The Quaternary glaciation , also known as the Quaternary Ice Age or Pleistocene glacier , is a series of glacial events separated by interglacial events during the Quaternary period of 2, 58 Ma (million years ago) to attend. This is the last 10% of the Current Ice Age, where long-term Antarctic glaciers have spread to the northern hemisphere. During this period, the ice sheet is expanded, mainly from beyond Antarctica and Greenland, and fluctuating ice sheets occur elsewhere (eg, Laurentide ice sheets). The main effects of the ice age are soil erosion and deposition of materials, both in most continents; modification of the river system; the creation of millions of lakes, changes in sea level, the development of pluvial lakes away from ice margins, isostatic adjustment of the earth's crust, floods, and abnormal winds. The ice layer itself, by raising albedo (the extent to which solar energy is reflected from the Earth) creates significant feedback to further cool the climate. These effects reshape the entire environment on land and in the ocean, and their associated biological communities.
Video Quaternary glaciation
Discovery
Quaternary Glaciation is the first ice age to be proved to have occurred in the field of geology, and thus proof of ice age is possible. This was done during the 1700s and 1800s as part of the scientific revolution.
Over the last century, extensive field observations have provided evidence that continental glaciers cover much of Europe, North America, and Siberia. The glacial feature map is compiled after years of fieldwork by hundreds of geologists mapping the location and orientation of drumlins, esks, moraines, striations, and glacial flow channels to reveal the extent of the ice sheets, the direction of the flow, and the location of the melting water channel system. They also allow scientists to break the history of various advances and ice retreats. Even before glaciation theories around the world are generally accepted, many observers acknowledge that more than one advance and ice decline have taken place.
Since then, other, earlier ice ages have been identified, and the Quaternary (s) event is restricted.
Maps Quaternary glaciation
Description
The Current Ice Age, including the Quaternary glaciation, is the last of the seven known glaciations, or ice ages, throughout the entire Earth's history.
On the other hand, in the Quaternary Period, or the ice age, also periodic fluctuations, of the total volume of soil ice, sea level, and global temperature. Colder episodes are referred to as glacial, or simply glacial, periods where the large ice sheet is at least 4 km in size at its maximum in Europe, North America, and Siberia. Shorter and warmer intervals between glacial are referred to as interglacial.
Initially the fluctuations were on a 41,000 year time scale, but recently they have been on a 100,000-year scale, proven most clearly by ice cores over the last 800,000 years and the core of marine sediments for the previous period. Over the last 740,000 years there have been eight glacial cycles.
The entire Quaternary Period, starting at 2.58 Ma, is referred to as the Ice Age because at least one permanent large ice sheet - Antarctic ice sheet - has existed continuously. There is uncertainty about how much Greenland was covered by ice during previous and earlier interglacial.
Currently, Earth is in an interglacial period, which marks the beginning of the Holocene period. The interglacial current began between 10,000 and 15,000 years ago, causing the ice sheets from the last glacial period to begin to disappear. The remains of this last glacier, now occupying about 10% of the world's soil surface, are still present in Greenland, Antarctica, and the mountains.
During the glacial period, the current hydrological system (interglacial) is completely disrupted throughout the great regions of the world and is heavily modified in others. Due to the volume of ice on land, the sea level is approximately 120 meters lower than it is today.
Broad evidence now suggests that a number of periods of growth and retreat of continental glaciers occurred during the ice age, called glacial and interglacial. Interglacial warm climatic periods are represented by buried soil profiles, peat beds, and lakes and river deposits that separate un-sorted and un-stratified glacial deposits.
Cause
There is no really satisfying theory proposed to explain the history of Earth's glaciation. The cause of the glaciation may be related to several simultaneous factors, such as the astronomical cycle, atmospheric composition, tectonic plates, and ocean currents.
The astronomical cycle
The role of Earth's orbital changes in climate control was first proposed by James Croll at the end of the 19th century. Later, Milutin Milankovi?, A Serbian geophysicist, elaborated on that theory and calculated this irregularity in Earth's orbit could lead to a climate cycle known as the Milankovitch cycle. They are the result of the additive behavior of some kind of cyclical change in the properties of Earth's orbit.
The change in the eccentricity of the Earth's orbital occurs in a cycle of about 100,000 years. The slope, or slope, of the Earth's axis varies periodically between 22 ° and 24.5 °. (The axial tilt of the Earth is responsible for the season, the greater the slope, the greater the contrast between summer and winter.) Tilt changes occur in 41,000-year cycle. Precession equinoxes, or wobble on the axis of the Earth's rotation, complete every 26,000 years. According to the Milankovitch theory, these factors cause periodic cooling of the Earth, with the coldest part in the cycle occurring around every 40,000 years. The main effect of the Milankovitch cycle is to change the contrast between seasons, not the amount of solar heat that Earth receives. This cycle in the cycle predicts that during the maximum glacial progress, the winter and summer temperatures are lower. The result is less ice melts than accumulates, and glaciers accumulate.
Milankovitch devised climate cycle ideas in the 1920s and 1930s, but it was not until the 1970s that a lengthy and detailed chronology of Quaternary temperature changes was worked out to test the theory adequately. The study of deep-sea nuclei, and the fossils contained in it show that climate fluctuations over the last few hundred thousand years are very close to that predicted by Milankovitch.
The problem with this theory is that the cycle of astronomy has been around for billions of years, but glaciation is a rare occurrence. The astronomical cycle perfectly correlates with the glacial and interglacial periods, and their transitions, within the ice age. Other factors such as the position of the continent and its impact on Earth's ocean currents, or long-term fluctuations in the Sun's core that cause Earth's temperature to fall below the critical threshold and thus start the ice age in the first place should also be involved. Once that happens, the Milankovitch cycle can act to force the planet in and out of the glacial period.
atmospheric composition
One theory states that the atmospheric depletion CO
2 , an important greenhouse gas, initiating a long-term cooling trend that eventually causes glaciation. Recent studies of CO
2 CO
2 since the middle of the Mesozoic Era. Analysis CO
2 Reconstruction of the record alkenone shows that CO
2 at the atmosphere decreases before and during Antarctic glaciers and supports CO
2 decreases as the main cause of Antarctic glaciers.
CO
2 level also play role important in the transition between interglacial and glacial. High CO
2 match content for warms the interglacial period, and CO
2 to the glacial period. However, research shows that CO
2 may not be the main cause of the interglacial-glacial transition, but it acts as a feedback. Explanation for this is observed CO
2 variations "remain a difficult attribution issue".
Plate tectonics and ocean currents
An important component in long-term temperature drop may be related to the position of the continent, relative to the poles (but can not explain the rapid retreat and progress of the glacier). This relationship can control the circulation of the oceans and the atmosphere, affecting how ocean currents carry heat to high latitudes. Throughout most of the geological time, the Arctic appears to be in a vast and open ocean that allows large ocean currents to move unhindered. Equatorial waters flow into the polar regions, warming them with water from temperate latitudes. This unlimited circulation produces a mild and uniform climate that persists throughout most of the geologic time.
Throughout the Kenozoic Era, the continental plates of North America and South America move west from the Eurasian plate. This current is intertwined with the development of the Atlantic Ocean, which trails north-south, with the North Pole in the Arctic Ocean basin almost covered by the land. The Isthmus of Panama expanded on the boundary of the convergent plate about 3 million years ago, and further separated the circulation of the oceans, closing the last strait, beyond the polar regions, connecting the Pacific and Atlantic Oceans.
Effects
The presence of so much ice in the continent has a profound effect on almost every aspect of the Earth's hydrological system. The most obvious effect is spectacular mountain scenery and other continental landscapes made by glacial erosion and deposition rather than running water. A truly new landscape spanning millions of square kilometers is formed in a relatively short geological time. In addition, the large glacial ice bodies affect the Earth far beyond the glacier margins. Directly or indirectly, glaciation effects are felt in every part of the world.
Lake
Quaternary Glaciation creates more lakes than all other geological processes combined. The reason is that continental glaciers really interfere with the preglacial drainage system. The surface on which the glacier moves is rubbed and eroded by ice, leaving a myriad of closed, undrained depressions in the bedrock. This depression is filled with water and becomes a lake.
Huge lakes are created along the glacial edge. Ice in North America and Europe has a thickness of about 3,000 m (9,800 ft) near the maximum accumulation centers, but tapers toward the glacier margins. The weight of ice causes the largest decrease of crust under the thickest accumulation of ice. As ice melts, rebounds from the crust are left behind, resulting in a regional slope toward the ice. This slope forms a basin that has lasted for thousands of years. This basin becomes a lake or is attacked by oceans. The Baltic Sea and Great Lakes of North America are formed primarily in this way.
The numerous lakes of the Canadian, Swedish and Finnish Shields are thought to derive at least part of the selective erosion of glaciers from the weathered bed.
Pluvial Lake
Climatic conditions that cause glaciation have an indirect effect on dry and semi-arid regions away from large ice sheets. Increased rainfall that feeds the glaciers also increases runoff from large rivers and intermittent streams, resulting in the growth and development of large lakes. Most of the pluvial lakes are developing in relatively dry areas where there is usually not enough rain to build drainage systems into the sea. Instead, the flow of runoff in these areas flowed into a closed pool and formed playa lakes. With the increase in rainfall, the lake playa enlarged and overflowed. The most extensive Pluvial Lake during the glacial period. During the interglacial stage, when rainfall is reduced, small lakes shrink to form small salt plains.
Isostatic Adjustment
The major isostatic adjustment of the lithosphere during Quaternary glaciation is due to the weight of the ice, which suppresses the continent. In Canada, large areas around the Hudson Bay are depressed below sea level, such as areas in Europe around the Baltic Sea. The soil has recovered from this depression since the ice melts. Some of these isostatic movements triggered a major earthquake in Scandinavia about 9,000 years ago. This earthquake is unique because it is not associated with tectonic plates.
Research has shown that rapture has taken place in two distinct phases. Early removal after deglaciation is rapid (called "elastic"), and occurs when ice is being lowered. After this "elastic" phase, the uplift is continued with "slow viscous flow" so that the rate decreases exponentially after that. Today, the typical increase rate is about 1 cm per year or less. In northern Europe, this is clearly demonstrated by GPS data obtained by the BIFROST GPS network. Studies show that the rebound will continue for at least another 10,000 years. The total lift from the tip of deglaciation depends on the local ice load and can be several hundred meters near the rebound center.
Winds
The presence of ice in so many continents greatly modifies the pattern of atmospheric circulation. The wind near the edge of glacial is strong and persistent due to the amount of cold and dense air coming from the glacier fields. These winds pick up and transport large amounts of loose and fine deposits brought down by glaciers. This dust accumulates as a loess, forming an irregular blanket in many Missouri River valleys, Central Europe, and northern China.
The dunes are much wider and active in many areas during the early Quaternary period. A good example is the Sand Hills area in Nebraska, USA, covering an area of ​​approximately 60,000 km 2 (23,166 sqÃ, mi). This area is a large mound field that was active during the Pleistocene period, but is now largely stabilized by the grass cover.
Ocean currents
The thick glaciers are heavy enough to reach the seafloor in some important areas, thus blocking the flow of sea water and thus affecting ocean currents. In addition to the direct effects, this feedback effect is due to ocean currents contributing to global heat transfer.
Previous glacial record
Glaciation has been a rare event in Earth's history, but there is evidence of widespread glaciation during the late Paleozoic Era (200 to 300 Ma) and during late Precambrian (ie in Neoproterozoic Era, 600 to 800 Ma). Before the current ice age, which started from 2 to 3 Ma, Earth's climate is usually mild and uniform for long periods of time. The history of this climate is implied by the types of fossil plants and animals and by the characteristics of sediments stored in the stratigraphic record. However, there is widespread glacial precipitation, recording some of the major periods of ancient glaciation in different parts of the geological record. Such evidence suggests a major period of glaciation before the Quaternary glaciation of today.
One of the best documented records of pre-Quranic glaciations, called the Ice Age of Karoo, is found in Paleozoic rocks in South Africa, India, South America, Antarctica and Australia. The exposure of many ancient glacial deposits in these areas. Older sedimentary glacial sediments exist on every continent except South America. This suggests that two other widespread glaciation periods occur during the final Precambrian, producing Earth Snowball during the Cryogenian Period.
Next glacial period
In popular culture, there are often references to the "next ice age". Technically, since Earth is already in the current ice age, despite the interglacial period, it usually refers to the next glacial period.
In the 1970s some paleoclimatologists were concerned about the possibility of global cooling, and suggested that the next glacial period could quickly approach. The earlier interglacial period seems to have lasted about 10,000 years each; a report in 1972 assuming that the current interglacial period would be concluded to be the same length, "it is possible that the current warmth will end soon if humans do not intervene". Since then, our understanding of the climate system has increased. It is well known that not all interglacial periods have the same length and that solar heating varies in non-linear mode imposed by the Milankovitch orbital cycle (see Cause above). At the same time, it is also known that greenhouse gases are increasing in concentration every year. Based on variations in solar warming and on the number of CO
2 in the atmosphere, some future temperature calculations have been made. According to this estimate, the interglacial period of the Earth can now survive for 50,000 years if CO
2 increased to 750 parts per million (ppm) while the recent atmospheric concentration CO
2 is about 407 ppm by volume. If CO
2 drops instead up to 210 ppm, then the next glacial period may be only 15,000 years away. In addition, studies of sea-floor sediments and ice cores from glaciers around the world, Greenland, show that climate change is not fluent. The study of isotopic composition of ice cores shows changes from warm to cold temperatures can occur within one or two decades. In addition, ice cores indicate that ice ages are not uniformly cold, nor are uniformly warm interglacial periods (see also stadial). Analysis of ice cores from all Greenland glacier thicknesses suggests that the climate over the last 250,000 years has changed frequently and suddenly. The current interglacial period (the last 10,000 to 15,000 years) has been quite stable and warm, but which was previously plagued by many cold spells that lasted for hundreds of years. If the earlier period was more typical than the present, a period of stable climate in which humans flourish - creating agriculture and thus civilization - may be possible only because of periods of extremely unusual stable temperatures.
References
External links
- Glaciers and Glaciation
- Pleistocene Gladiation and Missouri River Diversion in North Montana
- The final Pleistocene glaciation correlation in the western United States with the occurrence of North Atlantic Heinrich
- After the Ice Age: The Return of Life to Glaciated North America by E.C. Pielou
- Alaska Glacier and Esfield
- Pleistocene glaciation (last 2 million years)
- Palaeoclimate IPCC (pdf)
- Cause
- Astronomy Climate Change Theory
- Milutin Milankovitch and Milankovitch cycle
Source of the article : Wikipedia
0 Comments