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Definition:
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The climate from about 2 500 000 to 10 000 years ago, differing from earlier (Pliocene) climate in being generally colder and with greater extremes of glacial (cold) to interglacial (warm) climate. Characterized in the last 875 000 years by repeated glacials, each lasting approximately 110 000 years, punctuated by interglacials lasting 10 000 to 15 000 years. Before that, the predominant periodicity was 41 000 years rather than 110 000 years. The distribution of continents and oceans has been relatively stable during the Pleistocene, but the oscillation between glacials and interglacials has been characterized by major changes in atmospheric concentrations of optically active gases such as carbon dioxide and methane (higher in interglacials), and global changes in sea level (lower in glacials) associated with changes in the volume of ice on land (lower in interglacials). Changes in the amount, and the seasonal and latitudinal distribution, of insolation resulting from the evolving characteristics of the earth's orbit around the sun play a major role as the pacemaker of these changes.
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