The Quaternary is typically defined by theQuaternary glaciation, the cyclic growth and decay of continentalice sheets related to theMilankovitch cycles and the associated climate and environmental changes that they caused.[5][6]
The Quaternary Period follows theNeogene Period and extends to the present. The Quaternary covers the time span ofglaciations classified as thePleistocene, and includes the present interglacial time-period, theHolocene.
This places the start of the Quaternary at the onset ofNorthern Hemisphere glaciation approximately 2.6 million years ago (mya). 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 onGSSP's, which could be used internationally. The Quaternary subdivisions were defined based onbiostratigraphy instead ofpaleoclimate.
This led to the problem that the proposed base of the Pleistocene was at 1.805 million years ago, 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 theCenozoic Era with its base at 2.588 mya and including theGelasian Stage, which was formerly considered part of the Neogene Period and Pliocene Epoch.[11] This was later revised to 2.58 mya.[4][12]
The 2.58 million years of the Quaternary represents the time during which recognisable humans existed.[15] 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 straits ofBosphorus andSkagerrak during glacial epochs, which respectively turned theBlack Sea andBaltic Sea into fresh water lakes, followed by their flooding (and return to salt water) by rising sea level;[16] 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 ofScablands of the American Northwest by glacial water.[17]
The current extent ofHudson Bay, theGreat Lakes and other major lakes of North America are a consequence of theCanadian Shield's readjustment since the last ice age; different shorelines have existed over the course of Quaternary time.[18]
Theclimate was one of periodic glaciations with continental glaciers moving as far from the poles as 40 degreeslatitude. Glaciation took place repeatedly during the QuaternaryIce age – a term coined by Schimper in 1839 that began with the start of the Quaternary about 2.58 Mya and continues to the present day.
In 1821, aSwiss engineer,Ignaz Venetz, presented an article in which he suggested the presence of traces of the passage of a glacier at a considerable distance from the Alps. This idea was initially disputed by another Swiss scientist,Louis Agassiz, but when he undertook to disprove it, he ended up affirming his colleague's hypothesis. A year later, Agassiz raised the hypothesis of a great glacial period that would have had long-reaching general effects. This idea gained him international fame and led to the establishment of the Glacial Theory.
In time, thanks to the refinement of geology, it has been demonstrated that there were several periods of glacial advance and retreat and that past temperatures on Earth were very different from today.In particular, theMilankovitch cycles ofMilutin Milankovitch are based on the premise that variations in incomingsolar radiation are a fundamental factor controlling Earth's climate.
During this time, substantial glaciers advanced and retreated over much of North America and Europe, parts of South America and Asia, and all of Antarctica.
TheGreat Lakes formed and giant mammals thrived in parts of North America and Eurasia not covered in ice. These mammals became extinct when the glacial period ended about 11,700 years ago. Modernhumans evolved about 315,000 years ago. During the Quaternary Period, mammals, flowering plants, and insects dominated the land.[citation needed]
Arduino, Giovanni (1760). "Lettera Segonda di Giovanni Arduino … sopra varie sue osservazioni fatte in diverse parti del territorio di Vicenza, ed altrove, apparenenti alla Teoria terrestre, ed alla Mineralogia" [Second letter of Giovani Arduino … on his various observations made in different parts of the territory of Vincenza, and elsewhere, concerning the theory of the earth and mineralogy].Nuova Raccolta d'Opuscoli Scientifici e Filologici [New collection of scientific and philogical pamphlets] (in Italian).6: 133 (cxxxiii)–180(clxxx). Available at:Museo Galileo (Florence (Firenze), Italy) From p. 158 (clviii):"Per quanto ho potuto sinora osservavare, la serie di questi strati, che compongono la corteccia visibile della terra, mi pare distinta in quattro ordini generali, e successivi, senza considerarvi il mare." (As far as I have been able to observe, the series of these layers that compose the visible crust of the earth seems to me distinct in four general orders, and successive, not considering the sea.)
English translation:Ell, Theodore (2012). "Two letters of Signor Giovanni Arduino, concerning his natural observations: first full English translation. Part 2".Earth Sciences History.31 (2):168–192.Bibcode:2012ESHis..31..168E.doi:10.17704/eshi.31.2.c2q4076006wn7751.
^Desnoyers, J. (1829)."Observations sur un ensemble de dépôts marins plus récents que les terrains tertiaires du bassin de la Seine, et constituant une formation géologique distincte; précédées d'un aperçu de la nonsimultanéité des bassins tertiares" [Observations on a set of marine deposits [that are] more recent than the tertiary terrains of the Seine basin and [that] constitute a distinct geological formation; preceded by an outline of the non-simultaneity of tertiary basins].Annales des Sciences Naturelles (in French).16:171–214,402–491.From p. 193:"Ce que je désirerais … dont il faut également les distinguer." (What I would desire to prove above all is that the series of tertiary deposits continued – and even began in the more recent basins – for a long time, perhaps after that of the Seine had been completely filled, and that these later formations –Quaternary (1), so to say – should not retain the name of alluvial deposits any more than the true and ancient tertiary deposits, from which they must also be distinguished.) However, on the very same page, Desnoyers abandoned the use of the term "quaternary" because the distinction between quaternary and tertiary deposits wasn't clear. From p. 193:"La crainte de voir mal comprise … que ceux du bassin de la Seine." (The fear of seeing my opinion in this regard be misunderstood or exaggerated, has made me abandon the word "quaternary", which at first I had wanted to apply to all deposits more recent than those of the Seine basin.)
^Dyke, Arthur S. (2004). "An outline of North American deglaciation with emphasis on central and northern Canada".Developments in Quaternary Sciences.2:373–424.doi:10.1016/S1571-0866(04)80209-4.ISBN9780444515926.
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