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134-903: The river originated in the North American Cordillera of California in the Mojave / Alisitos arc , between the Nevadaplano farther north and the Mexicoplano farther south. It then flowed east-northeastward between the Sevier fold-and-thrust belt to the north and the Maria fold-and-thrust belt to the south. It continued northeastward between the Kaibab and the Circle Cliffs uplift and eventually turned due north between

268-431: A large body of water is also present. In an attempt to try to mitigate the cooling polar temperatures, large lakes were proposed to mitigate seasonal climate changes. To replicate this case, a lake was inserted into North America and a climate model was run using varying carbon dioxide levels. The model runs concluded that while the lake did reduce the seasonality of the region greater than just an increase in carbon dioxide,

402-540: A marine ecosystem)—one of the largest in the Cenozoic. This event happened around 55.8 Ma, and was one of the most significant periods of global change during the Cenozoic. The middle Eocene was characterized by the shift towards a cooler climate at the end of the EECO, around 47.8 Ma, which was briefly interrupted by another warming event called the middle Eocene climatic optimum (MECO). Lasting for about 400,000 years,

536-511: A role in triggering the ETM2 and ETM3. An enhancement of the biological pump proved effective at sequestering excess carbon during the recovery phases of these hyperthermals. These hyperthermals led to increased perturbations in planktonic and benthic foraminifera , with a higher rate of fluvial sedimentation as a consequence of the warmer temperatures. Unlike the PETM, the lesser hyperthermals of

670-533: A significant amount of water vapor is released. Another requirement for polar stratospheric clouds is cold temperatures to ensure condensation and cloud production. Polar stratospheric cloud production, since it requires the cold temperatures, is usually limited to nighttime and winter conditions. With this combination of wetter and colder conditions in the lower stratosphere, polar stratospheric clouds could have formed over wide areas in Polar Regions. To test

804-775: A wide variety of climate conditions that includes the warmest climate in the Cenozoic Era , and arguably the warmest time interval since the Permian-Triassic mass extinction and Early Triassic, and ends in an icehouse climate. The evolution of the Eocene climate began with warming after the end of the Paleocene–Eocene Thermal Maximum (PETM) at 56 Ma to a maximum during the Eocene Optimum at around 49 Ma. During this period of time, little to no ice

938-873: Is 40 to 60 miles (60 to 100 km) wide, with the Sierra Nevada to the east and the Coast Ranges to the west. In northwestern Oregon, the fertile Willamette Valley lies between the Oregon Coast Range and the Cascades ; this depression continues north into Washington as the Puget Trough . The Gulf of California is a body of water that separates the Peninsular Ranges from the Sierra Madre Occidental on

1072-739: Is a mountain range on the Olympic Peninsula of western Washington in the United States . The mountains , part of the Pacific Coast Ranges , are not especially high – Mount Olympus is the highest at 7,962 ft (2,427 m) – but the western slopes of the Olympics rise directly out of the Pacific Ocean and are the wettest place in the 48 contiguous states. Most of the mountains are protected within

1206-529: Is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era . The name Eocene comes from the Ancient Greek Ἠώς ( Ēṓs , " Dawn ") and καινός ( kainós , "new") and refers to the "dawn" of modern ('new') fauna that appeared during the epoch. The Eocene spans the time from the end of

1340-797: Is an extremely arid region characterized by basin and range topography. The Colorado Plateau is an area of high desert located in Arizona , New Mexico , Colorado , and Utah , bisected by the Colorado River which flows westward through the southern part, and the Green River which flows south from the northernmost part of the plateau. The Green is a tributary of the Colorado, the confluence being west of Moab, Utah in Canyonlands National Park. The Mexican Plateau

1474-459: Is an important factor in the creation of the primary Type II polar stratospheric clouds that were created in the early Eocene. Since water vapor is the only supporting substance used in Type II polar stratospheric clouds, the presence of water vapor in the lower stratosphere is necessary where in most situations the presence of water vapor in the lower stratosphere is rare. When methane is oxidized,

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1608-638: Is considered to be primarily due to carbon dioxide increases, because carbon isotope signatures rule out major methane release during this short-term warming. A sharp increase in atmospheric carbon dioxide was observed with a maximum of 4,000 ppm: the highest amount of atmospheric carbon dioxide detected during the Eocene. Other studies suggest a more modest rise in carbon dioxide levels. The increase in atmospheric carbon dioxide has also been hypothesised to have been driven by increased seafloor spreading rates and metamorphic decarbonation reactions between Australia and Antarctica and increased amounts of volcanism in

1742-594: Is conventionally divided into early (56–47.8 Ma), middle (47.8–38 Ma), and late (38–33.9 Ma) subdivisions. The corresponding rocks are referred to as lower, middle, and upper Eocene. The Ypresian Stage constitutes the lower, the Priabonian Stage the upper; and the Lutetian and Bartonian stages are united as the middle Eocene. The Western North American floras of the Eocene were divided into four floral "stages" by Jack Wolfe ( 1968 ) based on work with

1876-577: Is located in southern British Columbia and northern Washington . The Interior Plateau also includes the Quesnel Highland , Fraser Plateau , Nechako Plateau , and McGregor Plateau . California's Central Valley is a large, flat valley that dominates the central portion of California , stretching inland and parallel to the Pacific Ocean coast. Its northern half is referred to as the Sacramento Valley , and its southern half as

2010-606: Is one of six distinct physiographic sections of the Basin and Range Province , which in turn is part of the Intermontane Plateaus physiographic division. It is a large arid-to-semiarid plateau that occupies much of northern and central Mexico . Averaging 1,825 m (5,988 ft) above sea level, it extends from the United States border in the north to the Trans-Mexican Volcanic Belt in

2144-585: Is possible that the river created an early Grand Canyon during the Campanian or the Paleocene . The California River has been proposed to explain the origin of the deltaic Colton Formation , as it has a high volume and similar source rocks are rare in the area of the Uinta Basin. Rock formations of similar origin occur in southeastern California and southwestern Arizona and may have been located along

2278-720: Is short lived, as benthic oxygen isotope records indicate a return to cooling at ~40 Ma. At the end of the MECO, the MLEC resumed. Cooling and the carbon dioxide drawdown continued through the late Eocene and into the Eocene–Oligocene transition around 34 Ma. The post-MECO cooling brought with it a major aridification trend in Asia, enhanced by retreating seas. A monsoonal climate remained predominant in East Asia. The cooling during

2412-535: Is the period of time when the Antarctic ice sheet began to rapidly expand. Greenhouse gases, in particular carbon dioxide and methane , played a significant role during the Eocene in controlling the surface temperature. The end of the PETM was met with very large sequestration of carbon dioxide into the forms of methane clathrate , coal , and crude oil at the bottom of the Arctic Ocean , that reduced

2546-574: The Americas . The North American Cordillera covers an extensive area of mountain ranges , intermontane basins , and plateaus in Western and Northwestern Canada , Western United States , and Mexico , including much of the territory west of the Great Plains . The precise boundaries of this cordillera and its subregions, as well as the names of its various features, may differ depending on

2680-637: The Arctic Ocean . A drainage through the Little Colorado River valley towards the San Juan Basin is also possible but there is no evidence, and petrological information on sediments excludes that the Piceance Creek Basin as an endpoint of California River waters. This river system was of similar scale to the present-day Colorado River -Green River system, but with opposite direction. Analogies have been drawn between

2814-684: The Cascade Range and the Rocky Mountains , cut through by the Columbia River . In one of various usages, the term " Columbia Basin " refers to more or less the same area as the Columbia Plateau. The Basin and Range province covers most of the state of Nevada and parts of the states of Arizona , California , Idaho , New Mexico , Oregon , Texas , Utah , and Wyoming , as well as much of northern Mexico . It

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2948-713: The Coast Range Arc whereas the metamorphic formed when intruding magma heated the surrounding rock to produce schist . The Insular Mountains extend from Vancouver Island in the south to Haida Gwaii in the north on the British Columbia Coast . It contains two main mountain ranges, the Vancouver Island Ranges on Vancouver Island and the Queen Charlotte Mountains on Haida Gwaii. The Olympic Mountains

3082-686: The Grande Coupure (the "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 what is now Chesapeake Bay . As with other geologic periods , the strata that define the start and end of the epoch are well identified, though their exact dates are slightly uncertain. The term "Eocene" is derived from Ancient Greek Ἠώς ( Ēṓs ) meaning "Dawn", and καινός kainos meaning "new" or "recent", as

3216-725: The Hazelton Mountains and Coast Range to the west and northwest. Within the Interior plateau, the Shuswap Highland consists of a portion of the foothills between the Thompson Plateau and Bonaparte Plateau on the west, and the Monashee Mountains and Cariboo Mountains on the east and northeast. Also within the Interior plateau, the Thompson Plateau forms the southern portion of

3350-963: The Interior Plains to the east, and over the Great Basin to the west, and extend south to the Rio Grande in New Mexico. The United States definition of the Rockies includes the Cabinet and Salish Mountains of Idaho and Montana, whereas their counterparts north of the Kootenai River , the Columbia Mountains , are sometimes considered a separate system lying to the west of the huge Rocky Mountain Trench which runs

3484-786: The Interior Plateau . The southernmost extends into the Washington, where it is named by the American spelling Okanogan Highland (and was the first-named of these groupings). The Cascade Range (called the Cascade Mountains in Canada) extends from northern California in the United States to British Columbia , Canada. It consists of non-volcanic and volcanic mountains: all of the known historic eruptions in

3618-565: The Liard River , just south of the British Columbia – Yukon border near Watson Lake, Yukon . The trench bottom is 3 to 16 km (2 to 10 miles) wide and ranges from 600 to 900 m (2,000 to 3,000 ft) above sea level. The general orientation of the Trench is almost uniformly pointing north. Some of its topography has been carved into glacial valleys , but it is primarily a byproduct of faulting . The Trench separates

3752-488: The Mexican mainland. The Gulf of California is 1,126 km (700 miles) long and 48 to 241 km (30 to 150 miles) wide, with an area of 177,000 km (68,000 sq mi), a mean depth of 818.08 m (2,684.0 ft), and a volume of 145,000 km (35,000 cu mi). The Rocky Mountain Trench is a large valley that extends approximately 1,600 km (990 mi) from Flathead Lake , Montana , to

3886-713: The Middle Eocene Climatic Optimum (MECO). At around 41.5 Ma, stable isotopic analysis of samples from Southern Ocean drilling sites indicated a warming event for 600,000 years. A similar shift in carbon isotopes is known from the Northern Hemisphere in the Scaglia Limestones of Italy. Oxygen isotope analysis showed a large negative change in the proportion of heavier oxygen isotopes to lighter oxygen isotopes, which indicates an increase in global temperatures. The warming

4020-756: The Okanagan Range , which lies along the Cascades' northeastern margin, separated by the Similkameen River . The Sierra Nevada forms an inland mountain spine of northern California, extending from the terminus of the Cascade Range south of Lassen Peak southwards along the east flank of the Central Valley of California to the Transverse Ranges , forming a mountain region of complex terrain and varied geology which separates

4154-414: The Pacific Coast Ranges in the west, the Nevadan belt in the middle (including the Sierra Nevada ), and the Laramide belt in the east (including the Rocky Mountains ). These three orogenic belts (also called "orogens") arose due to the engagement of tectonic plates which deformed the Earth's lithosphere (crust and uppermost mantle). For example, the Laramide orogeny changed the topography of

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4288-408: The Paleocene Epoch to the beginning of the Oligocene Epoch. The start of the Eocene is marked by a brief period in which the concentration of the carbon isotope C in the atmosphere was exceptionally low in comparison with the more common isotope C . The average temperature of Earth at the beginning of the Eocene was about 27 degrees Celsius. The end is set at a major extinction event called

4422-411: The Puget Group fossils of King County, Washington . The four stages, Franklinian , Fultonian , Ravenian , and Kummerian covered the Early Eocene through early Oligocene, and three of the four were given informal early/late substages. Wolfe tentatively deemed the Franklinian as Early Eocene, the Fultonian as Middle Eocene, the Ravenian as Late, and the Kummerian as Early Oligocene. The beginning of

4556-423: The Rocky Mountains on its east from the Columbia Mountains and the Cassiar Mountains on its west. It is up to 25 km (16 miles) wide, if measured peak-to-peak. For convenience the Rocky Mountain Trench may be divided into northern and southern sections. The dividing point reflects the separation of north and easterly flows to the Arctic Ocean versus south and westerly flows to the Pacific Ocean. A break in

4690-454: The San Joaquin Valley . The two-halves meet at the huge Sacramento-San Joaquin River Delta of the Sacramento and San Joaquin Rivers, which along with their tributaries drain the majority of the valley and flow into San Francisco Bay . The Central Valley covers an area of approximately 22,500 square miles (58,000 km ), making it slightly smaller than the state of West Virginia and about 13.7% of California's total area. The Central Valley

4824-428: The Sierra Madre Occidental , and the Sierra Madre Oriental further east, surround the Mexican Plateau . To the west of the Sierra Madre Occidental, the Peninsular Ranges border the Pacific Ocean, and the Sierra Madre del Sur is the southern extension of the Peninsular Ranges. Sierra Madre means "Mother Range" in Spanish. The Nevadan belt runs up and down the middle of the North American Cordillera. Therefore,

4958-407: The Thompson Plateau in a less rugged fashion than in most other parts of the range. The North Cascades are very different in character from the series of high volcanic stratovolcanoes from Rainier southwards to Mount Shasta and Lassen Peak , and are more severely alpine and steeply rugged, particularly the Skagit Range . Inland portions of the range are dryland and plateau-like in character, e.g.

5092-400: The Turonian . During the Cretaceous and Paleogene , the beginning Laramide orogeny disrupted drainages in what today are the western United States, forming several closed basins where drainage ponded from as far as California . The California River existed in the Paleocene and Eocene. During the Paleocene , the collapse of the continental borderland and the Laramide orogeny reversed

5226-404: The Yukon Territory at Champagne Pass and Chilkat Pass northwest of Haines, Alaska . The Saint Elias Mountains lie to their west and northwest, while the Yukon Ranges and Yukon Basin lie to their north. On the inland side of the Boundary Ranges are the Tahltan and Tagish Highlands and also the Skeena Mountains , part of the Interior Mountains system, which also extend southwards on

5360-415: The Yukon , Canada. This range has an area of 364,710 km (140,820 sq mi). The Coast Mountains run from the lower Fraser River and the Fraser Canyon northwestward, separating the Interior Plateau from the Pacific Ocean. Their coastal flank is characterized by an intense network of fjords and associated islands, very similar to the Norwegian coastline , while their inland side against

5494-406: The amount of oxygen in the Earth's atmosphere more or less doubled. During the warming in the early Eocene between 55 and 52 Ma, there were a series of short-term changes of carbon isotope composition in the ocean. These isotope changes occurred due to the release of carbon from the ocean into the atmosphere that led to a temperature increase of 4–8 °C (7.2–14.4 °F) at the surface of

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5628-417: The proxy data . Using all different ranges of greenhouse gasses that occurred during the early Eocene, models were unable to produce the warming that was found at the poles and the reduced seasonality that occurs with winters at the poles being substantially warmer. The models, while accurately predicting the tropics, tend to produce significantly cooler temperatures of up to 20 °C (36 °F) colder than

5762-473: The southeast United States . After the Paleocene–Eocene Thermal Maximum, members of the Equoidea arose in North America and Europe, giving rise to some of the earliest equids such as Sifrhippus and basal European equoids such as the palaeothere Hyracotherium . Some of the later equoids were especially species-rich; Palaeotherium , ranging from small to very large in size, is known from as many as 16 species. Established large-sized mammals of

5896-479: The Azolla Event. This cooling trend at the end of the EECO has also been proposed to have been caused by increased siliceous plankton productivity and marine carbon burial, which also helped draw carbon dioxide out of the atmosphere. Cooling after this event, part of a trend known as the Middle-Late Eocene Cooling (MLEC), continued due to continual decrease in atmospheric carbon dioxide from organic productivity and weathering from mountain building . Many regions of

6030-413: The California River and the present-day Ili River in Central Asia, both in terms of its geomorphology and the sizes and shapes of their deltas and terminal lakes . The river had a high but variable discharge, which has been documented from the delta deposits. The age of the Western Grand Canyon is controversial, with evidence both of an old Mesozoic and a young Neozoic age. In the former case, it

6164-401: The California coast (the Transverse Ranges, Peninsular Ranges and the Klamath Mountains are not included). The Sierra Madre del Sur mountains in southwestern Mexico form a southern extension of the Peninsular Ranges of Baja California . The Peninsular Ranges are separated from the Sierra Madre del Sur by an expanse of ocean. The Nevadan belt is located between the Pacific coast belt and

6298-414: The Central Valley from the Great Basin to the east. The mean height of the mountain summits in the Sierra Nevada gradually increases from north to south, culminating at Mount Whitney (14,505 feet (4,421 m)), the highest point in the contiguous United States . From east to west, the Sierra is wedge-shaped: the west slope gradually rises and the east slope forms a steep escarpment , particularly so in

6432-404: The EECO. Relative to present-day values, bottom water temperatures are 10 °C (18 °F) higher according to isotope proxies. With these bottom water temperatures, temperatures in areas where deep water forms near the poles are unable to be much cooler than the bottom water temperatures. An issue arises, however, when trying to model the Eocene and reproduce the results that are found with

6566-404: The Early Eocene had negligible consequences for terrestrial mammals. These Early Eocene hyperthermals produced a sustained period of extremely hot climate known as the Early Eocene Climatic Optimum (EECO). During the early and middle EECO, the superabundance of the euryhaline dinocyst Homotryblium in New Zealand indicates elevated ocean salinity in the region. One of the unique features of

6700-440: The Earth including the poles. Tropical forests extended across much of modern Africa, South America, Central America, India, South-east Asia and China.  Paratropical forests grew over North America, Europe and Russia, with broad-leafed evergreen and broad-leafed deciduous forests at higher latitudes. Polar forests were quite extensive. Fossils and even preserved remains of trees such as swamp cypress and dawn redwood from

6834-409: The Eocene and Neogene for the Miocene and Pliocene in 1853. After decades of inconsistent usage, the newly formed International Commission on Stratigraphy (ICS), in 1969, standardized stratigraphy based on the prevailing opinions in Europe: the Cenozoic Era subdivided into the Tertiary and Quaternary sub-eras, and the Tertiary subdivided into the Paleogene and Neogene periods. In 1978, the Paleogene

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6968-457: The Eocene have been found on Ellesmere Island in the Arctic . Even at that time, Ellesmere Island was only a few degrees in latitude further south than it is today. Fossils of subtropical and even tropical trees and plants from the Eocene also have been found in Greenland and Alaska . Tropical rainforests grew as far north as northern North America and Europe . Palm trees were growing as far north as Alaska and northern Europe during

7102-503: The Eocene include the Uintatherium , Arsinoitherium , and brontotheres , in which the former two, unlike the latter, did not belong to ungulates but groups that became extinct shortly after their establishments. Large terrestrial mammalian predators had already existed since the Paleocene, but new forms now arose like Hyaenodon and Daphoenus (the earliest lineage of a once-successful predatory family known as bear dogs ). Entelodonts meanwhile established themselves as some of

7236-544: The Eocene's climate as mentioned before was the equable and homogeneous climate that existed in the early parts of the Eocene. A multitude of proxies support the presence of a warmer equable climate being present during this period of time. A few of these proxies include the presence of fossils native to warm climates, such as crocodiles , located in the higher latitudes, the presence in the high latitudes of frost-intolerant flora such as palm trees which cannot survive during sustained freezes, and fossils of snakes found in

7370-426: The Eocene, and compression was replaced with crustal extension that ultimately gave rise to the Basin and Range Province . The Kishenehn Basin, around 1.5 km in elevation during the Lutetian, was uplifted to an altitude of 2.5 km by the Priabonian. Huge lakes formed in the high flat basins among uplifts, resulting in the deposition of the Green River Formation lagerstätte . At about 35 Ma, an asteroid impact on

7504-399: The Eocene-Oligocene transition is the timing of the creation of the circulation is uncertain. For Drake Passage , sediments indicate the opening occurred ~41 Ma while tectonics indicate that this occurred ~32 Ma. Solar activity did not change significantly during the greenhouse-icehouse transition across the Eocene-Oligocene boundary. During the early-middle Eocene, forests covered most of

7638-430: The Interior Plains area, is the Rocky Mountain System, then the Intermontane Basins and Ranges, and in the southern part of the state are the Pacific Mountains and Valleys. In the Alaska panhandle , the mainland mountain ranges and offshore islands (the Alexander Archipelago ) are extensions of respective ranges further south. In Canada, the North American Cordillera is usually divided into three physiographic regions:

7772-408: The Interior Plateau. It is bordered on the south by the Canadian Cascades and on the north by the Thompson River . The Okanagan Highland is the part of the Interior Plateau to the east of the Thompson Plateau, and is bounded by the Okanagan River on the west, the Shuswap River on the north, and the Kettle River on the east side. The Okanagan Highland is described as being a hilly plateau, and

7906-439: The Kummerian was refined by Gregory Retallack et al (2004) as 40 Mya, with a refined end at the Eocene-Oligocene boundary where the younger Angoonian floral stage starts. During the Eocene, the continents continued to drift toward their present positions. At the beginning of the period, Australia and Antarctica remained connected, and warm equatorial currents may have mixed with colder Antarctic waters, distributing

8040-405: The Laramide belt. Nevada means "snow-covered" in Spanish. In Canada, the Northern Interior Mountains are a northern extension of the Columbia Mountains. They include the Hazelton Mountains , Cassiar Mountains , Omineca Mountains , and Skeena Mountains . The Columbia Mountains are a designation in British Columbia for a group of four ranges lying between the Rocky Mountain Trench (to

8174-426: The MECO was responsible for a globally uniform 4° to 6°C warming of both the surface and deep oceans, as inferred from foraminiferal stable oxygen isotope records. The resumption of a long-term gradual cooling trend resulted in a glacial maximum at the late Eocene/early Oligocene boundary. The end of the Eocene was also marked by the Eocene–Oligocene extinction event , also known as the Grande Coupure . The Eocene

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8308-625: The MECO. Both groups of modern ungulates (hoofed animals) became prevalent because of a major radiation between Europe and North America, along with carnivorous ungulates like Mesonyx . Early forms of many other modern mammalian orders appeared, including horses (most notably the Eohippus ), bats , proboscidians (elephants), primates, and rodents . Older primitive forms of mammals declined in variety and importance. Important Eocene land fauna fossil remains have been found in western North America, Europe, Patagonia , Egypt , and southeast Asia . Marine fauna are best known from South Asia and

8442-405: The North American continent, and it reduced the seasonal variation of temperature by up to 75%. While orbital parameters did not produce the warming at the poles, the parameters did show a great effect on seasonality and needed to be considered. Another method considered for producing the warm polar temperatures were polar stratospheric clouds . Polar stratospheric clouds are clouds that occur in

8576-415: The PETM event in the sea floor or wetland environments. For contrast, today the carbon dioxide levels are at 400 ppm or 0.04%. During the early Eocene, methane was another greenhouse gas that had a drastic effect on the climate. Methane has 30 times more of a warming effect than carbon dioxide on a 100-year scale (i.e., methane has a global warming potential of 29.8±11). Most of the methane released to

8710-428: The Pacific Coast Ranges, the Central Valley , the Sierra Nevada, the Basin and Range Province (forming many narrow ranges and valleys), the Colorado Plateau , and the Rocky Mountains. In the United States, another major feature of the Cordillera is the Columbia Plateau , located north of California between the Cascade Range – which is a northern extension of the Sierra Nevada – and the Rocky Mountains. In Mexico,

8844-477: The Rocky Mountains in the United States. To the west of the Monashees and Cariboos, there are three intermediary upland areas which are transitional between the mountain ranges and the plateaus flanking the Fraser and Thompson Rivers . These – the Quesnel , Shuswap and Okanagan Highlands , are sometimes considered as being part of the neighbouring ranges rather than the plateaus and are often spoken of that way locally but are formally designated as being part of

8978-449: The Selkirks and Monashees. The southward extension of the Selkirks, Purcells and Monashees into the United States are reckoned to be part of the Rocky Mountains and the designation Columbia Mountains is not used there (the Purcells, also, go by the name "Percell Mountains" in the United States). The Salish and Cabinet Mountains south of the Kootenai River are essentially part of the same landform, but are officially designated part of

9112-439: The Southern California coast the Channel Islands archipelago of the Santa Monica Mountains extends for 160 miles (260 km). In southern Alaska, the primary mountain ranges are the Alaska Range , Wrangell Mountains , Saint Elias Mountains , Kenai Mountains , Chugach Mountains , and Talkeetna Mountains . The Yukon Ranges comprise the mountains in the southeastern part of the U.S. state of Alaska and most of

9246-403: The Uncompahgre and San Rafael swells. The course of the river extended over 1,000 kilometres (620 mi). Ancestral Little Colorado River was a tributary, and the ancestral Mogollon Highlands also drained in this river system. The river ended in the Uinta Basin and Lake Uinta in present-day Utah roughly where the Green River exits the basin, forming a river delta that today comprises

9380-477: The United States that are considered part of the Rocky Mountains, and therefore the Columbia Mountains are often treated as being part of the Rockies. The Selkirks and Purcells lie entirely within the basin of the Columbia River, while the Monashees lie to the river's west on its southward course from its Big Bend and are flanked on the west by the basin of the Thompson and Okanagan Rivers . There are many named subranges of all four subgroupings, particularly in

9514-405: The actual determined temperature at the poles. This error has been classified as the "equable climate problem". To solve this problem, the solution would involve finding a process to warm the poles without warming the tropics. Some hypotheses and tests which attempt to find the process are listed below. Due to the nature of water as opposed to land, less temperature variability would be present if

9648-410: The addition of a large lake was unable to reduce the seasonality to the levels shown by the floral and faunal data. The transport of heat from the tropics to the poles, much like how ocean heat transport functions in modern times, was considered a possibility for the increased temperature and reduced seasonality for the poles. With the increased sea surface temperatures and the increased temperature of

9782-422: The amount of polar stratospheric clouds. While the polar stratospheric clouds could explain the reduction of the equator to pole temperature gradient and the increased temperatures at the poles during the early Eocene, there are a few drawbacks to maintaining polar stratospheric clouds for an extended period of time. Separate model runs were used to determine the sustainability of the polar stratospheric clouds. It

9916-456: The atmosphere during this period of time would have been from wetlands, swamps, and forests. The atmospheric methane concentration today is 0.000179% or 1.79 ppmv . As a result of the warmer climate and the sea level rise associated with the early Eocene, more wetlands, more forests, and more coal deposits would have been available for methane release. If we compare the early Eocene production of methane to current levels of atmospheric methane,

10050-528: The atmosphere may have been more important. Once the Antarctic region began to cool down, the ocean surrounding Antarctica began to freeze, sending cold water and icefloes north and reinforcing the cooling. The northern supercontinent of Laurasia began to fragment, as Europe , Greenland and North America drifted apart. In western North America, the Laramide Orogeny came to an end in

10184-524: The atmospheric carbon dioxide. This event was similar in magnitude to the massive release of greenhouse gasses at the beginning of the PETM, and it is hypothesized that the sequestration was mainly due to organic carbon burial and weathering of silicates. For the early Eocene there is much discussion on how much carbon dioxide was in the atmosphere. This is due to numerous proxies representing different atmospheric carbon dioxide content. For example, diverse geochemical and paleontological proxies indicate that at

10318-697: The bounds of the Olympic National Park . The Oregon Coast Range is the part of the Coast Range system that is denoted as between the mouth of the Columbia River and the Middle Fork Coquille River . It is about 200 miles (320 km) long. The highest peak is Marys Peak , at 4,101 ft (1,250 m). The California Coast Ranges are one of the eleven traditional geomorphic provinces of California. This province includes several – but not all – mountain ranges along

10452-756: The central Rocky Mountains and adjoining Laramide regions (from central Montana to central New Mexico) during the Late Cretaceous 80 million years ago. Prior to this time the Rocky Mountain region was occupied by a broad basin. Further topographical evolution occurred during the Eocene (55–50 million years ago) and Oligocene (34–23 million years ago), but since that time the region has been relatively stable. Generally speaking, it will be convenient here to consider these three belts going west to east, and north to south. In Alaska , south of

10586-785: The contiguous United States have been from the volcanoes of the Cascade Volcanic Arc . The highest peak in the Cascade Range is Mount Rainier (14,409 feet (4,392 m)), a stratovolcano . The small portion of the Cascade Range in Canada is called the Cascade Mountains or Canadian Cascades, and in its southwestern area is similar in terrain to the area north of Glacier Peak , known as the North Cascades , and its northern and eastern extremities verge on

10720-799: The course of the California River. In the Eocene , the drainage divide migrated northeastward. North American Cordillera The North American Cordillera , sometimes also called the Western Cordillera of North America , the Western Cordillera , or the Pacific Cordillera , is the North American portion of the American Cordillera , the mountain chain system along the Pacific coast of

10854-413: The decline into an icehouse climate and the rapid expansion of the Antarctic ice sheet . The transition from a warming climate into a cooling climate began at around 49 Ma. Isotopes of carbon and oxygen indicate a shift to a global cooling climate. The cause of the cooling has been attributed to a significant decrease of >2,000 ppm in atmospheric carbon dioxide concentrations. One proposed cause of

10988-437: The deep ocean water during the early Eocene, one common hypothesis was that due to these increases there would be a greater transport of heat from the tropics to the poles. Simulating these differences, the models produced lower heat transport due to the lower temperature gradients and were unsuccessful in producing an equable climate from only ocean heat transport. While typically seen as a control on ice growth and seasonality,

11122-410: The deep ocean. On top of that, MECO warming caused an increase in the respiration rates of pelagic heterotrophs , leading to a decreased proportion of primary productivity making its way down to the seafloor and causing a corresponding decline in populations of benthic foraminifera. An abrupt decrease in lakewater salinity in western North America occurred during this warming interval. This warming

11256-436: The definitions in each country or jurisdiction, and also depending on the scientific field; this cordillera is a particularly prominent subject in the scientific field of physical geography . The North American Cordillera extends from the U.S. state of Alaska to the southern border of Mexico , and includes some of the highest peaks on the continent. Its mountain ranges generally run north to south along three main belts:

11390-411: The early Eocene would have produced triple the amount of methane. The warm temperatures during the early Eocene could have increased methane production rates, and methane that is released into the atmosphere would 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

11524-901: The early Eocene, although they became less abundant as the climate cooled. Dawn redwoods were far more extensive as well. The earliest definitive Eucalyptus fossils were dated from 51.9 Ma, and were found in the Laguna del Hunco deposit in Chubut province in Argentina . Cooling began mid-period, and by the end of the Eocene continental interiors had begun to dry, with forests thinning considerably in some areas. The newly evolved grasses were still confined to river banks and lake shores, and had not yet expanded into plains and savannas . The cooling also brought seasonal changes. Deciduous trees, better able to cope with large temperature changes, began to overtake evergreen tropical species. By

11658-775: The east) and the Interior Plateau (to the west). These ranges are the Cariboo Mountains , which are the northernmost and sometimes considered to be part of the Interior Plateau, the Selkirk Mountains , the Purcell Mountains , and the Monashee Mountains . The Columbia Mountains are classified as being in Canada's interior system, rather than its eastern system. However, the Columbia Mountains are an extension of mountains in

11792-639: The eastern coast of North America formed the Chesapeake Bay impact crater . The Tethys Ocean finally closed with the collision of Africa and Eurasia, while the uplift of the Alps isolated its final remnant, the Mediterranean , and created another shallow sea with island archipelagos to the north. Planktonic foraminifera in the northwestern Peri-Tethys are very similar to those of the Tethys in

11926-544: The end of the period, deciduous forests covered large parts of the northern continents, including North America, Eurasia and the Arctic, and rainforests held on only in equatorial South America , Africa , India and Australia . Antarctica began the Eocene fringed with a warm temperate to sub-tropical rainforest . Pollen found in Prydz Bay from the Eocene suggest taiga forest existed there. It became much colder as

12060-508: The enhanced burial of azolla could have had a significant effect on the world atmospheric carbon content and may have been the event to begin the transition into an ice house climate. The azolla event could have led to a draw down of atmospheric carbon dioxide of up to 470 ppm. Assuming the carbon dioxide concentrations were at 900 ppmv prior to the Azolla Event they would have dropped to 430 ppmv, or 30 ppmv more than they are today, after

12194-472: The enhanced carbon dioxide levels found in the early Eocene. The isolation of the Arctic Ocean, evidenced by euxinia that occurred at this time, led to stagnant waters and as the azolla sank to the sea floor, they became part of the sediments on the seabed and effectively sequestered the carbon by locking it out of the atmosphere for good. The ability for the azolla to sequester carbon is exceptional, and

12328-689: The epoch saw the dawn of recent, or modern, life. Scottish geologist Charles Lyell (ignoring the Quaternary) divided the Tertiary Epoch into the Eocene, Miocene , Pliocene , and New Pliocene ( Holocene ) Periods in 1833. British geologist John Phillips proposed the Cenozoic in 1840 in place of the Tertiary, and Austrian paleontologist Moritz Hörnes introduced the Paleogene for

12462-494: The expansion of the ice sheet was the creation of the Antarctic Circumpolar Current . The creation of the Antarctic circumpolar current would isolate the cold water around the Antarctic, which would reduce heat transport to the Antarctic along with creating ocean gyres that result in the upwelling of colder bottom waters. The issue with this hypothesis of the consideration of this being a factor for

12596-399: The heat around the planet and keeping global temperatures high. When Australia split from the southern continent around 45 Ma, the warm equatorial currents were routed away from Antarctica. An isolated cold water channel developed between the two continents. However, modeling results call into question the thermal isolation model for late Eocene cooling, and decreasing carbon dioxide levels in

12730-402: The hot house to the cold house. The beginning of the Eocene is marked by the Paleocene–Eocene Thermal Maximum , a short period of intense warming and ocean acidification brought about by the release of carbon en masse into the atmosphere and ocean systems, which led to a mass extinction of 30–50% of benthic foraminifera (single-celled species which are used as bioindicators of the health of

12864-588: The initial stages of the opening of the Drake Passage ~38.5 Ma was not global, as evidenced by an absence of cooling in the North Atlantic. During the cooling period, benthic oxygen isotopes show the possibility of ice creation and ice increase during this later cooling. The end of the Eocene and beginning of the Oligocene is marked with the massive expansion of area of the Antarctic ice sheet that

12998-781: The inland side of the Kitimat Ranges . The terrain of the main spine of the Coast Mountains is typified by heavy glaciation, including several very large icefields of varying elevation. Of the three subdivisions, the Pacific Ranges are the highest and are crowned by Mount Waddington , while the Boundary Ranges contain the largest icefields, the Juneau Icefield being the largest. The Kitimat Ranges are lower and less glacier-covered than either of

13132-633: The intermontane areas of the cordillera can be divided up into the areas east of the Nevadan belt, and those west of the Nevadan belt. The Pacific Coast Ranges, comprising the Pacific Coast Belt, parallel the North American Pacific Coast, and comprise several mountain systems. Along the British Columbia and Alaska coast, the mountains intermix with the sea in a complex maze of fjords , with thousands of islands. Off

13266-516: The largest omnivores. The first nimravids , including Dinictis , established themselves as amongst the first feliforms to appear. Their groups became highly successful and continued to live past the Eocene. Basilosaurus is a very well-known Eocene whale , but whales as a group had become very diverse during the Eocene, which is when the major transitions from being terrestrial to fully aquatic in cetaceans occurred. The first sirenians were evolving at this time, and would eventually evolve into

13400-451: The length of British Columbia. The Sierra Madre Oriental mountains in eastern Mexico are a southern extension of the Rocky Mountains . The Sierra Madre Oriental spans about 1,000 km (600 miles). Mexico's Gulf Coastal Plain lies to the east of the range, between the mountains and the Gulf of Mexico coast. The Mexican Plateau lies to the west of the range. The Nevadan belt runs down

13534-556: The lower stratosphere at very low temperatures. Polar stratospheric clouds have a great impact on radiative forcing. Due to their minimal albedo properties and their optical thickness, polar stratospheric clouds act similar to a greenhouse gas and trap outgoing longwave radiation. Different types of polar stratospheric clouds occur in the atmosphere: polar stratospheric clouds that are created due to interactions with nitric or sulfuric acid and water (Type I) or polar stratospheric clouds that are created with only water ice (Type II). Methane

13668-610: The maximum of global warmth the atmospheric carbon dioxide values were at 700–900 ppm , while model simulations suggest a concentration of 1,680 ppm fits best with deep sea, sea surface, and near-surface air temperatures of the time. Other proxies such as pedogenic (soil building) carbonate and marine boron isotopes indicate large changes of carbon dioxide of over 2,000 ppm over periods of time of less than 1 million years. This large influx of carbon dioxide could be attributed to volcanic out-gassing due to North Atlantic rifting or oxidation of methane stored in large reservoirs deposited from

13802-530: The members of the new mammal orders were small, under 10 kg; based on comparisons of tooth size, Eocene mammals were only 60% of the size of the primitive Palaeocene mammals that preceded them. They were also smaller than the mammals that followed them. It is assumed that the hot Eocene temperatures favored smaller animals that were better able to manage the heat. Rodents were widespread. East Asian rodent faunas declined in diversity when they shifted from ctenodactyloid-dominant to cricetid–dipodid-dominant after

13936-480: The methane, as well as yielding infrared radiation. The breakdown of methane in an atmosphere containing oxygen produces carbon monoxide, water vapor and infrared radiation. The carbon monoxide is not stable, so it eventually becomes carbon dioxide and in doing so releases yet more infrared radiation. Water vapor traps more infrared than does carbon dioxide. At about the beginning of the Eocene Epoch (55.8–33.9 Ma)

14070-569: The middle Lutetian but become completely disparate in the Bartonian, indicating biogeographic separation. Though the North Atlantic was opening, a land connection appears to have remained between North America and Europe since the faunas of the two regions are very similar. Eurasia was separated in three different landmasses 50 Ma; Western Europe, Balkanatolia and Asia. About 40 Ma, Balkanatolia and Asia were connected, while Europe

14204-629: The middle of the North American Cordillera. Therefore, the intermontane areas can be divided up into the areas east of the Nevadan belt, and those west of the Nevadan belt. The Interior Plateau is the northern continuation of the Columbia Plateau , and covers much of inland British Columbia . The Cariboo Mountains and Monashee Mountains lie to the east, the Canadian Cascades are to the southwest, and

14338-462: The modern mammal orders appear within a brief period during the early Eocene . At the beginning of the Eocene, several new mammal groups arrived in North America. These modern mammals, like artiodactyls , perissodactyls , and primates , had features like long, thin legs , feet, and hands capable of grasping, as well as differentiated teeth adapted for chewing. Dwarf forms reigned. All

14472-822: The northern flank of the lower Yukon River basin, separating it from Alaska's North Slope region, facing the Beaufort Sea . The Brooks Range is considered part of (or an extension of) the Rockies . South of the Brooks Range are the Mackenzie Mountains , and the Canadian Rockies . In the Rocky Mountains , the highest peak is Mount Elbert in Colorado at 14,439 feet (4,401 m) above sea level. The American Rockies rise steeply over

14606-562: The northernmost of the major mountain systems of the North American Cordillera, and extends along an east–west axis across northern Alaska from near the northern opening of the Bering Strait to the northern Yukon Territory. Major subranges include the British Mountains and Richardson Mountains , towards their eastern end, and at their farthest west is the small subrange that De Long Mountains . The Brooks Range forms

14740-664: The ocean. Recent analysis of and research into these hyperthermals in the early Eocene has led to hypotheses that the hyperthermals are based on orbital parameters, in particular eccentricity and obliquity. The hyperthermals in the early Eocene, notably the Palaeocene–Eocene Thermal Maximum (PETM), the Eocene Thermal Maximum 2 (ETM2), and the Eocene Thermal Maximum 3 (ETM3), were analyzed and found that orbital control may have had

14874-416: The orbital parameters were theorized as a possible control on continental temperatures and seasonality. Simulating the Eocene by using an ice free planet, eccentricity , obliquity , and precession were modified in different model runs to determine all the possible different scenarios that could occur and their effects on temperature. One particular case led to warmer winters and cooler summer by up to 30% in

15008-508: The other two groupings, but are extremely rugged and dense. The Coast Mountains are made of igneous and metamorphic rock from an episode of arc volcanism related to subduction of the Kula and Farallon Plates during the Laramide orogeny about 100 million years ago. The widespread granite forming the Coast Mountains formed when magma intruded and cooled at depth beneath volcanoes of

15142-416: The period progressed; the heat-loving tropical flora was wiped out, and by the beginning of the Oligocene, the continent hosted deciduous forests and vast stretches of tundra . During the Eocene, plants and marine faunas became quite modern. Many modern bird orders first appeared in the Eocene. The Eocene oceans were warm and teeming with fish and other sea life. The oldest known fossils of most of

15276-671: The plateau they transition to the high plateau in dryland valleys notable for a series of large lakes similar to the alpine lakes of southern Switzerland, beginning in deep mountains and ending in flatland. They are subdivided in three main groupings, the Pacific Ranges between the Fraser and Bella Coola , the Kitimat Ranges from there northwards to the Nass River and the Boundary Ranges from there to their terminus in

15410-438: The polar stratospheric clouds effects on the Eocene climate, models were run comparing the effects of polar stratospheric clouds at the poles to an increase in atmospheric carbon dioxide. The polar stratospheric clouds had a warming effect on the poles, increasing temperatures by up to 20 °C in the winter months. A multitude of feedbacks also occurred in the models due to the polar stratospheric clouds' presence. Any ice growth

15544-458: The reduction in carbon dioxide during the warming to cooling transition was the azolla event . With the equable climate during the early Eocene, warm temperatures in the arctic allowed for the growth of azolla , which is a floating aquatic fern, on the Arctic Ocean . The significantly high amounts of carbon dioxide also acted to facilitate azolla blooms across the Arctic Ocean. Compared to current carbon dioxide levels, these azolla grew rapidly in

15678-459: The region. One possible cause of atmospheric carbon dioxide increase could have been a sudden increase due to metamorphic release due to continental drift and collision of India with Asia and the resulting formation of the Himalayas ; however, data on the exact timing of metamorphic release of atmospheric carbon dioxide is not well resolved in the data. Recent studies have mentioned, however, that

15812-445: The removal of the ocean between Asia and India could have released significant amounts of carbon dioxide. Another hypothesis still implicates a diminished negative feedback of silicate weathering as a result of continental rocks having become less weatherable during the warm Early and Middle Eocene, allowing volcanically released carbon dioxide to persist in the atmosphere for longer. Yet another explanation hypothesises that MECO warming

15946-622: The same drainage. Eroded material from the Kaiparowits Formation probably did not contribute much to the formation of the Colton Formation . The existence of the California river and whether the river that formed the deltaic Colton Formation and the early Grand Canyon were the same are subject to debate. A similar, but more north-northeasterly drainage to the present-day Kaiparowits Plateau may have existed during

16080-613: The south and is bounded by the Sierra Madre Occidental and Sierra Madre Oriental to the west and east, respectively. A low east–west mountain range in the state of Zacatecas divides the plateau into northern and southern sections. These two sections, called the Northern Plateau (Spanish: Mesa del Norte ) and Central Plateau (Spanish: Mesa Central ), are now generally regarded by geographers as sections of one plateau. Eocene The Eocene ( IPA : / ˈ iː ə s iː n , ˈ iː oʊ -/ EE -ə-seen, EE -oh- )

16214-589: The southern portion. The northern Sierra surface rocks are predominantly volcanic, while the southern Sierra granitic batholith has been sculpted by glaciers into dramatic U-shaped valleys and thin ridges called arêtes . The Sierra Madre Occidental mountain range is a southern extension of the Sierra Nevada. The range extends from near the Arizona border down to the Sierra Madre del Sur, along

16348-399: The tropics that would require much higher average temperatures to sustain them. TEX 86 BAYSPAR measurements indicate extremely high sea surface temperatures of 40 °C (104 °F) to 45 °C (113 °F) at low latitudes, although clumped isotope analyses point to a maximum low latitude sea surface temperature of 36.3 °C (97.3 °F) ± 1.9 °C (35.4 °F) during

16482-552: The valley system at around 54°N near Prince George , British Columbia may be used for this purpose. There are three main mountain ranges in the Canadian area named the Rocky Mountains, the Columbia Mountains, and the Coast Mountains. The Columbia Plateau is a geologic and geographic region that lies across parts of the U.S. states of Washington , Oregon , and Idaho . It is a wide flood basalt plateau between

16616-525: The voluminous Colton Formation and with its sediment covering an area of over 3,000 square kilometres (1,200 sq mi). The so-called "Sunnyside Delta" has also been interpreted as a product of the California River. In the Paleocene, this river system may have formed the headwater of river systems that ended in the Gulf of Mexico through a paleo- Platte River and before that it may have drained into

16750-651: The western mainland of Mexico. The high plateau that is formed by the range is cut by deep river valleys. The Laramide belt is on the side of the North American Cordillera most distant from the Pacific Coast Ranges. It is named for the Laramie Mountains of eastern Wyoming (in turn named for Jacques La Ramee , a trapper who disappeared in the Laramie Mountains in 1820 and was never heard from again). The Brooks Range includes

16884-539: The western system, the interior system, and the eastern system. The western system includes the Coast Mountains , the interior system includes the Columbia Mountains , and the eastern system includes the Canadian Rockies . At its midsection between San Francisco , California and Denver , Colorado , the North American Cordillera is about 1,000 miles (1,600 km) wide, and its physiographic provinces at this midpoint are as follows, going from west to east:

17018-463: The world became more arid and cold over the course of the stage, such as the Fushun Basin. In East Asia, lake level changes were in sync with global sea level changes over the course of the MLEC. Global cooling continued until there was a major reversal from cooling to warming in the Bartonian. This warming event, signifying a sudden and temporary reversal of the cooling conditions, is known as

17152-528: Was a major step into the icehouse climate. Multiple proxies, such as oxygen isotopes and alkenones , indicate that at the Eocene–Oligocene transition, the atmospheric carbon dioxide concentration had decreased to around 750–800 ppm, approximately twice that of present levels . Along with the decrease of atmospheric carbon dioxide reducing the global temperature, orbital factors in ice creation can be seen with 100,000-year and 400,000-year fluctuations in benthic oxygen isotope records. Another major contribution to

17286-476: Was caused by the simultaneous occurrence of minima in both the 400 kyr and 2.4 Myr eccentricity cycles. During the MECO, sea surface temperatures in the Tethys Ocean jumped to 32–36 °C, and Tethyan seawater became more dysoxic. A decline in carbonate accumulation at ocean depths of greater than three kilometres took place synchronously with the peak of the MECO, signifying ocean acidification took place in

17420-465: Was connected 34 Ma. The Fushun Basin contained large, suboxic lakes known as the paleo-Jijuntun Lakes. India collided with Asia , folding to initiate formation of the Himalayas . The incipient subcontinent collided with the Kohistan–Ladakh Arc around 50.2 Ma and with Karakoram around 40.4 Ma, with the final collision between Asia and India occurring ~40 Ma. The Eocene Epoch contained

17554-402: Was determined that in order to maintain the lower stratospheric water vapor, methane would need to be continually released and sustained. In addition, the amounts of ice and condensation nuclei would need to be high in order for the polar stratospheric cloud to sustain itself and eventually expand. The Eocene is not only known for containing the warmest period during the Cenozoic; it also marked

17688-512: Was officially defined as the Paleocene, Eocene, and Oligocene epochs; and the Neogene as the Miocene and Pliocene epochs. In 1989, Tertiary and Quaternary were removed from the time scale due to the arbitrary nature of their boundary, but Quaternary was reinstated in 2009. The Eocene is a dynamic epoch that represents global climatic transitions between two climatic extremes, transitioning from

17822-401: Was present on Earth with a smaller difference in temperature from the equator to the poles . Because of this the maximum sea level was 150 meters higher than current levels. Following the maximum was a descent into an icehouse climate from the Eocene Optimum to the Eocene–Oligocene transition at 34 Ma. During this decrease, ice began to reappear at the poles, and the Eocene–Oligocene transition

17956-437: Was slowed immensely and would lead to any present ice melting. Only the poles were affected with the change in temperature and the tropics were unaffected, which with an increase in atmospheric carbon dioxide would also cause the tropics to increase in temperature. Due to the warming of the troposphere from the increased greenhouse effect of the polar stratospheric clouds, the stratosphere would cool and would potentially increase

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