1.
North America
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North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be considered a subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, and to the southeast by South America and the Caribbean Sea. North America covers an area of about 24,709,000 square kilometers, about 16. 5% of the land area. North America is the third largest continent by area, following Asia and Africa, and the fourth by population after Asia, Africa, and Europe. In 2013, its population was estimated at nearly 565 million people in 23 independent states, or about 7. 5% of the worlds population, North America was reached by its first human populations during the last glacial period, via crossing the Bering land bridge. The so-called Paleo-Indian period is taken to have lasted until about 10,000 years ago, the Classic stage spans roughly the 6th to 13th centuries. The Pre-Columbian era ended with the migrations and the arrival of European settlers during the Age of Discovery. Present-day cultural and ethnic patterns reflect different kind of interactions between European colonists, indigenous peoples, African slaves and their descendants, European influences are strongest in the northern parts of the continent while indigenous and African influences are relatively stronger in the south. Because of the history of colonialism, most North Americans speak English, Spanish or French, the Americas are usually accepted as having been named after the Italian explorer Amerigo Vespucci by the German cartographers Martin Waldseemüller and Matthias Ringmann. Vespucci, who explored South America between 1497 and 1502, was the first European to suggest that the Americas were not the East Indies, but a different landmass previously unknown by Europeans. In 1507, Waldseemüller produced a map, in which he placed the word America on the continent of South America. He explained the rationale for the name in the accompanying book Cosmographiae Introductio, for Waldseemüller, no one should object to the naming of the land after its discoverer. He used the Latinized version of Vespuccis name, but in its feminine form America, following the examples of Europa, Asia and Africa. Later, other mapmakers extended the name America to the continent, In 1538. Some argue that the convention is to use the surname for naming discoveries except in the case of royalty, a minutely explored belief that has been advanced is that America was named for a Spanish sailor bearing the ancient Visigothic name of Amairick. Another is that the name is rooted in a Native American language, the term North America maintains various definitions in accordance with location and context. In Canadian English, North America may be used to refer to the United States, alternatively, usage sometimes includes Greenland and Mexico, as well as offshore islands
2.
Arctic Ocean
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The Arctic Ocean is the smallest and shallowest of the worlds five major oceans. Alternatively, the Arctic Ocean can be seen as the northernmost part of the all-encompassing World Ocean, located mostly in the Arctic north polar region in the middle of the Northern Hemisphere, the Arctic Ocean is almost completely surrounded by Eurasia and North America. It is partly covered by sea ice throughout the year and almost completely in winter, the summer shrinking of the ice has been quoted at 50%. The US National Snow and Ice Data Center uses satellite data to provide a record of Arctic sea ice cover. The Arctic may become ice free for the first time in human history within a few years or by 2040, for much of European history, the north polar regions remained largely unexplored and their geography conjectural. He was probably describing loose sea ice known today as growlers or bergy bits, his Thule was probably Norway, early cartographers were unsure whether to draw the region around the North Pole as land or water. The makers of navigational charts, more conservative than some of the more fanciful cartographers, tended to leave the region blank and this lack of knowledge of what lay north of the shifting barrier of ice gave rise to a number of conjectures. In England and other European nations, the myth of an Open Polar Sea was persistent, john Barrow, longtime Second Secretary of the British Admiralty, promoted exploration of the region from 1818 to 1845 in search of this. In the United States in the 1850s and 1860s, the explorers Elisha Kane, even quite late in the century, the eminent authority Matthew Fontaine Maury included a description of the Open Polar Sea in his textbook The Physical Geography of the Sea. Nevertheless, as all the explorers who travelled closer and closer to the reported, the polar ice cap is quite thick. Fridtjof Nansen was the first to make a crossing of the Arctic Ocean. The first surface crossing of the ocean was led by Wally Herbert in 1969, in a dog sled expedition from Alaska to Svalbard, with air support. The first nautical transit of the pole was made in 1958 by the submarine USS Nautilus. Since 1937, Soviet and Russian manned drifting ice stations have extensively monitored the Arctic Ocean, scientific settlements were established on the drift ice and carried thousands of kilometres by ice floes. In World War II, the European region of the Arctic Ocean was heavily contested, the Arctic Ocean occupies a roughly circular basin and covers an area of about 14,056,000 km2, almost the size of Antarctica. The coastline is 45,390 km long and it is surrounded by the land masses of Eurasia, North America, Greenland, and by several islands. It is connected to the Pacific Ocean by the Bering Strait and to the Atlantic Ocean through the Greenland Sea, countries bordering the Arctic Ocean are, Russia, Norway, Iceland, Greenland, Canada and the United States. There are several ports and harbours around the Arctic Ocean In Alaska, in Canada, ships may anchor at Churchill in Manitoba, Nanisivik in Nunavut, Tuktoyaktuk or Inuvik in the Northwest territories
3.
Canadian Shield
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Composed of igneous rock resulting from its long volcanic history, the area is covered by a thin layer of soil. Human population is sparse, and industrial development is minimal, while mining is prevalent, the Canadian Shield is a physiographic division, consisting of five smaller, physiographic provinces, the Laurentian Upland, Kazan Region, Davis, Hudson and James. The shield extends into the United States as the Adirondack Mountains, the Canadian Shield is U-shaped and is a subsection of the Laurentia craton signifying the area of greatest glacial impact creating the thin soils. The Canadian Shield is more than 3.96 billion years old, the Canadian Shield once had jagged peaks, higher than any of todays mountains, but millions of years of erosion have changed these mountains to rolling hills. The Canadian Shield was the first part of North America to be elevated above sea level and has remained almost wholly untouched by successive encroachments of the sea upon the continent. It is the Earths greatest area of exposed Archean rock, the metamorphic base rocks are mostly from the Precambrian Supereon, and have been repeatedly uplifted and eroded. Today it consists largely of an area of low relief 300 to 610 m above sea level with a few monadnocks, during the Pleistocene Epoch, continental ice sheets depressed the land surface, scooped out thousands of lake basins, and carried away much of the regions soil. When the Greenland section is included, the Shield is approximately circular, bounded on the northeast by the northeast edge of Greenland and it covers much of Greenland, Labrador, most of Quebec north of the St. In total, the area of the Shield covers approximately 8,000,000 km2. The underlying rock structure also includes Hudson Bay, the Canadian Shield is among the oldest on earth, with regions dating from 2.5 to 4.2 billion years. The multitude of rivers and lakes in the region is caused by the watersheds of the area being so young. It has some of the oldest volcanoes on the planet and it has over 150 volcanic belts whose bedrock ranges from 600 to 1200 million years old. Each belt probably grew by the coalescence of accumulations erupted from numerous vents, many of Canadas major ore deposits are associated with Precambrian volcanoes. The Sturgeon Lake Caldera in Kenora District, Ontario, is one of the worlds best preserved mineralized Neoarchean caldera complexes, the Canadian Shield also contains the Mackenzie dike swarm, which is the largest dike swarm known on Earth. Mountains have deep roots and float on the denser mantle much like an iceberg at sea, as mountains erode, their roots rise and are eroded in turn. The rocks that now form the surface of the Shield were once far below the Earths surface, the high pressures and temperatures at those depths provided ideal conditions for mineralization. Although these mountains are now eroded, many large mountains still exist in Canadas far north called the Arctic Cordillera. This is a vast deeply dissected mountain range, stretching from northernmost Ellesmere Island to the northernmost tip of Labrador, the ranges highest peak is Nunavuts Barbeau Peak at 2,616 metres above sea level
4.
Great Plains
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The region is known for supporting extensive cattle ranching and dry farming. The Canadian portion of the Plains is known as the Prairies, some geographers include some territory of northern Mexico in the Plains, but many stop at the Rio Grande. The term Great Plains is used in the United States to describe a sub-section of the even more vast Interior Plains physiographic division and it also has currency as a region of human geography, referring to the Plains Indians or the Plains States. There is no region referred to as the Great Plains in The Atlas of Canada, in terms of human geography, the term prairie is more commonly used in Canada, and the region is known as the Prairie Provinces or simply the Prairies. The region is about 500 mi east to west and 2,000 mi north to south, much of the region was home to American bison herds until they were hunted to near extinction during the mid/late 19th century. It has an area of approximately 500,000 sq mi, current thinking regarding the geographic boundaries of the Great Plains is shown by this map at the Center for Great Plains Studies, University of Nebraska–Lincoln. The term Great Plains, for the region west of about the 96th or 98th meridian, nevin Fennemans 1916 study, Physiographic Subdivision of the United States, brought the term Great Plains into more widespread usage. Before that the region was almost invariably called the High Plains, today the term High Plains is used for a subregion of the Great Plains. The Great Plains are the westernmost portion of the vast North American Interior Plains, during the Cretaceous Period, the Great Plains were covered by a shallow inland sea called the Western Interior Seaway. However, during the Late Cretaceous to the Paleocene, the seaway had begun to recede, leaving thick marine deposits. During the Cenozoic era, specifically about 25 million years ago during the Miocene and Pliocene epochs, existing forest biomes declined and grasslands became much more widespread. The grasslands provided a new niche for mammals, including many ungulates and glires, traditionally, the spread of grasslands and the development of grazers have been strongly linked. The vast majority of animals became extinct in North America at the end of the Pleistocene. In general, the Great Plains have a variety of weather through the year, with very cold and harsh winters and very hot. Wind speeds are very high, especially in winter. Grasslands are among the least protected biomes, humans have converted much of the prairies for agricultural purposes or to create pastures. The Great Plains have dust storms mostly every year or so, the 100th meridian roughly corresponds with the line that divides the Great Plains into an area that receive 20 in or more of rainfall per year and an area that receives less than 20 in. The region is subjected to extended periods of drought, high winds in the region may then generate devastating dust storms
5.
Tallgrass prairie
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The tallgrass prairie is an ecosystem native to central North America. They were characteristically found in the central forest-grasslands transition, the tall grasslands, the upper Midwest forest-savanna transition. They flourished in areas with loess soils and moderate rainfall around 30 to 35 inches per year. To the east were the eastern savannas. In the northeast, where fire was infrequent and periodic windthrow represented the source of disturbance. In contrast, shortgrass prairie was typical in the western Great Plains, due to expansive agricultural land use, very little tallgrass prairie remains. Retreating glaciers deposited the parent material for soil in the form of till, i. e. unsorted sediment, wind-dropped loess and organic matter accumulated, resulting in deep levels of topsoil. Animals such as bison, elk, deer, and rabbits added nitrogen to the soil through urine, Prairie dogs, a ground squirrel-like rodent considered to be a keystone species, dug tunnels that aerated the soil and channeled water several feet below the surface. For 5,000 to 8,000 years, more than 240 million acres of prairie grasslands were a feature of the landscape. Between 1800 and 1930, the vast majority was destroyed, settlers transformed what they named the Great American Desert or The Inland Sea into farmland. Further, extensive tile drainage has changed the water content and hydrodynamics. Tallgrass prairie is capable of supporting significant biodiversity, parts of the ecoregion among the top ten ecoregions for reptiles, birds, butterflies, and tree species. Tallgrass species are found in the understory layer, oak and hickory tree species occur in some areas, but generally in moderate densities. The tallgrass prairie biome depends on fires, a form of wildfire. Tree seedlings and intrusive alien species without fire tolerance are eliminated by periodic fires, such fires may either be set by humans or started naturally by lightning. Technically, prairies have less than 5–11% tree cover, a grass-dominated plant community with 10–49% tree cover is a savanna. After the steel plow was invented by John Deere, this fertile soil became one of Americas most important resources, over 95% of the original tallgrass prairie is now farmland. In Oklahoma, the tallgrass prairie has been maintained by ranchers and they have reintroduced plains bison to the vast expanses of grass
6.
Great Lakes
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Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth, containing 21% of the worlds surface fresh water by volume. The total surface is 94,250 square miles, and the volume is 5,439 cubic miles. Due to their sea-like characteristics the five Great Lakes have also long been referred to as inland seas, Lake Superior is the second largest lake in the world by area, and Lake Michigan is the largest lake that is entirely within one country. The southern half of the Great Lakes is bordered by the Great Lakes Megalopolis, the lakes have been a major highway for transportation, migration and trade, and they are home to a large number of aquatic species. Many invasive species have been introduced due to trade, and some threaten the regions biodiversity, though the five lakes reside in separate basins, they form a single, naturally interconnected body of fresh water, within the Great Lakes Basin. The lakes form a chain connecting the interior of North America to the Atlantic Ocean. From the interior to the outlet at the Saint Lawrence River, water flows from Superior to Huron and Michigan, southward to Erie, the lakes drain a large watershed via many rivers, and are studded with approximately 35,000 islands. There are also several smaller lakes, often called inland lakes. The surface area of the five primary lakes combined is roughly equal to the size of the United Kingdom, while the area of the entire basin is about the size of the UK. Lake Michigan is the one of the Great Lakes that is located entirely within the United States. The lakes are divided among the jurisdictions of the Canadian province of Ontario and the U. S. states of Minnesota, Wisconsin, Michigan, Illinois, Indiana, Ohio, Pennsylvania, and New York. Both Ontario and Michigan include in their boundaries portions of four of the lakes, Ontario does not border Lake Michigan, New York and Wisconsins jurisdictions extend into two lakes, and the remaining states into one of the lakes. This designation, however, is not universal and those living on the shore of Lake Superior often refer to all the other lakes as the lower lakes, because they are farther south. This corresponds to thinking of Lakes Erie and Ontario as down south, vessels sailing north on Lake Michigan are considered upbound even though they are sailing toward its effluent current. The Chicago River and Calumet River systems connect the Great Lakes Basin to the Mississippi River System through man-made alterations, the St. Marys River, including the Soo Locks, connects Lake Superior to Lake Huron. The Straits of Mackinac connect Lake Michigan to Lake Huron, the St. Clair River connects Lake Huron to Lake St. Clair. The Detroit River connects Lake St. Clair to Lake Erie, the Niagara River, including Niagara Falls, connects Lake Erie to Lake Ontario. The Welland Canal, bypassing the Falls, connects Lake Erie to Lake Ontario, the Saint Lawrence River connects Lake Ontario to the Gulf of St. Lawrence, which connects to the Atlantic Ocean
7.
Appalachian Plateau
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The Appalachian Plateau is a series of rugged, high plains located on the western side of the Appalachian Highlands. The Appalachian Highlands are a range that run down the entire east coast of the United States. The Appalachian Plateau is the part of the Appalachian Mountains. The formation of the plateau began during the Paleozoic Era, regional uplift during this time caused the area to rise altogether without changing the topography of the land. The eastern side of the plateau appears as a mountain range and this false appearance is due to a very steep slope on the eastern side known as the Allegheny Front. The eastern edge is the highest part of the Appalachian Plateau, in Pennsylvania, the altitude ranges from 1,750 to 3,000 feet and continues to rise towards West Virginia, where the elevation is around 4,800 feet. From West Virginia to Tennessee the elevation lowers to 3,000 feet, on the western side of the plateau, the elevation is 900 feet in Ohio, increasing to about 2,000 feet in Kentucky. From Kentucky the elevation drops down to 500 feet in northwestern Alabama, the plateau has a slight slant towards the northwest making it higher on the eastern side. A large portion of the plateau is a coalfield that was formed approximately 320 million years ago during the Pennsylvanian Age, the plateau was subjected to glaciation during the Pleistocene ice age. As a result, the topography of this section of the plateau is flat in comparison to the rest of the province. This portion of the plateau is marked evidence of a glaciated past including bogs, lakes. The topography of the rest of the plateau was created mainly from stream erosion, the result is a rugged landscape, unlike many other plateaus, that includes many narrow stream valleys surrounded by steep ridges. A physiographic region is a portion of land that is grouped together by several factors. Each region has similar geology, topography, and groups of plants, there are eight physiographic regions in the United States. Each region is divided into provinces, there are 25 provinces in the United States, each region is then divided into sections, creating 85 different physio-graphic sections in the United States. The Appalachian Plateau is a province of the physio-graphic region Appalachian Highlands, each section is classified under the Appalachian Plateau province because of its similarities in geologic makeup, topography, and wildlife. Likewise, the Appalachian Plateau falls under the classification of Appalachian Highlands because of similar characteristics. The rock underlying the Appalachian Plateau consists of a base of Precambrian rock, on top of the basement is a thick layer, approximately 20,000 feet, of a mixture of Cambrian, Ordovician, and Middle Silurian rock
8.
Craton
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A craton is an old and stable part of the continental lithosphere, where the lithosphere consists of the Earths two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and rifting of continents, cratons are found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by sedimentary rock. They have a thick crust and deep roots that extend as much as several hundred kilometres into the Earths mantle. The term craton is used to distinguish the stable portion of the continental crust from regions that are geologically active. Cratons can be described as shields, in which the basement rock crops out at the surface, the word craton was first proposed by the Austrian geologist Leopold Kober in 1921 as Kratogen, referring to stable continental platforms, and orogen as a term for mountain or orogenic belts. Later authors shortened the term to kraton and then to craton. Cratons are subdivided geographically into geologic provinces, a geologic province is a spatial entity with common geologic attributes. A province may include a single dominant structural element such as a basin or a fold belt. Adjoining provinces may appear similar in structure but be considered due to differing histories. At that depth, craton roots extend into the asthenosphere, craton lithosphere is distinctly different from oceanic lithosphere because cratons have a neutral or positive buoyancy, and a low intrinsic isopycnic density. This low density offsets density increases due to contraction and prevents the craton from sinking into the deep mantle. Cratonic lithosphere is much older than oceanic lithosphere—up to 4 billion years versus 180 million years, rock fragments carried up from the mantle by magmas containing peridotite have been delivered to the surface as inclusions in subvolcanic pipes called kimberlites. These inclusions have densities consistent with composition and are composed of mantle material residual from high degrees of partial melt. Peridotite is strongly influenced by the inclusion of moisture, craton peridotite moisture content is unusually low, which leads to much greater strength. It also contains high percentages of low-weight magnesium instead of higher-weight calcium, peridotites are important for understanding the deep composition and origin of cratons because peridotite nodules are pieces of mantle rock modified by partial melting. Harzburgite peridotites represent the crystalline residues after extraction of melts of compositions like basalt, an associated class of inclusions called eclogites, consists of rocks corresponding compositionally to oceanic crust that has metamorphosed under deep mantle conditions. Isotopic studies reveal that many eclogite inclusions are samples of ancient oceanic crust subducted billions of years ago to depths exceeding 150 km into the deep kimberlite diamond areas and they remained fixed there within the drifting tectonic plates until carried to the surface by deep-rooted magmatic eruptions
9.
Trans-Hudson orogeny
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It gave rise to the Trans-Hudson orogen, or Trans-Hudson Orogen Transect, which is the largest Paleoproterozoic orogenic belt in the world. It consists of a network of belts that were formed by Proterozoic crustal accretion, the event occurred 2. 0-1.8 billion years ago. The Trans-Hudson orogen sutured together the Hearne-Rae, Superior, and Wyoming cratons to form the core of North America in a network of Paleoproterozoic orogenic belts. To the south, the orogen contributed to the subsurface Phanerozoic strata in Montana, the Trans-Hudson orogeny was the culminating event of the Paleoproterozoic Laurentian assembly, which occurred after the Wopmay orogeny. Similar to the Himalayas, the Trans-Hudson orogeny was also the result of continent-continent collision along a suture zone, only the roots of this mountain chain remain, but these can be seen in northeastern Saskatchewan and in the Black Hills of South Dakota. The Black Hills of South Dakota is one of the few remaining exposed portions of the Trans-Hudson orogenic belt. The peaks of the Black Hills are 3,000 to 4,000 feet above the surrounding plains and these central spires and peaks all are carved from granite and other igneous and metamorphic rocks that form the core of the uplift. The nature and timing of this portion of the THO event in southern Laurentia is poorly understood, based on geophysical evidence, this zone has been broadly interpreted to be the southern extension of the THO that was later truncated by the ~1.680 Ga. Marine evidence indicates that the area opened to form an ocean called the Manikewan Ocean. Faulting, sedimentary and igneous rocks all indicate that divergence formed a valley that continued to spread until it resulted in a passive margin in which there was no tectonic activity. Shallow marine deposits formed on the shelves, and oceanic crust formed on the margins of the continental cratons as the divergence continued. Eventually the divergence stopped, then reversed direction, and collision occurred between continental land masses, during the Wopmay orogeny, subduction occurred as oceanic crust of the Slave Craton was subducted beneath an eastward moving continental plate. Likewise, during the Trans-Hudson orogeny, rifting at first separated the Superior craton from the rest of the continent, then the Superior Craton reversed its direction and the ocean basin began to close. A subduction zone formed as the oceanic crust of the Superior Craton was subducted beneath the Hearne, volcanic arcs developed as the cratons collided, eventually resulting in the THO mountain building. The Reindeer zone to the north is a 500 km wide collage of Paleoproterozoic arc volcanic rocks, plutons, volcanogenic sediments, most of these rocks evolved in an oceanic to transitional, subduction-related arc setting, with increasing influence of Archean crustal components to the northwest. The zone overlies Archean basement exposed in structural window that are now recognized as the Sask craton, the Wathaman-Chipewyan batholith is an Andean-type continental-margin, magmatic arc emplaced 1. 86-1.85 Ga. The Flin Flon domain is in the center of the Trans-Hudson Suture Zone and it is west of the Superior Craton, south of the Kisseynew Domain, and east of the Glennie Domain. The Superior Boundary zone is a narrow, southeastern, ensialic foreland zone bordering Superior Craton, comprising the Thompson Belt, Split Lake Block, most of mined VMS deposits in the Flin Flon belt are associated with juvenile arc volcanic rocks providing a powerful focus for future explorations
10.
Metamorphic rock
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Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means change in form. The original rock is subjected to heat and pressure, causing profound physical and/or chemical change, the protolith may be a sedimentary, an igneous, or even an existing type of metamorphic rock. Metamorphic rocks make up a part of the Earths crust. They are classified by texture and by chemical and mineral assemblage and they may be formed simply by being deep beneath the Earths surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure and they are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earths interior. The study of rocks provides information about the temperatures and pressures that occur at great depths within the Earths crust. Some examples of rocks are gneiss, slate, marble, schist. Metamorphic minerals are those that only at the high temperatures and pressures associated with the process of metamorphism. These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet. Other minerals, such as olivines, pyroxenes, amphiboles, micas, feldspars, and quartz, may be found in metamorphic rocks and these minerals formed during the crystallization of igneous rocks. They are stable at temperatures and pressures and may remain chemically unchanged during the metamorphic process. However, all minerals are only within certain limits. The change in the size of the rock during the process of metamorphism is called recrystallization. Both high temperatures and pressures contribute to recrystallization, high temperatures allow the atoms and ions in solid crystals to migrate, thus reorganizing the crystals, while high pressures cause solution of the crystals within the rock at their point of contact. The layering within metamorphic rocks is called foliation, and it occurs when a rock is being shortened along one axis during recrystallization. This causes the platy or elongated crystals of minerals, such as mica and chlorite and this results in a banded, or foliated rock, with the bands showing the colors of the minerals that formed them. Textures are separated into foliated and non-foliated categories, foliated rock is a product of differential stress that deforms the rock in one plane, sometimes creating a plane of cleavage. For example, slate is a metamorphic rock, originating from shale
11.
Igneous rock
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Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava, the magma can be derived from partial melts of existing rocks in either a planets mantle or crust. Typically, the melting is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earths crust by volume. Igneous rocks form about 15% of the Earths current land surface, most of the Earths oceanic crust is made of igneous rock. In terms of modes of occurrence, igneous rocks can be either intrusive or extrusive, the mineral grains in such rocks can generally be identified with the naked eye. Intrusive rocks can also be classified according to the shape and size of the intrusive body, typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes. When the magma solidifies within the earths crust, it cools slowly forming coarse textured rocks, such as granite, gabbro, the central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores may occupy huge areas of the Earths surface, intrusive igneous rocks that form at depth within the crust are termed plutonic rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks, hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, sills, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks, also known as rocks, are formed at the crusts surface as a result of the partial melting of rocks within the mantle. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks and they are formed by the cooling of molten magma on the earths surface. The magma, which is brought to the surface through fissures or volcanic eruptions, hence such rocks are smooth, crystalline and fine-grained. Basalt is an extrusive igneous rock and forms lava flows, lava sheets. Some kinds of basalt solidify to form long polygonal columns, the Giants Causeway in Antrim, Northern Ireland is an example. The molten rock, with or without suspended crystals and gas bubbles, is called magma and it rises because it is less dense than the rock from which it was created. When magma reaches the surface from beneath water or air, it is called lava, eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of volcanic activity
12.
Black Hills
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The Black Hills are a small, isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, United States. Black Elk Peak, which rises to 7,244 feet, is the ranges highest summit, the Black Hills encompass the Black Hills National Forest. The name Black Hills is a translation of the Lakota Pahá Sápa, the hills were so-called because of their dark appearance from a distance, as they were covered in trees. Native Americans have a history in the Black Hills. After conquering the Cheyenne in 1776, the Lakota took over the territory of the Black Hills, however, when settlers discovered gold there in 1874, as a result of George Armstrong Custers Black Hills Expedition, miners swept into the area in a gold rush. As the economy of the Black Hills has shifted from natural resources since the late 20th century, locals tend to divide the Black Hills into two areas, The Southern Hills and The Northern Hills. Attractions in the Northern Hills include Spearfish Canyon, historic Deadwood, the first Rally was held on August 14,1938 and the 75th Rally in 2015 saw more than 1 million bikers visit the Black Hills. Devils Tower National Monument, located in the Wyoming Black Hills, is an important nearby attraction and was the United States first national monument. Scientists have been able to utilize carbon-dating to evaluate the age of tools found in the area, stratigraphic records indicate environmental changes in the land, such as flood and drought patterns. For example, large-scale flooding of the Black Hill basins occurs at a probability rate of 0.01, however, during The Medieval Climate Anomaly, or the Medieval Warm Period, flooding increased in the basins. The Arikara arrived by AD1500, followed by the Cheyenne, Crow, Kiowa, the Lakota arrived from Minnesota in the 18th century and drove out the other tribes, who moved west. They claimed the land, which they called Ȟe Sápa, the mountains commonly became known as the Black Hills. François and Louis de La Vérendrye probably travelled near the Black Hills in 1743, fur trappers and traders had some dealings with the Native Americans. European Americans increasingly encroached on Lakota territory, in this treaty, they protected the Black Hills forever from European-American settlement. Both the Sioux and Cheyenne also claimed rights to the land, saying that in their cultures, it was considered the axis mundi, an official announcement of gold was made by the newspaper reporters accompanying the expedition. The following year, the Newton-Jenney Party conducted the first detailed survey of the Black Hills, the surveyor for the party, Dr. Valentine McGillycuddy, was the first European American to ascend to the top of Black Elk Peak. This highest point in the Black Hills is 7,242 feet above sea level, during the 1875–1878 gold rush, thousands of miners went to the Black Hills, in 1880, the area was the most densely populated part of the Dakota Territory. Three large towns developed in the Northern Hills, Deadwood, Central City, around these were groups of smaller gold camps, towns, and villages
13.
South Dakota
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South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux Native American tribes, South Dakota is the 17th most expansive, but the 5th least populous and the 5th least densely populated of the 50 United States. Once the southern portion of the Dakota Territory, South Dakota became a state on November 2,1889, Pierre is the state capital and Sioux Falls, with a population of about 171,000, is South Dakotas largest city. South Dakota is bordered by the states of North Dakota, Minnesota, Iowa, Nebraska, Wyoming, the state is bisected by the Missouri River, dividing South Dakota into two geographically and socially distinct halves, known to residents as East River and West River. Eastern South Dakota is home to most of the states population, West of the Missouri, ranching is the predominant agricultural activity, and the economy is more dependent on tourism and defense spending. Most of the Native American reservations are located in West River, the Black Hills, a group of low pine-covered mountains sacred to the Sioux, are located in the southwest part of the state. Mount Rushmore, a major tourist destination, is located there, South Dakota experiences a temperate continental climate, with four distinct seasons and precipitation ranging from moderate in the east to semi-arid in the west. The ecology of the state features species typical of a North American grassland biome, humans have inhabited the area for several millennia, with the Sioux becoming dominant by the early 19th century. In the late 19th century, European-American settlement intensified after a rush in the Black Hills. Encroaching miners and settlers triggered a number of Indian wars, ending with the Wounded Knee Massacre in 1890, historically dominated by an agricultural economy and a rural lifestyle, South Dakota has recently sought to diversify its economy in areas to attract and retain residents. South Dakotas history and rural character still strongly influence the culture of the state, South Dakota is situated in the north-central United States, and is considered a part of the Midwest by the U. S. Census Bureau, it is also part of the Great Plains region. The culture, economy, and geography of western South Dakota have more in common with the West than the Midwest, South Dakota has a total area of 77,116 square miles, making the state the 17th largest in the Union. Black Elk Peak, formerly named Harney Peak, with an elevation of 7,242 ft, is the states highest point, while the shoreline of Big Stone Lake is the lowest, with an elevation of 966 ft. South Dakota is bordered to the north by North Dakota, to the south by Nebraska, to the east by Iowa and Minnesota, the geographical center of the U. S. is 17 miles west of Castle Rock in Butte County. The North American continental pole of inaccessibility is located between Allen and Kyle,1,024 mi from the nearest coastline, the Missouri River is the largest and longest river in the state. Other major South Dakota rivers include the Cheyenne, James, Big Sioux, Eastern South Dakota has many natural lakes, mostly created by periods of glaciation. Additionally, dams on the Missouri River create four large reservoirs, Lake Oahe, Lake Sharpe, Lake Francis Case, South Dakota can generally be divided into three regions, eastern South Dakota, western South Dakota, and the Black Hills. The Missouri River serves as a boundary in terms of geographic, social, at times the Black Hills are combined with the rest of western South Dakota, and people often refer to the resulting two regions divided by the Missouri River as West River and East River
14.
Plate tectonics
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The theoretical model builds on the concept of continental drift developed during the first few decades of the 20th century. The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s, the lithosphere, which is the rigid outermost shell of a planet, is broken up into tectonic plates. The Earths lithosphere is composed of seven or eight major plates, where the plates meet, their relative motion determines the type of boundary, convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries. The relative movement of the plates typically ranges from zero to 100 mm annually, tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction carries plates into the mantle, the material lost is balanced by the formation of new crust along divergent margins by seafloor spreading. In this way, the surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle, earlier theories, since disproven, proposed gradual shrinking or gradual expansion of the globe. Tectonic plates are able to move because the Earths lithosphere has greater strength than the underlying asthenosphere. Lateral density variations in the result in convection. Plate movement is thought to be driven by a combination of the motion of the seafloor away from the ridge and drag, with downward suction. Another explanation lies in the different forces generated by forces of the Sun. The relative importance of each of these factors and their relationship to other is unclear. The outer layers of the Earth are divided into the lithosphere and asthenosphere and this is based on differences in mechanical properties and in the method for the transfer of heat. Mechanically, the lithosphere is cooler and more rigid, while the asthenosphere is hotter, in terms of heat transfer, the lithosphere loses heat by conduction, whereas the asthenosphere also transfers heat by convection and has a nearly adiabatic temperature gradient. The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, Plate motions range up to a typical 10–40 mm/year, to about 160 mm/year. The driving mechanism behind this movement is described below, tectonic lithosphere plates consist of lithospheric mantle overlain by either or both of two types of crustal material, oceanic crust and continental crust. Average oceanic lithosphere is typically 100 km thick, its thickness is a function of its age, as passes, it conductively cools
15.
United States
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Forty-eight of the fifty states and the federal district are contiguous and located in North America between Canada and Mexico. The state of Alaska is in the northwest corner of North America, bordered by Canada to the east, the state of Hawaii is an archipelago in the mid-Pacific Ocean. The U. S. territories are scattered about the Pacific Ocean, the geography, climate and wildlife of the country are extremely diverse. At 3.8 million square miles and with over 324 million people, the United States is the worlds third- or fourth-largest country by area, third-largest by land area. It is one of the worlds most ethnically diverse and multicultural nations, paleo-Indians migrated from Asia to the North American mainland at least 15,000 years ago. European colonization began in the 16th century, the United States emerged from 13 British colonies along the East Coast. Numerous disputes between Great Britain and the following the Seven Years War led to the American Revolution. On July 4,1776, during the course of the American Revolutionary War, the war ended in 1783 with recognition of the independence of the United States by Great Britain, representing the first successful war of independence against a European power. The current constitution was adopted in 1788, after the Articles of Confederation, the first ten amendments, collectively named the Bill of Rights, were ratified in 1791 and designed to guarantee many fundamental civil liberties. During the second half of the 19th century, the American Civil War led to the end of slavery in the country. By the end of century, the United States extended into the Pacific Ocean. The Spanish–American War and World War I confirmed the status as a global military power. The end of the Cold War and the dissolution of the Soviet Union in 1991 left the United States as the sole superpower. The U. S. is a member of the United Nations, World Bank, International Monetary Fund, Organization of American States. The United States is a developed country, with the worlds largest economy by nominal GDP. It ranks highly in several measures of performance, including average wage, human development, per capita GDP. While the U. S. economy is considered post-industrial, characterized by the dominance of services and knowledge economy, the United States is a prominent political and cultural force internationally, and a leader in scientific research and technological innovations. In 1507, the German cartographer Martin Waldseemüller produced a map on which he named the lands of the Western Hemisphere America after the Italian explorer and cartographer Amerigo Vespucci
16.
Canada
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Canada is a country in the northern half of North America. Canadas border with the United States is the worlds longest binational land border, the majority of the country has a cold or severely cold winter climate, but southerly areas are warm in summer. Canada is sparsely populated, the majority of its territory being dominated by forest and tundra. It is highly urbanized with 82 per cent of the 35.15 million people concentrated in large and medium-sized cities, One third of the population lives in the three largest cities, Toronto, Montreal and Vancouver. Its capital is Ottawa, and other urban areas include Calgary, Edmonton, Quebec City, Winnipeg. Various aboriginal peoples had inhabited what is now Canada for thousands of years prior to European colonization. Pursuant to the British North America Act, on July 1,1867, the colonies of Canada, New Brunswick and this began an accretion of provinces and territories to the mostly self-governing Dominion to the present ten provinces and three territories forming modern Canada. With the Constitution Act 1982, Canada took over authority, removing the last remaining ties of legal dependence on the Parliament of the United Kingdom. Canada is a parliamentary democracy and a constitutional monarchy, with Queen Elizabeth II being the head of state. The country is officially bilingual at the federal level and it is one of the worlds most ethnically diverse and multicultural nations, the product of large-scale immigration from many other countries. Its advanced economy is the eleventh largest in the world, relying chiefly upon its abundant natural resources, Canadas long and complex relationship with the United States has had a significant impact on its economy and culture. Canada is a country and has the tenth highest nominal per capita income globally as well as the ninth highest ranking in the Human Development Index. It ranks among the highest in international measurements of government transparency, civil liberties, quality of life, economic freedom, Canada is an influential nation in the world, primarily due to its inclusive values, years of prosperity and stability, stable economy, and efficient military. While a variety of theories have been postulated for the origins of Canada. In 1535, indigenous inhabitants of the present-day Quebec City region used the word to direct French explorer Jacques Cartier to the village of Stadacona, from the 16th to the early 18th century Canada referred to the part of New France that lay along the St. Lawrence River. In 1791, the area became two British colonies called Upper Canada and Lower Canada collectively named The Canadas, until their union as the British Province of Canada in 1841. Upon Confederation in 1867, Canada was adopted as the name for the new country at the London Conference. The transition away from the use of Dominion was formally reflected in 1982 with the passage of the Canada Act, later that year, the name of national holiday was changed from Dominion Day to Canada Day
17.
Western Interior Seaway
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The ancient sea stretched from the Gulf of Mexico and through the middle of the modern-day countries of the United States and Canada, meeting with the Arctic Ocean to the north. At its largest, it was 2,500 feet deep,600 miles wide, the Seaway was created as the Farallon tectonic plate subducted under the North American Plate during the Cretaceous. As plate convergence proceeded, the younger and more buoyant lithosphere of the Farallon Plate subducted at a shallow angle, in what is known as a flat slab. This shallowly subducting slab exerted traction on the base of the lithosphere, pulling it down, in the south, the Gulf of Mexico was an extension of the Tethys Sea, which met with the Mowry Sea in the late Cretaceous, forming the complete Seaway. At its largest, the Western Interior Seaway stretched from the Rockies east to the Appalachians, at its deepest, it may have been only 800 or 900 metres deep, shallow in terms of seas. Two great continental watersheds drained into it from east and west, diluting its waters, there was little sedimentation on the eastern shores of the Seaway, the western boundary, however, consisted of a thick clastic wedge eroded eastward from the Sevier orogenic belt. The western shore was thus highly variable, depending on variations in sea level, widespread carbonate deposition suggests that the Seaway was warm and tropical, with abundant calcareous algae. Remnants of these deposits are found throughout the state of Kansas, one prominent example is Monument Rocks, an exposed chalk formation towering 70 feet over the surrounding range land. It is designated a National Natural Landmark and one of the Eight Wonders of Kansas and it is located 25 miles south of Oakley, Kansas. At a few times during the late Cretaceous the Western Interior Seaway went through periods of anoxia, where the water was devoid of oxygen. The Western Interior Seaway divided across the Dakotas and retreated south towards the Gulf of Mexico and this shrunken, regressive phase of the Western Interior Seaway is sometimes called the Pierre Seaway. During the early Paleocene, parts of the Western Interior Seaway still occupied areas of the Mississippi Embayment, later transgression, however, was associated with the Cenozoic Tejas sequence, rather than with the previous event responsible for the Seaway. The Western Interior Seaway was a sea, filled with abundant marine life. Interior Seaway denizens included predatory marine reptiles such as plesiosaurs, icthyornis shared the sky with large pterosaurs such as Nyctosaurus and Pteranodon. Pteranodon fossils are common and it was probably a major component of the surface ecosystem. On the bottom, the giant clam Inoceramus left common fossilized shells in the Pierre Shale and this clam had a thick shell paved with prisms of calcite deposited perpendicular to the surface, giving it a pearly luster in life
18.
Sediment
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For sediment in beverages, see dregs. For example, sand and silt can be carried in suspension in water and on reaching the sea be deposited by sedimentation. Sediments are most often transported by water, but also wind, beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of transport and deposition. Glacial moraine deposits and till are ice-transported sediments, sediment can be classified based on its grain size and/or its composition. Sediment size is measured on a log base 2 scale, called the Phi scale, composition of sediment can be measured in terms of, parent rock lithology mineral composition chemical make-up. This leads to an ambiguity in which clay can be used as both a size-range and a composition, sediment is transported based on the strength of the flow that carries it and its own size, volume, density, and shape. Stronger flows will increase the lift and drag on the particle, causing it to rise, rivers and streams carry sediment in their flows. This sediment can be in a variety of locations within the flow and these relationships are shown in the following table for the Rouse number, which is a ratio of sediment fall velocity to upwards velocity. If the upwards velocity is less than the settling velocity, but still high enough for the sediment to move, it will move along the bed as bed load by rolling, sliding. If the upwards velocity is higher than the velocity, the sediment will be transported high in the flow as wash load. As there are generally a range of different particle sizes in the flow, sediment motion can create self-organized structures such as ripples, dunes, antidunes on the river or stream bed. These bedforms are often preserved in rocks and can be used to estimate the direction. Overland flow can erode soil particles and transport them downslope, the erosion associated with overland flow may occur through different methods depending on meteorological and flow conditions. If the initial impact of rain droplets dislodges soil, the phenomenon is called rainsplash erosion, if overland flow is directly responsible for sediment entrainment but does not form gullies, it is called sheet erosion. If the flow and the substrate permit channelization, gullies may form, glaciers carry a wide range of sediment sizes, and deposit it in moraines. The overall balance between sediment in transport and sediment being deposited on the bed is given by the Exner equation and this expression states that the rate of increase in bed elevation due to deposition is proportional to the amount of sediment that falls out of the flow. This can be localized, and simply due to obstacles, examples are scour holes behind boulders, where flow accelerates
19.
Rocky Mountains
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The Rocky Mountains, commonly known as the Rockies, are a major mountain range in western North America. The Rocky Mountains stretch more than 3,000 miles from the northernmost part of British Columbia, in western Canada, to New Mexico, in the Southwestern United States. Within the North American Cordillera, the Rockies are somewhat distinct from the Pacific Coast Ranges, the Rocky Mountains were initially formed from 80 million to 55 million years ago during the Laramide orogeny, in which a number of plates began to slide underneath the North American plate. The angle of subduction was shallow, resulting in a belt of mountains running down western North America. Since then, further tectonic activity and erosion by glaciers have sculpted the Rockies into dramatic peaks, at the end of the last ice age, humans started to inhabit the mountain range. The first mention of their present name by a European was in the journal of Jacques Legardeur de Saint-Pierre in 1752, the Rocky Mountains are commonly defined as stretching from the Liard River in British Columbia south to the Rio Grande in New Mexico. The United States definition of the Rockies includes the Cabinet and Salish Mountains of Idaho and their counterparts north of the Kootenai River, the Columbia Mountains, are considered a separate system in Canada, lying to the west of the huge Rocky Mountain Trench. This runs the length of British Columbia from its beginnings in the middle Flathead River valley in western Montana to the bank of the Liard River. The Rockies vary in width from 70 to 300 miles, also west of the Rocky Mountain Trench, farther north and facing the Muskwa Range across the trench, are the Stikine Ranges and Omineca Mountains of the Interior Mountains system of British Columbia. A small area east of Prince George, British Columbia on the side of the Trench. In Canada geographers define three main groups of ranges, the Continental Ranges, Hart Ranges and Muskwa Ranges, the Muskwa and Hart Ranges together comprise what is known as the Northern Rockies. The western edge of the Rockies includes ranges such as the Wasatch near Salt Lake City, the Great Basin and Columbia River Plateau separate these sub-ranges from distinct ranges further to the west, most prominent among which are the Sierra Nevada, Cascade Range and Coast Mountains. The Rocky Mountain System within the United States is a United States physiographic region, the Rocky Mountains are notable for containing the highest peaks in central North America. The ranges highest peak is Mount Elbert located in Colorado at 14,440 feet above sea level, Mount Robson in British Columbia, at 12,972 feet, is the highest peak in the Canadian Rockies. The Continental Divide of the Americas is located in the Rocky Mountains, triple Divide Peak in Glacier National Park is so named because water that falls on the mountain reaches not only the Atlantic and Pacific, but Hudson Bay as well. Farther north in Alberta, the Athabasca and other rivers feed the basin of the Mackenzie River, see Rivers of the Rocky Mountains for a list of rivers. Human population is not very dense in the Rocky Mountains, with an average of four people per square kilometer, however, the human population grew rapidly in the Rocky Mountain states between 1950 and 1990. The 40-year statewide increases in range from 35% in Montana to about 150% in Utah
20.
Sedimentary rock
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Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earths surface and within bodies of water. Sedimentation is the name for processes that cause mineral and/or organic particles to settle in place. The particles that form a rock by accumulating are called sediment. Sedimentation may also occur as minerals precipitate from solution or shells of aquatic creatures settle out of suspension. The sedimentary rock cover of the continents of the Earths crust is extensive, sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding, sedimentary rocks are also important sources of natural resources like coal, fossil fuels, drinking water or ores. The study of the sequence of rock strata is the main source for an understanding of the Earths history, including palaeogeography, paleoclimatology. The scientific discipline that studies the properties and origin of rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps partly with other disciplines in the Earth sciences, such as pedology, geomorphology, geochemistry, sedimentary rocks have also been found on Mars. Clastic sedimentary rocks are composed of rock fragments that were cemented by silicate minerals. Clastic rocks are composed largely of quartz, feldspar, rock fragments, clay minerals, and mica, any type of mineral may be present, clastic sedimentary rocks, are subdivided according to the dominant particle size. Most geologists use the Udden-Wentworth grain size scale and divide unconsolidated sediment into three fractions, gravel, sand, and mud and this tripartite subdivision is mirrored by the broad categories of rudites, arenites, and lutites, respectively, in older literature. The subdivision of these three categories is based on differences in clast shape, conglomerates and breccias), composition. Conglomerates are dominantly composed of rounded gravel, while breccias are composed of dominantly angular gravel, composition of framework grains The relative abundance of sand-sized framework grains determines the first word in a sandstone name. Naming depends on the dominance of the three most abundant components quartz, feldspar, or the lithic fragments that originated from other rocks, all other minerals are considered accessories and not used in the naming of the rock, regardless of abundance. Clean sandstones with open space are called arenites. Muddy sandstones with abundant muddy matrix are called wackes, six sandstone names are possible using the descriptors for grain composition and the amount of matrix. Mudrocks are sedimentary rocks composed of at least 50% silt- and clay-sized particles and these relatively fine-grained particles are commonly transported by turbulent flow in water or air, and deposited as the flow calms and the particles settle out of suspension
21.
Coral reef
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Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups, the polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons which support, most reefs grow best in warm, shallow, clear, sunny and agitated waters. Often called rainforests of the sea, shallow coral reefs form some of the most diverse ecosystems on Earth, paradoxically, coral reefs flourish even though they are surrounded by ocean waters that provide few nutrients. They are most commonly found at depths in tropical waters. Coral reefs deliver ecosystem services to tourism, fisheries and shoreline protection, the annual global economic value of coral reefs is estimated between US$29. 8-375 billion. However, coral reefs are fragile ecosystems, partly because they are sensitive to water temperature. Most of the coral reefs we can see today were formed after the last glacial period when melting ice caused the sea level to rise and this means that most modern coral reefs are less than 10,000 years old. As communities established themselves on the shelves, the reefs grew upwards, Reefs that rose too slowly could become drowned reefs. They are covered by so much water there was insufficient light. Coral reefs are found in the sea away from continental shelves, around oceanic islands. The vast majority of islands are volcanic in origin. The few exceptions have tectonic origins where plate movements have lifted the deep ocean floor on the surface. In 1842 in his first monograph, The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs and he theorized uplift and subsidence of the Earths crust under the oceans formed the atolls. Darwin’s theory sets out a sequence of three stages in atoll formation and it starts with a fringing reef forming around an extinct volcanic island as the island and ocean floor subsides. As the subsidence continues, the reef becomes a barrier reef. Darwin predicted that underneath each lagoon would be a bed rock base, where the level of the underlying earth allows, the corals grow around the coast to form what he called fringing reefs, and can eventually grow out from the shore to become a barrier reef
22.
Paleozoic
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The Paleozoic Era is the earliest of three geologic eras of the Phanerozoic Eon, from 541 to 252.17 million years ago. It is the longest of the Phanerozoic eras, and is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous. The Paleozoic comes after the Neoproterozoic era of the Proterozoic and is followed by the Mesozoic, the Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earths history, known as the Cambrian explosion, fish, arthropods, amphibians, anapsids, synapsids, euryapsids and diapsids all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, Great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, large, sophisticated diapsids and synapsids were dominant, the Paleozoic Era ended with the largest extinction event in the history of Earth, the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover, recovery of life in the sea may have been much faster. The Paleozoic era began and ended with supercontinents and in between were the rise of mountains along the margins, and flooding and draining of shallow seas between. At its start, the supercontinent Pannotia broke up, paleoclimatic studies and evidence of glaciers indicate that central Africa was most likely in the polar regions during the early Paleozoic. During the early Paleozoic, the huge continent Gondwana formed or was forming, by mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. There are six periods in the Paleozoic Era, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, the Cambrian spans from 541 million years to 485 million years and is the first period of the Paleozoic era of the Phanerozoic. The Cambrian marked a boom in evolution in an event known as the Cambrian explosion in which the largest number of creatures evolved in any period of the history of the Earth. Creatures like algae evolved, but the most ubiquitous of that period were the armored arthropods, almost all marine phyla evolved in this period. During this time, the supercontinent Pannotia begins to break up, the Ordovician spanned from 485 million years to 443 million years ago. The Ordovician is a time in Earths history in many of the biological classes still prevalent today evolved, such as primitive fish, cephalopods. The most common forms of life, however, were trilobites, snails, more importantly, the first arthropods went ashore to colonize the empty continent of Gondwana. By the end of the Ordovican, Gondwana was at the pole, early North America had collided with Europe. Glaciation of Africa resulted in a drop in sea level
23.
Mesozoic
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The Mesozoic Era is an interval of geological time from about 252 to 66 million years ago. This Era is also called from a paleobotanist view the Age of Conifers, Mesozoic means middle life, deriving from the Greek prefix meso-/μεσο- for between and zōon/ζῷον meaning animal or living being. It is one of three eras of the Phanerozoic Eon, preceded by the Paleozoic and succeeded by the Cenozoic. The era is subdivided into three periods, the Triassic, Jurassic, and Cretaceous, which are further subdivided into a number of epochs. The Mesozoic was a time of significant tectonic, climate and evolutionary activity, the era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses that would eventually move into their current positions. The climate of the Mesozoic was varied, alternating between warming and cooling periods, overall, however, the Earth was hotter than it is today. Birds first appeared in the Jurassic, having evolved from a branch of theropod dinosaurs, the first mammals also appeared during the Mesozoic, but would remain small—less than 15 kg —until the Cenozoic. Following the Paleozoic, the Mesozoic extended roughly 186 million years and this time frame is separated into three geologic periods. It is also known as the Great Dying because it is considered the largest mass extinction in the Earths history, the upper boundary of the Mesozoic is set at the Cretaceous–Paleogene extinction event, which may have been caused by the impactor that created Chicxulub Crater on the Yucatán Peninsula. Towards the Late Cretaceous large volcanic eruptions are believed to have contributed to the Cretaceous–Paleogene extinction event. Approximately 50% of all genera became extinct, including all of the non-avian dinosaurs, the Triassic ranges roughly from 252 million to 201 million years ago. The Triassic is a time in Earths history bracketed between the Permian Extinction and the Triassic–Jurassic extinction event, two of the big five, and precedes the Jurassic Period and it has three major epochs, the Early Triassic, the Middle Triassic and the Late Triassic. The Early Triassic was between about 252 million to 247 million years ago and was dominated by deserts as Pangaea had not yet broken up, thus the interior was nothing, the Earth had just witnessed a massive die-off in which 95% of all life became extinct. The most common life on earth were Lystrosaurus, labyrinthodonts. Temnospondyls evolved during this time and would be the dominant predator for much of the Triassic, the Middle Triassic spans roughly from 247 million to 237 million years ago. The Middle Triassic featured the beginnings of the breakup of Pangaea, the ecosystem had recovered from the devastation that was the Great Dying. Algae, sponge, corals, and crustaceans all had recovered, new aquatic reptiles evolved, such as ichthyosaurs and nothosaurs. Meanwhile, on land, pine forests flourished, as did groups of insects like mosquitoes, the first ancient crocodilians evolved, which sparked competition with the large amphibians that had since ruled the freshwater world
24.
Orogeny
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An Orogeny is an event that leads to a large structural deformation of the Earths lithosphere due to the interaction between tectonic plates. Orogens or orogenic belts develop when a plate is crumpled and is pushed upwards to form mountain ranges. Orogeny is the mechanism by which mountains are built on continents. The word orogeny comes from Ancient Greek, though it was used before him, the term was employed by the American geologist G. K. Gilbert in 1890 to describe the process of mountain building as distinguished from epeirogeny. Formation of an orogen is accomplished in part by the processes of subduction or convergence of two or more continents. Orogeny usually produces long arcuate structures, known as orogenic belts, generally, orogenic belts consist of long parallel strips of rock exhibiting similar characteristics along the length of the belt. Orogenic belts are associated with zones, which consume crust, produce volcanoes. Geologists attribute the arcuate structure to the rigidity of the descending plate and these island arcs may be added to a continent during an orogenic event. The processes of orogeny can take tens of millions of years, frequently, rock formations that undergo orogeny are severely deformed and undergo metamorphism. Orogenic processes may push deeply buried rocks to the surface, sea-bottom and near-shore material may cover some or all of the orogenic area. If the orogeny is due to two continents colliding, very high mountains can result, an orogenic event may be studied, as a tectonic structural event, as a geographical event, and as a chronological event. The foreland basin forms ahead of the orogen due mainly to loading and resulting flexure of the lithosphere by the mountain belt. The basin migrates with the front and early deposited foreland basin sediments become progressively involved in folding and thrusting. Sediments deposited in the basin are mainly derived from the erosion of the actively uplifting rocks of the mountain range. The fill of many such shows an change in time from deepwater marine through shallow water to continental sediments. Although orogeny involves plate tectonics, the tectonic forces result in a variety of associated phenomena, including magmatism, metamorphism, crustal melting, what exactly happens in a specific orogen depends upon the strength and rheology of the continental lithosphere, and how these properties change during orogenesis. In addition to orogeny, the orogen is subject to other processes, for example, the Caledonian Orogeny refers to the Silurian and Devonian events that resulted from the collision of Laurentia with Eastern Avalonia and other former fragments of Gondwana. The Caledonian Orogen resulted from events and various others that are part of its peculiar orogenic cycle
25.
Jurassic
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The Jurassic is a geologic period and system that spans 56.3 million years from the end of the Triassic Period 201.3 million years ago to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles, the start of the period is marked by the major Triassic–Jurassic extinction event. The Jurassic is named after the Jura Mountains within the European Alps, by the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, on land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs, other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to a mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, the chronostratigraphic term Jurassic is directly linked to the Jura Mountains. The name Jura is derived from the Celtic root jor, which was Latinised into juria, the Jurassic period is divided into the Early Jurassic, Middle, and Late Jurassic epochs. The Jurassic System, in stratigraphy, is divided into the Lower Jurassic, Middle, the separation of the term Jurassic into three sections goes back to Leopold von Buch. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous period, the Tethys Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of glaciation, as in the Triassic, there was apparently no land over either pole, and no extensive ice caps existed. In contrast, the North American Jurassic record is the poorest of the Mesozoic, the Jurassic was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. Carbonate hardgrounds were thus very common, along with calcitic ooids, calcitic cements, the first of several massive batholiths were emplaced in the northern American cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. Important Jurassic exposures are found in Russia, India, South America, Japan, Australasia. As the Jurassic proceeded, larger and more groups of dinosaurs like sauropods and ornithopods proliferated in Africa. Middle Jurassic strata are well represented nor well studied in Africa. Late Jurassic strata are also poorly represented apart from the spectacular Tendaguru fauna in Tanzania, the Late Jurassic life of Tendaguru is very similar to that found in western North Americas Morrison Formation. During the Jurassic period, the primary living in the sea were fish
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Cretaceous
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The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago to the beginning of the Paleogene Period 66 Mya. It is the last period of the Mesozoic Era, the Cretaceous Period is usually abbreviated K, for its German translation Kreide. The Cretaceous was a period with a warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, during this time, new groups of mammals and birds, as well as flowering plants, appeared. The Cretaceous ended with a mass extinction, the Cretaceous–Paleogene extinction event, in which many groups, including non-avian dinosaurs, pterosaurs. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary, the name Cretaceous was derived from Latin creta, meaning chalk. The Cretaceous is divided into Early and Late Cretaceous epochs, or Lower and Upper Cretaceous series, in older literature the Cretaceous is sometimes divided into three series, Neocomian, Gallic and Senonian. A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide, in many parts of the world, alternative local subdivisions are still in use. As with other geologic periods, the rock beds of the Cretaceous are well identified. No great extinction or burst of diversity separates the Cretaceous from the Jurassic and this layer has been dated at 66.043 Ma. A140 Ma age for the Jurassic-Cretaceous boundary instead of the usually accepted 145 Ma was proposed in 2014 based on a study of Vaca Muerta Formation in Neuquén Basin. Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a first step toward formally changing the age in the International Union of Geological Sciences, due to the high sea level there was extensive space for such sedimentation. Because of the young age and great thickness of the system. Chalk is a type characteristic for the Cretaceous. It consists of coccoliths, microscopically small calcite skeletons of coccolithophores, the group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea. Chalk is not easily consolidated and the Chalk Group still consists of sediments in many places. The group also has other limestones and arenites, among the fossils it contains are sea urchins, belemnites, ammonites and sea reptiles such as Mosasaurus. In southern Europe, the Cretaceous is usually a marine system consisting of competent limestone beds or incompetent marls
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Appalachian Mountains
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The Appalachian Mountains, often called the Appalachians, are a system of mountains in eastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period and it once reached elevations similar to those of the Alps and the Rocky Mountains before naturally occurring erosion. The Appalachian chain is a barrier to east-west travel, as it forms a series of alternating ridgelines, definitions vary on the precise boundaries of the Appalachians. A common variant definition does not include the Adirondack Mountains, which belong to the Grenville Orogeny and have a different geological history from the rest of the Appalachians. The range covers parts of the islands of Saint Pierre and Miquelon, the system is divided into a series of ranges, with the individual mountains averaging around 3,000 ft. The highest of the group is Mount Mitchell in North Carolina at 6,684 feet, the term Appalachian refers to several different regions associated with the mountain range. Most broadly, it refers to the mountain range with its surrounding hills. The Ouachita Mountains in Arkansas and Oklahoma were originally part of the Appalachians as well, the name was soon altered by the Spanish to Apalachee and used as a name for the tribe and region spreading well inland to the north. Pánfilo de Narváezs expedition first entered Apalachee territory on June 15,1528, now spelled Appalachian, it is the fourth-oldest surviving European place-name in the US. After the de Soto expedition in 1540, Spanish cartographers began to apply the name of the tribe to the mountains themselves. The first cartographic appearance of Apalchen is on Diego Gutierrezs map of 1562, the name was not commonly used for the whole mountain range until the late 19th century. A competing and often more popular name was the Allegheny Mountains, Alleghenies, in the early 19th century, Washington Irving proposed renaming the United States either Appalachia or Alleghania. In U. S. dialects in the regions of the Appalachians. In northern parts of the range, it is pronounced /ˌæpəˈleɪtʃᵻnz/ or /ˌæpəˈleɪʃᵻnz/, the third syllable is like lay. There is often debate between the residents of the regions as to which pronunciation is the more correct one. Elsewhere, a commonly accepted pronunciation for the adjective Appalachian is /ˌæpəˈlætʃiən/, the whole system may be divided into three great sections, Northern, The northern section runs from the Canadian province of Newfoundland and Labrador to the Hudson River. The Monteregian Hills, which cross the Green Mountains in Quebec, are also unassociated with the Appalachians, Central, The central section goes from the Hudson Valley to the New River running through Virginia and West Virginia. Southern, The southern section runs from the New River onwards and it consists of the prolongation of the Blue Ridge, which is divided into the Western Blue Ridge Front and the Eastern Blue Ridge Front, the Ridge-and-Valley Appalachians, and the Cumberland Plateau
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Ozark Plateaus
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The Ozarks cover a significant portion of southern Missouri, extending as far northeast as the southwestern suburbs of St. Louis. In Arkansas, a portion is contained within the northwestern. Much smaller pieces of the Ozarks extend westward into northeastern Oklahoma, the Shawnee Hills of southwest Illinois, which lie near the eastern edge of this region, are commonly called the Illinois Ozarks, but are generally not considered part of the true Ozarks. Although sometimes referred to as the Ozark Mountains, the region is actually a high, geologically, the area is a broad dome around the Saint Francois Mountains. The Ozark Highlands area, covering nearly 47,000 square miles, is by far the most extensive mountainous region between the Appalachians and the Rocky Mountains, together, the Ozarks and Ouachita Mountains form an area known as the U. S. Interior Highlands, and are referred to collectively. Arkansas seems to be the French version of what the Illinois tribe called the Quapaw, eventually, the term came to refer to all Ozark Plateau drainage into the Arkansas and Missouri Rivers. An alternative origin for the name Ozark involves the French term aux arcs, in the later 17th and early 18th centuries, French cartographers mapped the Arkansas and Mississippi Rivers. The large, top most arc or bend in this part of the Arkansas River was referred to as the aux arcs—the top or most northern arc in the whole of the lower Arkansas. Travelers arriving by boat would disembark at this top bend of the river to explore the Ozarks, Other possible derivations include aux arcs meaning of the arches in reference to the dozens of natural bridges formed by erosion and collapsed caves in the Ozark region. These include Clifty Hollow Natural Bridge in Missouri, and Alum Cove in the Ozark – St. Francis National Forest and it is even suggested aux arcs is an abbreviation of aux arcs-en-ciel, French for toward the rainbows which are a common sight in the mountainous regions. After the Louisiana Purchase, American travelers in the referred to various features of the upland areas using the term Ozark, such as Ozark Mountains. By the early 20th century, the Ozarks had become a generic term, Missouri is known as The Cave State with over 6000 recorded caves, the majority of these caves are found in the Ozark counties. The Ozark Plateaus aquifer system affects groundwater movement in all areas except the core of the St. Francois Mountains. Geographic features include limestone and dolomite glades, which are rocky, summits can reach elevations of just over 2,560 feet with valleys 500 to 1,550 feet deep. Turner Ward Knob is the highest named peak, located in western Newton County, Arkansas, its elevation is 2,463 feet. Nearby, five unnamed peaks have elevations at or slightly above 2,560 feet, drainage is primarily to the White River, with the exception of the Illinois River, although there also is considerable drainage from the south slopes of the Boston Mountains to the Arkansas River. Major streams of this type include Lee Creek, Frog Bayou, Mulberry River, Spadra Creek, Big Piney Creek, Little Piney Creek, Illinois Bayou, Point Remove Creek, and Cadron Creek
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Ouachita Mountains
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The Ouachita Mountains are a mountain range in west central Arkansas and southeastern Oklahoma. The ranges subterranean roots may extend as far as central Texas, along with the Ozark Mountains, the Ouachita Mountains form the U. S. Interior Highlands, one of the few mountainous regions between the Rocky Mountains and the Appalachian Mountains. The highest peak in the Ouachitas is Mount Magazine in west-central Arkansas which rises to 2,753 feet, R. Harlan claimed that the word Ouachita is composed of two Choctaw words, ouac, a buffalo, and chito, large. It means the country of large buffaloes, numerous herds of the American bison having formerly covered the prairies of Ouachita, historian Muriel H. Wright wrote that the name was probably derived from the Choctaw words owa, meaning hunt and chito, meaning big. She said that meant a big hunt. The Ouachita Mountains are a section of the larger Ouachita province. The Ouachita Mountains are fold mountains like the Appalachian Mountains to the east, during the Pennsylvanian period, roughly 300 million years ago, the coastline of the Gulf of Mexico ran through the central parts of Arkansas. The South American Plate drifted northward, riding up over the denser North American continental crust, geologists call this collision the Ouachita orogeny. The collision buckled the overriding plate, producing the fold mountains we call the Ouachitas, at one time the Ouachita Mountains were very similar in height to the current elevations of the Rocky Mountains. Because of the Ouachitas age, the tops have eroded away. Unlike most other ranges in the United States, the Ouachitas run east and west rather than north and south. Also, the Ouachitas are distinctive in that volcanism, metamorphism, the Ouachitas tend to be clustered into distinct sub-ranges separated by relatively broad valleys. The Ouachitas are noted for quartz crystal deposits around the Mount Ida area and this quartz was formed during the Ouachita orogeny, as folded rocks cracked and allowed fluids from deep in the Earth to fill the cracks. The Atoka Formation, formed in the Pennsylvanian Period, is a sequence of marine, mostly tan to gray silty sandstones, some rare calcareous beds and siliceous shales are known. The Collier sequence is composed of gray to black, lustrous shale containing occasional thin beds of dense, black, an interval of bluish-gray, dense to spary, thin-bedded limestone may be present. Near its top, the limestone is conglomeratic and pelletoidal, in part, with pebbles and cobbles of limestone, chert, meta-arkose and it was formed during the Late Cambrian. Tree species native to the Ouachita area include red, post, black, and white oak, shortleaf and loblolly pine
