Misplaced Pages

#119880

68-672: The area includes land lying on the North American Plate and Siberian land east of the Chersky Range . At various times, it formed a land bridge referred to as the Bering land bridge , that was up to 1,000 km (620 mi) wide at its greatest extent and which covered an area as large as British Columbia and Alberta together, totaling about 1.6 million km (620,000 sq mi), allowing biological dispersal to occur between Asia and North America. Today,

136-509: A chart datum in cartography and marine navigation , or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels . A common and relatively straightforward mean sea-level standard is instead a long-term average of tide gauge readings at a particular reference location. Sea levels can be affected by many factors and are known to have varied greatly over geological time scales . Current sea level rise

204-494: A datum . For example, hourly measurements may be averaged over a full Metonic 19-year lunar cycle to determine the mean sea level at an official tide gauge . Still-water level or still-water sea level (SWL) is the level of the sea with motions such as wind waves averaged out. Then MSL implies the SWL further averaged over a period of time such that changes due to, e.g., the tides , also have zero mean. Global MSL refers to

272-495: A topographic map variations in elevation are shown by contour lines . A mountain's highest point or summit is typically illustrated with the AMSL height in metres, feet or both. In unusual cases where a land location is below sea level, such as Death Valley, California , the elevation AMSL is negative. It is often necessary to compare the local height of the mean sea surface with a "level" reference surface, or geodetic datum, called

340-440: A "mean sea level" is difficult because of the many factors that affect sea level. Instantaneous sea level varies substantially on several scales of time and space. This is because the sea is in constant motion, affected by the tides, wind , atmospheric pressure, local gravitational differences, temperature, salinity , and so forth. The mean sea level at a particular location may be calculated over an extended time period and used as

408-409: A defined barometric pressure . Generally, the pressure used to set the altimeter is the barometric pressure that would exist at MSL in the region being flown over. This pressure is referred to as either QNH or "altimeter" and is transmitted to the pilot by radio from air traffic control (ATC) or an automatic terminal information service (ATIS). Since the terrain elevation is also referenced to MSL,

476-432: A few metres, in timeframes ranging from minutes to months: Between 1901 and 2018, the average sea level rose by 15–25 cm (6–10 in), with an increase of 2.3 mm (0.091 in) per year since the 1970s. This was faster than the sea level had ever risen over at least the past 3,000 years. The rate accelerated to 4.62 mm (0.182 in)/yr for the decade 2013–2022. Climate change due to human activities

544-461: A land bridge from c.  30,000  – c.  11,000  YBP, followed by a Holocene sea-level rise that reopened the strait. Post-glacial rebound has continued to raise some sections of the coast. During the last glacial period , enough of the Earth's water became frozen in the great ice sheets covering North America and Europe to cause a drop in sea levels . For thousands of years

612-418: A mantle convective current is propelling the plate. Sea level Mean sea level ( MSL , often shortened to sea level ) is an average surface level of one or more among Earth 's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datum  – a standardised geodetic datum  – that is used, for example, as

680-472: A rich diversity of grasses and herbs. There were patches of shrub tundra with isolated refugia of larch ( Larix ) and spruce ( Picea ) forests with birch ( Betula ) and alder ( Alnus ) trees. It has been proposed that the largest and most diverse megafaunal community residing in Beringia at this time could only have been sustained in a highly diverse and productive environment. Analysis at Chukotka on

748-470: A sharp reduction in greenhouse gas emissions, this may increase to hundreds of millions in the latter decades of the century. Local factors like tidal range or land subsidence will greatly affect the severity of impacts. For instance, sea level rise in the United States is likely to be two to three times greater than the global average by the end of the century. Yet, of the 20 countries with

SECTION 10

#1732758007120

816-486: A spatial average over the entire ocean area, typically using large sets of tide gauges and/or satellite measurements. One often measures the values of MSL with respect to the land; hence a change in relative MSL or ( relative sea level ) can result from a real change in sea level, or from a change in the height of the land on which the tide gauge operates, or both. In the UK, the ordnance datum (the 0 metres height on UK maps)

884-575: Is a tectonic plate containing most of North America , Cuba , the Bahamas , extreme northeastern Asia , and parts of Iceland and the Azores . With an area of 76 million km (29 million sq mi), it is the Earth's second largest tectonic plate, behind the Pacific plate (which borders the plate to the west). It extends eastward to the seismically active Mid-Atlantic Ridge at

952-610: Is calibrated to the Amsterdam Peil elevation, which dates back to the 1690s. Satellite altimeters have been making precise measurements of sea level since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA and CNES , TOPEX/Poseidon was followed by Jason-1 in 2001 and the Ocean Surface Topography Mission on the Jason-2 satellite in 2008. Height above mean sea level ( AMSL )

1020-427: Is due to change in either the volume of water in the world's oceans or the volume of the oceanic basins . Two major mechanisms are currently causing eustatic sea level rise. First, shrinking land ice, such as mountain glaciers and polar ice sheets, is releasing water into the oceans. Second, as ocean temperatures rise, the warmer water expands. Many factors can produce short-term changes in sea level, typically within

1088-451: Is mainly caused by human-induced climate change . When temperatures rise, mountain glaciers and polar ice sheets melt, increasing the amount of water in the oceans, while the existing seawater also expands with heat. Because most of human settlement and infrastructure was built in response to a more-normalized sea level with limited expected change, populations affected by sea level rise will need to invest in climate adaptation to mitigate

1156-411: Is the elevation (on the ground) or altitude (in the air) of an object, relative to a reference datum for mean sea level (MSL). It is also used in aviation, where some heights are recorded and reported with respect to mean sea level (contrast with flight level ), and in the atmospheric sciences , and in land surveying . An alternative is to base height measurements on a reference ellipsoid approximating

1224-727: Is the main cause. Between 1993 and 2018, melting ice sheets and glaciers accounted for 44% of sea level rise , with another 42% resulting from thermal expansion of water . Sea level rise lags behind changes in the Earth 's temperature by many decades, and sea level rise will therefore continue to accelerate between now and 2050 in response to warming that has already happened. What happens after that depends on human greenhouse gas emissions . If there are very deep cuts in emissions, sea level rise would slow between 2050 and 2100. It could then reach by 2100 slightly over 30 cm (1 ft) from now and approximately 60 cm (2 ft) from

1292-764: Is the mean sea level measured at Newlyn in Cornwall between 1915 and 1921. Before 1921, the vertical datum was MSL at the Victoria Dock, Liverpool . Since the times of the Russian Empire , in Russia and its other former parts, now independent states, the sea level is measured from the zero level of Kronstadt Sea-Gauge. In Hong Kong, "mPD" is a surveying term meaning "metres above Principal Datum" and refers to height of 0.146 m (5.7 in) above chart datum and 1.304 m (4 ft 3.3 in) below

1360-705: The Anadyr River ), and Arctodus simus , American badger , American kiang -like equids, Bootherium and Camelops in North America, with the existence of Homotherium being disputed in Late Pleistocene Siberia. The lack of mastodon and Megalonyx has been attributed to their inhabitation of Alaska and the Yukon being limited to interglacials. However, ground sloth eDNA has potentially been recovered from Siberia. The peopling of

1428-544: The Azores triple junction plate boundary where it meets the Eurasian plate and Nubian plate . and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust . The interior of the main continental landmass includes an extensive granitic core called a craton . Along most of the edges of this craton are fragments of crustal material called terranes , which are accreted to

SECTION 20

#1732758007120

1496-801: The Fifteen-Twenty fracture zone around 16°N. On the northerly boundary is a continuation of the Mid-Atlantic Ridge called the Gakkel Ridge . The rest of the boundary in the far northwestern part of the plate extends into Siberia . This boundary continues from the end of the Gakkel Ridge as the Laptev Sea Rift , on to a transitional deformation zone in the Chersky Range , then the Ulakhan Fault between it and

1564-710: The Gonâve microplate , and the parallel Puerto Rico Trench running north of Puerto Rico and the Virgin Islands and bounding the Puerto Rico–Virgin Islands microplate , are also a part of the boundary. The rest of the southerly margin which extends east to the Mid-Atlantic Ridge and marks the boundary between the North American plate and the South American plate is vague but located near

1632-610: The Last Glacial Maximum , when ice sheets began advancing from 33,000   YBP and reached their maximum limits 26,500   YBP. Deglaciation commenced in the Northern Hemisphere approximately 19,000   YBP and in Antarctica approximately 14,500 years   YBP, which is consistent with evidence that glacial meltwater was the primary source for an abrupt rise in sea level 14,500   YBP and

1700-788: The Miocene period and are still geologically active, creating earthquakes and volcanoes. The Yellowstone hotspot is most notable for the Yellowstone Caldera and the many calderas that lie in the Snake River Plain , while the Anahim hotspot is most notable for the Anahim Volcanic Belt in the Nazko Cone area. For the most part, the North American plate moves in roughly a southwest direction away from

1768-991: The Okhotsk microplate , and finally the Aleutian Trench to the end of the Queen Charlotte Fault system (see also: Aleutian Arc ). The westerly boundary is the Queen Charlotte Fault running offshore along the coast of Alaska and the Cascadia subduction zone to the north, the San Andreas Fault through California , the East Pacific Rise in the Gulf of California , and the Middle America Trench to

1836-595: The geoid . In the absence of external forces, the local mean sea level would coincide with this geoid surface, being an equipotential surface of the Earth's gravitational field which, in itself, does not conform to a simple sphere or ellipsoid and exhibits gravity anomalies such as those measured by NASA's GRACE satellites . In reality, the geoid surface is not directly observed, even as a long-term average, due to ocean currents, air pressure variations, temperature and salinity variations, etc. The location-dependent but time-persistent separation between local mean sea level and

1904-973: The 19th century. With high emissions it would instead accelerate further, and could rise by 1.0 m ( 3 + 1 ⁄ 3  ft) or even 1.6 m ( 5 + 1 ⁄ 3  ft) by 2100. In the long run, sea level rise would amount to 2–3 m (7–10 ft) over the next 2000 years if warming stays to its current 1.5 °C (2.7 °F) over the pre-industrial past. It would be 19–22 metres (62–72 ft) if warming peaks at 5 °C (9.0 °F). Rising seas affect every coastal and island population on Earth. This can be through flooding, higher storm surges , king tides , and tsunamis . There are many knock-on effects. They lead to loss of coastal ecosystems like mangroves . Crop yields may reduce because of increasing salt levels in irrigation water. Damage to ports disrupts sea trade. The sea level rise projected by 2050 will expose places currently inhabited by tens of millions of people to annual flooding. Without

1972-784: The Americas began when Paleolithic hunter-gatherers ( Paleo-Indians ) entered North America from the North Asian Mammoth steppe via the Beringia land bridge , which had formed between northeastern Siberia and western Alaska due to the lowering of sea level during the Last Glacial Maximum (26,000 to 19,000 years ago). These populations expanded south of the Laurentide Ice Sheet and spread rapidly southward, occupying both North and South America by 12,000 to 14,000 years ago. The earliest populations in

2040-625: The Americas sometime after 16,500 years Before Present (YBP). This would have occurred as the American glaciers blocking the way southward melted, but before the bridge was covered by the sea about 11,000 YBP. The term Beringia was coined by the Swedish botanist Eric Hultén in 1937, from the Danish-born Russian explorer Vitus Bering . During the ice ages, Beringia, like most of Siberia and all of North and Northeast China ,

2108-488: The Americas, before roughly 10,000 years ago, are known as Paleo-Indians . Indigenous peoples of the Americas have been linked to Siberian populations by proposed linguistic factors , the distribution of blood types , and in genetic composition as reflected by molecular data, such as DNA . Around 3,000 years ago, the progenitors of the Yupik peoples settled along both sides of the straits. The governments of Russia and

Beringia - Misplaced Pages Continue

2176-487: The Cenozoic. [REDACTED] Africa [REDACTED] Antarctica [REDACTED] Asia [REDACTED] Australia [REDACTED] Europe [REDACTED] North America [REDACTED] South America [REDACTED] Afro-Eurasia [REDACTED] Americas [REDACTED] Eurasia [REDACTED] Oceania North American Plate The North American plate

2244-709: The Farallon plate. The boundary along the Gulf of California is complex. The gulf is underlain by the Gulf of California Rift Zone , a series of rift basins and transform fault segments from the northern end of the East Pacific Rise in the mouth of the gulf to the San Andreas Fault system in the vicinity of the Salton Trough rift/ Brawley seismic zone . It is generally accepted that a piece of

2312-490: The Last Glacial Maximum. This was followed by a single population of modern wolves expanding out of their Beringia refuge to repopulate the wolf's former range, replacing the remaining Late Pleistocene wolf populations across Eurasia and North America. The extinct pine species Pinus matthewsii has been described from Pliocene sediments in the Yukon areas of the refugium. The existence of fauna endemic to

2380-599: The Mid-Atlantic Ridge at a rate of about 2.3 centimeters (~1 inch) per year. At the same time, the Pacific plate is moving to the northwest at a speed of between 7 and 11 centimeters (~3-4 inches) per year. The motion of the plate cannot be driven by subduction as no part of the North American plate is being subducted, except for a small section comprising part of the Puerto Rico Trench ; thus other mechanisms continue to be investigated. One study in 2007 suggests that

2448-448: The North American plate was broken off and transported north as the East Pacific Rise propagated northward, creating the Gulf of California. However, it is as yet unclear whether the oceanic crust between the rise and the mainland coast of Mexico is actually a new plate beginning to converge with the North American plate, consistent with the standard model of rift zone spreading centers generally. A few hotspots are thought to exist below

2516-528: The North American plate. The most notable hotspots are the Yellowstone (Wyoming), Jemez Lineament (New Mexico), and Anahim (British Columbia) hotspots. These are thought to be caused by a narrow stream of hot mantle convecting up from the Earth's core–mantle boundary called a mantle plume , although some geologists think that upper mantle convection is a more likely cause. The Yellowstone and Anahim hotspots are thought to have first arrived during

2584-521: The Siberian edge of the land bridge indicated that from c.  57,000  – c.  15,000  YBP (MIS 3 to MIS 2) the environment was wetter and colder than the steppe–tundra to the east and west, with warming in parts of Beringia from c.  15,000  YBP. These changes provided the most likely explanation for mammal migrations after c.  15,000  YBP, as the warming provided increased forage for browsers and mixed feeders. At

2652-868: The United States announced a plan to formally establish "a transboundary area of shared Beringian heritage". Among other things this agreement would establish close ties between the Bering Land Bridge National Preserve and the Cape Krusenstern National Monument in the United States and Beringia National Park in Russia. Biogeographical evidence demonstrates previous connections between North America and Asia. Similar dinosaur fossils occur both in Asia and in North America . The dinosaur Saurolophus

2720-608: The Yukon where it was blocked by the Wisconsin glaciation . Therefore, the flora and fauna of Beringia were more related to those of Eurasia rather than North America. Beringia received more moisture and intermittent maritime cloud cover from the north Pacific Ocean than the rest of the Mammoth steppe, including the dry environments on either side of it. This moisture supported a shrub-tundra habitat that provided an ecological refugium for plants and animals. In East Beringia 35,000 YBP,

2788-591: The Yukon. In the driest and coldest periods of the Late Pleistocene, and possibly during the entire Pleistocene, moisture occurred along a north–south gradient with the south receiving the most cloud cover and moisture due to the air-flow from the North Pacific. In the Late Pleistocene, Beringia was a mosaic of biological communities. Commencing from c.  57,000  YBP ( MIS 3), steppe–tundra vegetation dominated large parts of Beringia with

Beringia - Misplaced Pages Continue

2856-606: The average sea level. In France, the Marégraphe in Marseilles measures continuously the sea level since 1883 and offers the longest collated data about the sea level. It is used for a part of continental Europe and the main part of Africa as the official sea level. Spain uses the reference to measure heights below or above sea level at Alicante , while the European Vertical Reference System

2924-662: The beginning of the Holocene , some mesic habitat -adapted species left the refugium and spread westward into what had become tundra-vegetated northern Asia and eastward into northern North America. The latest emergence of the land bridge was c.  70,000 years ago. However, from c.  24,000  – c.  13,000  YBP the Laurentide Ice Sheet fused with the Cordilleran Ice Sheet , which blocked gene flow between Beringia (and Eurasia) and continental North America. The Yukon corridor opened between

2992-518: The bridge was finally inundated around 11,000 YBP. The fossil evidence from many continents points to the extinction of large animals, termed Pleistocene megafauna , near the end of the last glaciation. During the Ice Age a vast, cold and dry Mammoth steppe stretched from the arctic islands southwards to China, and from Spain eastwards across Eurasia and over the Bering land bridge into Alaska and

3060-420: The climate was warmer and wetter. The environmental conditions were not homogenous in Beringia. Recent stable isotope studies of woolly mammoth bone collagen demonstrate that western Beringia ( Siberia ) was colder and drier than eastern Beringia ( Alaska and Yukon ), which was more ecologically diverse. Grey wolves suffered a species-wide population bottleneck (reduction) approximately 25,000 YBP during

3128-921: The craton by tectonic actions over a long span of time. Much of North America west of the Rocky Mountains is composed of such terranes. The southern boundary with the Cocos plate to the west and the Caribbean plate to the east is a transform fault , represented by the Swan Islands Transform Fault under the Caribbean Sea and the Motagua Fault through Guatemala . The parallel Septentrional and Enriquillo–Plantain Garden faults running through Hispaniola and bounding

3196-610: The dry beds of the English Channel and North Sea , and the dry bed of the South China Sea linked Sumatra , Java , and Borneo to Indochina . The last glacial period , commonly referred to as the "Ice Age", spanned 125,000–14,500   YBP and was the most recent glacial period within the current ice age , which occurred during the last years of the Pleistocene era. The Ice Age reached its peak during

3264-484: The entire Earth, which is what systems such as GPS do. In aviation, the reference ellipsoid known as WGS84 is increasingly used to define heights; however, differences up to 100 metres (328 feet) exist between this ellipsoid height and local mean sea level. Another alternative is to use a geoid -based vertical datum such as NAVD88 and the global EGM96 (part of WGS84). Details vary in different countries. When referring to geographic features such as mountains, on

3332-482: The geoid is referred to as (mean) ocean surface topography . It varies globally in a typical range of ±1 m (3 ft). Several terms are used to describe the changing relationships between sea level and dry land. The melting of glaciers at the end of ice ages results in isostatic post-glacial rebound , when land rises after the weight of ice is removed. Conversely, older volcanic islands experience relative sea level rise, due to isostatic subsidence from

3400-528: The globe. Today, the average water depth of the Bering Strait is 40–50 m (130–160 ft); therefore the land bridge opened when the sea level dropped more than 50 m (160 ft) below the current level. A reconstruction of the sea-level history of the region indicated that a seaway existed from c.  135,000  – c.  70,000  YBP, a land bridge from c.  70,000  – c.  60,000  YBP, an intermittent connection from c.  60,000  – c.  30,000  YBP,

3468-524: The greatest exposure to sea level rise, twelve are in Asia , including Indonesia , Bangladesh and the Philippines. The resilience and adaptive capacity of ecosystems and countries also varies, which will result in more or less pronounced impacts. The greatest impact on human populations in the near term will occur in the low-lying Caribbean and Pacific islands . Sea level rise will make many of them uninhabitable later this century. Pilots can estimate height above sea level with an altimeter set to

SECTION 50

#1732758007120

3536-504: The height of planetary features. Local mean sea level (LMSL) is defined as the height of the sea with respect to a land benchmark, averaged over a period of time long enough that fluctuations caused by waves and tides are smoothed out, typically a year or more. One must adjust perceived changes in LMSL to account for vertical movements of the land, which can occur at rates similar to sea level changes (millimetres per year). Some land movements occur because of isostatic adjustment to

3604-513: The ice mass balance, leading to global sea-level fluctuations were viewed as the cause of the Bering land bridge. In 1937, Eric Hultén proposed that around the Aleutians and the Bering Strait region were tundra plants that had originally dispersed from a now-submerged plain between Alaska and Chukotka, which he named Beringia after Vitus Bering who had sailed into the strait in 1728. The American arctic geologist David Hopkins redefined Beringia to include portions of Alaska and Northeast Asia. Beringia

3672-481: The melting of ice sheets at the end of the last ice age . The weight of the ice sheet depresses the underlying land, and when the ice melts away the land slowly rebounds . Changes in ground-based ice volume also affect local and regional sea levels by the readjustment of the geoid and true polar wander . Atmospheric pressure , ocean currents and local ocean temperature changes can affect LMSL as well. Eustatic sea level change (global as opposed to local change)

3740-421: The northern arctic areas experienced temperatures 1.5 °C (2.7 °F) degrees warmer than today but the southern sub-Arctic regions were 2 °C (4 °F) degrees cooler. During the LGM 22,000 YBP the average summer temperature was 3–5 °C (5–9 °F) degrees cooler than today, with variations of 2.9 °C (5.2 °F) degrees cooler on the Seward Peninsula to 7.5 °C (13.5 °F) cooler in

3808-408: The only land that is visible from the central part of the Bering land bridge are the Diomede Islands , the Pribilof Islands of St. Paul and St. George, St. Lawrence Island , St. Matthew Island , and King Island . It is believed that a small human population of at most a few thousand arrived in Beringia from eastern Siberia during the Last Glacial Maximum before expanding into the settlement of

3876-613: The origin of these wolves in eastern Beringia during the Middle Pleistocene . Fossil evidence also indicates an exchange of primates and plants between North America and Asia around 55.8 million years ago. 20 million years ago, evidence in North America shows the last natural interchange of mammalian species. Some, like the ancient saber-toothed cats , have a recurring geographical range: Europe, Africa, Asia, and North America. The pattern of bidirectional flow of biota has been asymmetric, with more plants, animals, and fungi generally migrating from Asia to North America than vice versa throughout

3944-479: The poles and 6,371.001 km (3,958.756 mi) on average. This flattened spheroid , combined with local gravity anomalies , defines the geoid of the Earth, which approximates the local mean sea level for locations in the open ocean. The geoid includes a significant depression in the Indian Ocean , whose surface dips as much as 106 m (348 ft) below the global mean sea level (excluding minor effects such as tides and currents). Precise determination of

4012-411: The receding ice sheets c.  13,000  YBP, and this once again allowed gene flow between Eurasia and continental North America until the land bridge was finally closed by rising sea levels c.  10,000  YBP. During the Holocene, many mesic-adapted species left the refugium and spread eastward and westward, while at the same time the forest-adapted species spread with the forests up from

4080-439: The respective Siberian and North American portions of Beringia has led to the 'Beringian Gap' hypothesis, wherein an unconfirmed geographic factor blocked migration across the land bridge when it emerged. Beringia did not block the movement of most dry steppe-adapted large species such as saiga antelope, woolly mammoth, and caballid horses. Notable restricted fauna include the woolly rhino in Siberia (which went no further east than

4148-417: The sea floors of many interglacial shallow seas were exposed, including those of the Bering Strait , the Chukchi Sea to the north, and the Bering Sea to the south. Other land bridges around the world have emerged and disappeared in the same way. Around 14,000 years ago, mainland Australia was linked to both New Guinea and Tasmania , the British Isles became an extension of continental Europe via

SECTION 60

#1732758007120

4216-444: The south. On its western edge, the Farallon plate has been subducting under the North American plate since the Jurassic period. The Farallon plate has almost completely subducted beneath the western portion of the North American plate, leaving that part of the North American plate in contact with the Pacific plate as the San Andreas Fault. The Juan de Fuca , Explorer , Gorda , Rivera , Cocos and Nazca plates are remnants of

4284-606: The south. The arid-adapted species were reduced to minor habitats or became extinct. Beringia constantly transformed its ecosystem as the changing climate affected the environment, determining which plants and animals were able to survive. The land mass could be a barrier as well as a bridge: during colder periods, glaciers advanced and precipitation levels dropped. During warmer intervals, clouds, rain and snow altered soils and drainage patterns. Fossil remains show that spruce , birch and poplar once grew beyond their northernmost range today, indicating that there were periods when

4352-411: The weight of cooling volcanos. The subsidence of land due to the withdrawal of groundwater is another isostatic cause of relative sea level rise. On planets that lack a liquid ocean, planetologists can calculate a "mean altitude" by averaging the heights of all points on the surface. This altitude, sometimes referred to as a "sea level" or zero-level elevation , serves equivalently as a reference for

4420-419: The worst effects or, when populations are at extreme risk, a process of managed retreat . The term above sea level generally refers to the height above mean sea level (AMSL). The term APSL means above present sea level, comparing sea levels in the past with the level today. Earth's radius at sea level is 6,378.137 km (3,963.191 mi) at the equator. It is 6,356.752 km (3,949.903 mi) at

4488-506: Was found in both Mongolia and western North America. Relatives of Troodon , Triceratops , and Tyrannosaurus rex all came from Asia. The earliest Canis lupus specimen was a fossil tooth discovered at Old Crow, Yukon , Canada. The specimen was found in sediment dated 1 million YBP, however the geological attribution of this sediment is questioned. Slightly younger specimens were discovered at Cripple Creek Sump, Fairbanks , Alaska, in strata dated 810,000 YBP. Both discoveries point to

4556-460: Was later regarded as extending from the Verkhoyansk Mountains in the west to the Mackenzie River in the east. The distribution of plants in the genera Erythranthe and Pinus are good examples of this, as very similar genera members are found in Asia and the Americas. During the Pleistocene epoch, global cooling led periodically to the expansion of glaciers and the lowering of sea levels. This created land connections in various regions around

4624-404: Was not glaciated because snowfall was very light . The remains of Late Pleistocene mammals that had been discovered on the Aleutians and islands in the Bering Sea at the close of the nineteenth century indicated that a past land connection might lie beneath the shallow waters between Alaska and Chukotka . The underlying mechanism was first thought to be tectonics, but by 1930 changes in

#119880