,440 years ago). The species was named in 1858, four years after the first specimen had been found. Two subspecies are recognized, these being Canis dirus guildayi and Canis dirus dirus. The dire wolf probably evolved from Armbruster's wolf (Canis armbrusteri) in North America. The largest collection of its fossils has been obtained from the Rancho La Brea Tar Pits in Los Angeles.
Dire wolf remains have been found across a broad range of habitats including the plains, grasslands, and some forested mountain areas of North America, and in the arid savannah of South America. The sites range in elevation from sea level to 2,255 meters (7,400 ft). Dire wolf fossils have rarely been found north of 42°N latitude, with five unconfirmed reports above this latitude. This range restriction is thought to be due to temperature, prey, or habitat limitations imposed by proximity to the Laurentide and Cordilleran ice sheets that existed at the time.
The dire wolf was about the same size as the largest modern gray wolves (Canis lupus), which are the Yukon wolf and the northwestern wolf. C. d. guildayi weighed on average 60 kilograms (132 lb) and C. d. dirus was on average 68 kg (150 lb). Its skull and dentition matched those of C. lupus, but its teeth were larger with greater shearing ability, and its bite force at the canine tooth was the strongest of any known Canis species. These characteristics are thought to be adaptations for preying on Late Pleistocene megaherbivores, and in North America its prey are known to have included horses, ground sloths, mastodons, bison, and camels. As with other large Canis hypercarnivores today, the dire wolf is thought to have been a pack hunter. Its extinction occurred during the Quaternary extinction event along with most of the American megafauna of the time, including a number of other carnivores, that occurred soon after the appearance of humans in the New World. Its reliance on megaherbivores has been proposed as the cause of its extinction, along with climate change and competition with other species, but the cause remains controversial. Dire wolves lived as recently as 9,440 years ago, according to dated remains.Early Pleistocene
The Early Pleistocene (also known as the Lower Pleistocene) is a subepoch in the international geologic timescale or a subseries in chronostratigraphy, being the earliest or lowest subdivision of the Quaternary period/system and Pleistocene epoch/series. It spans the time between 2.588 ± 0.005 Ma (million years ago) and 0.781 ± 0.005 Ma. The Early Pleistocene consists of the Gelasian and the Calabrian ages.Homo erectus
Homo erectus (meaning "upright man") is a species of archaic humans that lived throughout most of the Pleistocene geological epoch.
Its earliest fossil evidence dates to 1.8 million years ago (discovered 1991 in Dmanisi, Georgia).A debate regarding the classification, ancestry, and progeny of H. erectus, especially in relation to Homo ergaster, is ongoing, with two major positions:
1) H. erectus is the same species as H. ergaster, and thereby H. erectus is a direct ancestor of the later hominins including Homo heidelbergensis, Homo antecessor, Homo neanderthalensis, Homo Denisova, and Homo sapiens; or,
2) it is in fact an Asian species or subspecies distinct from African H. ergaster.Some paleoanthropologists consider H. ergaster to be a variety, that is, the "African" variety, of H. erectus; the labels "Homo erectus sensu stricto" (strict sense) for the Asian species and "Homo erectus sensu lato" (broad sense) have been offered for the greater species comprising both Asian and African populations.H. erectus eventually became extinct throughout its range in Africa, Europe and Asia, but developed into derived species, notably Homo heidelbergensis.
As a chronospecies, the time of its disappearance is thus a matter of convention. The species name proposed in 1950
defines Java Man as the type specimen (now H. e. erectus). Since then, there has been a trend in palaeoanthropology of reducing the number of proposed species of Homo, to the point where H. erectus includes all
early (Lower Paleolithic) forms of Homo sufficiently derived from H. habilis and
distinct from early H. heidelbergensis (in Africa also known as H. rhodesiensis). In this wider sense, H. erectus had mostly been replaced by H. heidelbergensis by about 500,000 years ago, with possible late survival in Java as late as 140,000 years ago.
The discovery of the morphologically divergent Dmanisi skull 5 in 2013 has reinforced the trend of subsuming fossils formerly given separate species names under H. erectus considered as a wide-ranging, polymorphous species. Thus, H. ergaster is now well within the accepted morphological range of H. erectus, and it has been suggested that even H. rudolfensis and H. habilis (alternatively suggested as late forms of Australopithecus rather than early Homo)
should be considered early varieties of H. erectus.Irish elk
The Irish elk (Megaloceros giganteus) also called the giant deer or Irish giant deer, is an extinct species of deer in the genus Megaloceros and is one of the largest deer that ever lived. Its range extended across Eurasia during the Pleistocene, from Ireland to Siberia to China. A related form is recorded in China during the Late Pleistocene. The most recent remains of the species have been carbon dated to about 7,700 years ago in Siberia.Although most skeletons have been found in bogs in Ireland, the animal was not exclusive to Ireland and was not closely related to either of the living species currently called elk: Alces alces (the European elk, known in North America as the moose) or Cervus canadensis (the North American elk or wapiti). For this reason, the name "giant deer" is used in some publications, instead of "Irish elk". A study has suggested that the Irish elk was closely related to the Red deer (Cervus elaphus). However, other phylogenetic analyses support a sister-group relationship with fallow deer (Dama dama).Jaguar
The jaguar (Panthera onca) is a wild cat species and the only extant member of the genus Panthera native to the Americas. The jaguar's present range extends from Southwestern United States and Mexico in North America, across much of Central America, and south to Paraguay and northern Argentina in South America. Though there are single cats now living within the western United States, the species has largely been extirpated from the United States since the early 20th century. It is listed as Near Threatened on the IUCN Red List; and its numbers are declining. Threats include loss and fragmentation of habitat.
Overall, the jaguar is the largest native cat species of the New World and the third largest in the world. This spotted cat closely resembles the leopard, but is usually larger and sturdier. It ranges across a variety of forested and open terrains, but its preferred habitat is tropical and subtropical moist broadleaf forest, swamps and wooded regions. The jaguar enjoys swimming and is largely a solitary, opportunistic, stalk-and-ambush predator at the top of the food chain. As a keystone species it plays an important role in stabilizing ecosystems and regulating prey populations.
While international trade in jaguars or their body parts is prohibited, the cat is still frequently killed, particularly in conflicts with ranchers and farmers in South America. Although reduced, its range remains large. Given its historical distribution, the jaguar has featured prominently in the mythology of numerous indigenous American cultures, including those of the Maya and Aztec.Late Pleistocene
The Late Pleistocene is a geochronological age of the Pleistocene Epoch and is associated with Upper Pleistocene (or Tarantian) stage rocks. The beginning of the stage is defined by the base of the Eemian interglacial phase before the final glacial episode of the Pleistocene 126,000 ± 5,000 years ago. Its end is defined at the end of the Younger Dryas, some 11,700 years ago. The age represents the end of the Pleistocene epoch and is followed by the Holocene epoch.
Much of the Late Pleistocene age was dominated by glaciations, such as the Wisconsin glaciation in North America and the Weichselian glaciation and Würm glaciation in Eurasia). Many megafauna became extinct during this age, a trend that continued into the Holocene. The Late Pleistocene contains the Upper Paleolithic stage of human development, including the out-of-Africa migration and dispersal of anatomically modern humans and the extinction of the last remaining archaic human species.List of volcanoes in Canada
A list of volcanoes in Canada.Mastodon
Mastodons (Greek: μαστός "breast" and ὀδούς, "tooth") are any species of extinct proboscideans in the genus Mammut (family Mammutidae), distantly related to elephants, that inhabited North and Central America during the late Miocene or late Pliocene up to their extinction at the end of the Pleistocene 10,000 to 11,000 years ago. Mastodons lived in herds and were predominantly forest-dwelling animals that fed on a mixed diet obtained by browsing and grazing with a seasonal preference for browsing, similar to living elephants.
M. americanum, the American mastodon, is the youngest and best-known species of the genus. They disappeared from North America as part of a mass extinction of most of the Pleistocene megafauna, widely believed to have been caused by overexploitation by Clovis hunters, and possibly also by climate change.Middle Pleistocene
The Middle Pleistocene is a subdivision of the Pleistocene Epoch, from 781,000 to 126,000 years ago (781–126 ka). It is preceded by the Calabrian stage, beginning with the Brunhes–Matuyama reversal, and succeeded by the Tarantian stage (equivalent ot the Late or Upper Pleistocene), taken as beginning with the last interglacial (MIS 5).
The tripartite subdivision of the Pleistocene into Lower (Early), Middle and Upper (Late) has been in use since the 1930s.
It is in use as a provisional or "quasi-formal" designation by the International Union of Geological Sciences (IUGS) as of 2018,
pending the ratification of the 2017 proposal by the International Commission on Stratigraphy (Subcommission on Quaternary Stratigraphy, ICSSQS) of a Chibanian stage.The Middle Pleistocene contains the transition from the Lower to Middle Paleolithic in palaeoanthropology, i.e. the emergence transition from Homo erectus to Homo sapiens.Paleo-Indians
Paleo-Indians, Paleoindians or Paleoamericans is a classification term given by scholars to 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), meaning "old" or "ancient". The term "Paleo-Indians" applies specifically to the lithic period in the Western Hemisphere and is distinct from the term "Paleolithic".Traditional theories suggest that big-animal hunters crossed the Bering Strait from North Asia into the Americas over a land-and-ice bridge (Beringia). This bridge existed from 45,000–12,000 BCE (47,000–14,000 BP). Small isolated groups of hunter-gatherers migrated alongside herds of large herbivores far into Alaska. From c. 16,500 – c. 13,500 BCE (c. 18,500 – c. 15,500 BP), ice-free corridors developed along the Pacific coast and valleys of North America. This allowed animals, followed by humans, to migrate south into the interior of the continent. The people went on foot or used primitive boats along the coastline. The precise dates and routes of the peopling of the New World remain subjects of ongoing debate.Stone tools, particularly projectile points and scrapers, are the primary evidence of the earliest human activity in the Americas. Archaeologists and anthropologists use surviving crafted lithic flaked tools to classify cultural periods. Scientific evidence links Indigenous Americans to eastern Siberian populations. 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. There is evidence for at least two separate migrations.
From 8000–7000 BCE (10,000–9,000 BP) the climate stabilized, leading to a rise in population and lithic technology advances, resulting in more sedentary lifestyle.Pika
A pika ( PY-kə; archaically spelled pica) is a small mammal, with short limbs, very round body, rounded ears, and no external tail. They resemble their close cousin the rabbit, but with shorter ears. They live in mountainous countries in Asia, and there are also two species in North America. Most pikas prefer rocky slopes. The large-eared pika of the Himalayas and nearby mountains is one of the highest living mammals; it is found at heights of more than 6,000 metres (20,000 ft). Pikas graze on a range of plants, mostly grasses, flowers and young stems. In the autumn, they pull hay, soft twigs and other stores of food into their burrows to eat during the long, cold winter. The name "pika" is used for any member of the Ochotonidae, a family within the order of lagomorphs; the latter also includes the Leporidae (rabbits and hares). One genus, Ochotona, is recognised within the family, and it includes 30 species. It is also known as the "whistling hare" due to its high-pitched alarm call when diving into its burrow. In the United States, the pika is colloquially called a "coney", a nonspecific term also used for rabbits, hares, and hyraxes. The name "pika" appears to be derived from the Tungus piika and the scientific name Ochotona is from the Mongolian word ogdoi which means pika.Pliocene
The Pliocene ( ; also Pleiocene) Epoch is the epoch in the geologic timescale that extends from 5.333 million to 2.58 million years BP. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch. Prior to the 2009 revision of the geologic time scale, which placed the four most recent major glaciations entirely within the Pleistocene, the Pliocene also included the Gelasian stage, which lasted from 2.588 to 1.806 million years ago, and is now included in the Pleistocene.As with other older geologic periods, the geological strata that define the start and end are well identified but the exact dates of the start and end of the epoch are slightly uncertain. The boundaries defining the Pliocene are not set at an easily identified worldwide event but rather at regional boundaries between the warmer Miocene and the relatively cooler Pliocene. The upper boundary was set at the start of the Pleistocene glaciations.Quaternary extinction event
The Quaternary period (from 2.588 ± 0.005 million years ago to the present) saw the extinctions of numerous predominantly megafaunal species, which resulted in a collapse in faunal density and diversity and the extinction of key ecological strata across the globe. The most prominent event in the Late Pleistocene is differentiated from previous Quaternary pulse extinctions by the widespread absence of ecological succession to replace these extinct species, and the regime shift of previously established faunal relationships and habitats as a consequence.
The earliest casualties were incurred at 130,000 BCE (the start of the Late Pleistocene). However, the great majority of extinctions in Afro-Eurasia and the Americas occurred during the transition from the Pleistocene to the Holocene epoch (13,000 BCE to 8,000 BCE). This extinction wave did not stop at the end of the Pleistocene, continuing, especially on isolated islands, in human-caused extinctions, although there is debate as to whether these should be considered separate events or part of the same event.Among the main causes hypothesized by paleontologists are overkill by the widespread appearance of humans and natural climate change. A notable modern human presence first appeared during the Middle Pleistocene in Africa, and started to establish continuous, permanent populations in Eurasia and Australasia from 120,000 BCE and 63,000 BCE respectively, and the Americas from 22,000 BCE.A variant of the former possibility is the second-order predation hypothesis, which focuses more on the indirect damage caused by overcompetition with nonhuman predators. Recent studies have tended to favor the human-overkill theory.Quaternary glaciation
The Quaternary glaciation describes a geological time in Earth history, also known in popular terminology as the Ice Age, or Pleistocene glaciation, is a series of glacial events separated by interglacial events during the Quaternary period that began 2.58 Ma (million years ago), and is ongoing.
It is one of five major glacial periods or "ice ages" in Earth's history since about 2.5 billion years ago; the preceding one, known as the Karoo Ice Age, lasted from about 360 to 260 Ma (Carboniferous to Mid-Permian). Outside of these ice ages, the Earth seems to have been completely ice-free, even at high latitudes.The definition of the Quaternary as beginning 2.58 Ma is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Ma, in the mid-Cenozoic (Eocene–Oligocene Boundary). The term Late Cenozoic Ice Age is used to include this early phase.During the Quaternary glaciation, ice sheets expanded, notably from out of Antarctica and Greenland, and fluctuating ice sheets occurred elsewhere (for example, the Laurentide ice sheet). The major effects of the ice age were the erosion of land and the deposition of material, both over large parts of the continents; the modification of river systems; the creation of millions of lakes, including the development of pluvial lakes far from the ice margins; changes in sea level; the isostatic adjustment of the Earth's crust; flooding; and abnormal winds. The ice sheets themselves, by raising the albedo (the extent to which the radiant energy of the Sun is reflected from Earth) created significant feedback to further cool the climate. These effects reshaped entire environments on land and in the oceans, and their associated biological communities.Smilodon
Smilodon is a genus of the extinct machairodont subfamily of the felids. It is one of the most famous prehistoric mammals, and the best known saber-toothed cat. Although commonly known as the saber-toothed tiger, it was not closely related to the tiger or other modern cats. Smilodon lived in the Americas during the Pleistocene epoch (2.5 mya–10,000 years ago). The genus was named in 1842, based on fossils from Brazil. Three species are recognized today: S. gracilis, S. fatalis, and S. populator. The two latter species were probably descended from S. gracilis, which itself probably evolved from Megantereon. The hundreds of individuals obtained from the La Brea Tar Pits in Los Angeles constitute the largest collection of Smilodon fossils.
Overall, Smilodon was more robustly built than any extant cat, with particularly well-developed forelimbs and exceptionally long upper canine teeth. Its jaw had a bigger gape than that of modern cats, and its upper canines were slender and fragile, being adapted for precision killing. S. gracilis was the smallest species at 55 to 100 kg (120 to 220 lb) in weight. S. fatalis had a weight of 160 to 280 kg (350 to 620 lb) and height of 100 cm (39 in). Both of these species are mainly known from North America, but remains from South America have also been attributed to them. S. populator from South America was the largest species, at 220 to 400 kg (490 to 880 lb) in weight and 120 cm (47 in) in height, and was among the largest known felids. The coat pattern of Smilodon is unknown, but it has been artistically restored with plain or spotted patterns.
In North America, Smilodon hunted large herbivores such as bison and camels, and it remained successful even when encountering new prey species in South America. Smilodon is thought to have killed its prey by holding it still with its forelimbs and biting it, but it is unclear in what manner the bite itself was delivered. Scientists debate whether Smilodon had a social or a solitary lifestyle; analysis of modern predator behavior as well as of Smilodon's fossil remains could be construed to lend support to either view. Smilodon probably lived in closed habitats such as forests and bush, which would have provided cover for ambushing prey. Smilodon died out at the same time that most North and South American megafauna disappeared, about 10,000 years ago. Its reliance on large animals has been proposed as the cause of its extinction, along with climate change and competition with other species, but the exact cause is unknown.Zaniolepis
Zaniolepis is a genus of scorpaeniform fish native to the eastern Pacific Ocean. Z. frenata is known to have been a source of food to the Native American inhabitants of San Nicolas Island off the coast of southern California, United States during the Middle Holocene.