The geologic time scale serves as the "calendar" for Earth's history. It subdivides all time into named units of abstract time called—in descending order of duration—eons, eras, periods, epochs, and ages. Stratigraphy, or the correlation and classification of rock strata, is used to enumerate and classify those geologic time units.
As mentioned, the geological time scale is divided into eras, and the last era, in which we live in is called Cenozoic. The Cenozoic era is divided into two periods, the Tertiary and Quaternary. Quaternary period covers a time span of two million years and is further divided into two epochs, Pleistocene and Holocene, Holocene being the recent time.
The Quaternary period and the first epoch of the period, Pleistocene, began about 2.58 million years ago. The Pleistocene too is divided into 3 parts, lower, middle, and upper Pleistocene.
The beginning of the Pleistocene was fixed by IUGS (International Union for Geological Science) in the year 2009, at the base of Matuyama, Palaeomagnetic event.
This epoch lasted from about 2,588,000 to 11,700 years ago, covering the World’s recent period of repeated glaciations. It is a very strange period in geological history of Earth, as it coincides with the history of man and also the time of dramatic climatic changes occurring on Earth.
Climatic Episodes of Pleistocene Period:
The work of Agssiz in 1840, followed by Penck and Bruckner in 1909. led to the classic Alpine chronology that includes 4 major glaciations, separated by 3 interglaciations, these stages form the framework for the Pleistocene and Palaeolithic studies. The glaciers were named after four little streams in the Alps, Günz, Mindel, Riss and Würm. Each glacial advance tied up huge volumes of water in continental ice sheets, resulting in temporary sea level drop of 100m or more. During the interglacial periods, such as the present time, the ice sheets melt, drowning the coastlines.
The terms pluvial and interpluvial are also used, corresponding to the terms glacial and interglacial. A pluvial refers to a warmer period, relatively wet climate, with increased rainfall, and interpluvial is a period with relatively dry conditions because of decreased rainfall. There are traces of lakes in regions which are now dry, which are evidence of the major climatic changes in the tropical region.
It is yet to be determined whether pluvial processes in low latitudes and glaciers in high latitudes occurred simultaneously.
The end of Pleistocene corresponds with the end of the last glacial period, and also with the end of the Paleolithic age in Archaeology.
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