Quaternary Period
Quaternary Period is the current and most recent of the threeperiodsof the CenozoicErain thegeologic time scaleof theInternational Commission on Stratigraphy(ICS). It follows theNeogenePeriodand spans from 2.588 0.005 million years ago to the present. The Quaternary Period is divided into two epochs: thePleistocene(2.588 million years ago to 11.7 thousand years ago) and theHolocene(11.7 thousand years ago to today). The informal term Late Quaternary refers to the past 0.51.0 million years.
The Quaternary Period is typically defined by the cyclic growth and decay of continentalice sheetsassociated withMilankovitch cyclesand the associated climate and environmental changes that occurred.
The Quaternary Period follows theNeogenePeriodand extends to the present. The Quaternary covers the time span ofglaciationsclassified as thePleistocene, and includes the present interglacial time-period, theHolocene.
This places the start of the Quaternary at the onset ofNorthern Hemisphereglaciation approximately 2.6 million years ago. Prior to 2009, the Pleistocene was defined to be from 1.805 million years ago to the present, so the current definition of the Pleistocene includes a portion of what was, prior to 2009, defined as thePliocene.
Quaternary stratigraphers usually worked with regional subdivisions. From the 1970s, theInternational Commission on Stratigraphy(ICS) tried to make a single geologic time scale based onGSSPs, which could be used internationally. The Quaternary subdivisions were defined based onbiostratigraphyinstead ofpaleoclimate.
This led to the problem that the proposed base of the Pleistocene was at 1.805 Mya, long after the start of the major glaciations of the northern hemisphere. The ICS then proposed to abolish use of the name Quaternary altogether, which appeared unacceptable to theInternational Union for Quaternary Research(INQUA).
In 2009, it was decided to make the Quaternary the youngest period of the CenozoicEra with its base at 2.588 Mya and including theGelasianstage, which was formerly considered part of the Neogene Period and Pliocene Epoch.
TheAnthropocenehas been proposed as a third epoch as a mark of the anthropogenic impact on the global environment starting with the Industrial Revolution, or about 200 years ago. The Anthropocene is not officially designated by the ICS, but a working group has been working on a proposal for the creation of an epoch or sub-period.
The 2.6 million years of the Quaternary represents the time during which recognizable humans existed. Over this geologically short time period, there has been relatively little change in the distribution of the continents due toplate tectonics.
The Quaternary geological record is preserved in greater detail than that for earlier periods.
The major geographical changes during this time period included the emergence of the Strait ofBosphorusandSkagerrakduring glacial epochs, which respectively turned theBlack SeaandBaltic Seainto fresh water, followed by their flooding (and return to salt water) by rising sea level; the periodic filling of theEnglish Channel, forming a land bridge between Britain and the European mainland; the periodic closing of theBering Strait, formingthe land bridge between Asia and North America; and the periodic flash flooding ofScablandsof the American Northwest by glacial water.
The current extent ofHudson Bay, theGreat Lakesand other major lakes of North America are a consequence of theCanadian Shields readjustment since the last ice age; different shorelines have existed over the course of Quaternary time.
Source : wikipedia.org and natgeo.com
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