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Quaternary Time and Its Significance

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Quaternary Time and Its Significance 3/23/2020 Quaternary Time and its Significance There have been periods of intense Glaciation (Global cooling) and Interglaciations (Global warming) in the geological past. Three major periods of glaciations are recorded at around 600-700 Ma, 280 Ma and during the last 2 Ma. Similarly, there have been periods of Warmer climate at around 400 Ma and between 240- 20 Ma. •The Quaternary (the Quaternary Period) is a • There have been five known ice ages in the Earth's subdivision of geological time scale. history, with the Earth experiencing the Quaternary •It covers approximately the last two million years Ice Age during the present time. Within ice ages, up to the present day. there exist periods of more severe glacial conditions •The exact duration has been debated: the onset and more temperate referred to as glacial periods and interglacial periods, respectively. of the Quaternary Period has previously been placed at 1.8 million years ago; but many workers now favour a longer Quaternary chronology, • The Earth is currently in an interglacial period of the Quaternary Ice Age, with the last glacial period of the placing its onset at 2.6 million years ago. Quaternary having ended approximately 10,000 • The Quaternary and the Tertiary Periods years ago with the start of the Holocene epoch. together form the Cenozoic Era. 1 3/23/2020 • Quaternary glaciation, also known as the • The Quaternary can be subdivided into Pleistocene glaciation, the current ice age or two epochs: simply the ice age, refers to the period of the • The Pleistocene (up to about 11,500 last few million years (2.58 Ma to present) in which permanent ice sheets were established in years ago) and Antarctica and perhaps Greenland, and • The Holocene (about 11,500 years ago fluctuating ice sheets have occurred elsewhere. to the present day). • The Quaternary Period has witnessed • The entire Quaternary Period (2.58 Ma) is one of extraordinary changes in global referred to as an ice age because at least one environment as well as the period permanent large ice sheet — Antarctica — during which much of human evolution has existed continuously. took place. • Holocene The Pleistocene is the epoch from 2,588,000 to • The Holocene is a geological epoch which began 11,700 ~12,000 years BP that spans the world's recent period of years ago (around 10 000 14C years ago) continues to the repeated glaciations. The name pleistocene is derived present. from the Greek πλεῖστος (pleistos "most") and καινός • The Holocene is part of the Quaternary period. Its name (kainos "new"). comes from the Greek words ὅλος (holos, whole or entire) and καινός (kainos, new), meaning "entirely recent". It has The Pleistocene Epoch follows the Pliocene Epoch and is been identified with the current warm period, known as MIS followed by the Holocene Epoch. 1, and can be considered an interglacial in the current ice age. The end of the Pleistocene corresponds with the retreat • All human written history and urban living has occurred of the last continental glacier. It also corresponds with within the Holocene. The word Anthropocene is also used the end of the Paleolithic age used in archaeology. for the time period from when humans have had a significant impact on the Earth's climate and ecosystems to the present. Thus • The Last glacial period was the most recent glacial period within the current ice age occurring during the • Pleistocene has been a Cooler phase (Periodic build last years of the Pleistocene, from approximately up of Ice Sheets) AND 110,000 to 10,000 years ago. • Holocene has been a Warmer phase • During this period there were several changes between • In general, Quaternary has been marked by major phases glacier advance and retreat. The Last Glacial of cooling ie. Glacial Stages and Shorter Inter glacial Maximum (LGM) refers to the time of maximum Stages. extent of the ice sheets during the last glacial period, • Not only the ice sheets expanded and covered the land, between 26,500 and 19,000–20,000 years ago but there has also been an impact on the • The maximum extent of glaciation was approximately Landscape/Fauna/ Flora -Their Extinction and 22,000 years ago. While the general pattern of global modifications. cooling and glacier advance was similar, local • Changes occurred at the scale of few centuries/ differences are present. decades/and even at few year scale. 2 3/23/2020 • Currently, the earth is in an interglacial period, which marked the beginning of the Holocene epoch. Quaternary glaciation /Pleistocene glaciation/ Current • The current interglacial began between 10,000 and 15,000 ice age/ Ice age: years ago, which caused the ice sheets from the last glacial Refers to the period of the last few million years (2.58 Ma to present) period to begin to disappear. Glacial Stages • Remnants of these last glaciers, now occupying about 10% of Interglacial Stages the world's land surface, still exist in Himalaya, Greenland and Antarctica etc Last glacial period: Most recent glacial period within • During the glacial periods, what we see as the normal (i.e. the current ice age occurring during the last years of interglacial) hydrologic system was completely interrupted the Pleistocene (110,000 to 10,000 years ago). throughout large areas of the world and was considerably modified in others. • Due to the volume of ice on land, sea level was Last Glacial Maximum (LGM): Time of maximum approximately 120 meters lower than present. The evidence extent of the ice sheets during the last glacial period, of such an event in the recent past is robust. between 26,500 –20,000 years ago • Over the last century, extensive field observations have There have been Small scale as well as provided evidence that continental glaciers covered Large scale Temperature fluctuations large parts of Europe, North America, and Siberia. • Even before the theory of worldwide glaciation was generally accepted, many observers recognized that more than a single advance and retreat of the ice had occurred. Extensive evidence now Cenozoic shows that a number of periods of growth and retreat of continental glaciers occurred during the ice age, called glacials and interglacials. • The interglacial periods of warm climate are represented by buried soil profiles, peat beds, and lake Quaternary and stream deposits separating the unsorted, unstratified deposits of glacial debris. High resolution studies indicate Thus, the climate on the Planet earth has been that there has been Centennial and is variable ever since its birth. and decadal level climatic fluctuations in geological past The changes have taken place in the geological past at various scales : . .P .D •At global level .P B A B s s rs r r nt a ea ea e ye y y es 0 00 00 Pr •At regional level 30 22 12 3 •At local level •At different latitudinal and altitudinal positions •At millennial scale •At centennial scale •At decadal scale 3 3/23/2020 • The major effects of the ice age have been: • The evidences of Glacial and Interglacial • Erosion and deposition of material over large parts of the continents periods are preserved in the form of Terrestrial as well as Marine records. • Modification of river systems • Creation of millions of lakes • Terrestrial records (mostly fragmentary) • Changes in sea level – Lake deposits • Development of pluvial lakes far from the ice – Ice Cores from Ice sheets margins Vostok Ice Core Data for 420,000 Years • Isostatic adjustment of the crust, and abnormal winds. Oxygen Isotope • It affected oceans, flooding, and biological • Marine records (undisturbed) communities. • The spread of ice sheets caused increase in the albedo that effected a major feedback on climate cooling Climatic changes during Quaternary • The interstadials show up strongly in the Interstadials Greenland ice core records. Between 115,000 • Sudden and short-lived warm events occurred many and 14,000 years ago, 24 of these warm times during the generally colder conditions that events have been recognized in the Greenland prevailed between 115,000 and 14,000 years ago ice cores. (isotope Stages 2-5.4). • Interstadials both began and ended suddenly, though in general the 'jump' in climate at the • First picked up as brief influxes of warm climate start of an interstadial was followed by a more plants and insects into the glacial tundra zone of northern Europe, they are known as interstadials' to gradual decline involving a stepwise series of smaller cooling events. distinguish them from the cold phases or ‘Stadials'. • Heinrich events • . • Opposite in sign to the Interstadials are extreme and short-lived • Heinrich events, occurred during the last cold events during the general colder climatic conditions, known as 'Heinrich events' which were first recognized as glacial period, or "ice age". Scientists drilling through periods with very ice-rafting in the North Atlantic. These events marine sediments can distinguish six distinct events. occur against the general background of the glacial climate, and represent the brief expression of the most extreme glacial • The last Heinrich event (known as H1) sensu stricto conditions. occurred just after the Last Glacial Maximum and • During such events, icebergs broke off from glaciers and traversed seems to mark the extreme cold and aridity that the North Atlantic. The icebergs contained rock mass eroded by occurs in many parts of the world around 17,000- the glaciers, and as they melted, this matter was dropped onto the sea floor. These deposits are called ice rafted debris (IRD) or ice 15,000 years ago. rafted deposits. • Ice rafting was a primary mechanism of sediment transport during glacial episodes of the Pleistocene when sea levels were very low and much of the land was covered by large masses (sheets) of ice.
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