Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Pleistocene
Contents
Overview
Defining and Dating the Pleistocene Boundary
Pleistocene Glacial Events
Pleistocene Ecosystems and Extinctions
Human Evolution during the Pleistocene
Evidence
Skeleton of the woolly mammoth
learn more
sample
Walrus
Saber-toothed cat
Human ancestor
references and links
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
Privacy Statement Copyright
Glossary Credits Email Us


OVERVIEW
Pleistocene 1.8 mya–11,500 years ago
Defining Characteristics:
  • • significant human geographic expansion and cultural development
  • • marked climatic fluctuations and glacial events
Secondary Characteristics:
  • • plants and animals very similar to surviving modern forms
  • • first major human-influenced extinctions

The term Pleistocene is derived from two Greek words, pleistos (meaning “most”) and kainos (meaning “new” or “recent”). Sir Charles Lyell introduced this term 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. It represents the first epoch of the Neogene Period, which is itself the last of the Cenozoic Era.

Between 1839 and 1846, after general acceptance of the glacial theory (which first suggested the existence of ice ages), geologist Ed Forbes redefined the Pleistocene to make it synchronous with glacial epochs. Although this new, glacial-age definition seemed reasonable at the time, it is now inaccurate to view the Pleistocene as equivalent to the occurrence of glaciation. The reasons for this are twofold. First, full-scale continental glaciation began around 1 million years ago, well after the start of the Pleistocene at 1.8 million years ago, and not all parts of the Earth were affected at the same time. Second, the existence of pre-Pleistocene glacial events was not known by Lyell or Forbes, but it is now known that glacial conditions existed periodically throughout Earth's history, even in Precambrian times.

The Pleistocene is a unique epoch because it is the period during which our own species, Homo sapiens, evolved. It is also marked by climatic fluctuations that culminated in widespread continental glaciers. Many species of vertebrates, especially large mammals, went extinct during the Pleistocene, but much of the modern flora and fauna are survivors from this epoch.


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Overview | Defining and Dating the Pleistocene Boundary | Pleistocene Glacial Events
Pleistocene Ecosystems and Extinctions | Human Evolution during the Pleistocene



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