The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago), and is ongoing.Although geologists describe the entire time period as an "ice age", in popular culture the term "ice age" is usually associated with just the most recent glacial period. Since earth still has ice sheets, geologists consider the Quaternary glaciation to be ongoing, with earth now experiencing an interglacial period.
A glacial period is an interval of time within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate between glacial periods. The last glacial period ended about 15,000 years ago. The Holocene epoch is the current interglacial. A time with no glaciers on Earth is considered a greenhouse climate state.
An interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene interglacial began at the end of the Pleistocene, about 11,700 years ago.
Quaternary is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.588 ± 0.005 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene and the Holocene. The informal term "Late Quaternary" refers to the past 0.5–1.0 million years.
During the Quaternary glaciation, ice sheets appeared. During glacial periods they expanded, and during interglacial periods they contracted. Since the end of the last glacial period the only surviving ice sheets are the Antarctic and Greenland ice sheets. Other ice sheets, such as the Laurentide ice sheet, formed during glacial periods and completely disappeared during interglacials. The major effects of the Quaternary glaciation have been the erosion of land and the deposition of material, both over large parts of the continents; the modification of river systems; the creation of millions of lakes, including the development of pluvial lakes far from the ice margins; changes in sea level; the isostatic adjustment of the Earth's crust; flooding; and abnormal winds. The ice sheets themselves, by raising the albedo (the extent to which the radiant energy of the Sun is reflected from Earth) created significant feedback to further cool the climate. These effects have been reshaping entire environments on land and in the oceans, and their associated biological communities.
The Antarctic ice sheet is one of the two polar ice caps of the Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth. It covers an area of almost 14 million square kilometres and contains 26.5 million cubic kilometres of ice. A cubic kilometer of ice weighs approximately one metric gigaton, meaning that the ice sheet weighs 26,500,000 gigatons. Approximately 61 percent of all fresh water on the Earth is held in the Antarctic ice sheet, an amount equivalent to about 58 m of sea-level rise. In East Antarctica, the ice sheet rests on a major land mass, while in West Antarctica the bed can extend to more than 2,500 m below sea level.
The Greenland ice sheet is a vast body of ice covering 1,710,000 square kilometres (660,000 sq mi), roughly 80% of the surface of Greenland.
In earth science, erosion is the action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, animals, and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolic) erosion, zoogenic erosion, and anthropogenic erosion. The particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by its dissolving into a solvent, followed by the flow away of that solution. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres.
Before the quaternary glaciation, land-based ice appeared, and then disappeared, at least four other times.
Evidence for the quaternary glaciation was first understood in the 18th and 19th centuries as part of the scientific revolution.
Over the last century, extensive field observations have provided evidence that continental glaciers covered large parts of Europe, North America, and Siberia. Maps of glacial features were compiled after many years of fieldwork by hundreds of geologists who mapped the location and orientation of drumlins, eskers, moraines, striations, and glacial stream channels in order to reveal the extent of the ice sheets, the direction of their flow, and the locations of systems of meltwater channels. They also allowed scientists to decipher a history of multiple advances and retreats of the ice. 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.
Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west and the Mediterranean Sea to the south. It comprises the westernmost part of Eurasia.
North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere; it is also considered by some to be a northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, and to the southeast by South America and the Caribbean Sea.
Siberia is an extensive geographical region spanning much of Eurasia and North Asia. Siberia has historically been a part of modern Russia since the 17th century.
To geologists, an ice age is marked by the presence of large amounts of land-based ice. Prior to the Quaternary glaciation, land-based ice formed during at least four earlier geologic periods: the Karoo (360–260 Ma), Andean-Saharan (450–420 Ma), Cryogenian (720–635 Ma) and Huronian (2,400–2,100 Ma).
An ice age is a long period of reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth is currently in the Quaternary glaciation, known in popular terminology as the Ice Age. Individual pulses of cold climate are termed "glacial periods", and intermittent warm periods are called "interglacials" or "interstadials" with both climatic pulses part of the Quaternary or other periods in Earth's history.
The Cryogenian is a geologic period that lasted from. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.
Within the Quaternary Period, or ice age, there were also periodic fluctuations of the total volume of land ice, the sea level, and global temperatures. During the colder episodes (referred to as glacial periods, or simply glacials) large ice sheets at least 4 km thick at their maximum existed in Europe, North America, and Siberia. The shorter and warmer intervals between glacials, when continental glaciers retreated, are referred to as interglacials. These are evidenced by buried soil profiles, peat beds, and lake and stream deposits separating the unsorted, unstratified deposits of glacial debris.
Initially the fluctuation period was about 41,000 years, but following the Mid-Pleistocene Transition it has slowed to about 100,000 years, as evidenced most clearly by ice cores for the past 800,000 years and marine sediment cores for the earlier period. Over the past 740,000 years there have been eight glacial cycles.
The entire Quaternary Period, starting 2.58 Ma, is referred to as an ice age because at least one permanent large ice sheet—the Antarctic ice sheet—has existed continuously. There is uncertainty over how much of Greenland was covered by ice during each interglacial.
Currently, Earth is in an interglacial period, which marked the beginning of the Holocene epoch. The current interglacial began between 15,000 and 10,000 years ago; this caused the ice sheets from the last glacial period to begin to disappear. Remnants of these last glaciers, now occupying about 10% of the world's land surface, still exist in Greenland, Antarctica and some mountainous regions.
During the glacial periods, the present (i.e. interglacial) hydrologic system was completely interrupted throughout large areas of the world and was considerably modified in others. Due to the volume of ice on land, sea level was about 120 meters lower than present.
Earth's history of glaciation is a product of the internal variability of Earth's climate system (e.g., ocean currents, carbon cycle) , plus the effects of "external forcing" due to phenomena external to the climate system (e.g., changes in earth's orbit, volcanism, and changes in solar output).
The role of Earth's orbital changes in controlling climate was first advanced by James Croll in the late 19th century.Later, Milutin Milanković, a Serbian geophysicist, elaborated on the theory and calculated that these irregularities in Earth's orbit could cause the climatic cycles now known as Milankovitch cycles. They are the result of the additive behavior of several types of cyclical changes in Earth's orbital properties.
Changes in the orbital eccentricity of Earth occur on a cycle of about 100,000 years.The inclination, or tilt, of Earth's axis varies periodically between 22° and 24.5° in a cycle 41,000 years long. The tilt of Earth's axis is responsible for the seasons; the greater the tilt, the greater the contrast between summer and winter temperatures. Precession of the equinoxes, or wobbles of Earth's spin axis, have a periodicity of 26,000 years. According to the Milankovitch theory, these factors cause a periodic cooling of Earth, with the coldest part in the cycle occurring about every 40,000 years. The main effect of the Milankovitch cycles is to change the contrast between the seasons, not the overall amount of solar heat Earth receives. The result is less ice melting than accumulating, and glaciers build up.
Milankovitch worked out the ideas of climatic cycles in the 1920s and 1930s, but it was not until the 1970s that a sufficiently long and detailed chronology of the Quaternary temperature changes was worked out to test the theory adequately.Studies of deep-sea cores, and the fossils contained in them, indicate that the fluctuation of climate during the last few hundred thousand years is remarkably close to that predicted by Milankovitch.
A problem with the theory is that these astronomical cycles have been in existence for many millions of years, but glaciation is a rare occurrence. Astronomical cycles correlate with glacial and interglacial periods, and their transitions, within a long-term ice age but do not initiate these long-term ice ages.
One theory holds that decreases in atmospheric CO
2 , an important greenhouse gas, started the long-term cooling trend that eventually led to glaciation. The geochemical cycle of carbon indicates a decrease of more than a 90% in atmospheric CO
2 since the middle of the Mesozoic Era. An analysis of CO
2 reconstructions from alkenone records shows that CO
2 in the atmosphere declined before and during Antarctic glaciation, and supports a substantial CO
2 decrease as the primary cause of Antarctic glaciation.
2 levels also play an important role in the transitions between interglacials and glacials. High CO
2 contents correspond to warm interglacial periods, and low CO
2 to glacial periods. However, studies indicate that CO
2 may not be the primary cause of the interglacial-glacial transitions, but instead acts as a feedback. The explanation for this observed CO
2 variation "remains a difficult attribution problem".
An important component in the development of long-term ice ages is the positions of the continents.These can control the circulation of the oceans and the atmosphere, affecting how ocean currents carry heat to high latitudes. Throughout most of geologic time, the North Pole appears to have been in a broad, open ocean that allowed major ocean currents to move unabated. Equatorial waters flowed into the polar regions, warming them. This produced mild, uniform climates that persisted throughout most of geologic time.
Throughout the Cenozoic Era, the large North American and South American continental plates moved westward from the Eurasian plate. This drift interlocked with the development of the Atlantic Ocean, trending north-south, with the North Pole in the small, nearly landlocked basin of the Arctic Ocean. The Isthmus of Panama developed at a convergent plate margin about 3 million years ago, and further separated oceanic circulation, closing the last strait, outside the polar regions, that had connected the Pacific and Atlantic Oceans.
The presence of so much ice upon the continents had a profound effect upon almost every aspect of Earth's hydrologic system. The most obvious effects are the spectacular mountain scenery and other continental landscapes fashioned both by glacial erosion and deposition instead of running water. Entirely new landscapes covering millions of square kilometers were formed in a relatively short period of geologic time. In addition, the vast bodies of glacial ice affected Earth well beyond the glacier margins. Directly or indirectly, the effects of glaciation were felt in every part of the world.
The Quaternary glaciation created more lakes than all other geologic processes combined. The reason is that a continental glacier completely disrupts the preglacial drainage system. The surface over which the glacier moved was scoured and eroded by the ice, leaving a myriad of closed, undrained depressions in the bedrock. These depressions filled with water and became lakes.
Very large lakes were created along the glacial margins. The ice on both North America and Europe was about 3,000 m (10,000 ft) thick near the centers of maximum accumulation, but it tapered toward the glacier margins. Ice weight caused crustal subsidence, which was greatest beneath the thickest accumulation of ice. As the ice melted, rebound of the crust lagged behind, producing a regional slope toward the ice. This slope formed basins that have lasted for thousands of years. These basins became lakes or were invaded by the ocean. The Baltic Sea and the Great Lakes of North America were formed primarily in this way.[ dubious ]
The numerous lakes of the Canadian Shield, Sweden, and Finland are thought to have originated at least partly from glaciers' selective erosion of weathered bedrock.
The climatic conditions that cause glaciation had an indirect effect on arid and semiarid regions far removed from the large ice sheets. The increased precipitation that fed the glaciers also increased the runoff of major rivers and intermittent streams, resulting in the growth and development of large pluvial lakes. Most pluvial lakes developed in relatively arid regions where there typically was insufficient rain to establish a drainage system leading to the sea. Instead, stream runoff flowed into closed basins and formed playa lakes. With increased rainfall, the playa lakes enlarged and overflowed. Pluvial lakes were most extensive during glacial periods. During interglacial stages, with less rain, the pluvial lakes shrank to form small salt flats.
Major isostatic adjustments of the lithosphere during the Quaternary glaciation were caused by the weight of the ice, which depressed the continents. In Canada, a large area around Hudson Bay was depressed below sea level, as was the area in Europe around the Baltic Sea. The land has been rebounding from these depressions since the ice melted. Some of these isostatic movements triggered large earthquakes in Scandinavia about 9,000 years ago. These earthquakes are unique in that they are not associated with plate tectonics.
Studies have shown that the uplift has taken place in two distinct stages. The initial uplift following deglaciation was rapid (called "elastic"), and took place as the ice was being unloaded. After this "elastic" phase, uplift proceed by "slow viscous flow" so the rate decreased exponentially after that. Today, typical uplift rates are of the order of 1 cm per year or less. In northern Europe, this is clearly shown by the GPS data obtained by the BIFROST GPS network. Studies suggest that rebound will continue for about at least another 10,000 years. The total uplift from the end of deglaciation depends on the local ice load and could be several hundred meters near the center of rebound.
The presence of ice over so much of the continents greatly modified patterns of atmospheric circulation. Winds near the glacial margins were strong and persistent because of the abundance of dense, cold air coming off the glacier fields. These winds picked up and transported large quantities of loose, fine-grained sediment brought down by the glaciers. This dust accumulated as loess (wind-blown silt), forming irregular blankets over much of the Missouri River valley, central Europe, and northern China.
Sand dunes were much more widespread and active in many areas during the early Quaternary period. A good example is the Sand Hills region in Nebraska, USA, which covers an area of about 60,000 km2 (23,166 sq mi). This region was a large, active dune field during the Pleistocene epoch, but today is largely stabilized by grass cover.
Thick glaciers were heavy enough to reach the sea bottom in several important areas, thus blocking the passage of ocean water and thereby affecting ocean currents. In addition to direct effects, this caused feedback effects as ocean currents contribute to global heat transfer.
Glaciation has been a rare event in Earth's history,but there is evidence of widespread glaciation during the late Paleozoic Era (300 to 200 Ma) and the late Precambrian (i.e. the Neoproterozoic Era, 800 to 600 Ma). Before the current ice age, which began 2 to 3 Ma, Earth's climate was typically mild and uniform for long periods of time. This climatic history is implied by the types of fossil plants and animals and by the characteristics of sediments preserved in the stratigraphic record. There are, however, widespread glacial deposits, recording several major periods of ancient glaciation in various parts of the geologic record. Such evidence suggests major periods of glaciation prior to the current Quaternary glaciation.
One of the best documented records of pre-Quaternary glaciation, called the Karoo Ice Age, is found in the late Paleozoic rocks in South Africa, India, South America, Antarctica, and Australia. Exposures of ancient glacial deposits are numerous in these areas. Deposits of even older glacial sediment exist on every continent except South America. These indicate that two other periods of widespread glaciation occurred during the late Precambrian, producing the Snowball Earth during the Cryogenian Period.
The warming trend following the Last Glacial Maximum, since about 20,000 years ago, has resulted in a sea level rise by about 130 metres. This warming trend has subsided about 6,000 years ago, and sea level has been comparatively stable since the Neolithic. The present interglacial period (the Holocene) has been fairly stable and warm, but the previous one was interrupted by numerous cold spells lasting hundreds of years. If the previous period was more typical than the present one, the period of stable climate, which allowed the Neolithic Revolution and by extension human civilization, may have been possible only because of a highly unusual period of stable temperature.
Based on orbital models, the cooling trend initiated about 6,000 years ago will continue for another 23,000 years.Slight changes in the Earth's orbital parameters might however indicate that, even without any human contribution, there will not be another glacial period for the next 50,000 years. It is possible that the current cooling trend may be interrupted by an interstadial in about 60,000 years, with the next glacial maximum reached only in about 100,000 years.
Based on past estimates for interglacial durations of about 10,000 years, in the 1970s there was some concern that the next glacial period would be imminent. However, slight changes in the eccentricity of Earth's orbit around the Sun suggest an extended interglacial for about 50,000 years. CO
2 in the atmosphere. Models assuming increased CO
2 levels at 750 parts per million (ppm; current levels are at 407 ppm ) have estimated the persistence of the current interglacial period for another 50,000 years. However, more recent studies concluded that due to the amount of heat trapping gases emitted into Earth's Oceans and atmosphere, that this will prevent the next glacial (ice age), which otherwise would begin in around 50,000 years, and likely more glacial cycles.
The Pleistocene is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology.
Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term is named for Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he hypothesized that variations in eccentricity, axial tilt, and precession of the Earth's orbit resulted in cyclical variation in the solar radiation reaching the Earth, and that this orbital forcing strongly influenced climatic patterns on Earth.
A pluvial lake is a body of water that accumulated in a basin because of a greater moisture availability resulting from changes in temperature and/or precipitation. These intervals of greater moisture availability are not always contemporaneous with glacial periods. Pluvial lakes are typically closed lakes that occupied endorheic basins. Pluvial lakes that have since evaporated and dried out may also be referred to as paleolakes.
The Last Glacial Period (LGP) occurred from the end of the Eemian interglacial to the end of the Younger Dryas, encompassing the period c. 115,000 – c. 11,700 years ago. This most recent glacial period is part of a larger pattern of glacial and interglacial periods known as the Quaternary glaciation extending from c. 2,588,000 years ago to present. The definition of the Quaternary as beginning 2.58 Ma is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Ma, in the mid-Cenozoic. The term Late Cenozoic Ice Age is used to include this early phase.
There have been five or six major ice ages in the history of Earth over the past 3 billion years. The Late Cenozoic Ice Age began 34 million years ago, its latest phase being the Quaternary glaciation, in progress since 2.58 million years ago.
The Würm glaciation, in the literature usually just referred to as the Würm, often spelt "Wurm", was the last glacial period in the Alpine region. It is the youngest of the major glaciations of the region that extended beyond the Alps themselves. It is, like most of the other ice ages of the Pleistocene epoch, named after a river, the Würm in Bavaria, a tributary of the Amper. The Würm ice age can be dated to the time about 115,000 to 11,700 years ago, the sources differing depending on whether the long transition phases between the glacials and interglacials are allocated to one or other of these periods. The average annual temperatures during the Würm ice age in the Alpine Foreland were below −3 °C. This has been determined from changes in the vegetation as well as differences in the facies.
Orbital forcing is the effect on climate of slow changes in the tilt of the Earth's axis and shape of the orbit. These orbital changes change the total amount of sunlight reaching the Earth by up to 25% at mid-latitudes. In this context, the term "forcing" signifies a physical process that affects the Earth's climate.
The Flandrian interglacial or stage is the name given by geologists and archaeologists in the British Isles to the first, and so far only, stage of the Holocene epoch, covering the period from around 12,000 years ago, at the end of the last glacial period to the present day. As such, it is in practice identical in span to the Holocene. Present climatological theory forecasts that the present Flandrian climate should decline in temperature towards a global climate similar to that of the ice age. Less orbital eccentricity may have the effect of moderating this temperature downturn.
Marine isotope stages (MIS), marine oxygen-isotope stages, or oxygen isotope stages (OIS), are alternating warm and cool periods in the Earth's paleoclimate, deduced from oxygen isotope data reflecting changes in temperature derived from data from deep sea core samples. Working backwards from the present, which is MIS 1 in the scale, stages with even numbers have high levels of oxygen-18 and represent cold glacial periods, while the odd-numbered stages are troughs in the oxygen-18 figures, representing warm interglacial intervals. The data are derived from pollen and foraminifera (plankton) remains in drilled marine sediment cores, sapropels, and other data that reflect historic climate; these are called proxies.
The neoglaciation describes the documented cooling trend in the Earth's climate during the Holocene, following the retreat of the Wisconsin glaciation, the most recent glacial period. Neoglaciation has followed the hypsithermal or Holocene Climatic Optimum, the warmest point in the Earth's climate during the current interglacial stage. The neoglaciation has no well-marked universal beginning: local conditions and ecological inertia affected the onset of detectably cooler conditions.
Marine Isotope Stage 11 or MIS 11 is a Marine Isotope Stage in the geologic temperature record, covering the interglacial period between 424,000 and 374,000 years ago. It corresponds to the Hoxnian Stage in Britain.
Deglaciation describes the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice sheet or frozen surface layer, and the resulting exposure of the Earth's surface. The decline of the cryosphere due to ablation can occur on any scale from global to localized to a particular glacier. After the Last Glacial Maximum, the last deglaciation begun, which lasted until the early Holocene. Around much of Earth, deglaciation during the last 100 years has been accelerating as a result of climate change, partly brought on by anthropogenic changes to greenhouse gases.
A climate oscillation or climate cycle is any recurring cyclical oscillation within global or regional climate, and is a type of climate pattern. These fluctuations in atmospheric temperature, sea surface temperature, precipitation or other parameters can be quasi-periodic, often occurring on inter-annual, multi-annual, decadal, multidecadal, century-wide, millennial or longer timescales. They are not perfectly periodic and a Fourier analysis of the data does not give a sharp spectrum.
Climate state describes a state of climate on Earth and similar terrestrial planets based on a thermal energy budget, such as the greenhouse or icehouse climate state.
The Late Cenozoic Ice Age, or Antarctic Glaciation began 33.9 million years ago at the Eocene-Oligocene Boundary and is ongoing. It is Earth's current ice age or icehouse period. Its beginning is marked by the formation of the Antarctic ice sheets. The Late Cenozoic Ice Age gets its name due to the fact that it covers roughly the last half of Cenozoic Era so far.
The Mid-Pleistocene Transition (MPT), also known as the Mid-Pleistocene Revolution (MPR), is a fundamental change in the behaviour of glacial cycles during the Quaternary glaciations. The transition happened approximately 1.25–0.7 million years ago, in the Pleistocene epoch. Before the MPT, the glacial cycles were dominated by a 41,000 year periodicity with low-amplitude, thin ice sheets and a linear relationship to the Milankovitch forcing from axial tilt. After the MPT there have been strongly asymmetric cycles with long-duration cooling of the climate and build-up of thick ice sheets, followed by a fast change from extreme glacial conditions to a warm interglacial. The cycle lengths have varied, with an average length of approximately 100,000 years.