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111-627: Geologically , the Sahul Shelf ( / s ə ˈ h uː l / ) is a part of the continental shelf of the Australian continent , lying off the northwest coast of mainland Australia . The name "Sahull" or "Sahoel" appeared on 17th century Dutch maps applied to a submerged sandbank between Australia and Timor . On his 1803 map, Matthew Flinders noted the "Great Sahul Shoal" where Malays came from Makassar to fish for trepang ( sea cucumber ). The name Sahul Shelf ( Dutch : Sahoel-plat )

222-535: A characteristic fabric . All three types may melt again, and when this happens, new magma is formed, from which an igneous rock may once again solidify. Organic matter, such as coal, bitumen, oil, and natural gas, is linked mainly to organic-rich sedimentary rocks. To study all three types of rock, geologists evaluate the minerals of which they are composed and their other physical properties, such as texture and fabric . Geologists also study unlithified materials (referred to as superficial deposits ) that lie above

333-485: A petrographic microscope , where the minerals can be identified through their different properties in plane-polarized and cross-polarized light, including their birefringence , pleochroism , twinning , and interference properties with a conoscopic lens . In the electron microprobe, individual locations are analyzed for their exact chemical compositions and variation in composition within individual crystals. Stable and radioactive isotope studies provide insight into

444-408: A sea level rise of hundreds of meters following the last ice age. Both routes may have been taken, although the genetic evidences suggests a single founding population. The micro-satellite diversity and distributions specific to South American Indigenous peoples indicates that certain populations have been isolated since the initial colonization of the region. A second migration occurred after

555-434: A definite homogeneous chemical composition and an ordered atomic arrangement. Each mineral has distinct physical properties, and there are many tests to determine each of them. Minerals are often identified through these tests. The specimens can be tested for: A rock is any naturally occurring solid mass or aggregate of minerals or mineraloids . Most research in geology is associated with the study of rocks, as they provide

666-573: A few hidden documents remain today, leaving modern historians with glimpses of ancient culture and knowledge. The first inhabitants migrated into the Americas from Asia. Habitation sites are known in Alaska and Yukon from at least 20,000 years ago, with suggested ages of up to 40,000 years. Beyond that, the specifics of the Paleo-Indian migration to and throughout the Americas, including

777-627: A length of less than a meter. Rocks at the depth to be ductilely stretched are often also metamorphosed. These stretched rocks can also pinch into lenses, known as boudins , after the French word for "sausage" because of their visual similarity. Where rock units slide past one another, strike-slip faults develop in shallow regions, and become shear zones at deeper depths where the rocks deform ductilely. The addition of new rock units, both depositionally and intrusively, often occurs during deformation. Faulting and other deformational processes result in

888-625: A lesser extent, Dutch . The Americas are home to more than a billion inhabitants, two-thirds of whom reside in the United States , Brazil , and Mexico . It is home to eight megacities ( metropolitan areas with 10 million inhabitants or more): Greater Mexico City (21.2 million), São Paulo (21.2 million), New York City (19.7 million), Los Angeles (18.8 million), Buenos Aires (15.6 million), Rio de Janeiro (13.0 million), Bogotá (10.4 million), and Lima (10.1 million). The name "America"

999-452: A means to provide information about geological history and the timing of geological events. The principle of uniformitarianism states that the geological processes observed in operation that modify the Earth's crust at present have worked in much the same way over geological time. A fundamental principle of geology advanced by the 18th-century Scottish physician and geologist James Hutton

1110-427: A million years, with the total spread of South American genera into North America far more limited in scope than the spread of North American genera into South America. There are 35 sovereign states in the Americas, as well as an autonomous country of Denmark , three overseas departments of France , three overseas collectivities of France, and one uninhabited territory of France, eight overseas territories of

1221-608: A number of fields, laboratory, and numerical modeling methods to decipher Earth history and to understand the processes that occur on and inside the Earth. In typical geological investigations, geologists use primary information related to petrology (the study of rocks), stratigraphy (the study of sedimentary layers), and structural geology (the study of positions of rock units and their deformation). In many cases, geologists also study modern soils, rivers , landscapes , and glaciers ; investigate past and current life and biogeochemical pathways, and use geophysical methods to investigate

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1332-485: A number of islands. The gaps in the archipelago of Central America filled in with material eroded off North America and South America, plus new land created by continued volcanism. By three million years ago, the continents of North America and South America were linked by the Isthmus of Panama , thereby forming the single landmass of the Americas. The Great American Interchange resulted in many species being spread across

1443-451: A sedimentary rock. Sedimentary rocks are mainly divided into four categories: sandstone, shale, carbonate, and evaporite. This group of classifications focuses partly on the size of sedimentary particles (sandstone and shale), and partly on mineralogy and formation processes (carbonation and evaporation). Igneous and sedimentary rocks can then be turned into metamorphic rocks by heat and pressure that change its mineral content, resulting in

1554-722: A series of rivers and streams that flow east with their terminus in the Atlantic Ocean, such as the Hudson River , Saint John River , and Savannah River . A similar instance arises with central Canadian rivers that drain into Hudson Bay ; the largest being the Churchill River . On the west coast of North America, the main rivers are the Colorado River , Columbia River , Yukon River , Fraser River , and Sacramento River . The Colorado River drains much of

1665-541: A shared population of flora and fauna around 2.5 million years ago, when continental drift brought the two continents into contact via the Isthmus of Panama . Initially, the exchange of biota was roughly equal, with North American genera migrating into South America in about the same proportions as South American genera migrated into North America. This exchange is known as the Great American Interchange . The exchange became lopsided after roughly

1776-499: A single environment and do not necessarily occur in a single order. The Hawaiian Islands , for example, consist almost entirely of layered basaltic lava flows. The sedimentary sequences of the mid-continental United States and the Grand Canyon in the southwestern United States contain almost-undeformed stacks of sedimentary rocks that have remained in place since Cambrian time. Other areas are much more geologically complex. In

1887-707: A synonym). Latin America is typically contrasted with Anglo-America , where English, a Germanic language , is prevalent, and which comprises Canada (with the exception of Francophone Canada rooted in Latin Europe [France]—see Quebec and Acadia ) and the United States. Both countries are located in North America, with cultures deriving predominantly from British and other Germanic roots. The transatlantic slave trade brought millions of Africans to

1998-400: A variety of applications. Dating of lava and volcanic ash layers found within a stratigraphic sequence can provide absolute age data for sedimentary rock units that do not contain radioactive isotopes and calibrate relative dating techniques. These methods can also be used to determine ages of pluton emplacement. Thermochemical techniques can be used to determine temperature profiles within

2109-453: A wide variety of indigenous religions, many of which can be categorized as animistic ; new age religions and many African and African-derived religions. Syncretic faiths can also be found throughout the Americas. Various languages are spoken in the Americas. Some are of European origin, others are spoken by indigenous peoples or are the mixture of various languages like the different creoles. The most widely spoken first language in

2220-419: Is a branch of natural science concerned with the Earth and other astronomical objects , the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth sciences , including hydrology . It is integrated with Earth system science and planetary science . Geology describes the structure of the Earth on and beneath its surface and

2331-422: Is accomplished in two primary ways: through faulting and folding . In the shallow crust, where brittle deformation can occur, thrust faults form, which causes the deeper rock to move on top of the shallower rock. Because deeper rock is often older, as noted by the principle of superposition , this can result in older rocks moving on top of younger ones. Movement along faults can result in folding, either because

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2442-460: Is an intimate coupling between the movement of the plates on the surface and the convection of the mantle (that is, the heat transfer caused by the slow movement of ductile mantle rock). Thus, oceanic parts of plates and the adjoining mantle convection currents always move in the same direction – because the oceanic lithosphere is actually the rigid upper thermal boundary layer of the convecting mantle. This coupling between rigid plates moving on

2553-470: Is generally quite flat. Similarly, the north-east of South America is covered by the flat Amazon basin . The Brazilian Highlands on the east coast are fairly smooth but show some variations in landform, while farther south the Gran Chaco and Pampas are broad lowlands . The climate of the Americas varies significantly from region to region. Tropical rainforest climate occurs in the latitudes of

2664-433: Is horizontal). The principle of superposition states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. Logically a younger layer cannot slip beneath a layer previously deposited. This principle allows sedimentary layers to be viewed as a form of the vertical timeline, a partial or complete record of the time elapsed from deposition of

2775-616: Is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources , understanding natural hazards , remediating environmental problems, and providing insights into past climate change . Geology is a major academic discipline , and it is central to geological engineering and plays an important role in geotechnical engineering . The majority of geological data comes from research on solid Earth materials. Meteorites and other extraterrestrial natural materials are also studied by geological methods. Minerals are naturally occurring elements and compounds with

2886-484: Is primarily accomplished through normal faulting and through the ductile stretching and thinning. Normal faults drop rock units that are higher below those that are lower. This typically results in younger units ending up below older units. Stretching of units can result in their thinning. In fact, at one location within the Maria Fold and Thrust Belt , the entire sedimentary sequence of the Grand Canyon appears over

2997-568: Is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now." The principle of intrusive relationships concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a formation of sedimentary rock , it can be determined that the igneous intrusion is younger than the sedimentary rock. Different types of intrusions include stocks, laccoliths , batholiths , sills and dikes . The principle of cross-cutting relationships pertains to

3108-691: Is that of the Mississippi , covering the second largest watershed on the planet. The Mississippi-Missouri river system drains most of 31 states of the United States, most of the Great Plains , and large areas between the Rocky and Appalachian mountains. This river is the fourth longest in the world and tenth most powerful in the world . In North America, to the east of the Appalachian Mountains , there are no major rivers but rather

3219-589: Is the 2nd largest continent right after Asia, and is the 3rd largest continent by population. The Americas make up most of the land in Earth 's Western Hemisphere and comprise the New World . Along with their associated islands , the Americas cover 8% of Earth's total surface area and 28.4% of its land area. The topography is dominated by the American Cordillera , a long chain of mountains that runs

3330-523: Is used for geologically young materials containing organic carbon . The geology of an area changes through time as rock units are deposited and inserted, and deformational processes alter their shapes and locations. Rock units are first emplaced either by deposition onto the surface or intrusion into the overlying rock . Deposition can occur when sediments settle onto the surface of the Earth and later lithify into sedimentary rock, or when as volcanic material such as volcanic ash or lava flows blanket

3441-533: The Amazon , American cloud forests , southeastern Florida and Darién Gap . In the Rocky Mountains and Andes , dry and continental climates are observed. Often the higher altitudes of these mountains are snow-capped. Southeastern North America is well known for its occurrence of tornadoes and hurricanes , of which the vast majority of tornadoes occur in the United States' Tornado Alley , as well as in

Sahul Shelf - Misplaced Pages Continue

3552-663: The Arafura Sea north to New Guinea . The Aru Islands rise from the Arafura Shelf. The Sahul Shelf is sometimes taken to also include the Rowley Shelf to the southwest of Cape Leveque , girding the north coast of Western Australia as far as North West Cape . The existence of an extensive Sahul Shelf was suggested in 1845 by George Windsor Earl who called it the "Great Australian Bank" and noted that macropods (kangaroos) were found on Australia, New Guinea, and

3663-715: The Arctic small tool tradition , a broad cultural entity that developed along the Alaska Peninsula , around Bristol Bay , and on the eastern shores of the Bering Strait c.  2500 BCE moved into North America. The Arctic small tool tradition, a Paleo-Eskimo culture branched off into two cultural variants, including the Pre-Dorset , and the Independence traditions of Greenland. The descendants of

3774-708: The Boothia Peninsula in northern Canada and Cape Froward in Chilean Patagonia , is roughly 14,000 km (8,700 mi). The mainland's most westerly point is the end of the Seward Peninsula in Alaska; Attu Island , further off the Alaskan coast to the west, is considered the westernmost point of the Americas. Ponta do Seixas in northeastern Brazil forms the easternmost extremity of

3885-530: The Last Glacial Maximum about 18,000 years ago, the Sahul Shelf was exposed as dry land. Evidence of the shoreline of this time has been identified in locations which now lie 100 to 140 metres below sea level. A Flash -based interactive timeline of sea level changes was developed by Monash University in the 2000s. The Arafura Shelf formed a land bridge between Australia, New Guinea, and

3996-495: The Latin version of Italian explorer Amerigo Vespucci 's first name. The feminine form America was originally used to refer to the newly discovered continent, which is why it was accorded with the feminine names of the other continents: Asia , Africa , and Europa . Since the 1950s, however, North America and South America have generally been considered by English speakers as separate continents, and taken together are called

4107-574: The Quaternary glaciation . These people are believed to have followed herds of now-extinct pleistocene megafauna along ice-free corridors that stretched between the Laurentide and Cordilleran ice sheets. Another route proposed is that, either on foot or using primitive boats , they migrated down the Pacific coast to South America. Evidence of the latter would since have been covered by

4218-648: The Southern Rockies and parts of the Basin and Range Province . The river flows approximately 1,450 miles (2,330 km) into the Gulf of California , during which over time it has carved out natural phenomena such as the Grand Canyon and created phenomena such as the Salton Sea . The Columbia is a large river, 1,243 miles (2,000 km) long, in central western North America and is the most powerful river on

4329-606: The United Kingdom , three constituent countries of the Netherlands , three public bodies of the Netherlands, two unincorporated territories of the United States , and one uninhabited territory of the United States. In 2021 the total population of the Americas was about 1.03 billion people, divided as follows: There are three urban centers that each hold titles for being the largest population area based on

4440-448: The bedrock . This study is often known as Quaternary geology , after the Quaternary period of geologic history, which is the most recent period of geologic time. Magma is the original unlithified source of all igneous rocks . The active flow of molten rock is closely studied in volcanology , and igneous petrology aims to determine the history of igneous rocks from their original molten source to their final crystallization. In

4551-477: The enslavement of large numbers of the indigenous population of America. Diseases introduced from Europe and West Africa devastated the indigenous peoples , and the European powers colonized the Americas . Mass emigration from Europe , including large numbers of indentured servants , and importation of African slaves largely replaced the indigenous peoples in much of the Americas. Decolonization of

Sahul Shelf - Misplaced Pages Continue

4662-512: The geochemical evolution of rock units. Petrologists can also use fluid inclusion data and perform high temperature and pressure physical experiments to understand the temperatures and pressures at which different mineral phases appear, and how they change through igneous and metamorphic processes. This research can be extrapolated to the field to understand metamorphic processes and the conditions of crystallization of igneous rocks. This work can also help to explain processes that occur within

4773-402: The mantle below (separated within itself by seismic discontinuities at 410 and 660 kilometers), and the outer core and inner core below that. More recently, seismologists have been able to create detailed images of wave speeds inside the earth in the same way a doctor images a body in a CT scan . These images have led to a much more detailed view of the interior of the Earth, and have replaced

4884-440: The 1960s, it was discovered that the Earth's lithosphere , which includes the crust and rigid uppermost portion of the upper mantle , is separated into tectonic plates that move across the plastically deforming, solid, upper mantle, which is called the asthenosphere . This theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity. There

4995-957: The American continents, spanning the time of the original settlement in the Upper Paleolithic to European colonization during the Early Modern period . The term Pre-Columbian is used especially often in the context of the great indigenous civilizations of the Americas , such as those of Mesoamerica ( Olmec , Toltec , Teotihuacano , Zapotec , Mixtec , Aztec , Maya ) and the Andean civilizations ( Inca , Moche , Chavín , Muisca , Cañari ). Many pre-Columbian civilizations established characteristics and hallmarks which included permanent or urban settlements, agriculture, civic and monumental architecture, and complex societal hierarchies . Some of these civilizations had long faded by

5106-610: The Americas began with the American Revolution in the 1770s and largely ended with the Spanish–American War in the late 1890s. Currently, almost all of the population of the Americas resides in independent countries; however, the legacy of the colonization and settlement by Europeans is that the Americas share many common cultural traits, most notably Christianity and the use of West European languages: primarily Spanish , English , Portuguese , French , and, to

5217-582: The Americas from Asia between 20,000 and 16,000 years ago. A second migration of Na-Dene speakers followed later from Asia. The subsequent migration of the Inuit into the neoarctic c.  3500 BCE completed what is generally regarded as the settlement by the Indigenous peoples of the Americas . The first known European settlement in the Americas was by the Norse explorer Leif Erikson . However,

5328-495: The Americas , or more rarely America . When conceived as a unitary continent, the form is generally the continent of America in the singular. However, without a clarifying context, singular America in English commonly refers to the United States of America . The pre-Columbian era incorporates all period subdivisions in the history and prehistory of the Americas before the appearance of significant European influences on

5439-476: The Americas began with the first voyage of Christopher Columbus in 1492. The first Spanish settlement in the Americas was La Isabela in northern Hispaniola . This town was abandoned shortly after in favor of Santo Domingo de Guzmán , founded in 1496, the oldest American city of European foundation. This was the base from which the Spanish monarchy administered its new colonies and their expansion. Santo Domingo

5550-534: The Americas is Spanish , followed by English and Portuguese . The dominant language of Latin America is Spanish, though the most populous nation in Latin America, Brazil , speaks Portuguese . Small enclaves of French -, Dutch - and English-speaking regions also exist in Latin America, notably in French Guiana , Suriname , and Belize and Guyana respectively. Haitian Creole is dominant in

5661-597: The Americas is made up of the descendants of four large ethnic groups and their combinations. The majority of the population lives in Latin America , named for its predominant cultures, rooted in Latin Europe (including the two dominant languages, Spanish and Portuguese , both Romance languages ), more specifically in the Iberian nations of Portugal and Spain (hence the use of the term Ibero-America as

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5772-489: The Americas, such as the cougar , porcupine , opossums , armadillos , and hummingbirds . The geography of the western Americas is dominated by the American Cordillera , with the Andes running along the west coast of South America and the Rocky Mountains and other North American Cordillera ranges running along the western side of North America. The 2,300-kilometer-long (1,400 mi) Appalachian Mountains run along

5883-506: The Americas. Migration continued as people moved to the Americas fleeing religious persecution or seeking economic opportunities. Millions of individuals were forcibly transported to the Americas as slaves , prisoners or indentured servants . Decolonization of the Americas began with the American Revolution and the Haitian Revolution in the late 1700s. This was followed by numerous Latin American wars of independence in

5994-1165: The Aru Islands, and these lands share many Marsupial mammals, land birds, and freshwater fish as a result. Lydekker's Line , a biogeographical line, runs along the northwestern edge of the Sahul Shelf where it drops off into the deep waters of the Wallacea biogeographical area. Wallacea sits in a gap between the Sahul Shelf and the Sunda Shelf , part of the continental shelf of Southeast Asia. The land bridge enabled early human migrations to Australia . [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 Geology Geology (from Ancient Greek γῆ ( gê )  'earth' and λoγία ( -logía )  'study of, discourse')

6105-526: The Aru Islands. Earl also suggested the existence of the Sunda Shelf (which he called the "Great Asiatic Bank") covering the western Malay Archipelago and the Malay Peninsula . In the 1970s, biogeographers coined " Sundaland " and " Sahul " as contrastive names for the continental regions extending from the adjacent shelves. When sea levels fell during the Pleistocene ice age , including

6216-603: The Atlantic Ocean. The Mackenzie River is the largest in Canada and drains 1,805,200 square kilometers (697,000 sq mi). The largest river basin in South America is that of the Amazon , which has the highest volume flow of any river on Earth. The second largest watershed of South America is that of the Paraná River , which covers about 2.5 million km . North America and South America began to develop

6327-731: The Caribbean began to achieve peaceful independence well after World War II . Jamaica and Trinidad and Tobago became independent in 1962, and Guyana and Barbados both achieved independence in 1966. In the 1970s, the Bahamas , Grenada , Dominica , St. Lucia , and St. Vincent and the Grenadines all became independent of the United Kingdom, and Suriname became independent of the Netherlands. Belize , Antigua and Barbuda , and Saint Kitts and Nevis achieved independence from

6438-424: The Earth, such as subduction and magma chamber evolution. Structural geologists use microscopic analysis of oriented thin sections of geological samples to observe the fabric within the rocks, which gives information about strain within the crystalline structure of the rocks. They also plot and combine measurements of geological structures to better understand the orientations of faults and folds to reconstruct

6549-484: The Grand Canyon in the southwestern United States being a very visible example, the lower rock units were metamorphosed and deformed, and then deformation ended and the upper, undeformed units were deposited. Although any amount of rock emplacement and rock deformation can occur, and they can occur any number of times, these concepts provide a guide to understanding the geological history of an area. Geologists use

6660-534: The Hudson River Valley, and what later became New Jersey. The spread of new diseases brought by Europeans and African slaves killed many of the inhabitants of North America and South America, with a general population crash of Native Americans occurring in the mid-16th century, often well ahead of European contact. One of the most devastating diseases was smallpox . European immigrants were often part of state-sponsored attempts to found colonies in

6771-602: The Norse colonies and Europe was maintained, as James Watson Curran states: From 985 to 1410, Greenland was in touch with the world. Then silence. In 1492 the Vatican noted that no news of that country "at the end of the world" had been received for 80 years, and the bishopric of the colony was offered to a certain ecclesiastic if he would go and "restore Christianity" there. He didn't go. Although there had been previous trans-oceanic contact , large-scale European colonization of

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6882-778: The Pre-Dorset cultural group, the Dorset culture was displaced by the final migrants from the Bering sea coast line, the Thule people (the ancestors of modern Inuit ), by 1000  CE . Around the same time as the Inuit migrated into Greenland, Viking settlers began arriving in Greenland in 982 and Vinland shortly thereafter, establishing a settlement at L'Anse aux Meadows , near the northernmost tip of Newfoundland . Contact between

6993-496: The United Kingdom in the 1980s. The Americas make up most of the land in Earth's Western Hemisphere . The northernmost point of the Americas is Kaffeklubben Island , which is the most northerly point of land on Earth. The southernmost point is the islands of Southern Thule , although they are sometimes considered part of Antarctica . The mainland of the Americas is the world's longest north-to-south landmass. The distance between its two polar extremities, Murchison Promontory on

7104-635: The United Kingdom, starting with the Balfour Declaration of 1926 , Statute of Westminster 1931 , and ending with the patriation of the Canadian Constitution in 1982. The Dominion of Newfoundland similarly achieved independence under the Balfour Declaration and Statute of Westminster, but relinquished self-rule in 1934. It was subsequently confederated with Canada in 1949. The remaining European colonies in

7215-496: The United States, and more specifically in the US state of Colorado . The highest peaks of the Americas are located in the Andes , with Aconcagua of Argentina being the highest; in North America Denali (Mount McKinley) in the US state of Alaska is the tallest. Between its coastal mountain ranges, North America has vast flat areas. The Interior Plains spread over much of the continent, with low relief. The Canadian Shield covers almost 5 million km of North America and

7326-433: The West Coast of the Americas. In the far northwest of North America, the Yukon drains much of the Alaskan peninsula and flows 1,980 miles (3,190 km) from parts of Yukon and the Northwest Territory to the Pacific. Draining to the Arctic Ocean of Canada, the Mackenzie River drains waters from the Arctic Great Lakes of Arctic Canada, as opposed to the Saint-Lawrence River that drains the Great Lakes of Southern Canada into

7437-537: The beginning of the 20th century, advancement in geological science was facilitated by the ability to obtain accurate absolute dates to geological events using radioactive isotopes and other methods. This changed the understanding of geological time. Previously, geologists could only use fossils and stratigraphic correlation to date sections of rock relative to one another. With isotopic dates, it became possible to assign absolute ages to rock units, and these absolute dates could be applied to fossil sequences in which there

7548-425: The colonization never became permanent and was later abandoned. The Spanish voyages of Christopher Columbus from 1492 to 1504 resulted in permanent contact with European (and subsequently, other Old World ) powers, which eventually led to the Columbian exchange and inaugurated a period of exploration , conquest, and colonization whose effects and consequences persist to the present. The Spanish presence involved

7659-515: The creation of topographic gradients, causing material on the rock unit that is increasing in elevation to be eroded by hillslopes and channels. These sediments are deposited on the rock unit that is going down. Continual motion along the fault maintains the topographic gradient in spite of the movement of sediment and continues to create accommodation space for the material to deposit. Deformational events are often also associated with volcanism and igneous activity. Volcanic ashes and lavas accumulate on

7770-437: The crust, the uplift of mountain ranges, and paleo-topography. Fractionation of the lanthanide series elements is used to compute ages since rocks were removed from the mantle. Other methods are used for more recent events. Optically stimulated luminescence and cosmogenic radionuclide dating are used to date surfaces and/or erosion rates. Dendrochronology can also be used for the dating of landscapes. Radiocarbon dating

7881-423: The dates and routes traveled, are subject to ongoing research and discussion. Widespread habitation of the Americas occurred after the Late Glacial Maximum , from 16,000 to 13,000 years ago. The traditional theory has been that these early migrants moved into the Beringia land bridge between eastern Siberia and present-day Alaska around 40,000–17,000 years ago, when sea levels were significantly lowered during

7992-685: The early 1800s. Between 1811 and 1825, Paraguay , Argentina , Chile , Gran Colombia , the United Provinces of Central America , Mexico , Brazil , Peru , and Bolivia gained independence from Spain and Portugal in armed revolutions. After the Dominican Republic won independence from Haiti , it was re-annexed by Spain in 1861, but reclaimed its independence in 1865 at the conclusion of the Dominican Restoration War . The last violent episode of decolonization

8103-604: The east coast of North America from Alabama to Newfoundland . North of the Appalachians, the Arctic Cordillera runs along the eastern coast of Canada. The largest mountain ranges are the Andes and Rocky Mountains . The Sierra Nevada and the Cascade Range reach similar altitudes as the Rocky Mountains , but are significantly smaller. In North America, the greatest number of fourteeners are in

8214-570: The fault is a normal fault or a thrust fault . The principle of inclusions and components states that, with sedimentary rocks, if inclusions (or clasts ) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in

8325-403: The faults are not planar or because rock layers are dragged along, forming drag folds as slip occurs along the fault. Deeper in the Earth, rocks behave plastically and fold instead of faulting. These folds can either be those where the material in the center of the fold buckles upwards, creating " antiforms ", or where it buckles downwards, creating " synforms ". If the tops of the rock units within

8436-645: The first half of the 16th century, Spanish colonists conducted raids throughout the Caribbean Basin , bringing captives from Central America, northern South America, and Florida back to Hispaniola and other Spanish settlements. France, led by Jacques Cartier and Giovanni da Verrazzano , focused primarily on North America. English explorations of the Americas were led by Giovanni Caboto and Sir Walter Raleigh . The Dutch in New Netherland confined their operations to Manhattan Island, Long Island,

8547-483: The folds remain pointing upwards, they are called anticlines and synclines , respectively. If some of the units in the fold are facing downward, the structure is called an overturned anticline or syncline, and if all of the rock units are overturned or the correct up-direction is unknown, they are simply called by the most general terms, antiforms, and synforms. Even higher pressures and temperatures during horizontal shortening can cause both folding and metamorphism of

8658-404: The formation of faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault. Finding the key bed in these situations may help determine whether

8769-579: The geological history of the Earth as a whole. One aspect is to demonstrate the age of the Earth . Geology provides evidence for plate tectonics , the evolutionary history of life , and the Earth's past climates . Geologists broadly study the properties and processes of Earth and other terrestrial planets. Geologists use a wide variety of methods to understand the Earth's structure and evolution, including fieldwork , rock description , geophysical techniques , chemical analysis , physical experiments , and numerical modelling . In practical terms, geology

8880-412: The history of rock deformation in the area. In addition, they perform analog and numerical experiments of rock deformation in large and small settings. Americas The Americas , sometimes collectively called America , known initially as India Nova , are a landmass comprising the totality of North America and South America . When viewed as a single continent, the Americas or America

8991-525: The initial peopling of the Americas; Na Dene speakers found predominantly in North American groups at varying genetic rates with the highest frequency found among the Athabaskans at 42% derive from this second wave. Linguists and biologists have reached a similar conclusion based on analysis of Amerindian language groups and ABO blood group system distributions. Then the people of

9102-423: The internal composition and structure of the Earth. Seismologists can use the arrival times of seismic waves to image the interior of the Earth. Early advances in this field showed the existence of a liquid outer core (where shear waves were not able to propagate) and a dense solid inner core . These advances led to the development of a layered model of the Earth, with a lithosphere (including crust) on top,

9213-464: The later end of the scale, it is marked by the present day (in the Holocene epoch ). The following five timelines show the geologic time scale to scale. The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon. The second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in

9324-549: The length of the west coast. The flatter eastern side of the Americas is dominated by large river basins, such as the Amazon , St. Lawrence River – Great Lakes , Mississippi , and La Plata basins. Since the Americas extend 14,000 km (8,700 mi) from north to south, the climate and ecology vary widely, from the arctic tundra of Northern Canada , Greenland , and Alaska , to the tropical rainforests in Central America and South America. Humans first settled

9435-454: The lowest layer to deposition of the highest bed. The principle of faunal succession is based on the appearance of fossils in sedimentary rocks. As organisms exist during the same period throughout the world, their presence or (sometimes) absence provides a relative age of the formations where they appear. Based on principles that William Smith laid out almost a hundred years before the publication of Charles Darwin 's theory of evolution ,

9546-604: The mainland, while Nordostrundingen , in Greenland, is the most easterly point of the continental shelf. South America broke off from the west of the supercontinent Gondwana around 135 million years ago, forming its own continent. Around 15 million years ago, the collision of the Caribbean Plate and the Pacific Plate resulted in the emergence of a series of volcanoes along the border that created

9657-497: The mantle and show the crystallographic structures expected in the inner core of the Earth. The geological time scale encompasses the history of the Earth. It is bracketed at the earliest by the dates of the first Solar System material at 4.567 Ga (or 4.567 billion years ago) and the formation of the Earth at 4.54 Ga (4.54 billion years), which is the beginning of the Hadean eon  – a division of geological time. At

9768-405: The matrix. As a result, xenoliths are older than the rock that contains them. The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-bedding is inclined, the overall orientation of cross-bedded units

9879-413: The primary record of the majority of the geological history of the Earth. There are three major types of rock: igneous , sedimentary , and metamorphic . The rock cycle illustrates the relationships among them (see diagram). When a rock solidifies or crystallizes from melt ( magma or lava ), it is an igneous rock . This rock can be weathered and eroded , then redeposited and lithified into

9990-569: The principles of succession developed independently of evolutionary thought. The principle becomes quite complex, however, given the uncertainties of fossilization, localization of fossil types due to lateral changes in habitat ( facies change in sedimentary strata), and that not all fossils formed globally at the same time. Geologists also use methods to determine the absolute age of rock samples and geological events. These dates are useful on their own and may also be used in conjunction with relative dating methods or to calibrate relative methods. At

10101-423: The processes that have shaped that structure. Geologists study the mineralogical composition of rocks in order to get insight into their history of formation. Geology determines the relative ages of rocks found at a given location; geochemistry (a branch of geology) determines their absolute ages . By combining various petrological, crystallographic, and paleontological tools, geologists are able to chronicle

10212-428: The rocks. This metamorphism causes changes in the mineral composition of the rocks; creates a foliation , or planar surface, that is related to mineral growth under stress. This can remove signs of the original textures of the rocks, such as bedding in sedimentary rocks, flow features of lavas , and crystal patterns in crystalline rocks . Extension causes the rock units as a whole to become longer and thinner. This

10323-433: The simplified layered model with a much more dynamic model. Mineralogists have been able to use the pressure and temperature data from the seismic and modeling studies alongside knowledge of the elemental composition of the Earth to reproduce these conditions in experimental settings and measure changes within the crystal structure. These studies explain the chemical changes associated with the major seismic discontinuities in

10434-499: The southerly Dixie Alley in the North American late-winter and early spring seasons. Often parts of the Caribbean are exposed to the violent effects of hurricanes. These weather systems are formed by the collision of dry, cool air from Canada and wet, warm air from the Atlantic. With coastal mountains and interior plains, the Americas have several large river basins that drain the continents. The largest river basin in North America

10545-532: The southwestern United States, sedimentary, volcanic, and intrusive rocks have been metamorphosed, faulted, foliated, and folded. Even older rocks, such as the Acasta gneiss of the Slave craton in northwestern Canada , the oldest known rock in the world have been metamorphosed to the point where their origin is indiscernible without laboratory analysis. In addition, these processes can occur in stages. In many places,

10656-550: The subsurface. Sub-specialities of geology may distinguish endogenous and exogenous geology. Geological field work varies depending on the task at hand. Typical fieldwork could consist of: In addition to identifying rocks in the field ( lithology ), petrologists identify rock samples in the laboratory. Two of the primary methods for identifying rocks in the laboratory are through optical microscopy and by using an electron microprobe . In an optical mineralogy analysis, petrologists analyze thin sections of rock samples using

10767-407: The surface of the Earth and the convecting mantle is called plate tectonics . The development of plate tectonics has provided a physical basis for many observations of the solid Earth . Long linear regions of geological features are explained as plate boundaries: Plate tectonics has provided a mechanism for Alfred Wegener 's theory of continental drift , in which the continents move across

10878-488: The surface of the Earth over geological time. They also provided a driving force for crustal deformation, and a new setting for the observations of structural geology. The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convecting mantle. Advances in seismology , computer modeling , and mineralogy and crystallography at high temperatures and pressures give insights into

10989-479: The surface, and igneous intrusions enter from below. Dikes , long, planar igneous intrusions, enter along cracks, and therefore often form in large numbers in areas that are being actively deformed. This can result in the emplacement of dike swarms , such as those that are observable across the Canadian shield, or rings of dikes around the lava tube of a volcano. All of these processes do not necessarily occur in

11100-742: The surface. Igneous intrusions such as batholiths , laccoliths , dikes , and sills , push upwards into the overlying rock, and crystallize as they intrude. After the initial sequence of rocks has been deposited, the rock units can be deformed and/or metamorphosed . Deformation typically occurs as a result of horizontal shortening, horizontal extension , or side-to-side ( strike-slip ) motion. These structural regimes broadly relate to convergent boundaries , divergent boundaries , and transform boundaries, respectively, between tectonic plates. When rock units are placed under horizontal compression , they shorten and become thicker. Because rock units, other than muds, do not significantly change in volume , this

11211-473: The territories of the Americas under the colonial rule of European powers. In South America, Portugal played a significant role in the trafficking of enslaved Africans, with estimates suggesting that around 40% of all Africans forcibly brought to the Americas were taken to Brazil alone, to work primarily in sugar cane plantations, mining, and agricultural endeavors. In North America, the British Empire

11322-407: The third timeline, the most recent period is expanded in the fourth timeline, and the most recent epoch is expanded in the fifth timeline. Horizontal scale is Millions of years (above timelines) / Thousands of years (below timeline) Epochs: Methods for relative dating were developed when geology first emerged as a natural science . Geologists still use the following principles today as

11433-475: The three main demographic concepts: In accordance with these definitions, the three largest population centers in the Americas are: Mexico City , anchor to the largest metropolitan area in the Americas; New York City, anchor to the largest urban area in the Americas; and São Paulo, the largest city proper in the Americas. All three cities maintain Alpha classification and large scale influence. The population of

11544-533: The time of the first permanent European arrivals ( c.  late 15th –early 16th centuries), and are known only through archeological investigations. Others were contemporary with this period, and are also known from historical accounts of the time. A few, such as the Maya, had their own written records. However, most Europeans of the time viewed such texts as pagan, and much was destroyed in Christian pyres. Only

11655-519: Was coined in 1919 by G.A.F. Molengraaff , an authority on the geology of the then Dutch East Indies . The Sahul Shelf proper stretches northwest from Australia much of the way under the Timor Sea towards Timor, ending where the seabed begins descending into the Timor Trough . To the northeast, the Sahul Shelf merges into the Arafura Shelf, which runs from the northern coast of Australia under

11766-615: Was datable material, converting the old relative ages into new absolute ages. For many geological applications, isotope ratios of radioactive elements are measured in minerals that give the amount of time that has passed since a rock passed through its particular closure temperature , the point at which different radiometric isotopes stop diffusing into and out of the crystal lattice . These are used in geochronologic and thermochronologic studies. Common methods include uranium–lead dating , potassium–argon dating , argon–argon dating and uranium–thorium dating . These methods are used for

11877-566: Was first recorded in 1507. A two-dimensional globe created by Martin Waldseemüller was the earliest recorded use of the term. The name was also used (together with the related term Amerigen ) in the Cosmographiae Introductio , apparently written by Matthias Ringmann , in reference to South America. It was applied to both North and South America by Gerardus Mercator in 1538. "America" derives from Americus ,

11988-440: Was heavily involved in the transatlantic slave trade, with the establishment of colonies such as Virginia, where enslaved Africans were primarily used as labor in tobacco plantations and later in other agricultural and domestic sectors. This system perpetuated for centuries, shaping the socio-economic landscape of all nations of the hemisphere. After the Haitian Revolution led by Jean-Jacques Dessalines , which started in 1791 and

12099-570: Was subject to frequent raids by English and French pirates . On the continent, Panama City on the Pacific coast of Central America, founded on August 15, 1519, played an important role, being the base for the Spanish conquest of South America. Conquistador Lucas Vázquez de Ayllón established San Miguel de Guadalupe , the first European settlement in what is now the United States , on the Pee Dee River in South Carolina . During

12210-585: Was the Cuban War of Independence which became the Spanish–American War , which resulted in the independence of Cuba in 1898, and the transfer of sovereignty over Puerto Rico from Spain to the United States. Peaceful decolonization began with the United States's purchase of Louisiana from France in 1803, Florida from Spain in 1819, of Alaska from Russia in 1867, and the Danish West Indies from Denmark in 1916. Canada became independent of

12321-505: Was the only successful slave revolt in history, the world's first black republic was established. It started with the massacre of the white population, between 3,000 and 5,000 white men and women of all ages were killed. Dessalines declared: — Dessalines, first president of the Republic of Haiti, 1804 The most prevalent faiths in the Americas are as follows: Other faiths include Buddhism ; Hinduism ; Sikhism ; Baháʼí Faith ;

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