Metamorphism is the change of minerals or geologic texture in pre-existing rocks, without the protolith melting into liquid magma. The change occurs due to heat and the introduction of chemically active fluids; the chemical components and crystal structures of the minerals making up the rock may change though the rock remains a solid. Changes at or just beneath Earth's surface due to weathering or diagenesis are not classified as metamorphism. Metamorphism occurs between diagenesis, melting; the geologists who study metamorphism are known as "metamorphic petrologists." To determine the processes underlying metamorphism, they rely on statistical mechanics and experimental petrology. Three types of metamorphism exist: contact and regional. Metamorphism produced with increasing pressure and temperature conditions is known as prograde metamorphism. Conversely, decreasing temperatures and pressure characterize retrograde metamorphism. Metamorphic rocks can change without melting. Heat causes atomic bonds to break, the atoms move and form new bonds with other atoms, creating new minerals with different chemical components or crystalline structures, or enabling recrystallization.
When pressure is applied, somewhat flattened grains that orient in the same direction have a more stable configuration. The temperature lower limit on what is considered to be a metamorphic process is considered to be 100 – 200 °C; the upper boundary of metamorphic conditions is related to the onset of melting processes in the rock. The maximum temperature for metamorphism is 700 – 900 °C, depending on the pressure and on the composition of the rock. Migmatites are rocks formed at this upper limit, which contains pods and veins of material that has started to melt but has not segregated from the refractory residue. Since the 1980s it has been recognized that rocks are dry enough and of a refractory enough composition to record without melting "ultra-high" metamorphic temperatures of 900 – 1100 °C; the metamorphic process has to be over pressure of at least 100 mega pascals but below 300 mega pascals, the depth of 100 mega pascals varies depending on what type of rock is applying pressure. Regional or Barrovian metamorphism covers large areas of continental crust associated with mountain ranges those associated with convergent tectonic plates or the roots of eroded mountains.
Conditions producing widespread regionally metamorphosed rocks occur during an orogenic event. The collision of two continental plates or island arcs with continental plates produce the extreme compressional forces required for the metamorphic changes typical of regional metamorphism; these orogenic mountains are eroded, exposing the intensely deformed rocks typical of their cores. The conditions within the subducting slab as it plunges toward the mantle in a subduction zone produce regional metamorphic effects, characterized by paired metamorphic belts; the techniques of structural geology are used to unravel the collisional history and determine the forces involved. Regional metamorphism can be described and classified into metamorphic facies or metamorphic zones of temperature/pressure conditions throughout the orogenic terrane. Contact metamorphism occurs around intrusive igneous rocks as a result of the temperature increase caused by the intrusion of magma into cooler country rock; the area surrounding the intrusion where the contact metamorphism effects are present is called the metamorphic aureole.
Contact metamorphic rocks are known as hornfels. Rocks formed by contact metamorphism may not present signs of strong deformation and are fine-grained. Contact metamorphism is greater adjacent to the intrusion and dissipates with distance from the contact; the size of the aureole depends on the heat of the intrusion, its size, the temperature difference with the wall rocks. Dikes have small aureoles with minimal metamorphism whereas large ultramafic intrusions can have thick and well-developed contact metamorphism; the metamorphic grade of an aureole is measured by the peak metamorphic mineral which forms in the aureole. This is related to the metamorphic temperatures of pelitic or aluminosilicate rocks and the minerals they form; the metamorphic grades of aureoles are sillimanite hornfels, pyroxene hornfels. Magmatic fluids coming from the intrusive rock may take part in the metamorphic reactions. An extensive addition of magmatic fluids can modify the chemistry of the affected rocks. In this case the metamorphism grades into metasomatism.
If the intruded rock is rich in carbonate the result is a skarn. Fluorine-rich magmatic waters which leave a cooling granite may form greisens within and adjacent to the contact of the granite. Metasomatic altered aureoles can localize the deposition of metallic ore minerals and thus are of economic interest. A special type of contact metamorphism, associated with fossil fuel fires, is known as pyrometamorphism. Hydrothermal metamorphism is the result of the interaction of a rock with a high-temperature fluid of variable composition; the difference in composition between an existing rock and the invading fluid triggers a set of metamorphic and metasomatic reactions. The hydrothermal fluid may be magmatic, circulating ocean water. Convective circulation of hydrothermal fluids in the ocean floor basalts produces extensive hydrothermal metamorphism adjacent to spreading centers and other submarine volcanic areas
The Northwest Territories is a federal territory of Canada. At a land area of 1,144,000 km2 and a 2016 census population of 41,786, it is the second-largest and the most populous of the three territories in Northern Canada, its estimated population as of 2018 is 44,445. Yellowknife became the territorial capital in 1967, following recommendations by the Carrothers Commission; the Northwest Territories, a portion of the old North-Western Territory, entered the Canadian Confederation on July 15, 1870, but the current borders were formed on April 1, 1999, when the territory was subdivided to create Nunavut to the east, via the Nunavut Act and the Nunavut Land Claims Agreement. While Nunavut is Arctic tundra, the Northwest Territories has a warmer climate and is both boreal forest, tundra, its most northern regions form part of the Canadian Arctic Archipelago; the Northwest Territories is bordered by Canada's two other territories, Nunavut to the east and Yukon to the west, by the provinces of British Columbia and Saskatchewan to the south.
The name is descriptive, adopted by the British government during the colonial era to indicate where it lay in relation to Rupert's Land. It is shortened from North-Western Territory. In Inuktitut, the Northwest Territories are referred to as ᓄᓇᑦᓯᐊᖅ, "beautiful land."There was some discussion of changing the name of the Northwest Territories after the splitting off of Nunavut to a term from an Aboriginal language. One proposal was "Denendeh", among others. One of the most popular proposals for a new name – one to name the territory "Bob" – began as a prank, but for a while it was at or near the top in the public-opinion polls. In the end, a poll conducted prior to division showed that strong support remained to keep the name "Northwest Territories"; this name arguably became more appropriate following division than it had been when the territories extended far into Canada's north-central and northeastern areas. Located in northern Canada, the territory borders Canada's two other territories, Yukon to the west and Nunavut to the east, three provinces: British Columbia to the southwest, Alberta and Saskatchewan to the south.
It meets Manitoba at a quadripoint to the extreme southeast, though surveys have not been completed. It has a land area of 1,183,085 km2. Geographical features include Great Bear Lake, the largest lake within Canada, Great Slave Lake, the deepest body of water in North America at 614 m, as well as the Mackenzie River and the canyons of the Nahanni National Park Reserve, a national park and UNESCO World Heritage Site. Territorial islands in the Canadian Arctic Archipelago include Banks Island, Borden Island, Prince Patrick Island, parts of Victoria Island and Melville Island, its highest point is Mount Nirvana near the border with Yukon at an elevation of 2,773 m. The Northwest Territories extends for more than 1,300,000 km2 and has a large climate variant from south to north; the southern part of the territory has a subarctic climate, while the islands and northern coast have a polar climate. Summers in the north are short and cool, with daytime highs of 14-17 Celsius, lows of 1-5 Celsius. Winters are long and harsh, daytime highs in the mid −20 °C and lows around −40 °C.
Extremes are common with summer highs in the south reaching 36 °C and lows reaching into the negatives. In winter in the south, it is not uncommon for the temperatures to reach −40 °C, but they can reach the low teens during the day. In the north, temperatures can reach highs of 30 °C, lows can reach into the low negatives. In winter in the north it is not uncommon for the temperatures to reach −50 °C but they can reach the single digits during the day. Thunderstorms are not rare in the south. In the north they are rare, but do occur. Tornadoes are rare but have happened with the most notable one happening just outside Yellowknife that destroyed a communications tower; the Territory has a dry climate due to the mountains in the west. About half of the territory is above the tree line. There are not many trees in the north islands; the present-day territory came under government authority in July 1870, after the Hudson's Bay Company transferred Rupert's Land and the North-Western Territory to the British Crown, which subsequently transferred them to Canada, giving it the name the North-west Territories.
This immense region comprised all of today's Canada except that, encompassed within the early signers of Canadian Confederation, that is, British Columbia, early forms of present-day Ontario and Quebec, the Maritimes, the Labrador coast, the Arctic Islands, except the southern half of Baffin Island. The first residential school opened in 1867 in Fort Resolution, followed by several others in regions across the territory, thus contributing to the Northwest Territories reaching the highest percentage of students in residential schools of any area in Canada. After the 1870 transfer, some of the North-west Territories was whittled away; the province of Manitoba was created on July 15, 1870, at first a small square area around Winnipeg
The Tłı̨chǫ people, sometimes spelled Tlicho and known as the Dogrib, are a Dene First Nations people of the Athabaskan-speaking ethnolinguistic group living in the Northwest Territories, Canada. The name Dogrib is an English adaptation of their own name, Tłı̨chǫ Done - “Dog-Flank People”, referring to their fabled descent from a supernatural dog-man. Like their Dene neighbours they called themselves oft Done or Done Do; the Tłı̨chǫ's land is known as Ndé. On the 1682 Franquelin map, Dogrib was recorded as "Alimouspgoiak". There are now six settlements with Dogrib populations or of Dogrib background: Behchoko, Whatì, Gamèti, Wekweeti and Ndilǫ; the Tłı̨chǫ Yatıı̀ or Dogrib language belongs to the Athabaskan languages, which are part of the Na-Dené languages family. The dialect spoken in the communities of Dettah and Ndilǫ developed from intermarriage between Yellowknives and Tłįchǫ. In June 1899, negotiation began on Treaty No. 8, which covered 840,000 square kilometers in the Northwest Territory.
It was the Dene groups in the area in question. The Canadian Government and the various Dene groups, including Yellowknives and Tłįchǫ under chief Drygeese with headmen Benaiyah and Sek'eglinan, signed the treaty in 1900 at Fort Resolution. After the signing, the group that signed the treaty was called the "Yellowknife B Band". At that point in history, Treaty No.8 was the largest land settlement the Canadian Government had made. Twenty years after Treaty No. 8 was signed, oil was discovered in the Mackenzie River Valley. Upon the discovery, the Canadian Government proposed another treaty that would clear the way for miners and development of the area; the treaty was debated, as the Natives did not want to lose their right to hunt, fish and trap in the area. They opposed being "confined to Indian reserves." Many Dene felt that Treaty No. 8 was not honored by the Canadian Government, some were afraid that this treaty would turn out similarly. Treaty No. 11 was signed by the Tłįchǫ trading chief Monfwi in the summer of 1921.
The Tłįchǫ groups that signed this treaty were known as the "Dog Rib Rae Band", constituting the majority of the Tłįchǫ population. Both Treaty No. 8 and Treaty No. 11 overlap in several of their boundaries, continue to cause conflict between the two separate treaty bands. Not all members of the Dene and Tłįchǫ communities signed these treaties. In the fall of 1992, the Tłįchǫ submitted their own regional claim to the Canadian government. Negotiations were scheduled to begin in 1994 between the Yellowknife B Band and the Dog Rib Rae Band, but the Yellowknife B Band refused to enter into negotiations; this complicated matters. Self-governance seemed to be the issue between the two groups, as both wanted to have their say in the agreement; this halted the negotiations in 1994 while the Canadian government explored the boundary and self-government issue. A new mandate in April 1997 allowed negotiation of a "joint land claims and self-government agreement with the Dogrib Treaty 11 Council". In 1999, the Agreement-in-Principle was available for Dogrib approval and was accepted on January 7, 2000.
Ninety-three percent of the Dog Rib Rae Band turned out to vote with over 84% voting for the agreement. After several community discussions and revisions, in March 2003 the Chief Negotiators initialed the agreement; the Yellowknife B Band formed the Yellowknives Dene First Nation in 1991 following the collapse of this territorial-wide comprehensive land claim negotiation. They negotiate a land claim settlement for their lands as part of the Akaitcho Land Claim Process by the Akaitcho Territory Government; the Yellowknives Dene First Nation is the umbrella organization for the Dettah Yellowknives Dene First Nation and Ndilǫ Yellowknives Dene First Nation. They speak the Dettah-Ndilǫ dialect of Tłįchǫ and are descendants of Tłįchǫ, Yellowknives and Chipewyan; the act of signing the agreement began the ratification process for the Tlicho Agreement. On Thursday, August 4, 2005, the Tlicho Agreement went into full effect, "The first official day of the Tlicho Government and the Tlicho community governments".
On August 25, 2003, they signed a land claims agreement called Tłįchǫ, as the Tlicho Government, with the Government of Canada. The agreement will cede a 39,000 square kilometres area between Great Bear Lake and Great Slave Lake in the NWT to Tłįchǫ ownership; the territory includes the communities of Behchoko, Gamèti, Wekweeti and Whatì along with Diavik Diamond Mine and Ekati Diamond Mine. The four bands, Dogrib Rae Band, Whatí First Nation, Gaméti First Nation and Dechi Laot’i First Nation and the Dogrib Treaty 11 Council, ceased to exist on August 4, 2005 and have been succeeded by the Tlicho Government; the Tłįchǫ will have their own le
The Smithsonian Institution, founded on August 10, 1846 "for the increase and diffusion of knowledge," is a group of museums and research centers administered by the Government of the United States. The institution is named after British scientist James Smithson. Organized as the "United States National Museum," that name ceased to exist as an administrative entity in 1967. Termed "the nation's attic" for its eclectic holdings of 154 million items, the Institution's nineteen museums, nine research centers, zoo include historical and architectural landmarks located in the District of Columbia. Additional facilities are located in Arizona, Massachusetts, New York City, Texas and Panama. More than 200 institutions and museums in 45 states, Puerto Rico, Panama are Smithsonian Affiliates; the Institution's thirty million annual visitors are admitted without charge. Its annual budget is around $1.2 billion with two-thirds coming from annual federal appropriations. Other funding comes from the Institution's endowment and corporate contributions, membership dues, earned retail and licensing revenue.
Institution publications include Air & Space magazines. The British scientist James Smithson left most of his wealth to his nephew Henry James Hungerford; when Hungerford died childless in 1835, the estate passed "to the United States of America, to found at Washington, under the name of the Smithsonian Institution, an Establishment for the increase & diffusion of knowledge among men", in accordance with Smithson's will. Congress accepted the legacy bequeathed to the nation, pledged the faith of the United States to the charitable trust on July 1, 1836; the American diplomat Richard Rush was dispatched to England by President Andrew Jackson to collect the bequest. Rush returned in August 1838 with 105 sacks containing 104,960 gold sovereigns. Once the money was in hand, eight years of Congressional haggling ensued over how to interpret Smithson's rather vague mandate "for the increase and diffusion of knowledge." The money was invested by the US Treasury in bonds issued by the state of Arkansas, which soon defaulted.
After heated debate, Massachusetts Representative John Quincy Adams persuaded Congress to restore the lost funds with interest and, despite designs on the money for other purposes, convinced his colleagues to preserve it for an institution of science and learning. On August 10, 1846, President James K. Polk signed the legislation that established the Smithsonian Institution as a trust instrumentality of the United States, to be administered by a Board of Regents and a Secretary of the Smithsonian. Though the Smithsonian's first Secretary, Joseph Henry, wanted the Institution to be a center for scientific research, it became the depository for various Washington and U. S. government collections. The United States Exploring Expedition by the U. S. Navy circumnavigated the globe between 1838 and 1842; the voyage amassed thousands of animal specimens, an herbarium of 50,000 plant specimens, diverse shells and minerals, tropical birds, jars of seawater, ethnographic artifacts from the South Pacific Ocean.
These specimens and artifacts became part of the Smithsonian collections, as did those collected by several military and civilian surveys of the American West, including the Mexican Boundary Survey and Pacific Railroad Surveys, which assembled many Native American artifacts and natural history specimens. In 1846, the regents developed a plan for weather observation; the Institution became a magnet for young scientists from 1857 to 1866, who formed a group called the Megatherium Club. The Smithsonian played a critical role as the U. S. partner institution in early bilateral scientific exchanges with the Academy of Sciences of Cuba. Construction began on the Smithsonian Institution Building in 1849. Designed by architect James Renwick Jr. its interiors were completed by general contractor Gilbert Cameron. The building opened in 1855; the Smithsonian's first expansion came with construction of the Arts and Industries Building in 1881. Congress had promised to build a new structure for the museum if the 1876 Philadelphia Centennial Exposition generated enough income.
It did, the building was designed by architects Adolf Cluss and Paul Schulze, based on original plans developed by Major General Montgomery C. Meigs of the United States Army Corps of Engineers, it opened in 1881. The National Zoological Park opened in 1889 to accommodate the Smithsonian's Department of Living Animals; the park was designed by landscape architect Frederick Law Olmsted. The National Museum of Natural History opened in June 1911 to accommodate the Smithsonian's United States National Museum, housed in the Castle and the Arts and Industries Building; this structure was designed by the D. C. architectural firm of Hornblower & Marshall. When Detroit philanthropist Charles Lang Freer donated his private collection to the Smithsonian and funds to build the museum to hold it, it was among the Smithsonian's first major donations from a private individual; the gallery opened in 1923. More than 40 years would pass before the next museum, the Museum of History and Technology, opened in 1964.
It was designed by the world-renowned firm of Mead & White. The Anacostia Community Museum, an "experimental store-front" museum created at the initiative of Smithsonian Secretary S. Dillon Ripley, opened in the Anacostia neighborhood of
Vienna is the federal capital and largest city of Austria, one of the nine states of Austria. Vienna is Austria's primate city, with a population of about 1.9 million, its cultural and political centre. It is the 7th-largest city by population within city limits in the European Union; until the beginning of the 20th century, it was the largest German-speaking city in the world, before the splitting of the Austro-Hungarian Empire in World War I, the city had 2 million inhabitants. Today, it has the second largest number of German speakers after Berlin. Vienna is host to many major international organizations, including the United Nations and OPEC; the city is located in the eastern part of Austria and is close to the borders of the Czech Republic and Hungary. These regions work together in a European Centrope border region. Along with nearby Bratislava, Vienna forms a metropolitan region with 3 million inhabitants. In 2001, the city centre was designated a UNESCO World Heritage Site. In July 2017 it was moved to the list of World Heritage in Danger.
Apart from being regarded as the City of Music because of its musical legacy, Vienna is said to be "The City of Dreams" because it was home to the world's first psychoanalyst – Sigmund Freud. The city's roots lie in early Celtic and Roman settlements that transformed into a Medieval and Baroque city, the capital of the Austro-Hungarian Empire, it is well known for having played an essential role as a leading European music centre, from the great age of Viennese Classicism through the early part of the 20th century. The historic centre of Vienna is rich in architectural ensembles, including Baroque castles and gardens, the late-19th-century Ringstraße lined with grand buildings and parks. Vienna is known for its high quality of life. In a 2005 study of 127 world cities, the Economist Intelligence Unit ranked the city first for the world's most liveable cities. Between 2011 and 2015, Vienna was ranked second, behind Melbourne. In 2018, it replaced Melbourne as the number one spot. For ten consecutive years, the human-resource-consulting firm Mercer ranked Vienna first in its annual "Quality of Living" survey of hundreds of cities around the world.
Monocle's 2015 "Quality of Life Survey" ranked Vienna second on a list of the top 25 cities in the world "to make a base within."The UN-Habitat classified Vienna as the most prosperous city in the world in 2012/2013. The city was ranked 1st globally for its culture of innovation in 2007 and 2008, sixth globally in the 2014 Innovation Cities Index, which analyzed 162 indicators in covering three areas: culture and markets. Vienna hosts urban planning conferences and is used as a case study by urban planners. Between 2005 and 2010, Vienna was the world's number-one destination for international congresses and conventions, it attracts over 6.8 million tourists a year. The English name Vienna is borrowed from the homonymous Italian version of the city's name or the French Vienne; the etymology of the city's name is still subject to scholarly dispute. Some claim that the name comes from Vedunia, meaning "forest stream", which subsequently produced the Old High German Uuenia, the New High German Wien and its dialectal variant Wean.
Others believe that the name comes from the Roman settlement name of Celtic extraction Vindobona meaning "fair village, white settlement" from Celtic roots, vindo-, meaning "bright" or "fair" – as in the Irish fionn and the Welsh gwyn –, -bona "village, settlement". The Celtic word Vindos may reflect a widespread prehistorical cult of a Celtic God. A variant of this Celtic name could be preserved in the Czech and Polish names of the city and in that of the city's district Wieden; the name of the city in Hungarian, Serbo-Croatian and Ottoman Turkish has a different Slavonic origin, referred to an Avar fort in the area. Slovene-speakers call the city Dunaj, which in other Central European Slavic languages means the Danube River, on which the city stands. Evidence has been found of continuous habitation in the Vienna area since 500 BC, when Celts settled the site on the Danube River. In 15 BC the Romans fortified the frontier city they called Vindobona to guard the empire against Germanic tribes to the north.
Close ties with other Celtic peoples continued through the ages. The Irish monk Saint Colman is buried in Melk Abbey and Saint Fergil served as Bishop of Salzburg for forty years. Irish Benedictines founded twelfth-century monastic settlements. Evidence of these ties persists in the form of Vienna's great Schottenstift monastery, once home to many Irish monks. In 976 Leopold I of Babenberg became count of the Eastern March, a 60-mile district centering on the Danube on the eastern frontier of Bavaria; this initial district grew into the duchy of Austria. Each succeeding Babenberg ruler expanded the march east along the Danube encompassing Vienna and the lands east. In 1145 Duke Henry II Jasomirgott moved the Babenberg family residence from Klosterneuburg in Lower Austria to Vienna. From that time, Vienna remained the center of the Babenberg dynasty. In 1440 Vienna became the resident city of the Habsburg dynasty, it grew to become the de facto capital of the Holy Roman Empire in 1437 and a cultural centre for arts and science and fine cuisine.
Hungary occupied the city between 1485 and 1490. In the 16th and 1
Timeline of natural history
This timeline of natural history summarizes significant geological and biological events from the formation of the Earth to the arrival of modern humans. Times are listed in megaanni; the Geologic record is the strata of rock in the planet's crust and the science of geology is much concerned with the age and origin of all rocks to determine the history and formation of Earth and to understand the forces that have acted upon it. Geologic time is the timescale used to calculate dates in the planet's geologic history from its origin to the present day. Radiometric dating measures the steady decay of radioactive elements in an object to determine its age, it is used to calculate dates for the older part of the planet's geological record. The theory is complicated but, in essence, the radioactive elements within an object decay to form isotopes of each chemical element. Isotopes are atoms of the element that share the same general properties. Geologists are most interested in the decay of isotopes carbon-14 and potassium-40.
Carbon-14 aka radiocarbon dating works for organic materials that are less than about 50,000 years old. For older periods, the potassium-argon dating process is more accurate. Radiocarbon dating is carried out by measuring how much of the carbon-14 and nitrogen-14 isotopes are found in a material; the ratio between the two is used to estimate the material's age. Suitable materials include wood, paper, fabrics and shells, it is assumed that rock exists in layers according to age, with older beds below ones. This is the basis of stratigraphy; the ages of more recent layers are calculated by the study of fossils, which are remains of ancient life preserved in the rock. These occur and so a theory is feasible. Most of the boundaries in recent geologic time coincide with extinctions and with the appearances of new species. In the earliest solar system history, the Sun, the planetesimals and the jovian planets were formed; the inner solar system aggregated more than the outer, so the terrestrial planets were not yet formed, including Earth and Moon.
C.4,570 Ma – A supernova explosion seeds our galactic neighborhood with heavy elements that will be incorporated into the Earth, results in a shock wave in a dense region of the Milky Way galaxy. The Ca-Al-rich inclusions, which formed 2 million years before the chondrules, are a key signature of a supernova explosion. C.4,567±3 Ma – Rapid collapse of hydrogen molecular cloud, forming a third-generation Population I star, the Sun, in a region of the Galactic Habitable Zone, about 25,000 light years from the center of the Milky Way Galaxy. C.4,566±2 Ma – A protoplanetary disc emerges around the young Sun, in its T Tauri stage. C.4,560–4,550 Ma – Proto-Earth forms at the outer edge of the habitable zone of the Solar System. At this stage the solar constant of the Sun was only about 73% of its current value, but liquid water may have existed on the surface of the Proto-Earth due to the greenhouse warming of high levels of methane and carbon dioxide present in the atmosphere. Early bombardment phase begins: because the solar neighbourhood is rife with large planetoids and debris, Earth experiences a number of giant impacts that help to increase its overall size.
C.4,533 Ma – The Precambrian, now termed a "supereon" but an era, is split into three geological periods called eons: Hadean and Proterozoic. The latter two are sub-divided into several eras as defined. In total, the Precambrian comprises some 85% of geological time from the formation of Earth to the time when creatures first developed exoskeletons and thereby left abundant fossil remains. C.4,533 Ma – Hadean Eon, Precambrian Supereon and unofficial Cryptic era start as the Earth-Moon system forms as a result of a glancing collision between proto-Earth and the hypothetical protoplanet Theia. This impact vaporized a large amount of the crust, sent material into orbit around Earth, which lingered as rings, similar to those of Saturn, for a few million years, until they coalesced to become the Moon; the Moon geology pre-Nectarian period starts. Earth was covered by a magmatic ocean 200 kilometres deep resulting from the impact energy from this and other planetesimals during the early bombardment phase, energy released by the planetary core forming.
Outgassing from crustal rocks gives Earth a reducing atmosphere of methane, hydrogen and water vapour, with lesser amounts of hydrogen sulfide, carbon monoxide carbon dioxide. With further full outgassing over 1000-1500 K, nitrogen and ammonia become lesser constituents, comparable amounts of methane, carbon monoxide, carbon dioxide, water vapour, hydrogen are released. C.4,500 Ma – Sun enters main sequence: a solar wind sweeps the Earth-Moon system clear of debris. End of the Early Bombardment Phase. Basin Groups Era begins on Earth. C.4,450 Ma – 100 million years after the Moon formed, the first lunar crust, formed of lunar anorthosite, differentiates from lower magmas. The earliest Earth crust forms out of similar material. On Earth the pluvial period starts. C.4,404 Ma – First known mineral, found at Jack Hills in Western Australia. Detrital zircons show presence of liquid water. Latest possible date for a secondary atmosphere to form, produced by the Earth's crust outgass
An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be seen or examined closely. However, in places where the overlying cover is removed through erosion or tectonic uplift, the rock may be exposed, or crop out; such exposure will happen most in areas where erosion is rapid and exceeds the weathering rate such as on steep hillsides, mountain ridges and tops, river banks, tectonically active areas. In Finland, glacial erosion during the last glacial maximum, followed by scouring by sea waves, followed by isostatic uplift has produced a large number of smooth coastal and littoral outcrops. Bedrock and superficial deposits may be exposed at the Earth's surface due to human excavations such as quarrying and building of transport routes. Outcrops allow direct observation and sampling of the bedrock in situ for geologic analysis and creating geologic maps.
In situ measurements are critical for proper analysis of geological history and outcrops are therefore important for understanding the geologic time scale of earth history. Some of the types of information that cannot be obtained except from bedrock outcrops or by precise drilling and coring operations, are structural geology features orientations, depositional features orientations, paleomagnetic orientations. Outcrops are very important for understanding fossil assemblages, paleo-environment, evolution as they provide a record of relative changes within geologic strata. Accurate description and sampling for laboratory analysis of outcrops made possible all of the geologic sciences and the development of fundamental geologic laws such as the law of superposition, the principle of original horizontality, principle of lateral continuity, the principle of faunal succession. On Ordnance Survey maps in Great Britain, cliffs are distinguished from outcrops: cliffs have a continuous line along the top edge with lines protruding down.
An outcrop example in California is the Vasquez Rocks, familiar from location shooting use in many films, composed of uplifted sandstone. Yana is another example of outcrops, located in Uttara Kannada district in India. Digital outcrop model List of rock formations Geological formation Geologic time scale Media related to Outcrops at Wikimedia Commons