Epoch Eocene) ( ), lasting from 56 to 33.9 million years ago , is a major division of the geological time scale and the second period of the Paleogene Period at The Kenozoic Era. Eocene includes the time from the end of the Epoch Paleocene to the beginning of the Epoch Oligocene. Early Eocene is characterized by a short period in which the concentration of carbon isotope 13 C in the atmosphere is very low compared to the more common isotope 12 C. The end is set on a major extinction event called Grande Coupure ("Great Break" in continuity) or the Eocene-Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in the present place Chesapeake Bay. As with any other geological period, the stratum that determines the beginning and end times is well identified, although the exact date is a bit uncertain.
The name Eocene comes from Ancient Greek ??? ( ?? s , "dawn") and ?????? ( kainós , "new") and refers to the "dawn" of modern fauna ('new') that appeared over time.
Video Eocene
Subdivision Edit
The Eocene Eposes are conventionally divided into initial, middle, and end subdivisions. Suitable rocks are referred to as low, middle, and upper Eocene. The Ypresian stage is a lower, upper Priabonian stage; and the Lutetian and Bartonian stages are united as the middle Eocene.
Maps Eocene
Climate Edit
The Eocene Epoch contains a variety of different climatic conditions that include the hottest climates in the Kenozoic Era and ends in a home ice climate. Eocene climate evolution begins with warming after the final Thermal Maximum of Palaeocene-Eocene (PETM) at 56 million years ago to a maximum during the Eocene Optimum about 49 million years ago. During this time period, little or no ice on Earth with a temperature difference smaller than the equator to the poles. Maximum follow is descend into the ice climate of the home of the Eocene Optimum into the Eocene-Oligocene transition 34 million years ago. As the decline of this ice begins to reappear at the poles, and the Eocene-Oligocene transition is the period of time in which the Antarctic ice sheet begins to grow rapidly.
Evolution of atmospheric greenhouse gases Edit
Greenhouse gases, especially carbon dioxide and methane, play an important role during the Eocene in controlling surface temperatures. The end of the PETM meets with a very large sequestration of carbon dioxide in the form of clay, coal, and crude methane at the bottom of the Arctic Ocean, which reduces atmospheric carbon dioxide. This incident is similar to the large release of greenhouse gases at the beginning of PETM, and it is hypothesized that the absorption is primarily due to the pollution of organic carbon and silicate weathering. For the early Eocene there was much discussion about how much carbon dioxide in the atmosphere. This is due to the many proxies representing different atmospheric carbon dioxide contents. For example, various geochemical and paleontological proxies show that at a maximum of global warmth, atmospheric carbon dioxide values ​​are at 700-900 ppm while other proxies such as pedogenic (soil building) carbonates and marine boron isotopes show large changes in carbon dioxide over 2,000 ppm during the period less than 1 million years. Sources for the entry of this large carbon dioxide can be attributed to volcanic assault due to gassing due to the decomposition or oxidation of methane in the North Atlantic stored in large reservoirs stored from PETM events on the seafloor or wetland environments. On the contrary, today carbon dioxide levels reach 400 ppm or 0.04%.
At about the beginning of the Eocene Eocene (55.8-33.9 million years ago) the amount of oxygen in the Earth's atmosphere is approximately twice that.
During the early Eocene, methane was another greenhouse gas that had a drastic effect on climate. Compared to carbon dioxide, methane has a much greater effect on temperature because methane is about 34 times more effective per molecule than carbon dioxide on a 100-year scale (it has a higher global warming potential). Most of the methane released into the atmosphere over this period of time will come from wetlands, swamps and forests. The concentration of atmospheric methane today is 0.000179% or 1.79 ppmv. Due to the warmer climates and sea level rise associated with early Eocene, more wetlands, more forests, and more coal deposits will be available for methane release. Comparing the production of early Eocene methane to current atmospheric methane levels, the early Eocene will be able to produce three times the amount of methane production today. Warm temperatures during early Eocene can increase the rate of methane production, and methane released into the atmosphere will in turn warm the troposphere, cool the stratosphere, and produce water vapor and carbon dioxide through oxidation. Biogenic production of methane produces carbon dioxide and water vapor along with methane, and produces infrared radiation. Methane damage in the oxygen atmosphere produces carbon monoxide, water vapor and infrared radiation. Carbon monoxide is so unstable that it eventually becomes carbon dioxide and thereby releases more infrared radiation. Water vapor entraps more infrared than carbon dioxide.
The middle eocene to the end marks not only the switch from heating to cooling, but also the change in carbon dioxide from rising to decreasing. At the end of the Eocene Optimum, carbon dioxide begins to decline due to increased productivity of plankton containing silica and ocean carbon cemetery. At the beginning of the middle Eocene an event that may have triggered or assisted with the withdrawal of carbon dioxide was an Azolla event about 49 million years ago. With the same climate during early Eocene, warm temperatures in the Arctic allow for the growth of azollas, which are floating water ferns, in the Arctic Ocean. Compared to current levels of carbon dioxide, this Azolla is growing rapidly in the increased levels of carbon dioxide found in early Eocene. As this azolla sinks into the Arctic Ocean, they are buried and confiscate their carbon into the ocean floor. This event can cause atmospheric carbon dioxide withdrawal up to 470 ppm. Assuming the concentration of carbon dioxide is at 900 ppmv before their Azolla Event will drop to 430 ppmv, or 30 ppmv more than the current one, after the Azolla Event. Another event during the middle Eocene which is a sudden and temporary reversal of the cooling conditions is the Optimal Climax of the Middle Eocene. About 41.5 million years ago, stable isotope analyzes of samples from the Southern Ocean drilling site indicated warming events over 600,000 years. A sharp increase in atmospheric carbon dioxide was observed with a maximum of 4000 ppm: the highest amount of atmospheric carbon dioxide detected during the Eocene. The main hypothesis for a radical transition is due to continental drift and collision of the Indian subcontinent with the Asian continent and the formation of the Himalayas. Another hypothesis involves altering the ocean floor and metamorphic decarbonation reactions that release large amounts of carbon dioxide into the atmosphere.
At the end of the Middle Eocene Optimal, the cooling and withdrawal of carbon dioxide continued into the Eocene end and entered the Eocene-Oligocene transition about 34 million years ago. Some proxies, such as the isotopes of oxygen and alkenon, show that in the Eocene-Oligocene transition, the concentration of carbon dioxide in the atmosphere has decreased to about 750-800 ppm, about twice that of the current rate.
Beginning Eocene and equivalent climate issues Edit
One of the unique features of the Eocene climate as mentioned earlier is the equivalent and homogeneous climate that exists at the beginning of the Eocene. A large number of proxies support the presence of a warmer climate that could be present during this time period. Some of these proxies include the presence of fossils originating from warm climates, such as crocodiles, located at higher latitudes, presence in high latitudes of ice-intolerant flora such as palms that can not survive during continuous frozen, and fossils snakes found in tropical regions that require higher mean temperatures to support. Using an isotope proxy for determining sea temperature shows sea surface temperatures in the tropics as high as 35 ° C (95 ° F) and, relative to current values, lower water temperatures of 10 ° C (18 ° F) more high. With the water temperature below, the temperature in areas where the water in shape near the poles can not become colder than the water temperature at the bottom.
The problem arises, when trying to model the Eocene and reproduce the results found with the proxy data. Using all the different greenhouse gas ranges that occurred during the early Eocene, the model could not produce the warming found at the poles and the reduced seasons that occurred with the warmer polar winters. The models, while accurately predicting the tropics, tend to produce significantly cooler temperatures up to 20 ° C (36 ° F) cooler than the actual temperature specified at the poles. This error has been classified as "the same climate problem". To solve this problem, the solution will involve finding processes to warm the poles without warming the tropics. Some hypotheses and tests that seek to find the process are listed below.
Big lake Edit
Due to the nature of the water as opposed to the soil, less temperature variability will be present if a large body of water is also present. In an attempt to try to reduce the temperature of the cooling poles, large lakes are proposed to reduce seasonal climate change. To replicate the case, a lake is incorporated into North America and climate models are run using various levels of carbon dioxide. The walking model concludes that while lakes do indeed reduce seasonal seasons greater than just increases in carbon dioxide, the addition of large lakes can not reduce seasonally to levels indicated by floral and fauna data.
Sea Transportation Edit
The transport of heat from the tropics to the poles, such as how the function of sea heat transport in modern times, is considered the possibility of increasing temperatures and reducing seasons for the poles. With rising sea surface temperatures and rising temperatures of deepwater during the early Eocene, one common hypothesis was that due to this increase there would be greater heat transport from the tropics to the poles. Simulating this difference, the model produces lower heat transport due to lower temperature gradients and is unsuccessful in generating an equivalent climate than just ocean heat transport.
Orbit Parameters Edit
While usually seen as controls on ice and seasonal growth, the orbital parameters are theorized as possible controls at continental and seasonal temperatures. Eocene simulations using free ice planets, eccentricity, slope, and precession are modified in different models to determine all possible different scenarios that can occur and their effects on temperature. One particular case leads to warmer winters and colder summers of up to 30% in the North American continent, and that reduces seasonal temperature variations by up to 75%. While the orbital parameters do not produce polar heating, the parameters do show a great influence on the season and need to be considered.
Polar stratospheric cloud Edit
Another method considered to produce warm polar temperatures is the stratospheric polar cloud. The stratospheric cloud pole is a cloud that occurs in the lower stratosphere at very low temperatures. Polar polar clouds have a major impact on radiative coercion. Due to their minimal albedo nature and optical thickness, stratospheric polar clouds act similar to greenhouse gases and long-wave radiation out. Different types of stratospheric polar clouds occur in the atmosphere: stratospheric polar clouds created due to interactions with nitric or sulfuric acid and water (Type I) or stratospheric polar clouds created only with water ice (Type II).
Methane is an important factor in the creation of primary Type II stratospheric stratum clouds created at the beginning of the Eocene. Since water vapor is the only supplementary substance used in a Type II stratospheric stratospheric cloud, the presence of water vapor in the lower stratosphere is needed where in most situations the presence of water vapor in the lower stratosphere is rare. When methane is oxidized, large amounts of moisture are released. Another requirement for polar stratospheric clouds is the cold temperature to ensure condensation and cloud production. The production of polar stratospheric clouds, as they require cold temperatures, is usually limited to night and winter conditions. With a combination of wet and cold conditions in the lower stratosphere, polar polar clouds can form over a large area of ​​the Polar Territory.
To test the effect of stratospheric polar clouds on Eocene climates, the model was run comparing the effects of polar polar pole shells at the poles to an increase in atmospheric carbon dioxide. Polar polar clouds have a polar heating effect, increasing temperatures by 20 ° C in winter. Much feedback also occurs in the model due to the presence of stratospheric polar clouds. Any ice growth is very slow and will cause the ice to melt. Only the poles are affected by changes in temperature and the tropics are not affected, which with increasing carbon dioxide in the atmosphere will also cause the tropics to increase the temperature. Due to the tropospheric warming of the increasing greenhouse effect of polar stratospheric clouds, the stratosphere cools and potentially increases the number of polar stratospheric clouds.
While polar polar clouds could explain the equatorial decrease to the temperature gradient poles and increase in polar temperatures during the early Eocene, there were some disadvantages to maintaining polar stratospheric clouds for long periods of time. Separate run models are used to determine the continuity of polar stratospheric clouds. Methane needs to be released in a sustainable and sustainable way to maintain lower stratospheric water vapor. Increasing the number of ice cores and condensation will need to be high for polar stratosphere clouds to defend itself and eventually develop.
Hyperthermals via Initial Eosen Edit
During warming up in early Eocene between 52 and 55 million years ago, there was a series of short-term changes in carbon isotopic composition in the oceans. This isotope change occurs due to the release of carbon from the ocean to the atmosphere causing an increase in temperature of 4-8 Â ° C (7-14 Â ° F) at sea level. This hyperthermal causes increased disturbance in planktonic and benthic foraminifera, with higher sedimentation rates as a consequence of warmer temperatures. This latest analysis and research on hyperthermal at the beginning of the Eocene has led to the hypothesis that hyperthermal is based on orbital parameters, particularly eccentricity and tilt. Hyperthermal at the start of the Eocene, particularly the Maximum Thermal Palaeocene-Eocene (PETM), Maximum Thermal Eocene 2 (ETM2), and Maximum Thermal Eocene 3 (ETM3), were analyzed and found that orbital controls may have a role in triggering ETM2 and ETM3.
Greenhouse to the eshouse climate Edit
The Eocene is not only known for it contains the hottest period during the Kenozoic, but also marks a decline into the ice climate and the rapid expansion of the Antarctic ice sheet. The transition from a warming climate to a cooling climate began at ~ 49 million years ago. Carbon and oxygen isotopes show a shift to a global cooling climate. The cause of cooling has been associated with a significant decrease & gt; 2000 ppm in the atmospheric carbon dioxide concentration. One of the proposed causes of carbon dioxide reduction during heating for cooling transitions is the azolla event. Increased warmth in the Arctic, an isolated Arctic basin during early Eocene, and a significantly higher amount of carbon dioxide may cause azolla flowers to bloom in the Arctic Ocean. Isolation of the Arctic Ocean causes stagnant waters and when azolla sinks to the seabed, they become part of the sediment and effectively sequester carbon. The ability to azolla to sequester carbon is remarkable, and enhanced burial of azollas can have a significant effect on the atmospheric carbon content of the world and may have been an event to begin the transition into an ice house climate. The cooling after this event continues due to the continuous decline of atmospheric carbon dioxide from organic productivity and weathering of mountain buildings.
Global cooling continued until there was a major reversal of cooling to warming shown in the Southern Ocean about 42-41 million years ago. Oxygen isotope analysis showed a large negative change in the proportion of heavier isotopes of oxygen to the lighter isotope of oxygen, which indicates an increase in global temperature. This warming event is known as the Central Optimal Climate Eocene. The cause of warming is thought to be primarily due to an increase in carbon dioxide, as carbon isotope signatures get rid of major methane releases during this short-term warming. Increased atmospheric carbon dioxide is thought to be due to the increasing rate of seafloor deployment between Australia and Antarctica and an increase in the number of volcanism in the region. Another possible increase in atmospheric carbon dioxide may occur during a sudden increase in metamorphic release during Himalayan orogeny, but timely data from atmospheric carbon dioxide releases are not well resolved in the data. However, recent research says that the removal of oceans between Asia and India can release large amounts of carbon dioxide. This warming is short-lived, since the notes of benthic oxygen isotopes show the return of cooling at ~ 40 million years ago.
The cooling continues throughout the remainder of the final Eocene into the Eocene-Oligocene transition. During the cooling period, benthic oxygen isotopes show the possibility of ice creation and increased ice during this cooling later. The Eocene end and the Oligocene beginning are marked by the massive expansion of the Antarctic ice sheet region which is a major step into the ice climate. Along with a decrease in atmospheric carbon dioxide that reduces global temperatures, the orbital factor in the creation of ice can be seen with fluctuations of 100,000 years and 400,000 years in the notes of benthic oxygen isotopes. Another major contribution to the expansion of the ice sheet is the creation of Antarctic circumpolar currents. The creation of Antarctic circumpolar currents will isolate the cold water around Antarctica, which will reduce the heat transport to the Antarctic along with creating a sea gyre that produces upwelling of the cold bottom waters. The problem with this hypothesis of this consideration being a factor for the Eocene-Oligocene transition is the timing of uncertain circulatory creation. For the Drake Passage, the sediment shows the opening occurred ~ 41 million years ago while tectonics showed that this happened ~ 32 million years ago.
Palaeogeography Edit
During the Eocene, the continents continued to drift towards their present position.
Early in the period, Australia and Antarctica stayed connected, and warm equatorial currents mixed with the cooler Antarctic waters, distributed heat around the planet and kept global temperatures high, but when Australia broke away from the southern continent around 45 Ma, the warm equator flowed from Antarctica. The isolated cold channel is developed between two continents. The Antarctic region cools, and the seas around Antarctica begin to freeze, sending cold water and esfloes northward, strengthening the cooling.
The northern supercontinent continent of Laurasia begins to split, as Europe, Greenland, and North America are far apart.
In western North America, mountain buildings began in the Eocene, and large lakes formed in the high flat basins between the uplift, which resulted in the deposition of the formation of the Green River Formation.
At about 35 Ma, the impact of asteroids on the east coast of North America formed the Chesapeake Bay impact crater.
In Europe, the Tethys Sea has finally disappeared, while Alpine appointment closes the final rest, the Mediterranean Sea, and creates another shallow sea with island islands in the north. Although the North Atlantic is opened, land connections seem to still exist between North America and Europe because the fauna of both regions are very similar.
India began a collision with Asia, folding to start the formation of the Himalayas.
It is hypothesized that the Eocene hothouse world is caused by global warming that escapes the release of methane clathrates deep in the oceans. Clathrates is buried under mud that is disturbed as the ocean warms up. Methane (CH 4 ) has ten to twenty times the greenhouse gas effect of carbon dioxide (CO 2 ).
Flora Edit
At the beginning of the Eocene, high temperatures and warm oceans create a humid and comfortable environment, with forests spreading throughout the Earth from pole to pole. Regardless of the driest desert, Earth must be completely covered in forest.
The polar forests are wide enough. Fossils and even preserved remains of trees such as cypress swamps and dawn redwood from Eocene have been found on Ellesmere Island in the Arctic. Even at that time, Ellesmere Island was just a few degrees in latitude further south than it is now. Fossils of tree and subtropical and even tropical plants from Eocene have also been found in Greenland and Alaska. Tropical rain forests grow as far north as North America and Europe.
The palm trees grow considerably in the north such as Alaska and northern Europe at the start of the Eocene, although they become less abundant when the climate cools. Redwood Dawn is much wider too.
The cooling began in the middle of the period, and at the end the interior of the Eocene continent began to dry, with the forest thinned away in some areas. Newly evolved grasses are still confined to the banks of rivers and lakesides, and have not yet developed into plains and savannahs.
Cooling also brings about seasonal changes. Fallen trees, better able to cope with large temperature changes, are beginning to take over green tropical species. At the end of that period, forests cover most of the northern continents, including North America, Eurasia, and the Arctic, and rain forests held only in South America, Africa, India and Australia at the equator.
Antarctica, which started the Eocene flanked by warm subtropical rainforests, became colder during the period; loving hot tropical flora was swept away, and at the beginning of the Oligocene, this continent became the site of deciduous forests and extensive tundra stretches.
Fauna Edit
The oldest known fossils of most modern mammals emerged in a brief period during the early Eocene. At the beginning of the Eocene, several new mammal groups arrived in North America. These modern mammals, such as artiodactyl, perissodactyls and primates, have features like long, thin legs, legs and hands that are capable of grasping, as well as different teeth that are tailored to chew. The dwarf form commands. All members of the new mammal command were small, under 10 kg; based on tooth size ratio, Eocene mammals are only 60% of the size of the primitive Palaeocene mammal that preceded it. They are also smaller than the mammals that follow them. It is estimated that the hot Eocene temperature prefers smaller animals that are better able to manage heat.
Both groups of modern ungulates (hoofed animals) become prevalent due to the major radiation between Europe and North America, along with ungulates carnivores such as Mesonyx . Early forms of many other modern mammal orders emerged, including bats, proboscidians (elephants), primates, rodents and marsupials. Older forms of primitive mammals decline in variation and importance. An important Eocene faunal fauna of faunal fauna has been found in western North America, Europe, Patagonia, Egypt and Southeast Asia. The best known marine fauna of South Asia and the southeastern United States.
The reptile fossils of this era, such as the fossils of pythons and turtles, are abundant. The remains of Titanoboa, a snake along the school bus, are found in South America along with megafauna of other large reptiles. During the Eocene, plants and marine fauna became very modern. Many modern bird orders first appeared in Eocene.
Some of the rich fossil-rich fauna known from the Eocene, especially Baltic amber are found mainly along the southern shores of the Baltic Sea, amber from the Basins of Paris, France, the Formation of Feathers, Danish and Bembridge Marls of the Isle of Wight, England. The insects found in Eocene deposits can mostly be transmitted to modern genera, although often these genera do not occur in the current region. For example the genus of Plecia is common in fossil fauna from temperate regions, but only live in the tropics and subtropics of today.
Oceans Edit
The sea of ​​Eocene is warm and full of fish and other marine life. The first carcharinid sharks evolved, as did early marine mammals, including Basilosaurus , the early species of whales suspected to be from terrestrial animals that existed at the beginning of the Eocene, a hoof predator called mesonychids, from which Mesonyx is a member. The first siren, the elephant's relative, also evolved at this time.
Eocene-Oligocene Extinction Edit
The Eocene end is characterized by the Eocene-Oligocene extinction event, also known as Grande Coupure.
See also Edit
- Maximum Paleocene-Eocene
- Green River Formation in western North America
- List of fossil sites (with link directory)
- London Clay
- Fur Formation in Denmark
- Messel hole in Germany
- Bolca in Italy
- Wadi El Hitan in Egypt
References Edit
Further reading Edit
- Ogg, Jim; June, 2004, Overview of the Global Stratotype Section and Longitude (GSSP) https://web.archive.org/web/20060716071827/http://www.stratigraphy.org/gssp.htm Accessed 30 April 2006.
- Stanley, Steven M. The History of the Earth System. New York: W.H. Freeman and Company, 1999. ISBNÃ, 0-7167-2882-6
External links Edit
- PaleoMap Project
- Paleos Eocene page
- PBS Deep Time: Eocene
- Eocene and Oligocene Fossils
- The UPenn Fossil Forest Project, focusing on the Eocene polar forests on Ellesmere Island, Canada
- Primos Primos Basilosaurus Primitive
- Basilosaurus - a plesiosaur who does not....
- Detailed map of Tertiary Western North America
- Eocene Earth Map
- Eocene Microfossil: 60 Foraminifera images
- Epoch Eocene. (2011). In EncyclopÃÆ'Â|dia Britannica. Retrieved from http://www.britannica.com/EBchecked/topic/189322/Eocene-Epoch
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