Misplaced Pages

#334665

57-650: The boundary between the Eocene and Oligocene epochs is marked by the glaciation of Antarctica and the consequent beginning of the Late Cenozoic Ice Age . This enormous shift in climatic regime is the leading candidate for the extinction event's cause. Though ephemeral ice sheets may have existed on the Antarctic continent during parts of the Middle and Late Eocene, this interval of severe global cooling marked

114-595: A more literal translation). For a long time, the term referred only to glacial periods. Over time, this developed into the concept that they were all part of a much longer ice age. The concept that the Earth is currently in an ice age that began around 30 million years ago can be dated back to at least 1966. As a geologic time period, the Late Cenozoic Ice Age was used at least as early as 1973. The last greenhouse period began 260 million years ago during

171-631: A short-term size increase during the biotic recovery. Orthophragminid foraminifera (late Paleocene–early Eocene larger benthic foraminifera of two families, Discocyclinidae and Orbitoclypeidae) disappeared in the extinction event; in Alpine carbonates, bryozoan facies show an expansion in response to the loss of orthophragminids. The EOT is often considered to be a critical turning point in the rise of diatoms to their present-day evolutionary prominence, though this paradigm has been criticised for being based on incomplete evidence. Some sites contain evidence that

228-471: Is 70 m (230 ft) lower than it would be without the ice sheets of Antarctica and Greenland. Based on the Milankovitch cycles, the current interglacial period is predicted to be unusually long, continuing for another 25,000 to 50,000 years beyond present times. There are also high concentrations of greenhouse gases in the atmosphere from human activity, and it is almost certain to get higher in

285-405: Is a major reason for why Antarctica has such an exceptionally cold climate. The Eocene-Oligocene Boundary 33.9 million years ago was the transition from the last greenhouse period to the present icehouse climate. At this point, when ~25% more of Antarctica's surface was above sea level and able to support land-based ice sheets relative to today, CO 2 levels had dropped to 750 ppm. This

342-613: Is associated with climatic change, though the ultimate cause according to the study was not the drop in average temperatures themselves but colder winters and increased seasonality. On land, the increased seasonality brought on by this abrupt cooling caused the Grande Coupure faunal turnover in Europe. In the Ebro Basin , major aridification occurred amidst the Grande Coupure, suggesting causality. The remarkable cooling period in

399-481: Is due to the Milankovitch cycles . These are cycles that have to do with Earth's axial tilt and orbital eccentricity. Earth is currently tilted at 23.5 degrees. Over a 41,000 year cycle, the tilt oscillates between 22.1 and 24.5 degrees. When the tilt is greater (high obliquity), the seasons are more extreme. During times when the tilt is less (low obliquity), the seasons are less extreme. Less tilt also means that

456-588: Is open to interpretation because the IPCC does not specify 1850-1829 as being the present, or give any exact set of years as being the present. It also does not state whether or not they agree with the figures given by Berkeley Earth. According to the United States Geographical Survey (USGS), permanent summer ice covered about 8% of Earth's surface and 25% of the land area during the last glacial maximum. The USGS also states that sea level

513-657: Is the Quaternary , which started 2.58 million years ago. It is divided into the Pleistocene , which ended 11,700 years ago, and the current Holocene . The Quaternary is also divided into alternating stadials (colder periods) and interstadials (warmer periods) The last stadial reached its peak in the Last Glacial Maximum , between 26,000 and 20,000 years ago, and the Earth is now in an interstadial. The oscillation between glacial and interglacial periods

570-638: The Cenozoic Era which started 66 million years ago. The Cenozoic Era is part of the Phanerozoic Eon which started ~538.8 million years ago. The Late Cenozoic Ice Age , or Antarctic Glaciation , began 34 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. Six million years after

627-582: The Eocene Epoch , summer high temperatures in Antarctica were around 25 °C (77 °F). Temperatures during winter were around 10 °C (50 °F). It did not frost during the winter. The climate was so warm that trees grew in Antarctica. Arecaceae (palm trees) grew on the coastal lowlands, and Fagus (beech trees) and Pinophyta (conifers) grew on the hills just inland from

SECTION 10

#1732769811335

684-611: The Northern Hemisphere , which means that there is more ice on Earth than there was during the first 31 million years of the Late Cenozoic Ice Age. During that time, only the Antarctic ice sheets existed. Currently (as of 2012), about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice according to the USGS. The total volume of ice presently on Earth is about 33,000,000 km (7,900,000 cu mi) (as of 2004). The current sea level (as of 2009)

741-460: The Quaternary glaciation developed with decreasing mean temperatures and increasing amplitudes between glacials and interglacials. During the glacial periods of the Pleistocene, large areas of northern North America and northern Eurasia have been covered by ice sheets. In 1837, German naturalist Karl Friedrich Schimper coined the term Eiszeit , meaning ice age (or ice time for

798-478: The fourth largest verified impact structure on Earth . A large bolide impact created the 100-kilometre (62 mi) diameter crater approximately 35 million years ago during the late Eocene epoch ( Priabonian stage ). It might be linked to the Eocene–Oligocene extinction event . The structure is 300 km (190 mi) east from the outpost of Khatanga and 880 km (550 mi) northeast of

855-678: The silicate weathering of the Deccan Traps . Another factor was the opening of the Drake Passage and the creation of the Antarctic Circumpolar Current (ACC), which had the effect of creating ocean gyres that promote upwelling of cold bottom waters and diminishing heat transport to Antarctica by isolating the water around it. Likewise, the Tasmanian Gateway also opened up around the time of

912-588: The 100-kilometre (62 mi) diameter Popigai impact structure of central Siberia , which scattered debris perhaps as far as Europe. New dating of the Popigai meteor strengthens its association with the extinction. However, other studies have failed to find any association between the extinction event and any impact event. Imprints of sunspot cycles from the Bohai Bay Basin (BBB) show no evidence that any significant change in solar activity occurred across

969-556: The Antarctic ice sheets were similar in size and volume to present times. Glaciers were starting to form in the mountains of the Northern Hemisphere. Between 3.6 and 3.4 million years ago, there was a sudden but brief warming period. The glaciation of the Arctic in the Northern Hemisphere commenced with Greenland becoming increasingly covered by an ice sheet in late Pliocene (2.9-2.58 Ma ago). The current period

1026-507: The EOT. In central North America, reptiles, amphibians, and gastropods underwent drastic faunal turnover likely spurred on by a precipitous drop in mean annual temperature (MAT) over approximately 400,000 years. Malagasy lemurs experienced a significant extinction during the EOT. The Grande Coupure, or 'great break' in French , with a major European turnover in mammalian fauna about 33.5 Ma, marks

1083-454: The EOT. Ocean circulation changes were, however, not as significant in engendering cooling as the decline in p CO 2 . On top of that, the timing of the creation of the ACC is uncertain. The deepening of the calcite compensation depth increased carbonate ion storage in the ocean shortly before the onset of the Antarctic glaciation, suggesting the events may have been coupled. Evidence points to

1140-784: The Eocene–Oligocene boundary. A comparable turnover in Asian fauna has since been called the "Mongolian Remodelling". The Grande Coupure marks a break between endemic European faunas before the break and mixed faunas with a strong Asian component afterwards. Before the Grande Coupure, European faunas were dominated by anoplotheriid, xiphodontid, choeropotamid, cebochoerid, dichobunid, and amphimerycid artiodactyls, palaeotheriid perissodactyls, pseudosciurid rodents, adapid and omomyid primates, and nyctitheriids. Post-Grande Coupure artiodactyl faunas in Europe are dominated by gelocids, anthracotheriids, and entelodontids, with true rhinoceroses representing

1197-435: The Eocene–Oligocene extinction was not a sudden event but a prolonged biotic transition drawn out over as much as 6 million years. Localities near Eugene, Oregon , record a plant extinction 33.4 Ma (million years ago) and a marine invertebrate turnover 33.2 Ma; both of these turnovers post-date the supposed extinction event by hundreds of thousands of years. Late Cenozoic Ice Age The Late Cenozoic Ice Age falls within

SECTION 20

#1732769811335

1254-459: The Gamburtsev ice cap was now much larger due to the colder climate. CO 2 continued to fall and the climate continued to get colder. At 28.1 million years ago, the Gamburtsev and Transantarctic ice caps merged into a main central ice cap. At this point, ice was now covering a majority of the continent. The Dronning Maud ice cap merged with the main ice cap 27.9 million years ago. This was

1311-639: The Grande Coupure as occurring in the earliest Oligocene, with a hiatus of about 350 millennia prior to the first record of post-Grande Coupure Asian immigrant taxa. Research suggests that in the Ebro Basin of Spain, the turnover lagged the Eocene-Oligocene boundary by at most 500,000 years (500 kyr). Additionally, a second dispersal event of Asian taxa into Europe, known as the Bachitherium Dispersal Event (named after

1368-502: The Grande Coupure. It has been suggested that this was caused by climate change associated with the earliest polar glaciations and a major fall in sea levels, or by competition with taxa dispersing from Asia. However, few argue for an isolated single cause . Other possible causes are related to the impact of one or more large bolides in the Northern Hemisphere at Popigai , Toms Canyon , and Chesapeake Bay . Improved correlation of northwest European successions to global events confirms

1425-428: The Grande Coupure. However, the 1999 discovery of a mouse -sized early Oligocene omomyid , reflecting the better survival chances of small mammals, undercut the Grande Coupure paradigm . Herpetotheriids, cainotheriids, dormice, and theridomyids survived the Grande Coupure undiminished. Balkanatolia acted as a staging ground for Asian taxa that immigrated into Europe following the extinction of its own mammal fauna during

1482-458: The Homo sapiens and Neanderthals interbred. Currently, persons of European descent are two to four percent Neanderthal. With the exception of this small amount of Neanderthal DNA that exists today, Neanderthals became extinct 30,000 years ago. The Last Glacial Maximum ran from 26,500 years ago to 20,000 years ago. Although different ice sheets reached maximum extent at somewhat different times, this

1539-574: The Intergovernmental Panel On Climate Change (IPCC) estimate a slightly lower global temperature than the figures given by the Zurich University of Applied Sciences. However, these figures are not exact figures and are open more to interpretation. According to the IPCC, average global temperatures increased by 5.5 ± 1.5 °C (9.9 ± 2.7 °F) since the last glacial maximum, and the rate of warming

1596-501: The Pleistocene epoch. Between 9,000 and 5,000 years ago there was a warm period called the Holocene climatic optimum . Being in an interglacial, there is less ice than there was during the last glacial period. However, the last glacial period was just one part of the ice age that still continues today. Even though Earth is in an interglacial, there is still more ice than times outside of ice ages. There are also currently ice sheets in

1653-494: The beginning of permanent ice sheet coverage of Antarctica , and thus the end of the greenhouse climate of the Early Palaeogene. In central North America, the mean annual temperature (MAT) fell by about 8.2  ±  3.1 °C over a span of 400,000 years. Near-freezing conditions existed in central Tibet. The global cooling also correlated with marked drying conditions in low-latitudes Asia, though a causal relationship between

1710-410: The beginning of records in 1850 until 1929. The average temperature during these years was 13.8 °C (56.8 °F). When subtracting 5.5 ± 1.5 °C (9.9 ± 2.7 °F) from the 1850-1929 average, the average temperature for the last glacial maximum comes out to 8.3 ± 1.5 °C (46.9 ± 2.7 °F). This is about 6.7 ± 1.5 °C (12.0 ± 2.7 °F) colder than the 2011-2020 average. This figure

1767-484: The city of Norilsk , NNE of the Anabar Plateau . It is designated by UNESCO as a Geopark , a site of special geological heritage. There is a small possibility that the Popigai impact crater may have formed simultaneously with the approximately 35-million-year-old Chesapeake Bay and Toms Canyon impact craters. For decades, the Popigai impact structure has fascinated paleontologists and geologists , but

Eocene–Oligocene extinction event - Misplaced Pages Continue

1824-547: The coast. As the global climate became cooler, the planet was seeing a decrease in forests, and an increase in savannas. Animals were evolving to have a larger body size. Australia drifted away from Antarctica forming the Tasmanian Passage , and South America drifted away from Antarctica forming the Drake Passage . This caused the formation of the Antarctic Circumpolar Current , a current of cold water surrounding Antarctica. This current still exists today, and

1881-466: The coming decades. This will lead to higher temperatures. In 25,000 to 50,000 years, the climate will begin to cool due to the Milankovich cycles. However, the high levels of greenhouse gases are predicted to keep it from getting cold enough to build up enough ice to meet the criteria of a glacial period. This would effectively extend the current interglacial period an additional 100,000 years placing

1938-518: The end of the last phase of Eocene assemblages, the Priabonian , and the arrival in Europe of Asian species. The Grande Coupure is characterized by widespread extinctions and allopatric speciation in small isolated relict populations . It was given its name in 1910 by the Swiss palaeontologist Hans Georg Stehlin , to characterise the dramatic turnover of European mammalian fauna, which he placed at

1995-399: The entire area was completely off limits because of the diamonds found there. However, a major investigatory expedition was undertaken in 1997, which greatly advanced understanding of the structure. The impactor is suggested to have been a H chondrite asteroid based on ejecta layers from Italy, with the impactor thought to have been several kilometeres in diameter. The shock pressures from

2052-534: The final hundreds of thousands of years prior to the start of major Antarctic glaciation. This cooling reached some threshold approximately 34 million years ago, precipitating the formation of a large ice sheet in East Antarctica in response to falling carbon dioxide levels. The cause of the drop in p CO 2 was the drift of the Indian Subcontinent into equatorial latitudes, supercharging

2109-560: The formation of the East Antarctic Ice Sheet . Global refrigeration set in 22 million years ago. About 15 million years ago was the warmest part of the Late Cenozoic Ice Age, with average global temperatures around 18.4 °C (65.1 °F). Atmospheric CO 2 levels were around 700 ppm. This time period was called the Mid-Miocene Climatic Optimum (MMCO). By 14 million years ago,

2166-426: The glaciation of Antarctica occurring in two steps, with the first step, the less pronounced and more modest step of the two, taking place at the Eocene-Oligocene boundary itself. This first step is referred to as EOT-1, which occurred approximately 34.1-33.9 Ma. Carbon dioxide concentrations dropped from about 885 ppm to about 560 ppm. The Oligocene Oi-1 event, an oxygen isotope excursion that occurred around 33.55 Ma,

2223-555: The impact instantaneously transformed graphite in the ground into diamonds within a 13.6 km (8.5 mi) radius of the impact point. These diamonds are usually 0.5 to 2 mm (0.020 to 0.079 in) in diameter, though a few exceptional specimens are 10 mm (0.39 in) in size. The diamonds inherited the tabular shape of the original graphite grains and also the original crystals' delicate striations . Most modern industrial diamonds are produced synthetically . The diamond deposits at Popigai have not been mined because of

2280-665: The late Permian Period at the end of the Karoo Ice Age . It lasted all through the time of the non-avian dinosaurs during the Mesozoic Era , and ended 33.9 million years ago in the middle of the Cenozoic Era (the current Era). This greenhouse period lasted 226.1 million years. The hottest part of the last greenhouse earth was the Late Paleocene - Early Eocene. This was a hothouse period that lasted from 65 to 55 million years ago. The hottest part of this torrid age

2337-453: The middle latitudes of the Northern Hemisphere. The Toba eruption 75,000 years ago in present-day Sumatra , Indonesia has been linked to a bottleneck in the human DNA, although such a causal link remains highly controversial. 50,000 years ago, Homo sapiens migrated out of Africa. They began replacing other Hominins in Asia. They also began replacing Neanderthals in Europe. However, some of

Eocene–Oligocene extinction event - Misplaced Pages Continue

2394-477: The next glacial period 125,000 to 150,000 years in the future. Hypothetical runaway greenhouse state Tropical temperatures may reach poles Global climate during an ice age Earth's surface entirely or nearly frozen over Popigai impact structure The Popigai impact structure is the eroded remnant of an impact crater in northern Siberia , Russia. It is tied with the Manicouagan structure as

2451-548: The ocean is correlated with pronounced mammalian faunal replacement within continental Asia as well. The Asian biotic reorganization events are comparable to the Grande Coupure in Europe and the Mongolian Remodeling of mammalian communities. Another speculation points to several large meteorite impacts near this time, including those of the 40-kilometre (25 mi) diameter Chesapeake Bay crater and

2508-421: The perissodactyl fauna, eomyids, hamsters, and beavers representing the rodent fauna, and hedgehogs representing the eulipothyphlan fauna. The speciose genus Palaeotherium plus Anoplotherium and the families Xiphodontidae and Amphimerycidae were observed to disappear completely during the Grande Coupure. An element of the paradigm of the Grande Coupure was the apparent extinction of all European primates at

2565-450: The polar regions receive less light from the sun. This causes a colder global climate as ice sheets start to build up. The shape of Earth's orbit around the Sun affects the Earth's climate. Over a 100,000 year cycle, Earth oscillates between having a circular orbit to having a more elliptical orbit. From 2.58 million years ago to about 1.73 million ± 50,000 years ago, the degree of axial tilt

2622-486: The present day. This turnover has been named the Caribbean Mangrove Revolution. In the marine realm, the frequency of drilling in recovery faunas, especially among bivalves, was drastically higher than in assemblages before the extinction event, a phenomenon attributed to a high extinction rate among escalated prey taxa with highly evolved defences against predators. Veneroid bivalves experienced

2679-417: The remote location and lack of infrastructure, and are unlikely to be competitive with synthetic diamonds. Many of the diamonds at Popigai contain crystalline lonsdaleite , an allotrope of carbon that has a hexagonal lattice. Pure, laboratory-created lonsdaleite is up to 58% harder than ordinary diamonds. These types of diamonds are known as "impact diamonds" because they are thought to be produced when

2736-461: The ruminant Bachitherium ), occurred later, around 31 Ma. Unlike the Grande Coupure, which took place via Central and Northern Asia, this later dispersal occurred via a southern corridor. In the Caribbean , mangroves dominated by Pelliciera rapidly disappeared, becoming replaced by mangroves that were dominated by Rhizophora , which remains the main constituent of Caribbean mangroves in

2793-466: The start of the Late Cenozoic Ice Age, the East Antarctic Ice Sheet had formed, and 14 million years ago it had reached its current extent. In the last three million years, glaciations have spread to the northern hemisphere. It commenced with Greenland becoming increasingly covered by an ice sheet in late Pliocene (2.9-2.58 Ma ago) During the Pleistocene Epoch (starting 2.58 Ma ago),

2850-433: The two has been contradicted by some research. The equatorial seas were marked by exceptionally low palaeoproductivity in the EOT's aftermath. Deep ocean temperatures plummeted in the eastern equatorial Pacific during the EOT. A leading model of climate cooling at this time predicts a decrease in atmospheric carbon dioxide , which slowly declined over the course of the Middle to Late Eocene. Significant cooling took place in

2907-399: Was about 10 times slower than that of the 20th century. It appears that they are defining the present as the early period of instrumental records when temperatures were less affected by human activity, but they do not specify exact years, or give a temperature for the present. Berkeley Earth publishes a list of average global temperatures by year. It shows that temperatures were stable from

SECTION 50

#1732769811335

2964-408: Was about 125 m (410 ft) lower than in present times (2012). The volume of ice on Earth was around 17,000,000 cu mi (71,000,000 km ), which is about 2.1 times Earth's current volume of ice. The Earth is currently in an interglacial period called the Holocene epoch. However, there is debate as to whether it is actually a separate epoch or merely an interglacial period within

3021-664: Was the Paleocene–Eocene Thermal Maximum , 55.5 million years ago. Average global temperatures were around 30 °C (86 °F). This was only the second time that Earth reached this level of warmth since the Precambrian . The other time was during the Cambrian Period , which ran from 538.8 million years ago to 485.4 million years ago. During the early Eocene , Australia and South America were connected to Antarctica. 53 million years ago during

3078-722: Was the beginning of the Late Cenozoic Ice Age. This was when the ice sheets reached the ocean, the defining point. At 29.2 million years ago, there were three ice caps in the high elevations of Antarctica. One ice cap formed in the Dronning Maud Land . Another ice cap formed in the Gamburtsev Mountain Range . Another ice cap formed in the Transantarctic Mountains . At this point, the ice caps weren't very big yet. Most of Antarctica wasn't covered by ice. By 28.7 million years ago,

3135-411: Was the main cause of glacial and interglacial periods. Around 850,000 ± 50,000 years ago, the degree of orbital eccentricity became the main driver of glacial and interglacial periods rather than the degree of tilt, and this pattern continues to present-day. The Last Glacial Period began 115,000 years ago and ended 11,700 years ago. This time period saw the great advancement of polar ice sheets into

3192-485: Was the second major pulse of Antarctic ice sheet formation. These large climate changes have been linked to biotic turnovers. Even before the Eocene-Oligocene boundary itself, during the early Priabonian, extinction rates went up in connection with falling global temperatures. Radiolarians suffered major losses thanks to a decrease in nutrient availability in deep and intermediate waters. In the Gulf of Mexico , marine turnover

3249-426: Was the time when ice sheets overall were at maximum extent. According to Blue Marble 3000 (a video by the Zurich University of Applied Sciences), the average global temperature around 19,000 BCE (about 21,000 years ago) was 9.0 °C (48.2 °F). This is about 4.8 °C (8.6 °F) colder than the 1850-1929 average, and 6.0 °C (10.8 °F) colder than the 2011-2020 average. The figures given by

#334665