1.
Absolute dating
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Absolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word implies a unwarranted certainty of accuracy. Absolute dating provides an age or range in contrast with relative dating which places events in order without any measure of the age between events. Techniques include tree rings in timbers, radiocarbon dating of wood or bones, radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes. Particular isotopes are suitable for different applications due to the type of atoms present in the mineral or other material, one of the most widely used and well-known absolute dating techniques is carbon-14 dating, which is used to date organic remains. This is a technique since it is based on radioactive decay. Cosmic radiation entering the earth’s atmosphere produces carbon-14, and plants take in carbon-14 as they fix carbon dioxide, carbon-14 moves up the food chain as animals eat plants and as predators eat other animals. With death, the uptake of carbon-14 stops and it takes 5,730 years for half the carbon-14 to change to nitrogen, this is the half-life of carbon-14. After another 5,730 years only one-quarter of the original carbon-14 will remain, after yet another 5,730 years only one-eighth will be left. By measuring the carbon-14 in organic material, scientists can determine the date of death of the matter in an artifact or ecofact. The relatively short half-life of carbon-14,5,730 years, an additional problem with carbon-14 dates from archeological sites is known as the old wood problem. Thus dating that particular tree does not necessarily indicate when the fire burned or the structure was built, for this reason, many archaeologists prefer to use samples from short-lived plants for radiocarbon dating. The development of mass spectrometry dating, which allows a date to be obtained from a very small sample, has been very useful in this regard. Other radiometric dating techniques are available for earlier periods, one of the most widely used is potassium-argon dating. Potassium-40 is an isotope of potassium that decays into argon-40. The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated. Argon, a gas, is not commonly incorporated into such samples except when produced in situ through radioactive decay. The date measured reveals the last time that the object was heated past the closure temperature at which the trapped argon can escape the lattice, k-Ar dating was used to calibrate the geomagnetic polarity time scale
2.
Megaannum
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A year is the orbital period of the Earth moving in its orbit around the Sun. Due to the Earths axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the globe, four seasons are recognized, spring, summer, autumn. In tropical and subtropical regions several geographical sectors do not present defined seasons, but in the seasonal tropics, a calendar year is an approximation of the number of days of the Earths orbital period as counted in a given calendar. The Gregorian, or modern, calendar, presents its calendar year to be either a common year of 365 days or a year of 366 days, as do the Julian calendars. For the Gregorian calendar the average length of the year across the complete leap cycle of 400 years is 365.2425 days. The ISO standard ISO 80000-3, Annex C, supports the symbol a to represent a year of either 365 or 366 days, in English, the abbreviations y and yr are commonly used. In astronomy, the Julian year is a unit of time, it is defined as 365.25 days of exactly 86400 seconds, totalling exactly 31557600 seconds in the Julian astronomical year. The word year is used for periods loosely associated with, but not identical to, the calendar or astronomical year, such as the seasonal year, the fiscal year. Similarly, year can mean the period of any planet, for example. The term can also be used in reference to any long period or cycle, west Saxon ġēar, Anglian ġēr continues Proto-Germanic *jǣran. Cognates are German Jahr, Old High German jār, Old Norse ár and Gothic jer, all the descendants of the Proto-Indo-European noun *yeh₁rom year, season. Cognates also descended from the same Proto-Indo-European noun are Avestan yārǝ year, Greek ὥρα year, season, period of time, Old Church Slavonic jarŭ, Latin annus is from a PIE noun *h₂et-no-, which also yielded Gothic aþn year. Both *yeh₁-ro- and *h₂et-no- are based on verbal roots expressing movement, *h₁ey- and *h₂et- respectively, the Greek word for year, ἔτος, is cognate with Latin vetus old, from the PIE word *wetos- year, also preserved in this meaning in Sanskrit vat-sa- yearling and vat-sa-ras year. Derived from Latin annus are a number of English words, such as annual, annuity, anniversary, etc. per annum means each year, anno Domini means in the year of the Lord. No astronomical year has an number of days or lunar months. Financial and scientific calculations often use a 365-day calendar to simplify daily rates, in the Julian calendar, the average length of a year is 365.25 days. In a non-leap year, there are 365 days, in a year there are 366 days
3.
Neogene
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The Neogene is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago to the beginning of the present Quaternary Period 2.58 Mya. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene, some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary. During this period, mammals and birds continued to evolve into modern forms. Early hominids, the ancestors of humans, appeared in Africa near the end of the period, some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the ocean currents from the Pacific to the Atlantic ocean. The global climate cooled considerably over the course of the Neogene, the terms Neogene System and upper Tertiary System describe the rocks deposited during the Neogene Period. The continents in the Neogene were very close to their current positions, the Isthmus of Panama formed, connecting North and South America. The Indian subcontinent continued to collide with Asia, forming the Himalayas, sea levels fell, creating land bridges between Africa and Eurasia and between Eurasia and North America. The global climate became seasonal and continued an overall drying and cooling trend which began at the start of the Paleogene. The ice caps on both poles began to grow and thicken, and by the end of the period the first of a series of glaciations of the current Ice Age began, marine and continental flora and fauna have a modern appearance. The reptile group Choristodera became extinct in the part of the period. Mammals and birds continued to be the dominant terrestrial vertebrates, the first hominids, the ancestors of humans, appeared in Africa and spread into Eurasia. In response to the cooler, seasonal climate, tropical plant species gave way to deciduous ones, grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses, antelope, and bison. The Neogene traditionally ended at the end of the Pliocene Epoch, just before the definition of the beginning of the Quaternary Period. However, there was a movement amongst geologists to also include ongoing geological time in the Neogene, by dividing the Cenozoic Era into three periods instead of seven epochs, the periods are more closely comparable to the duration of periods in the Mesozoic and Paleozoic eras. The International Commission on Stratigraphy once proposed that the Quaternary be considered a sub-era of the Neogene, with a date of 2.58 Ma. In the 2004 proposal of the ICS, the Neogene would have consisted of the Miocene and Pliocene epochs, thus the Neogene Period ends bounding the succeeding Quaternary Period at 2.58 Mya. Digital Atlas of Neogene Life for the Southeastern United States — by San Jose State University via Web Archive
4.
Miocene
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The Miocene is the first geological epoch of the Neogene Period and extends from about 23.03 to 5.333 million years ago. The Miocene was named by Sir Charles Lyell and its name comes from the Greek words μείων and καινός and means less recent because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene Epoch and is followed by the Pliocene Epoch, the earth went from the Oligocene through the Miocene and into the Pliocene, with the climate slowly cooling towards a series of ice ages. The Miocene boundaries are not marked by a single distinct global event, the apes arose and diversified during the Miocene, becoming widespread in the Old World. By the end of this epoch, the ancestors of humans had split away from the ancestors of the chimpanzees to follow their own evolutionary path, as in the Oligocene before it, grasslands continued to expand and forests to dwindle in extent. In the Miocene seas, kelp forests made their first appearance, the plants and animals of the Miocene were fairly modern. The Miocene faunal stages from youngest to oldest are typically named according to the International Commission on Stratigraphy, Two subdivisions each form the lower, middle, continents continued to drift toward their present positions. Mountain building took place in western North America, Europe, both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in the North American Great Plains, India continued to collide with Asia, creating dramatic new mountain ranges. The Tethys Seaway continued to shrink and then disappeared as Africa collided with Eurasia in the Turkish–Arabian region between 19 and 12 Ma. The subsequent uplift of mountains in the western Mediterranean region and a fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea near the end of the Miocene. The global trend was towards increasing aridity caused primarily by global cooling reducing the ability of the atmosphere to absorb moisture, climates remained moderately warm, although the slow global cooling that eventually led to the Pleistocene glaciations continued. Although a long-term cooling trend was well underway, there is evidence of a period during the Miocene when the global climate rivalled that of the Oligocene. The Miocene warming began 21 million years ago and continued until 14 million years ago, by 8 million years ago, temperatures dropped sharply once again, and the Antarctic ice sheet was already approaching its present-day size and thickness. Greenland may have begun to have large glaciers as early as 7 to 8 million years ago, life during the Miocene Epoch was mostly supported by the two newly formed biomes, kelp forests and grasslands. This allows for more grazers, such as horses, rhinoceroses, ninety five percent of modern plants existed by the end of this epoch. The higher organic content and water retention of the deeper and richer grassland soils, with long term burial of carbon in sediments, produced a carbon and this, combined with higher surface albedo and lower evapotranspiration of grassland, contributed to a cooler, drier climate. The expansion of grasslands and radiations among terrestrial herbivores correlates to fluctuations in CO2
5.
Paleogene
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The Paleogene is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 million years ago to the beginning of the Neogene Period 23.03 Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic Eon and this period consists of the Paleocene, Eocene and Oligocene epochs. The terms Paleogene System and lower Tertiary System are applied to the rocks deposited during the Paleogene Period. By dividing the Tertiary Period into two periods instead of directly into five epochs, the periods are more comparable to the duration of periods of the preceding Mesozoic and Paleozoic Eras. The trend was caused by the formation of the Antarctic Circumpolar Current. During the Paleogene, the continued to drift closer to their current positions. India was in the process of colliding with Asia, subsequently forming the Himalayas, the Atlantic Ocean continued to widen by a few centimeters each year. Africa was moving north to meet with Europe and form the Mediterranean, inland seas retreated from North America early in the period. Australia had also separated from Antarctica and was drifting towards Southeast Asia, mammals began a rapid diversification during this period. Some of these mammals would evolve into forms that would dominate the land, while others would become capable of living in marine, specialized terrestrial. Those that took to the oceans became modern cetaceans, while those that took to the trees became primates, the group to which humans belong. Birds, which were well established by the end of the Cretaceous. In comparison to birds and mammals, most other branches of life remained unchanged during this period. As the Earth cooled, tropical plants became less numerous and were now restricted to equatorial regions, deciduous plants, which could survive through the seasonal climates the world was now experiencing, became more common. The Paleogene is notable in the context of offshore oil drilling, and especially in Gulf of Mexico oil exploration and these rock formations represent the current cutting edge of deep-water oil discovery. Lower Tertiary explorations to date include, Kaskida Oil Field Tiber Oil Field Jack 2 Paleogene Microfossils, 180+ images of Foraminifera
6.
Oligocene
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The Oligocene is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present. As with other geologic periods, the rock beds that define the epoch are well identified but the exact dates of the start. The name Oligocene comes from the Ancient Greek ὀλίγος and καινός, the Oligocene is preceded by the Eocene Epoch and is followed by the Miocene Epoch. The Oligocene is the third and final epoch of the Paleogene Period, the Oligocene is often considered an important time of transition, a link between the archaic world of the tropical Eocene and the more modern ecosystems of the Miocene. Major changes during the Oligocene included an expansion of grasslands. By contrast, the Oligocene–Miocene boundary is not set at an easily identified worldwide event, Oligocene faunal stages from youngest to oldest are, The Paleogene Period general temperature decline is interrupted by an Oligocene 7-million-year stepwise climate change. A deeper 8.2 °C,400, 000-year temperature depression leads the 2 °C, the stepwise climate change began 32.5 Ma and lasted through to 25.5 Ma, as depicted in the PaleoTemps chart. The Oligocene climate change was a increase in ice volume. The 7-million-year depression abruptly terminated within 1–2 million years of the La Garita Caldera eruption at 28–26 Ma, a deep 400, 000-year glaciated Oligocene Miocene boundary event is recorded at McMurdo Sound and King George Island. During this epoch, the continued to drift toward their present positions. Antarctica became more isolated and finally developed an ice cap, a brief marine incursion marks the early Oligocene in Europe. Marine fossils from the Oligocene are rare in North America, there appears to have been a land bridge in the early Oligocene between North America and Europe, since the faunas of the two regions are very similar. Sometime during the Oligocene, South America was finally detached from Antarctica and it also allowed the Antarctic Circumpolar Current to flow, rapidly cooling the Antarctic continent. Angiosperms continued their expansion throughout the world as tropical and sub-tropical forests were replaced by deciduous forests. Open plains and deserts became more common and grasses expanded from their habitat in the Eocene moving out into open tracts. However, even at the end of the period, grass was not quite enough for modern savannas. In North America, subtropical species dominated with cashews and lychee trees present, and temperate trees such as roses, beeches, the legumes spread, while sedges, bulrushes, and ferns continued their ascent. Even more open landscapes allowed animals to grow to larger sizes than they had earlier in the Paleocene epoch 30 million years earlier, marine faunas became fairly modern, as did terrestrial vertebrate fauna on the northern continents
7.
Paleocene
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The Paleocene or Palaeocene, the old recent, is a geologic epoch that lasted from about 66 to 56 million years ago. It is the first epoch of the Paleogene Period in the modern Cenozoic Era, as with many geologic periods, the strata that define the epochs beginning and end are well identified, but the exact ages remain uncertain. The Paleocene Epoch brackets two major events in Earths history and it started with the mass extinction event at the end of the Cretaceous, known as the Cretaceous–Paleogene boundary. This was a marked by the demise of non-avian dinosaurs, giant marine reptiles and much other fauna. The die-off of the dinosaurs left unfilled ecological niches worldwide, the Paleocene ended with the Paleocene–Eocene Thermal Maximum, a geologically brief interval characterized by extreme changes in climate and carbon cycling. The name Paleocene comes from Ancient Greek and refers to the old new fauna that arose during the epoch. The K–Pg boundary that marks the separation between Cretaceous and Paleocene is visible in the record of much of the Earth by a discontinuity in the fossil fauna. There is also evidence of abrupt changes in flora and fauna. There is some evidence that a substantial but very short-lived climatic change may have happened in the early decades of the Paleocene. The end of the Paleocene was also marked by a time of major change, the Paleocene–Eocene Thermal Maximum upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and a major turnover in mammals on land. The Paleocene is divided into three stages, the Danian, the Selandian and the Thanetian, as shown in the table above, additionally, the Paleocene is divided into six Mammal Paleogene zones. The early Paleocene was cooler and dryer than the preceding Cretaceous, in many ways, the Paleocene continued processes that had begun during the late Cretaceous Period. During the Paleocene, the continued to drift toward their present positions. The Laramide orogeny of the late Cretaceous continued to uplift the Rocky Mountains in the American west, africa was heading north towards Europe, slowly closing the Tethys Ocean, and India began its migration to Asia that would lead to a tectonic collision and the formation of the Himalayas. The inland seas in North America and Europe had receded by the beginning of the Paleocene, making way for new land-based flora, warm seas circulated throughout the world, including the poles. The earliest Paleocene featured a low diversity and abundance of marine life, tropical conditions gave rise to abundant marine life, including coral reefs. With the demise of marine reptiles at the end of the Cretaceous, at the end of the Cretaceous, the ammonites and many species of foraminifera became extinct. Marine fauna also came to resemble modern fauna, with only the marine mammals, terrestrial Paleocene strata immediately overlying the K–Pg boundary is in places marked by a fern spike, a bed especially rich in fern fossils
8.
Danian
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With the exception of some ectothermic species like the leatherback sea turtle and crocodiles, no tetrapods weighing more than 25 kilograms survived. It marked the end of the Cretaceous period and with it, in the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows high levels of the metal iridium, which is rare in the Earths crust, the fact that the extinctions occurred at the same time as the impact provides strong situational evidence that the K–Pg extinction was caused by the asteroid. It was possibly accelerated by the creation of the Deccan Traps, however, some scientists maintain the extinction was caused or exacerbated by other factors, such as volcanic eruptions, climate change, or sea level change, separately or together. A wide range of species perished in the K–Pg extinction, the most well-known victims are the non-avian dinosaurs. However, the extinction also destroyed a plethora of other organisms, including certain mammals, pterosaurs, birds, lizards, insects. In the oceans, the K–Pg extinction killed off plesiosaurs and the giant marine lizards and devastated fish, sharks, mollusks and it is estimated that 75% or more of all species on Earth vanished. Yet the devastation caused by the extinction also provided evolutionary opportunities, mammals in particular diversified in the Paleogene, producing new forms such as horses, whales, bats, and primates. Birds, fish and perhaps lizards also radiated, the K–Pg boundary represents one of the most dramatic turnovers in the fossil record for various calcareous nanoplankton that formed the calcium deposits that gave the Cretaceous its name. The turnover in this group is marked at the species level. Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by an increase in extinctions than by a decrease in speciation. Recent studies indicate that there were no major shifts in dinoflagellates through the boundary layer, the K–Pg extinction event was severe, global, rapid, and selective. In terms of severity, the event eliminated a vast number of species, based on marine fossils, it is estimated that 75% or more of all species were made extinct by the K–Pg extinction event. The event appears to have affected all continents at the same time, non-avian dinosaurs, for example, are known from the Maastrichtian of North America, Europe, Asia, Africa, South America and Antarctica, but are unknown from the Cenozoic anywhere in the world. Similarly, fossil pollen shows devastation of the plant communities in areas as far apart as New Mexico, Alaska, China, even though the boundary event was severe, there was significant variability in the rate of extinction between and within different clades. Species that depended on photosynthesis declined or became extinct as atmospheric particles blocked sunlight and this plant extinction caused a major reshuffling of the dominant plant groups. Omnivores, insectivores and carrion-eaters survived the event, perhaps because of the increased availability of their food sources. No purely herbivorous or carnivorous mammals seem to have survived, rather, the surviving mammals and birds fed on insects, worms, and snails, which in turn fed on dead plant and animal matter
9.
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
10.
Maastrichtian
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The Maastrichtian is, in the ICS geologic timescale, the latest age of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned the interval from 72.1 to 66 million years ago, the Maastrichtian was preceded by the Campanian and succeeded by the Danian. At the end of period, there was a mass extinction known as the Cretaceous–Paleogene extinction event. At this extinction event, many commonly recognized groups such as dinosaurs, plesiosaurs and mosasaurs, as well as many other lesser-known groups. The cause of the extinction is most commonly linked to an asteroid about 10 kilometres wide colliding with Earth at the end of the Cretaceous. The Maastrichtian was introduced into scientific literature by Belgian geologist André Hubert Dumont in 1849 and these strata are now classified as the Maastricht Formation - both formation and stage derive their names from the city. The Maastricht Formation is known for its fossils from this age, most notably those of the giant sea reptile Mosasaurus, the base of the Maastrichtian stage is at the first appearance of ammonite species Pachydiscus neubergicus. At the original type locality near Maastricht, the record was later found to be incomplete. A reference profile for the base was then appointed in a section along the Ardour river called Grande Carrière, the Maastrichtian is commonly subdivided into two substages and three ammonite biozones. The following are summaries of the characteristics of specific Maastrichtian aged formations, the Bearpaw Formation, also called the Bearpaw Shale, is a sedimentary rock formation found in northwestern North America. It is exposed in the U. S. state of Montana, as well as the Canadian provinces of Alberta and Saskatchewan, east of the Rocky Mountains. It overlies the older Two Medicine, Judith River and Dinosaur Park Formations, and is in turn overlain by the Horseshoe Canyon Formation in Canada, to the east and south it blends into the Pierre Shale. Other fossils found in this include many types of shellfish, bony fish, sharks, rays, birds. The occasional dinosaur remains have also discovered, presumably from carcasses washed out to sea. The Hell Creek Formation is an intensely studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The Hell Creek Formation occurs in badlands of eastern Montana and portions of North Dakota, South Dakota, in Montana, the Hell Creek Formation overlies the Fox Hills Formation and is the uppermost formation of the Cretaceous period. The Horseshoe Canyon Formation is part of the Edmonton Group and is up to 230 m in depth and it is Late Campanian to Early Maastrichtian in age and is composed of mudstone, sandstone, and carbonaceous shales. There are a variety of environments, which have yielded a diversity of fossil material, the Horseshoe Canyon Formation outcrops extensively in the area of Drumheller, Alberta, as well as further north along the Red Deer River near Trochu, and also in the city of Edmonton
11.
Geologic time scale
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The table of geologic time spans, presented here, agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy. Evidence from radiometric dating indicates that Earth is about 4.54 billion years old, the geology or deep time of Earth’s past has been organized into various units according to events which took place in each period. Older time spans, which predate the reliable record, are defined by their absolute age. Some other planets and moons within the Solar System have sufficiently rigid structures to have preserved records of their own histories, for example, Venus, Mars, dominantly fluid planets, such as the gas giants, do not preserve their history in a comparable manner. Apart from the Late Heavy Bombardment, events on other planets probably had little influence on the Earth. Construction of a scale that links the planets is, therefore, of only limited relevance to the Earths time scale. The existence, timing, and terrestrial effects of the Late Heavy Bombardment is still debated, the largest defined unit of time is the supereon, composed of eons. Eons are divided into eras, which are in turn divided into periods, epochs, the terms eonothem, erathem, system, series, and stage are used to refer to the layers of rock that correspond to these periods of geologic time in Earths history. Geologists qualify these units as early, mid, and late when referring to time, and lower, middle, for example, the lower Jurassic Series in chronostratigraphy corresponds to the early Jurassic Epoch in geochronology. The adjectives are capitalized when the subdivision is formally recognized, and lower case when not, thus early Miocene but Early Jurassic. Geologic units from the time but different parts of the world often look different and contain different fossils. For example, in North America the Lower Cambrian is called the Waucoban series that is subdivided into zones based on succession of trilobites. In East Asia and Siberia, the unit is split into Alexian, Atdabanian. A key aspect of the work of the International Commission on Stratigraphy is to reconcile this conflicting terminology, the term Anthropocene is used informally by popular culture and a growing number of scientists to describe the current epoch in which we are living. The term was coined by Paul Crutzen and Eugene Stoermer in 2000 to describe the current time, others say that humans have not even started to leave their biggest impact on Earth, and therefore the Anthropocene hasnt even started yet. Whatever the case, the ICS has not officially approved the term, leonardo da Vinci concurred with Aristotles interpretation that fossils represented the remains of ancient life. The 11th-century Persian geologist Avicenna and the 13th-century Dominican bishop Albertus Magnus extended Aristotles explanation into a theory of a petrifying fluid. Avicenna also first proposed one of the principles underlying geologic time scales, the Chinese naturalist Shen Kuo also recognized the concept of deep time
12.
Cenozoic
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The Cenozoic Era is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and covering the period from 66 million years ago to the present day. The Cenozoic is also known as the Age of Mammals, because of the mammals that dominated, such as Entelodont, Paraceratherium. The extinction of many large groups such as non-avian dinosaurs, Plesiosauria and Pterosauria allowed the mammals and birds to greatly diversify. Early in the Cenozoic, following the K-Pg event, the planet was dominated by relatively small fauna, including mammals, birds, reptiles. From a geological perspective, it did not take long for mammals, some flightless birds grew larger than humans. These species are referred to as terror birds, and were formidable predators. Mammals came to occupy almost every available niche, and some also grew very large, the Earths climate had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, and partially offset by the Paleocene-Eocene Thermal Maximum. The continents also began looking roughly familiar at this time and moved into their current positions. The Cenozoic is divided into three periods, the Paleogene, Neogene, and Quaternary, and seven epochs, the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. The common use of epochs during the Cenozoic helps paleontologists better organize, there is also more detailed knowledge of this era than any other because of the relatively young, well-preserved rocks associated with it. The Paleogene spans from the extinction of dinosaurs,66 million years ago. It features three epochs, the Paleocene, Eocene and Oligocene, the Paleocene ranged from 66 million to 56 million years ago. The Paleocene is a point between the devastation that is the K-T extinction, to the rich jungles environment that is the Early Eocene. The Early Paleocene saw the recovery of the earth, the continents began to take their modern shape, but all the continents and subcontinent India were separated from each other. Afro-Eurasia was separated by the Tethys Sea, and the Americas were separated by the strait of Panama and this epoch featured a general warming trend, with jungles eventually reaching the poles. The oceans were dominated by sharks as the large reptiles that had once ruled became extinct, archaic mammals filled the world such as creodonts and early primates that evolved during the Mesozoic, and as a result, there was nothing over 10 kilograms. The Eocene Epoch ranged from 56 million years to 33.9 million years ago, in the Early-Eocene, life was small and lived in cramped jungles, much like the Paleocene. There was nothing over the weight of 10 kilograms, among them were early primates, whales and horses along with many other early forms of mammals
13.
Carbon
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Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds, three isotopes occur naturally, 12C and 13C being stable, while 14C is a radioactive isotope, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity, Carbon is the 15th most abundant element in the Earths crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is the second most abundant element in the body by mass after oxygen. The atoms of carbon can bond together in different ways, termed allotropes of carbon, the best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form, for example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to form a streak on paper, while diamond is the hardest naturally occurring material known, graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials, all carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form. They are chemically resistant and require high temperature to react even with oxygen, the most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes. The largest sources of carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil. For this reason, carbon has often referred to as the king of the elements. The allotropes of carbon graphite, one of the softest known substances, and diamond. It bonds readily with other small atoms including other carbon atoms, Carbon is known to form almost ten million different compounds, a large majority of all chemical compounds. Carbon also has the highest sublimation point of all elements, although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperature. Carbon is the element, with a ground-state electron configuration of 1s22s22p2. Its first four ionisation energies,1086.5,2352.6,4620.5 and 6222.7 kJ/mol, are higher than those of the heavier group 14 elements. Carbons covalent radii are normally taken as 77.2 pm,66.7 pm and 60.3 pm, although these may vary depending on coordination number, in general, covalent radius decreases with lower coordination number and higher bond order. Carbon compounds form the basis of all life on Earth
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Isotope
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Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of an element have the same number of protons in each atom. The number of protons within the nucleus is called atomic number and is equal to the number of electrons in the neutral atom. Each atomic number identifies a specific element, but not the isotope, the number of nucleons in the nucleus is the atoms mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12,13 and 14 respectively. The atomic number of carbon is 6, which means that carbon atom has 6 protons. Nuclide refers to a rather than to an atom. Identical nuclei belong to one nuclide, for each nucleus of the carbon-13 nuclide is composed of 6 protons and 7 neutrons. The nuclide concept emphasizes nuclear properties over chemical properties, whereas the isotope concept emphasizes chemical over nuclear, the neutron number has large effects on nuclear properties, but its effect on chemical properties is negligible for most elements. Because isotope is the term, it is better known than nuclide. An isotope and/or nuclide is specified by the name of the particular element followed by a hyphen, when a chemical symbol is used, e. g. C for carbon, standard notation is to indicate the number with a superscript at the upper left of the chemical symbol. Because the atomic number is given by the element symbol, it is common to only the mass number in the superscript. The letter m is sometimes appended after the number to indicate a nuclear isomer. For example, 14C is a form of carbon, whereas 12C. There are about 339 naturally occurring nuclides on Earth, of which 286 are primordial nuclides, primordial nuclides include 32 nuclides with very long half-lives and 254 that are formally considered as stable nuclides, because they have not been observed to decay. In most cases, for reasons, if an element has stable isotopes. Theory predicts that many apparently stable isotopes/nuclides are radioactive, with extremely long half-lives, of the 254 nuclides never observed to decay, only 90 of these are theoretically stable to all known forms of decay
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Extinction event
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An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a change in the diversity. It occurs when the rate of extinction increases with respect to the rate of speciation, Extinction occurs at an uneven rate. Based on the record, the background rate of extinctions on Earth is about two to five taxonomic families of marine animals every million years. Marine fossils are used to measure extinction rates because of their superior fossil record. The Great Oxygenation Event was probably the first major extinction event, since the Cambrian explosion five further major mass extinctions have significantly exceeded the background extinction rate. In addition to the five mass extinctions, there are numerous minor ones as well. Mass extinctions seem to be a mainly Phanerozoic phenomenon, with extinction rates low before large complex organisms arose, estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from the chosen for describing an extinction event as major. In a landmark paper published in 1982, Jack Sepkoski and David M. Raup identified five mass extinctions, the Big Five cannot be so clearly defined, but rather appear to represent the largest of a relatively smooth continuum of extinction events. Cretaceous–Paleogene extinction event,66 Ma at the Cretaceous -Paleogene transition interval, the event formerly called the Cretaceous-Tertiary or K–T extinction or K-T boundary is now officially named the Cretaceous–Paleogene extinction event. About 17% of all families, 50% of all genera and 75% of all species became extinct, in the seas all the ammonites, plesiosaurs and mosasaurs disappeared and the percentage of sessile animals was reduced to about 33%. All non-avian dinosaurs became extinct during that time, the boundary event was severe with a significant amount of variability in the rate of extinction between and among different clades. Mammals and birds, the latter descended from dinosaurs, emerged as dominant large land animals. Triassic–Jurassic extinction event,201.3 Ma at the Triassic-Jurassic transition, about 23% of all families, 48% of all genera and 70% to 75% of all species became extinct. Most non-dinosaurian archosaurs, most therapsids, and most of the amphibians were eliminated. Non-dinosaurian archosaurs continued to dominate aquatic environments, while non-archosaurian diapsids continued to dominate marine environments, the Temnospondyl lineage of large amphibians also survived until the Cretaceous in Australia. Permian–Triassic extinction event,252 Ma at the Permian-Triassic transition, Earths largest extinction killed 57% of all families, 83% of all genera and 90% to 96% of all species
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Bolide
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A bolide is an extremely bright meteor, especially one that explodes in the atmosphere. In astronomy, it refers to a fireball about as bright as the full moon, in geology, a bolide is a very large impactor. One definition describes a bolide as a fireball reaching an apparent magnitude of −14 or brighter – more than twice as bright as the full moon, another definition describes a bolide as any generic large crater-forming impacting body whose composition is unknown. A superbolide is a bolide which reaches an apparent magnitude of −17 or brighter, recent examples of superbolides include the Sutters Mill meteorite and the Chelyabinsk meteor. The IAU has no definition of bolide, and generally considers the term synonymous with fireball. However, the term applies to fireballs reaching an apparent magnitude −14 or brighter. Astronomers tend to use bolide to identify a bright fireball. It may also be used to mean a fireball that is audible, selected superbolide air-bursts events, Tunguska event 2009 Sulawesi superbolide Chelyabinsk meteor Geologists use the term bolide in a somewhat different context than astronomers do. In geology, it indicates a large impactor. jpl. nasa. gov
17.
Popigai crater
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The Popigai crater in Siberia, Russia is tied with the Manicouagan Crater as the fourth largest verified impact crater on Earth. A large bolide impact created the 100-kilometre diameter crater approximately 35 million years ago during the late Eocene epoch and it is conjectured that it may have influenced the Eocene–Oligocene extinction event. The crater is 300 km east from the outpost of Khatanga and 880 km NE of the city of Norilsk and it is designated by UNESCO as a Geopark, a site of special geological heritage. There is a possibility that Popigai impact crater formed simultaneous with the approximately 35-million-year-old Chesapeake Bay. However, a major expedition was undertaken in 1997, which greatly advanced understanding of the enigmatic structure. The impactor in this event has been identified as either an 8 km diameter chondrite asteroid, the shock pressures from the impact instantaneously transformed graphite in the ground into diamonds within a 13.6 km radius of the impact point. These diamonds are usually 0.5 to 2 mm in diameter, the diamonds not only inherited the tabular shape of the original graphite grains but they additionally preserved the original crystals delicate striations. Most modern industrial diamonds are produced synthetically, so the deposits at Popigai may not be profitable because of the remote location, many of the diamonds at Popigai contain crystalline lonsdaleite, an allotrope of carbon that has a hexagonal lattice. Pure, laboratory-created lonsdaleite is 58% harder than diamonds, though it is unknown whether the natural. The diamonds also contain unusual abrasive features and large size which could make them extremely useful for industrial. These types of diamonds are known as impact diamonds because they are thought to be produced when a meteorite strikes a graphite deposit at high velocity and they may have industrial uses but are considered unsuitable as gems. Additionally, carbon polymorphs even harder than lonsdaleite have been discovered in the crater
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Chesapeake Bay impact crater
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The Chesapeake Bay impact crater was formed by a bolide that impacted the eastern shore of North America about 35.5 ±0.3 million years ago, in the late Eocene epoch. It is one of the best-preserved wet-target or marine impact craters, continued slumping of sediments over the rubble of the crater has helped shape the Chesapeake Bay. During the warm late Eocene, sea levels were high, the bolide made impact at a speed of many kilometers per second, punching a deep hole through the sediments and into the granite continental basement rock. The bolide itself was completely vaporized, with the basement rock being fractured to depths of 8 km, the deep crater,38 km across, is surrounded by a flat-floored terrace-like ring trough with an outer edge of collapsed blocks forming ring faults. The entire circular crater is about 85 km in diameter and 1.3 km deep, an area twice the size of Rhode Island, and nearly as deep as the Grand Canyon. However, numerical modeling techniques by Collins et al. indicate that the diameter was likely to have been around 40 km. The surrounding region suffered massive devastation, an enormous tsunami engulfed the land and possibly even reached the Blue Ridge Mountains. The sedimentary walls of the crater progressively slumped in, widened the crater, the slump blocks were then covered with the rubble or breccia. The entire bolide event, from impact to the termination of breccia deposition. In the perspective of time, the 1.2 km breccia is an instantaneous deposit. The crater was buried by additional sedimentary beds that have accumulated during the 35 million years following the impact. The impact has been identified as the source of the North American tektite field, until 1983, no one suspected the existence of a large impact crater buried beneath the lower part of the Chesapeake Bay and its surrounding peninsulas. The first hint was a 20 cm -thick layer of ejecta that turned up in a drilling core taken off Atlantic City, New Jersey, the layer contained the fused glass beads called tektites and shocked quartz grains that are unmistakable signs of a bolide impact. In 1993, data from oil exploration revealed the extent of the crater, the continual slumping of the rubble within the crater has affected the flow of the rivers and shaped the Chesapeake Bay. The impact crater created a long-lasting topographic depression which helped predetermine the course of local rivers, most important for present-day inhabitants of the area, the impact disrupted aquifers. The crater is one of three factors contributing to the sinking of land near the Chesapeake Bay. For example, Hampton Roads is gradually sinking at a rate between 15 and 23 centimeters per century, toms Canyon structure probable impact crater 322 km to the northeast. Popigai crater of similar age Grande Coupure Poag, C, Chesapeake Invader, Discovering Americas Giant Meteorite Crater
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Stratum
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In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers. The stratum is the unit in a stratigraphic column and forms the basis of the study of stratigraphy. Each layer is one of a number of parallel layers that lie one upon another. They may extend over hundreds of thousands of kilometers of the Earths surface. Strata are typically seen as bands of different colored or differently structured material exposed in cliffs, road cuts, quarries, individual bands may vary in thickness from a few millimeters to a kilometer or more. Each band represents a mode of deposition, river silt, beach sand, coal swamp, sand dune, lava bed. Geologists study rock strata and categorize them by the material of beds, each distinct layer is typically assigned to the name of sheet, usually based on a town, river, mountain, or region where the formation is exposed and available for study. For example, the Burgess Shale is an exposure of dark, occasionally fossiliferous. Slight distinctions in material in a formation may be described as members, formations are collected into groups while groups may be collected into supergroups. Archaeological horizon Geologic formation Geologic map Geologic unit Law of superposition Bed GeoWhen Database
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Ancient Greek
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Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
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Dawn
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Dawn or astronomical dawn is the time that marks, depending on the specific usage, the beginning of the twilight before sunrise, the period of the pre-sunrise twilight or the time of sunrise. When identified as the beginning of or the period of twilight, it is recognized by the presence of weak sunlight, different definitions exist for the start of dawn. The difference between these definitions is the amount of sunlight that must be present and this occurs when the Sun is 18 degrees below the horizon in the morning. Though it is possible to localize the direction of the Sun during astronomical dawn and dusk, astronomical dawn and dusk are night, the zenith is extremely dark and more than just the brightest stars can be seen. Nautical Dawn is still dark and is considered night. At civil dawn there is darkness and at the zenith. The sky is still a bit dark and civil dawn is still considered night, at all places on the earth, dawn and dusk times are fastest around the equinoxes and slowest at the summer and winter solstices. As the calendar approaches the summer or winter solstice, the days or nights, respectively, get longer, which can have a potential impact on the time and duration of dawn and dusk. This effect is pronounced closer to the poles, where the Sun rises at the spring equinox and sets at the autumn equinox, with a long period of dawn/dusk. The polar circle is defined as the lowest latitude at which the Sun does not set at the summer solstice, therefore, the angular radius of the polar circle is equal to the angle between the plane of Earths equator and that of the ecliptic. This period of time with no sunset lengthens closer to the pole, near the summer solstice, latitudes higher than 54°30′ get no darker than nautical dawn/dusk, the darkness of the night varies greatly in these latitudes. At latitudes higher than about 59°20, summer nights get no darker than civil dusk or dawn and this period of bright nights is longer at higher latitudes. When the sun gets 9.0 to 9.5 degrees below the horizon, many Indo-European mythologies have a dawn goddess, separate from the male Solar deity, her name deriving from PIE *h2ausos-, derivations of which include Greek Eos, Roman Aurora and Indian Ushas. Also related is Lithuanian Aušrinė, and possibly a Germanic *Austrōn-, in Sioux mythology, Anpao is an entity with two faces. The Hindu dawn deity Ushas is female, whereas Surya, the Sun, and Aruṇa, Ushas is one of the most prominent Rigvedic deities. The time of dawn is also referred to as the Brahmamuhurtham, in some parts of India, both Usha and Pratyusha are worshiped along with the Sun during the festival of Chhath. Prime is the time of prayer of the traditional Divine Office in Christian liturgy. In Islam, astronomical dawn is the time of the first prayer of the day, in Judaism, the question of how to calculate dawn is posed by the Talmud, as it is has many ramifications for Jewish law
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Fauna
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Fauna is all of the animal life of any particular region or time. The corresponding term for plants is flora, flora, fauna and other forms of life such as fungi are collectively referred to as biota. Zoologists and paleontologists use fauna to refer to a collection of animals found in a specific time or place. Paleontologists sometimes refer to a sequence of stages, which is a series of rocks all containing similar fossils. Fauna comes from the Greek names Fauna, a Roman goddess of earth and fertility, the Roman god Faunus, all three words are cognates of the name of the Greek god Pan, and panis is the Greek equivalent of fauna. Fauna is also the word for a book that catalogues the animals in such a manner, the term was first used by Carl Linnaeus from Sweden in the title of his 1745 work Fauna Suecica. Cryofauna are animals that live in, or very close to, cryptofauna are the fauna that exist in protected or concealed microhabitats. Infauna are benthic organisms that live within the substratum of a body of water, especially within the bottom-most oceanic sediments. Bacteria and microalgae may also live in the interstices of bottom sediments, epifauna, also called epibenthos, are aquatic animals that live on the bottom substratum as opposed to within it, that is, the benthic fauna that live on top of the sediment surface at the seafloor. Macrofauna are benthic or soil organisms which are retained on a 0.5 mm sieve, studies in the deep sea define macrofauna as animals retained on a 0.3 mm sieve to account for the small size of many of the taxa. Megafauna are large animals of any region or time. Meiofauna are small invertebrates that live in both marine and fresh water environments. The term Meiofauna loosely defines a group of organisms by their size, larger than microfauna but smaller than macrofauna, one environment for meiofauna is between grains of damp sand. In practice these are metazoan animals that can pass unharmed through a 0.5 –1 mm mesh but will be retained by a 30–45 μm mesh, but the exact dimensions will vary from researcher to researcher. Whether an organism passes through a 1 mm mesh also depends upon whether it is alive or dead at the time of sorting, mesofauna are macroscopic soil invertebrates such as arthropods or nematodes. Mesofauna are extremely diverse, considering just the springtails, as of 1998, microfauna are microscopic or very small animals. Other terms include avifauna, which means bird fauna and piscifauna, which means fish fauna
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Rocks
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Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
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Cenozoic Era
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The Cenozoic Era is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and covering the period from 66 million years ago to the present day. The Cenozoic is also known as the Age of Mammals, because of the mammals that dominated, such as Entelodont, Paraceratherium. The extinction of many large groups such as non-avian dinosaurs, Plesiosauria and Pterosauria allowed the mammals and birds to greatly diversify. Early in the Cenozoic, following the K-Pg event, the planet was dominated by relatively small fauna, including mammals, birds, reptiles. From a geological perspective, it did not take long for mammals, some flightless birds grew larger than humans. These species are referred to as terror birds, and were formidable predators. Mammals came to occupy almost every available niche, and some also grew very large, the Earths climate had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, and partially offset by the Paleocene-Eocene Thermal Maximum. The continents also began looking roughly familiar at this time and moved into their current positions. The Cenozoic is divided into three periods, the Paleogene, Neogene, and Quaternary, and seven epochs, the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. The common use of epochs during the Cenozoic helps paleontologists better organize, there is also more detailed knowledge of this era than any other because of the relatively young, well-preserved rocks associated with it. The Paleogene spans from the extinction of dinosaurs,66 million years ago. It features three epochs, the Paleocene, Eocene and Oligocene, the Paleocene ranged from 66 million to 56 million years ago. The Paleocene is a point between the devastation that is the K-T extinction, to the rich jungles environment that is the Early Eocene. The Early Paleocene saw the recovery of the earth, the continents began to take their modern shape, but all the continents and subcontinent India were separated from each other. Afro-Eurasia was separated by the Tethys Sea, and the Americas were separated by the strait of Panama and this epoch featured a general warming trend, with jungles eventually reaching the poles. The oceans were dominated by sharks as the large reptiles that had once ruled became extinct, archaic mammals filled the world such as creodonts and early primates that evolved during the Mesozoic, and as a result, there was nothing over 10 kilograms. The Eocene Epoch ranged from 56 million years to 33.9 million years ago, in the Early-Eocene, life was small and lived in cramped jungles, much like the Paleocene. There was nothing over the weight of 10 kilograms, among them were early primates, whales and horses along with many other early forms of mammals
25.
Antarctic ice sheet
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The Antarctic ice sheet is one of the two polar ice caps of the Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth and it covers an area of almost 14 million square kilometres and contains 26.5 million cubic kilometres of ice. That is, approximately 61 percent of all water on the Earth is held in the Antarctic ice sheet. In East Antarctica, the ice sheet rests on a land mass. Much of the land in this area would be seabed if the ice sheet were not there, in contrast to the melting of the Arctic sea ice, sea ice around Antarctica was expanding as of 2013. CO2 levels were then about 760 ppm and had been decreasing from earlier levels in the thousands of ppm, carbon dioxide decrease, with a tipping point of 600 ppm, was the primary agent forcing Antarctic glaciation. The opening of the Drake Passage may have played a role as well though models of the changes suggest declining CO2 levels to have more important. According to a 2009 study, the average surface temperature trend of Antarctica is positive. West Antarctica has warmed by more than 0.1 °C/decade in the last 50 years, although this is partly offset by fall cooling in East Antarctica, this effect is restricted to the 1980s and 1990s. Ice enters the sheet through precipitation as snow and this snow is then compacted to form glacier ice which moves under gravity towards the coast. Most of it is carried to the coast by fast moving ice streams, the ice then passes into the ocean, often forming vast floating ice shelves. These shelves then melt or calve off to give icebergs that eventually melt, if the transfer of the ice from the land to the sea is balanced by snow falling back on the land then there will be no net contribution to global sea levels. A2006 paper derived from data, measures changes in the gravity of the ice mass. A2008 study compared the ice leaving the ice sheet, by measuring the ice velocity and thickness along the coast and this found that the East Antarctic Ice Sheet was in balance but the West Antarctic Ice Sheet was losing mass. This was largely due to acceleration of ice streams such as Pine Island Glacier and these results agree closely with the gravity changes. The mass loss was geographically uneven, mainly occurring along the Amundsen Sea coast, while the West Antarctic Ice Sheet mass was roughly constant, Antarctic sea ice anomalies have roughly followed the pattern of warming, with the greatest declines occurring off the coast of West Antarctica. East Antarctica sea ice has been increasing since 1978, though not at a significant rate. The atmospheric warming has been linked to the mass losses in West Antarctica of the first decade of the twenty-first century
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Methane clathrate
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Methane clathrates are common constituents of the shallow marine geosphere and they occur in deep sedimentary structures and form outcrops on the ocean floor. Methane hydrates are believed to form by migration of gas from deep along geological faults, the ice-core methane clathrate record is a primary source of data for global warming research, along with oxygen and carbon dioxide. The observed density is around 0.9 g/cm3, which means that methane hydrate will float to the surface of the sea or of a lake unless it is bound in place by being formed in or anchored to sediment. One litre of fully saturated methane clathrate solid would therefore contain about 120 grams of methane, methane forms a structure I hydrate with two dodecahedral and six tetradecahedral water cages per unit cell. This compares with a number of 20 for methane in aqueous solution. A methane clathrate MAS NMR spectrum recorded at 275 K and 3.1 MPa shows a peak for each cage type, in 2003, a clay-methane hydrate intercalate was synthesized in which a methane hydrate complex was introduced at the interlayer of a sodium-rich montmorillonite clay. The upper temperature stability of this phase is similar to that of structure I hydrate, methane clathrates are restricted to the shallow lithosphere. In addition, deep fresh water lakes may host gas hydrates as well, e. g. the fresh water Lake Baikal, continental deposits have been located in Siberia and Alaska in sandstone and siltstone beds at less than 800 m depth. Oceanic deposits seem to be widespread in the shelf and can occur within the sediments at depth or close to the sediment-water interface. They may cap even larger deposits of gaseous methane, there are two distinct types of oceanic deposit. The most common is dominated by methane contained in a structure I clathrate, here, the methane is isotopically light, which indicates that it is derived from the microbial reduction of CO2. The clathrates in these deposits are thought to have formed in situ from the microbially produced methane, since the δ13C values of clathrate. These deposits are located within a zone around 300–500 m thick in the sediments where they coexist with methane dissolved in the fresh, not salt. Above this zone methane is present in its dissolved form at concentrations that decrease towards the sediment surface. At Blake Ridge on the Atlantic continental rise, the GHSZ started at 190 m depth and continued to 450 m, measurements indicated that methane occupied 0-9% by volume in the GHSZ, and ~12% in the gaseous zone. In the less common type found near the sediment surface some samples have a higher proportion of longer-chain hydrocarbons contained in a structure II clathrate. Carbon from this type of clathrate is isotopically heavier and is thought to have migrated upwards from deep sediments, examples of this type of deposit have been found in the Gulf of Mexico and the Caspian Sea. Some deposits have characteristics intermediate between the microbially and thermally sourced types and are considered to be formed from a mixture of the two
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