Pleistocene Epoch
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What is the Pleistocene Epoch?
The Pleistocene Epoch is the earlier of two epochs in the Quaternary Period. Beginning about 2.58 million years ago, the Pleistocene is often called the "Great Ice Age" because it was marked by recurring glacial and interglacial climate cycles.
During the Pleistocene, plant and animal habitats changed, causing large-scale migrations and evolutionary adaptations. A significant development of the Pleistocene was the evolution of the genus Homo, including the emergence of Homo sapiens. The end of the epoch saw the extinction of many genera of large mammals. The Pleistocene ended 11,700 years ago and was followed by the Holocene Epoch.
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When did the Pleistocene Epoch occur?
The Pleistocene Epoch occurred between 2,588,000 and 11,700 years ago. It is part of the Quaternary Period and is known for cycles of glacial and interglacial climatic changes. The plants and animals of the Pleistocene are, in many respects, similar to those living today, but important differences exist.
The Pleistocene is subdivided into four ages and their corresponding rock units: the Gelasian (2.6 million to 1.8 million years ago), the Calabrian (1.8 million to 774,000 years ago), the Chibanian (774,000 to 129,000 years ago), and Stage 4 (129,000 to 11,700 years ago).
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What is geochronology?
Geochronology is a scientific field that determines the age and history of Earth's rocks and rock assemblages. It studies rock strata distribution, succession, and fossil character to determine time and decipher past geologic events.
The Pleistocene Epoch is best known for extensive ice sheets and glaciers on landmasses and is informally called the Great Ice Age. The start of the Pleistocene is marked by the base of the Gelasian Stage (2,588,000 to 1,800,000 years ago) and ended 11,700 years ago.
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How do scientists determine the age of the Pleistocene Epoch?
Scientists use a combination of methods to determine the age of the Pleistocene Epoch. The start of the Pleistocene is marked by the base of the Gelasian Stage. The base marker for the Gelasian is found in rock dated to 2,588,000 years ago and is correlated with the Gauss-Matuyama geomagnetic reversal. The Pleistocene ended 11,700 years ago and is followed by the Holocene Epoch.
To establish a firm chronology, scientists use:
* Isotopic dating Measuring the amounts of radioactive elements and their decay products in materials provides a way to determine how old they are. Carbon-14 dating is useful for dating materials younger than 30,000 years old.
* Ice core analysis By analyzing ice cores from Antarctica, Greenland, and Arctic Canada, scientists can count annual layers of snow and ice to reconstruct a timescale. The oxygen and hydrogen isotopic composition of the snow can be studied to reconstruct temperature variations.
* Biostratigraphy Fossil assemblages are used to correlate strata. Micropaleontologists have created zones based on the distribution of plankton, making it possible to correlate sediments from different latitudes.5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What major events happened on Earth during the Pleistocene Epoch?
The Pleistocene Epoch, informally known as the "Great Ice Age," was characterized by recurring glacial and interglacial cycles. These climatic shifts influenced environments globally, causing significant migrations and adaptations in plant and animal species.
Major events include:
* Glaciation: Extensive ice sheets formed repeatedly across landmasses. The most recent glacial period peaked around 21,000 years ago.
* Tectonic and isostatic movements: The shifting of lithospheric plates and vertical movements of Earth’s crust occurred due to the formation and melting of large ice sheets.
* Evolution of Homo: The genus Homo evolved, with Homo sapiens appearing in the middle Pleistocene and spreading worldwide.
* Megafauna: The development of large mammals, such as the woolly mammoth and others adapted to Arctic conditions, took place.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How did climate changes in the Pleistocene Epoch affect the development of humans and animals?
During the Pleistocene Epoch, climate changes spurred significant migrations, adaptations, and extinctions of plants and animals. Glacial intervals led to the southward displacement of climatic and vegetation zones, causing disruptions in ecosystems.
The evolution of Homo during the Pleistocene is of particular importance, as is the extinction of many large mammal genera at the end of the epoch. Some scientists believe that human hunters contributed to these extinctions.
The Quaternary Period, which includes the Pleistocene, is notable for its high rate of evolutionary change, driven by disturbances such as glacial advances and shifts in ocean currents. Many species of mammals adapted to the cold tundra regions, while others experienced gigantism, possibly as a response to colder conditions or to better resist predators.
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Pleistocene Epoch, earlier and major of the two epochs that constitute the Quaternary Period of Earth’s history, an epoch during which a succession of glacial and interglacial climatic cycles occurred. The base of the Gelasian Stage (2,588,000 to 1,800,000 years ago) marks the beginning of Pleistocene, which is also the base of the Quarternary Period. It is coincident with the bottom of a marly layer resting atop a sapropel called MPRS 250 on the southern slopes of Monte San Nicola in Sicily, Italy, and is associated with the Gauss-Matuyama geomagnetic reversal. The Pleistocene ended 11,700 years ago. It is preceded by the Pliocene Epoch of the Neogene Period and is followed by the Holocene Epoch.
The Pleistocene Epoch is best known as a time during which extensive ice sheets and other glaciers formed repeatedly on the landmasses and has been informally referred to as the “Great Ice Age.” The timing of the onset of this cold interval, and thus the formal beginning of the Pleistocene Epoch, was a matter of substantial debate among geologists during the late 20th and early 21st centuries. By 1985 a number geological societies agreed to set the beginning of the Pleistocene Epoch about 1,800,000 years ago, a figure coincident with the onset of glaciation in Europe and North America. Modern research, however, has shown that large glaciers had formed in other parts of the world earlier than 1,800,000 years ago. This fact precipitated a debate among geologists over the formal start of the Pleistocene, as well as the status of the Quaternary Period, that was not resolved until 2009.
Stratigraphy
Pliocene–Pleistocene boundary
Definition of the base of the Pleistocene has had a long and controversial history. Because the epoch is best recognized for glaciation and climatic change, many have suggested that its lower boundary should be based on climatic criteria—for example, the oldest glacial deposits or the first occurrence of a fossil of a cold-climate life-form in the sediment record. Other criteria that have been used to define the Pliocene–Pleistocene include the appearance of humans, the appearance of certain vertebrate fossils in Europe, and the appearance or extinction of certain microfossils in deep-sea sediments. These criteria continue to be considered locally, and some workers advocate a climatic boundary at about 2.4 million years.
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Pre-Pleistocene intervals of time are defined on the basis of chronostratigraphic and geochronologic principles related to a marine sequence of strata. Following studies by a series of international working groups, correlation programs, and stratigraphic commissions, agreement was reached in 1985 to place the lower boundary of the Pleistocene series at the base of marine claystones that conformably overlie a specific marker bed in the Vrica section in Calabria. The boundary occurs near the level of several important marine biostratigraphic events and, more significantly, is just above the position of the magnetic reversal that marks the top of the Olduvai Normal Polarity Subzone, thus allowing worldwide correlation.
Since evidence of Cenozoic glaciation was discovered in rocks laid down earlier than those of the Vrica section, some geologists proposed that the base of the Pleistocene be moved to an earlier time. To many geologists, the most reasonable time coincided with the type section for the Gelasian Stage, the rock layer laid down during the Gelasian Age, found at Monte San Nicola near Gela, Sicily. The base marker for the Gelasian—that is, the global stratotype section and point (GSSP)—was placed in rock dated to 2,588,000 years ago (a notable point because it is within 20,000 years of the Gauss-Matuyama geomagnetic reversal). In addition, the date of the rock is closely correlated with the timing of a substantial change in the size of granules found in Chinese loess deposits. (Changes in loess grain size suggest regional climate changes.) After years of discussion, the International Union of Geological Sciences (IUGS) and the International Commission on Stratigraphy (ICS) designated the Gelasian as the lowermost stage of the Pleistocene Epoch.
The Pleistocene is subdivided into four ages and their corresponding rock units: the Gelasian (2.6 million to 1.8 million years ago), the Calabrian (1.8 million to 774,000 years ago), the Chibanian (774,000 to 129,000 years ago), and Stage 4 (129,000 to 11,700 years ago). Of these, only the Gelasian, Calabrian, and Chibanian are formal intervals; Stage 4 awaits naming and ratification by the ICS.
Chronology and correlation
The chronology of the Pleistocene originally developed through observation and study of the glacial succession, which in both Europe and the United States was found to contain either soils that developed under warm climatic conditions or marine deposits enclosed between glacial deposits. From these studies, as well as studies of river terraces in the Alps, a chronology was developed that suggested the Pleistocene consisted of four or five major glacial stages which were separated by interglacial stages with climates generally similar to those of today. Beginning with studies in the 1950s, a much better chronology and record of Pleistocene climatic events have evolved through analyses of deep-sea sediments, particularly from the oxygen isotope record of the shells of microorganisms that lived in the oceans.
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