1.
Precambrian
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The Precambrian is the earliest period of Earths history, set before the current Phanerozoic Eon. The Precambrian is a supereon that is subdivided into three eons of the time scale. It spans from the formation of Earth about 4.6 billion years ago to the beginning of the Cambrian Period, about 541 million years ago, the Precambrian accounts for 89% of geologic time. Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earths history, the Precambrian fossil record is poorer than that of the succeeding Phanerozoic, and fossils from that time are of limited biostratigraphic use. This is because many Precambrian rocks have been metamorphosed, obscuring their origins, while others have been destroyed by erosion. A stable crust was apparently in place by 4,412 Ma, the term Precambrian is recognized by the International Commission on Stratigraphy as a general term including the Archean and Proterozoic eons. It is still used by geologists and paleontologists for general discussions not requiring the more specific eon names and it was briefly called the Cryptozoic eon. A specific date for the origin of life has not been determined, carbon found in 3.8 billion year old rocks from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have found in Western Australia. Probable fossils 100 million years older have been found in the same area, there is a fairly solid record of bacterial life throughout the remainder of the Precambrian. The oldest fossil evidence from that era of such complex life comes from the Lantian formation of the Ediacarian period, a very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as Ediacaran or Vendian biota, hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic era. By the middle of the following Cambrian period, a diverse fauna is recorded in the Burgess Shale. The explosion in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life, while land seems to have been devoid of plants and animals, cyanobacteria and other microbes formed prokaryotic mats that covered terrestrial areas. Evidence of the details of plate motions and other activity in the Precambrian has been poorly preserved. It is generally believed that small proto-continents existed prior to 4280 Ma, the supercontinent, known as Rodinia, broke up around 750 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch, one of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a Snowball Earth. The atmosphere of the early Earth is not well understood, most geologists believe it was composed primarily of nitrogen, carbon dioxide, and other relatively inert gases, and was lacking in free oxygen
2.
Cambrian
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The Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya and its subdivisions, and its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latinised form of Cymru, the Welsh name for Wales, as a result, our understanding of the Cambrian biology surpasses that of some later periods. The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia, the seas were relatively warm, and polar ice was absent for much of the period. The United States Federal Geographic Data Committee uses a barred capital C ⟨Є⟩ character similar to the capital letter Ukrainian Ye ⟨Є⟩ to represent the Cambrian Period, the proper Unicode character is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR. Despite the long recognition of its distinction from younger Ordovician Period rocks and older Supereon Precambrian rocks, the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. Pedum in Namibia, Spain and Newfoundland, and possibly, in the western USA, the stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain. The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period, the Cambrian is divided into four epochs and ten ages. Currently only two series and five stages are named and have a GSSP, because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian, Middle Cambrian and Furongian, rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian, each of the local epochs is divided into several stages. The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago, the lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier and this formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago quickly gained favour, though the used to obtain this number are now considered to be unsuitable. A more precise date using modern radiometric dating yield a date of 541 ±0.3 million years ago, most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian, the sea levels fluctuated somewhat, suggesting there were ice ages, associated with pulses of expansion and contraction of a south polar ice cap. In Baltoscandia a Lower Cambrian transgression transformed large swathes of the Sub-Cambrian peneplain into a epicontinental sea, the Earth was generally cold during the early Cambrian, probably due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents
3.
Ordovician
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The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.2 million years from the end of the Cambrian Period 485.4 million years ago to the start of the Silurian Period 443.8 Mya. Lapworth recognized that the fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods. It received international sanction in 1960, when it was adopted as a period of the Paleozoic Era by the International Geological Congress. Life continued to flourish during the Ordovician as it did in the earlier Cambrian period, invertebrates, namely molluscs and arthropods, dominated the oceans. The Great Ordovician Biodiversification Event considerably increased the diversity of life, fish, the worlds first true vertebrates, continued to evolve, and those with jaws may have first appeared late in the period. Life had yet to diversify on land, about 100 times as many meteorites struck the Earth during the Ordovician compared with today. The Ordovician Period began with a major extinction called the Cambrian–Ordovician extinction event and it lasted for about 42 million years and ended with the Ordovician–Silurian extinction event, about 443.8 Mya which wiped out 60% of marine genera. The dates given are recent radiometric dates and vary slightly from those found in other sources and this second period of the Paleozoic era created abundant fossils that became major petroleum and gas reservoirs. The boundary chosen for the beginning of both the Ordovician Period and the Tremadocian stage is highly significant and it correlates well with the occurrence of widespread graptolite, conodont, and trilobite species. The base of the Tremadocian allows scientists to relate these species not only to each other and this makes it easier to place many more species in time relative to the beginning of the Ordovician Period. A number of terms have been used to subdivide the Ordovician Period. In 2008, the ICS erected an international system of subdivisions. There exist Baltoscandic, British, Siberian, North American, Australian, the Ordovician Period in Britain was traditionally broken into Early, Middle and Late epochs. The corresponding rocks of the Ordovician System are referred to as coming from the Lower, Middle, the Floian corresponds to the lower Arenig, the Arenig continues until the early Darriwilian, subsuming the Dapingian. The Llanvirn occupies the rest of the Darriwilian, and terminates with it at the base of the Late Ordovician. The Sandbian represents the first half of the Caradoc, the Caradoc ends in the mid-Katian, during the Ordovician, the southern continents were collected into Gondwana. Gondwana started the period in equatorial latitudes and, as the period progressed, drifted toward the South Pole, the small continent Avalonia separated from Gondwana and began to move north towards Baltica and Laurentia, opening the Rheic Ocean between Gondwana and Avalonia
4.
Silurian
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The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago, to the beginning of the Devonian Period,419.2 Mya. As with other periods, the rock beds that define the periods start and end are well identified. The base of the Silurian is set at a major Ordovician-Silurian extinction event when 60% of marine species were wiped out, a significant evolutionary milestone during the Silurian was the diversification of jawed and bony fish. However, terrestrial life would not greatly diversify and affect the landscape until the Devonian, the Silurian system was first identified by British geologist Sir Roderick Impey Murchison, who was examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s. He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick and this naming does not indicate any correlation between the occurrence of the Silurian rocks and the land inhabited by the Silures. As it was first identified, the Silurian series when traced farther afield quickly came to overlap Sedgwicks Cambrian sequence, however, charles Lapworth resolved the conflict by defining a new Ordovician system including the contested beds. An early alternative name for the Silurian was Gotlandian after the strata of the Baltic island of Gotland, the French geologist Joachim Barrande, building on Murchisons work, used the term Silurian in a more comprehensive sense than was justified by subsequent knowledge. He divided the Silurian rocks of Bohemia into eight stages and his interpretation was questioned in 1854 by Edward Forbes, and the later stages of Barrande, F, G and H, have since been shown to be Devonian. Despite these modifications in the groupings of the strata, it is recognized that Barrande established Bohemia as a classic ground for the study of the earliest fossils. The epoch is named for the town of Llandovery in Carmarthenshire, the Wenlock, which lasted from 433.4 ±1.5 to 427.4 ±2.8 mya, is subdivided into the Sheinwoodian and Homerian ages. It is named after Wenlock Edge in Shropshire, England, during the Wenlock, the oldest known tracheophytes of the genus Cooksonia, appear. The first terrestrial animals also appear in the Wenlock, represented by air-breathing millipedes from Scotland. The Ludlow, lasting from 427.4 ±1.5 to 423 ±2.8 mya, comprises the Gorstian stage, lasting until 425.6 million years ago, and it is named for the town of Ludlow in Shropshire, England. The Pridoli, lasting from 423 ±1.5 to 419.2 ±2.8 mya, is the final and it is named after one locality at the Homolka a Přídolí nature reserve near the Prague suburb Slivenec in the Czech Republic. Přídolí is the old name of a field area. The high sea levels of the Silurian and the flat land resulted in a number of island chains. The southern continents remained united during this period, the melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity. The continents of Avalonia, Baltica, and Laurentia drifted together near the equator and this event is the Caledonian orogeny, a spate of mountain building that stretched from New York State through conjoined Europe and Greenland to Norway
5.
Devonian
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The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian,419.2 million years ago, to the beginning of the Carboniferous,358.9 Mya. It is named after Devon, England, where rocks from this period were first studied, the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents, by the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established, Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fish. The first ray-finned and lobe-finned bony fish appeared, while the placodermi began dominating almost every aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral, in the oceans, primitive sharks became more numerous than in the Silurian and Late Ordovician. The first ammonites, species of molluscs, appeared, trilobites, the mollusk-like brachiopods and the great coral reefs, were still common. The Late Devonian extinction which started about 375 million years ago severely affected marine life, killing off all placodermi, and all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, while the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, another common term is Age of the Fishes, referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian, Breconian and Farlovian stages, in the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common. The Devonian Period is formally broken into Early, Middle and Late subdivisions, the rocks corresponding to those epochs are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System. Early Devonian The Early Devonian lasted from 419.2 ±2.8 to 393.3 ±2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ±2.8 to 407.6 ±2.5, and was followed by the Emsian, which lasted until the Middle Devonian began,393. 3±2.7 million years ago. Middle Devonian The Middle Devonian comprised two subdivisions, first the Eifelian, which gave way to the Givetian 387. 7±2.7 million years ago. Late Devonian Finally, the Late Devonian started with the Frasnian,382.7 ±2.8 to 372.2 ±2.5, during which the first forests took shape on land. The first tetrapods appeared in the record in the ensuing Famennian subdivision. This lasted until the end of the Devonian,358. 9±2.5 million years ago, the Devonian was a relatively warm period, and probably lacked any glaciers
6.
Permian
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The Permian is a geologic period and system which spans 46.7 million years from the end of the Carboniferous Period 298.9 million years ago, to the beginning of the Triassic Period 252.2 Mya. It is the last period of the Paleozoic Era, the following Triassic Period belongs to the Mesozoic Era, the concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the city of Perm. The Permian witnessed the diversification of the early amniotes into the groups of the mammals, turtles, lepidosaurs. The world at the time was dominated by two known as Pangaea and Siberia, surrounded by a global ocean called Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior, amniotes, who could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors. The Permian ended with the Permian–Triassic extinction event, the largest mass extinction in Earths history, in which nearly 90% of marine species and it would take well into the Triassic for life to recover from this catastrophe. Recovery from the Permian-Triassic extinction event was protracted, on land, the term Permian was introduced into geology in 1841 by Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil, the region now lies in the Perm Krai of Russia. This could have in part caused the extinctions of marine species at the end of the period by severely reducing shallow coastal areas preferred by many marine organisms. During the Permian, all the Earths major landmasses were collected into a supercontinent known as Pangaea. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, a new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic Era. Large continental landmass interiors experience climates with extreme variations of heat and cold, deserts seem to have been widespread on Pangaea. Such dry conditions favored gymnosperms, plants with seeds enclosed in a cover, over plants such as ferns that disperse spores in a wetter environment. The first modern trees appeared in the Permian, the climate in the Permian was quite varied. At the start of the Permian, the Earth was still in an Ice Age, glaciers receded around the mid-Permian period as the climate gradually warmed, drying the continents interiors. In the late Permian period, the drying continued although the temperature cycled between warm and cool cycles, Permian marine deposits are rich in fossil mollusks, echinoderms, and brachiopods. By the close of the Permian, trilobites and a host of other groups became extinct. Terrestrial life in the Permian included diverse plants, fungi, arthropods, the period saw a massive desert covering the interior of Pangaea
7.
Triassic
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The Triassic is a geologic period and system which spans 50.9 million years from the end of the Permian Period 252.17 million years ago, to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the first period of the Mesozoic Era, both the start and end of the period are marked by major extinction events. Therapsids and archosaurs were the terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic, the vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south. The global climate during the Triassic was mostly hot and dry, however, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another mass extinction, the Triassic-Jurassic extinction event. The Triassic is usually separated into Early, Middle, and Late Triassic Epochs, from the east, along the equator, the Tethys sea penetrated Pangaea, causing the Paleo-Tethys Ocean to be closed. Later in the mid-Triassic a similar sea penetrated along the equator from the west, the remaining shores were surrounded by the world-ocean known as Panthalassa. All the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates, thus, the supercontinent Pangaea was rifting during the Triassic—especially late in that period—but had not yet separated. In North America, for example, marine deposits are limited to a few exposures in the west, thus Triassic stratigraphy is mostly based on organisms that lived in lagoons and hypersaline environments, such as Estheria crustaceans. At the beginning of the Mesozoic Era, Africa was joined with Earths other continents in Pangaea, Africa shared the supercontinents relatively uniform fauna which was dominated by theropods, prosauropods and primitive ornithischians by the close of the Triassic period. Late Triassic fossils are found throughout Africa, but are common in the south than north. The time boundary separating the Permian and Triassic marks the advent of an event with global impact. At Paleorrota geopark, located in Rio Grande do Sul, Brazil, in these formations, one of the earliest dinosaurs, Staurikosaurus, as well as the mammal ancestors Brasilitherium and Brasilodon have been discovered. The Triassic continental interior climate was hot and dry, so that typical deposits are red bed sandstones and evaporites. Pangaeas large size limited the effect of the global ocean, its continental climate was highly seasonal, with very hot summers. The strong contrast between the Pangea supercontinent and the global ocean triggered intense cross-equatorial monsoons, the best studied of such episodes of humid climate, and probably the most intense and widespread, was the Carnian Pluvial Event. On land, the vascular plants included the lycophytes, the dominant cycadophytes, ginkgophyta, ferns, horsetails
8.
Jurassic
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The Jurassic is a geologic period and system that spans 56.3 million years from the end of the Triassic Period 201.3 million years ago to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles, the start of the period is marked by the major Triassic–Jurassic extinction event. The Jurassic is named after the Jura Mountains within the European Alps, by the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, on land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs, other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to a mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, the chronostratigraphic term Jurassic is directly linked to the Jura Mountains. The name Jura is derived from the Celtic root jor, which was Latinised into juria, the Jurassic period is divided into the Early Jurassic, Middle, and Late Jurassic epochs. The Jurassic System, in stratigraphy, is divided into the Lower Jurassic, Middle, the separation of the term Jurassic into three sections goes back to Leopold von Buch. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous period, the Tethys Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of glaciation, as in the Triassic, there was apparently no land over either pole, and no extensive ice caps existed. In contrast, the North American Jurassic record is the poorest of the Mesozoic, the Jurassic was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. Carbonate hardgrounds were thus very common, along with calcitic ooids, calcitic cements, the first of several massive batholiths were emplaced in the northern American cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. Important Jurassic exposures are found in Russia, India, South America, Japan, Australasia. As the Jurassic proceeded, larger and more groups of dinosaurs like sauropods and ornithopods proliferated in Africa. Middle Jurassic strata are well represented nor well studied in Africa. Late Jurassic strata are also poorly represented apart from the spectacular Tendaguru fauna in Tanzania, the Late Jurassic life of Tendaguru is very similar to that found in western North Americas Morrison Formation. During the Jurassic period, the primary living in the sea were fish
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.
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
11.
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
12.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
13.
Parts per million
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In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e. g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement, commonly used are ppm, ppb, ppt and ppq. Parts-per notation is often used describing dilute solutions in chemistry, for instance, the unit “1 ppm” can be used for a mass fraction if a water-borne pollutant is present at one-millionth of a gram per gram of sample solution. When working with aqueous solutions, it is common to assume that the density of water is 1.00 g/mL, therefore, it is common to equate 1 kilogram of water with 1 L of water. Consequently,1 ppm corresponds to 1 mg/L and 1 ppb corresponds to 1 μg/L, similarly, parts-per notation is used also in physics and engineering to express the value of various proportional phenomena. For instance, a metal alloy might expand 1.2 micrometers per meter of length for every degree Celsius. For instance, the accuracy of distance measurements when using a laser rangefinder might be 1 millimeter per kilometer of distance, this could be expressed as “Accuracy =1 ppm. ”Parts-per notations are all dimensionless quantities, in mathematical expressions. In fractions like “2 nanometers per meter” so the quotients are pure-number coefficients with positive values less than 1, when parts-per notations, including the percent symbol, are used in regular prose, they are still pure-number dimensionless quantities. However, they take the literal “parts per” meaning of a comparative ratio. Parts-per notations may be expressed in terms of any unit of the same measure, in nuclear magnetic resonance spectroscopy, chemical shift is usually expressed in ppm. It represents the difference of a frequency in parts per million from the reference frequency. The reference frequency depends on the magnetic field and the element being measured. It is usually expressed in MHz, typical chemical shifts are rarely more than a few hundred Hz from the reference frequency, so chemical shifts are conveniently expressed in ppm. Parts-per notation gives a quantity that does not depend on the instruments field strength. One part per hundred is generally represented by the percent symbol and denotes one part per 100 parts, one part in 102, and this is equivalent to approximately one drop of water diluted into 5 milliliters or about fifteen minutes out of one day. One part per thousand should generally be spelled out in full and it may also be denoted by the millage symbol. Note however, that specific disciplines such as oceanography, as well as educational exercises, one part per thousand denotes one part per 1000 parts, one part in 103, and a value of 1 × 10−3. This is equivalent to one drop of water diluted into 50 milliliters or about one, one part per ten thousand is denoted by the permyriad symbol
14.
Paleozoic
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The Paleozoic Era is the earliest of three geologic eras of the Phanerozoic Eon, from 541 to 252.17 million years ago. It is the longest of the Phanerozoic eras, and is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous. The Paleozoic comes after the Neoproterozoic era of the Proterozoic and is followed by the Mesozoic, the Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earths history, known as the Cambrian explosion, fish, arthropods, amphibians, anapsids, synapsids, euryapsids and diapsids all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, Great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, large, sophisticated diapsids and synapsids were dominant, the Paleozoic Era ended with the largest extinction event in the history of Earth, the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover, recovery of life in the sea may have been much faster. The Paleozoic era began and ended with supercontinents and in between were the rise of mountains along the margins, and flooding and draining of shallow seas between. At its start, the supercontinent Pannotia broke up, paleoclimatic studies and evidence of glaciers indicate that central Africa was most likely in the polar regions during the early Paleozoic. During the early Paleozoic, the huge continent Gondwana formed or was forming, by mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. There are six periods in the Paleozoic Era, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, the Cambrian spans from 541 million years to 485 million years and is the first period of the Paleozoic era of the Phanerozoic. The Cambrian marked a boom in evolution in an event known as the Cambrian explosion in which the largest number of creatures evolved in any period of the history of the Earth. Creatures like algae evolved, but the most ubiquitous of that period were the armored arthropods, almost all marine phyla evolved in this period. During this time, the supercontinent Pannotia begins to break up, the Ordovician spanned from 485 million years to 443 million years ago. The Ordovician is a time in Earths history in many of the biological classes still prevalent today evolved, such as primitive fish, cephalopods. The most common forms of life, however, were trilobites, snails, more importantly, the first arthropods went ashore to colonize the empty continent of Gondwana. By the end of the Ordovican, Gondwana was at the pole, early North America had collided with Europe. Glaciation of Africa resulted in a drop in sea level
15.
Pennsylvanian (geology)
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The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly 323.2 million years ago to 298.9 million years ago Ma. As with most other units, the rock beds that define the Pennsylvanian are well identified. The Pennsylvanian is named after the U. S. state of Pennsylvania, the division between Pennsylvanian and Mississippian comes from North American stratigraphy. In Europe, the Mississippian and Pennsylvanian are one continuous sequence of lowland continental deposits and are grouped together as the Carboniferous Period. The current internationally used geologic timescale of the ICS gives the Mississippian and Pennsylvanian the rank of subperiods, all modern classes of fungi have been found in rocks of Pennsylvanian age. Amphibians were diverse and common, some were several meters long as adults, the collapse of the rainforest ecology in the mid Pennsylvanian removed many amphibian species that did not survive as well in the cooler, drier conditions. Reptiles, however, prospered due to specific key adaptations, one of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed for the further exploitation of the land by certain tetrapods. These included the earliest sauropsid reptiles, and the earliest known synapsid, small lizard-like animals quickly gave rise to many descendants. Reptiles underwent an evolutionary radiation, in response to the drier climate that followed the rainforest collapse. The Pennsylvanian has been variously subdivided, the Missourian or Monongahela corresponds to the rest of the Kasimovian. The Desmoinesian or Allegheny corresponds to the half of the Moscovian. The Atokan or upper Pottsville corresponds to the half of the Moscovian. The Morrowan corresponds to the Bashkirian, in the European subdivision, the Carboniferous is divided into two epochs, Dinantian and Silesian. The Silesian starts earlier than the Pennsylvanian and is divided in three ages, Namurian Westphalian Stephanian, the Late Carboniferous a Time of Great Coal Swamps, Paleomap project. World map from this time period, the Carboniferous -354 to 290 Million Years Ago, University of California Museum of Paleontology. Information on stratigraphies, localities, tectonics, and life, the Pennsylvanian Epoch of the Carboniferous Period,318 to 299 Mya, Paleos. com US Geological Survey comparison of time scales
16.
Carboniferous rainforest collapse
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The Carboniferous Rainforest Collapse was a minor extinction event that occurred around 305 million years ago in the Carboniferous period. It altered the vast coal forests that covered the region of Euramerica. This event may have fragmented the forests into isolated islands, which in turn caused dwarfism and, shortly after, extinction of many plant, following the event, coal-forming tropical forests continued in large areas of the Earth, but their extent and composition were changed. The event occurred at the end of the Moscovian and continued into the early Kasimovian stages of the Pennsylvanian, the rise of rainforests in the Carboniferous greatly altered the landscapes by eroding low-energy, organic-rich anastomosing river systems with multiple channels and stable alluvial islands. Collapse occurred through a series of step changes, first there was a gradual rise in the frequency of opportunistic ferns in late Moscovian times. This was followed in the earliest Kasimovian by a major, abrupt extinction of the dominant lycopsids, rainforests were fragmented forming shrinking islands further and further apart and in latest Kasimovian time, rainforests vanished from the fossil record. Many amphibian species became extinct while reptiles diversified into more species after the initial crisis and these patterns are explained by the theory of insular biogeography, a concept that explains how evolution progresses when populations are restricted into isolated pockets. This theory was developed for oceanic islands but can be applied equally to any other ecosystem that is fragmented, only existing in small patches. According to this theory, the impact of habitat fragmentation is devastating. Then, as surviving plants and animals reestablish themselves, they adapt to their environment to take advantage of the new allotment of resources. After the Carboniferous Rainforest Collapse, each pocket of life evolved in its own way, the fragmentation of wetlands left a few isolated refugia in Europe, however, even these were unable to maintain the diversity of Moscovian flora. The depletion of the plant life contributed to the levels of oxygen in the atmosphere. This sudden collapse affected several large groups, labyrinthodont amphibians were particularly devastated, while the first reptiles fared better, being physiologically better adapted to the drier conditions that followed. Reptiles acquired new niches at a faster rate than before the collapse and they acquired new feeding strategies including herbivory and carnivory, previously only having been insectivores and piscivores. This extinction event had long term implications for the evolution of amphibians, under prolonged cold conditions, amphibians can survive by decreasing metabolic rates and resorting to overwintering strategies. However, this is only a short term strategy and not a way of dealing with prolonged unfavourable conditions. Since amphibians had a capacity to adapt to the drier conditions that dominated Permian environments, many amphibian families failed to occupy new ecological niches. There are several hypotheses about the nature and cause of the Carboniferous Rainforest Collapse, following a late Bashkirian interval of glaciation, high-frequency shifts in seasonality from humid to arid times began
17.
Mazon Creek fossil beds
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The Mazon Creek fossil beds are a conservation lagerstätte found near Morris, in Grundy County, Illinois. The fossils are preserved in ironstone concretions, formed approximately 300 million years ago in the epoch of the Carboniferous period. These concretions frequently preserve both hard and soft tissues of animal and plant materials, as well as many soft-bodied organisms that do not normally fossilize, the locality was declared a National Historic Landmark in 1997. The Mazon Creek fossils are found in the Upper Carboniferous Francis Creek Shale, the locality is the Mazon River. The 25 to 30 meters of shale were formed approximately 300 million years ago, the fossiliferous concretions are usually found within the thickest deposits of Francis Creek. The concretions occur in localized deposits within the silty to sandy mudstones, the paleoecosystem is believed to be a large river delta system, deposited by at least one major river system flowing from the northeast. The sediments are believed to derive from the Appalachian orogeny events, the delta had a tropical climate, a result of the area being within 10° north latitude of the equator during the Pennsylvanian. The remains of plants and animals were buried by the sediment deposited in the deltaic system. Bacterial decomposition of the remains produced carbon dioxide that combined with dissolved iron from the groundwater and this process formed siderite in the sediments surrounding the remains, forming detailed casts of their structure. Lithification of the sediments formed protective nodules of ironstone around the now fossilized remains and this mode of preservation is known as authigenic mineralisation. The fossiliferous concretions are found in the Mazon River area of Grundy, Will, Kankakee, additional fossils are found in LaSalle County, Illinois, between the Vermilion River and Marseilles, Illinois. The ironstone concretions are recovered from exposures along streams, roadcuts, most concretions are found among the shale and sandstone that was piled up in either a spoil tip of an older underground mine, or ridges of the later surface mining. The Peabody Energy company operated several large mines in Grundy County that are now abandoned. They were named Pit 1 through Pit 11, the northern pits 1-8 are known for the Braidwood Biota with mostly terrestrial fauna and flora. Pit 11, which was located southwest of the town of Braidwood, Pit 11 is now Braidwood State Fish and Wildlife Area, an Illinois state park. Fossil collecting is allowed at the park with a permit, the sites importance was realized in the mid-nineteenth century, the nodules of Mazon Creek, where fragments of plants, even of the softest texture, have been preserved in their integrity. The Mazon Creek flora comprises over 400 species from at least 130 genera, however, the true number of species is difficult to determine. Paleobotanists name separate plant structures with different names by convention, inflating the number of plant taxa
18.
Romer's gap
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Romers gap is an example of an apparent gap in the tetrapod fossil record used in the study of evolutionary biology. Such gaps represent periods from which excavators have not yet found relevant fossils, Romers gap is named after paleontologist Alfred Romer, who first recognised it. Recent discoveries in Scotland are beginning to close this gap in palaeontological knowledge, Romers gap ran from approximately 360 to 345 million years ago, corresponding to the first 15 million years of the Carboniferous, the early Mississippian. The gap forms a discontinuity between the forests and high diversity of fishes in the end Devonian and more modern aquatic. There has been debate as to why there are so few fossils from this time period. Some have suggested the problem was of itself, suggesting that there may have been differences in the geochemistry of the time that did not favour fossil formation. Also, excavators simply may not have dug in the right places and they have also allowed the most accurate logging of the geology of this period. This new evidence suggests that - at least locally - there was no gap in diversity or changes in oxygen geochemistry, the new sedimentary logging in the Ballagan Formation in Scotland challenges this, suggesting oxygen was stable throughout Romers Gap. In this Hangenberg event, most marine and freshwater groups became extinct or were reduced to a few lineages, before the event, oceans and lakes were dominated by lobe-finned fishes and armored fishes called placoderms. After the gap, modern ray finned fish, as well as sharks, the period also saw the demise of the Ichthyostegalia, the early fish-like amphibians with more than five digits. The Tournaisian has even called the Age of Crinoids. There is increasing evidence that lungfish and stem tetrapods and amphibians recovered quickly and diversified in the changing environment of the end-Devonian. The gap in the record has been progressively closed with the discoveries of such early Carboniferous tetrapods as Pederpes. In 2016, five new species were found across the Ballagan Formation, Perittodus apsconditus, Koilops herma, Ossirarus kierani, Diploradus austiumensis and these stem tetrapods and amphibians provide evidence for an early split between the two groups, and rapid diversification in the Early Carboniferous. Blue Beach maintains a museum that displays hundreds of Tournaisian fossils. In 2012, 350-million-year-old tetrapod remains from four new Tournaisian sites in Scotland were announced, in 2016, five more species were unearthed from these localities, proving Scotland to be one of the most important sites in the world for understanding this time period. These localities are the coast of Burnmouth, the banks of the Whiteadder Water near Chirnside, the River Tweed near Coldstream, and the rocks near Tantallon Castle alongside the Firth of Forth. These new localities may represent a larger fauna, as all lie within a distance of each other and share many fishes with the nearby
19.
Annum
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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
20.
Latin
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Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets, Latin was originally spoken in Latium, in the Italian Peninsula. Through the power of the Roman Republic, it became the dominant language, Vulgar Latin developed into the Romance languages, such as Italian, Portuguese, Spanish, French, and Romanian. Latin, Italian and French have contributed many words to the English language, Latin and Ancient Greek roots are used in theology, biology, and medicine. By the late Roman Republic, Old Latin had been standardised into Classical Latin, Vulgar Latin was the colloquial form spoken during the same time and attested in inscriptions and the works of comic playwrights like Plautus and Terence. Late Latin is the language from the 3rd century. Later, Early Modern Latin and Modern Latin evolved, Latin was used as the language of international communication, scholarship, and science until well into the 18th century, when it began to be supplanted by vernaculars. Ecclesiastical Latin remains the language of the Holy See and the Roman Rite of the Catholic Church. Today, many students, scholars and members of the Catholic clergy speak Latin fluently and it is taught in primary, secondary and postsecondary educational institutions around the world. The language has been passed down through various forms, some inscriptions have been published in an internationally agreed, monumental, multivolume series, the Corpus Inscriptionum Latinarum. Authors and publishers vary, but the format is about the same, volumes detailing inscriptions with a critical apparatus stating the provenance, the reading and interpretation of these inscriptions is the subject matter of the field of epigraphy. The works of several hundred ancient authors who wrote in Latin have survived in whole or in part and they are in part the subject matter of the field of classics. The Cat in the Hat, and a book of fairy tales, additional resources include phrasebooks and resources for rendering everyday phrases and concepts into Latin, such as Meissners Latin Phrasebook. The Latin influence in English has been significant at all stages of its insular development. From the 16th to the 18th centuries, English writers cobbled together huge numbers of new words from Latin and Greek words, dubbed inkhorn terms, as if they had spilled from a pot of ink. Many of these words were used once by the author and then forgotten, many of the most common polysyllabic English words are of Latin origin through the medium of Old French. Romance words make respectively 59%, 20% and 14% of English, German and those figures can rise dramatically when only non-compound and non-derived words are included. Accordingly, Romance words make roughly 35% of the vocabulary of Dutch, Roman engineering had the same effect on scientific terminology as a whole
21.
Coal
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Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon, along with quantities of other elements, chiefly hydrogen, sulfur, oxygen. A fossil fuel, coal forms when plant matter is converted into peat, which in turn is converted into lignite, then sub-bituminous coal, after that bituminous coal. This involves biological and geological processes that take place over time, throughout history, coal has been used as an energy resource, primarily burned for the production of electricity and heat, and is also used for industrial purposes, such as refining metals. Coal is the largest source of energy for the generation of electricity worldwide, the extraction of coal, its use in energy production and its byproducts are all associated with environmental and health effects including climate change. Coal is extracted from the ground by coal mining, since 1983, the worlds top coal producer has been China. In 2015 China produced 3,747 million tonnes of coal –47. 7% of 7,861 million tonnes world coal production, in 2015 other large producers were United States, India, European Union and Australia. The word originally took the col in Old English, from Proto-Germanic *kula. In Old Turkic languages, kül is ash, cinders, öčür is quench, the compound charcoal in Turkic is öčür kül, literally quenched ashes, cinders, coals with elided anlaut ö- and inflection affixes -ülmüş. At various times in the geologic past, the Earth had dense forests in low-lying wetland areas, due to natural processes such as flooding, these forests were buried underneath soil. As more and more soil deposited over them, they were compressed, the temperature also rose as they sank deeper and deeper. As the process continued the plant matter was protected from biodegradation and oxidation and this trapped the carbon in immense peat bogs that were eventually covered and deeply buried by sediments. Under high pressure and high temperature, dead vegetation was slowly converted to coal, as coal contains mainly carbon, the conversion of dead vegetation into coal is called carbonization. The wide, shallow seas of the Carboniferous Period provided ideal conditions for coal formation, the exception is the coal gap in the Permian–Triassic extinction event, where coal is rare. Coal is known from Precambrian strata, which predate land plants — this coal is presumed to have originated from residues of algae, in its dehydrated form, peat is a highly effective absorbent for fuel and oil spills on land and water. It is also used as a conditioner for soil to make it able to retain. Lignite, or brown coal, is the lowest rank of coal, jet, a compact form of lignite, is sometimes polished and has been used as an ornamental stone since the Upper Palaeolithic
22.
William Conybeare (geologist)
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William Daniel Conybeare FRS, dean of Llandaff, was an English geologist, palaeontologist and clergyman. He was a grandson of John Conybeare, bishop of Bristol, a preacher and divine. Having entered holy orders he became in 1814 curate of Wardington, near Banbury, during this period he was one of the founders of the Bristol Philosophical Institution. He was rector of Sully in Glamorganshire from 1823 to 1836 and he was instituted to the deanery of Llandaff in 1845. Attracted to the study of geology by the lectures of Dr John Kidd he pursued the subject with ardour, as soon as he had left college he made extended journeys in Britain and on the continent, and he became one of the early members of The Geological Society. Both Buckland and Sedgwick acknowledged their indebtedness to him for instruction received when they first began to devote attention to geology and he contributed geological memoirs to the Transactions of the Geological Society, the Annals of Philosophy, and the Philosophical Magazine. His predictions about the plesiosaur were proved correct by the discovery of a complete skeleton by Mary Anning in 1823. Among his most important memoirs is that on the south-western coal district of England, written in conjunction with Dr Buckland, and published in 1824. He wrote also on the valley of the Thames, on Elie de Beaumonts theory of mountain-chains, and on the great landslip which occurred near Lyme Regis in 1839 when he was vicar of Axminster. His principal work, however, is the Outlines of the Geology of England and Wales, being an edition of the small work issued by William Phillips. The original contributions of Conybeare formed the portion of this edition, of which only Part 1, dealing with the Carboniferous. It affords evidence throughout of the extensive and accurate knowledge possessed by Conybeare and he was a fellow of the Royal Society and a corresponding member of the Institute of France. In 1844, he was awarded the Wollaston medal by the Geological Society of London and his elder brother, John Josias Conybeare, was also interested in geology. He is buried near the Chapter House at Llandaff Cathedral and his tomb is marked by a cross on a memorial shaft De la Beche, Henry & Conybeare. Notice of the discovery of a new Fossil Animal, forming a link between the Ichthyosaurus and Crocodile, together -with general remarks on the Osteology of the Ichthyosaurus, on the Discovery of an almost perfect Skeleton of the Plesiosaurus. Works written by or about William Conybeare at Wikisource This article incorporates text from a now in the public domain, Chisholm, Hugh, ed. Conybeare
23.
William Phillips (geologist)
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William Phillips FGS FRS was an English mineralogist and geologist. Phillips was the son of James Phillips, printer and bookseller in London and he became interested in mineralogy and geology, and was one of the founders of the Geological Society of London. His Outlines of Mineralogy and Geology and Elementary Introduction to the Knowledge of Mineralogy became standard textbooks and this book had a major influence on the development of geology in Britain. In this work Phillips reprinted his description of the cliffs of Dover and other parts of East Kent. Phillips was a member of the Religious Society of Friends and he was elected a Fellow of the Royal Society in 1827. In 1796 he and his brother Richard Phillips, together with William Allen and Luke Howard, the zeolite mineral phillipsite is named for him. This article incorporates text from a now in the public domain, Chisholm, Hugh, ed. Phillips
24.
Amphibian
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Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. They inhabit a variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out as larvae living in water, the young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a respiratory surface and some small terrestrial salamanders and frogs lack lungs. They are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes, the earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura, Urodela, and Apoda, the number of known amphibian species is approximately 7,000, of which nearly 90% are frogs. The smallest amphibian in the world is a frog from New Guinea with a length of just 7.7 mm. The largest living amphibian is the 1.8 m Chinese giant salamander, the study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology. The word amphibian is derived from the Ancient Greek term ἀμφίβιος, the term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes, the numbers of species cited above follows Frost and the total number of known amphibian species is over 7,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a group without unique defining features apart from shared primitive characteristics. Classification varies according to the phylogeny of the author and whether they use a stem-based or a node-based classification. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within groups, like the Temnospondyli or the Lepospondyli. If the common ancestor of amphibians and amniotes is included in Amphibia, all modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. The three modern orders are Anura, Caudata, and Gymnophiona, although the fossils of several older proto-frogs with primitive characteristics are known, the oldest true frog is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. It is anatomically similar to modern frogs. The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia, the earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China
25.
Amniote
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Amniotes are a clade of tetrapod vertebrates comprising the reptiles, birds, and mammals that lay their eggs on land or retain the fertilized egg within the mother. They are distinguished from the anamniotes, which lay their eggs in water. Older sources, particularly prior to the 20th century, may refer to amniotes as higher vertebrates and anamniotes as lower vertebrates, based on the discredited idea of the Great Chain of Being. Amniotes are tetrapods that are characterised by having an egg equipped with an amnion, amniotes include synapsids and sauropsids, as well as their ancestors, back to amphibians. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes, in eutherian mammals, these membranes include the amniotic sac that surrounds the fetus. These embryonic membranes and the lack of a larval stage distinguish amniotes from tetrapod amphibians, the first amniotes, referred to as basal amniotes, resembled small lizards and evolved from the amphibian reptiliomorphs about 312 million years ago, in the Carboniferous geologic period. Their eggs could survive out of the water, allowing amniotes to branch out into drier environments, the eggs could also breathe and cope with wastes, allowing the eggs and the amniotes themselves to evolve into larger forms. From this point the amniotes spread around the globe, eventually to become the dominant land vertebrates, very early in the evolutionary history of amniotes, basal amniotes diverged into two main lines, the synapsids and the sauropsids, both of which persist into the modern era. Amniotes can be characterized in part by embryonic development that includes the formation of several extensive membranes, the amnion, chorion, and allantois. Amniotes develop directly into a form with limbs and a thick stratified epithelium. In amniotes, the transition from a two-layered periderm to cornified epithelium is triggered by thyroid hormone during embryonic development and their kidneys and large intestines are also well-suited to water retention. Most mammals do not lay eggs, but corresponding structures may be found inside the placenta, the ancestors of true amniotes, such as Casineria kiddi, which lived about 340 million years ago, evolved from amphibian reptiliomorphs and resembled small lizards. At the late Devonian mass extinction 360 million years ago, all known tetrapods were essentially aquatic, indeed, many modern day amniotes are dependent on moisture to keep their eggs from desiccating. Although some modern amphibians lay eggs on land, they all lack advanced traits like an amnion, the amniotic egg was formed through a series of evolutionary steps. This allowed the egg to both its size and the rate of gas exchange, permitting a larger, metabolically more active embryo to reach full development before hatching. Further development of the design, like extraembryonic membranes and a shell, were not essential. The only way for the eggs to increase in size would be to develop new internal structures specialized for respiration, as this happened, it would also affect how much the juveniles could grow before they reached adulthood. In fish and amphibians there is one inner membrane, the embryonic membrane
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Arthropod
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An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and jointed appendages. Arthropods form the phylum Arthropoda, which includes the insects, arachnids, myriapods, arthropods are characterized by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages, the rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Their versatility has enabled them to become the most species-rich members of all guilds in most environments. They have over a million described species, making up more than 80% of all described living species, some of which. Arthropods range in size from the microscopic crustacean Stygotantulus up to the Japanese spider crab, arthropods primary internal cavity is a hemocoel, which accommodates their internal organs, and through which their haemolymph – analogue of blood – circulates, they have open circulatory systems. Like their exteriors, the organs of arthropods are generally built of repeated segments. Their nervous system is ladder-like, with paired ventral nerve cords running through all segments and their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong, arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many setae that project through their cuticles. Aquatic species use internal or external fertilization. Almost all arthropods lay eggs, but scorpions give birth to live young after the eggs have hatched inside the mother, arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and eventually undergo a total metamorphosis to produce the adult form. The level of care for hatchlings varies from nonexistent to the prolonged care provided by scorpions. The evolutionary ancestry of arthropods dates back to the Cambrian period, the group is generally regarded as monophyletic, and many analyses support the placement of arthropods with cycloneuralians in a superphylum Ecdysozoa. Overall however, the relationships of Metazoa are not yet well resolved. Likewise, the relationships between various groups are still actively debated. Arthropods contribute to the food supply both directly as food, and more importantly indirectly as pollinators of crops. Some species are known to spread disease to humans, livestock. The word arthropod comes from the Greek ἄρθρον árthron, joint, and πούς pous, i. e. foot or leg, arthropods are invertebrates with segmented bodies and jointed limbs
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Meganeura
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Meganeura is a genus of extinct insects from the Carboniferous period, which resembled and are related to the present-day dragonflies. With wingspans of up to 65 cm, M. monyi is one of the largest known flying insect species, Meganeura were predatory, and fed on other insects. Fossils were discovered in the French Stephanian Coal Measures of Commentry in 1880, in 1885, French paleontologist Charles Brongniart described and named the fossil Meganeura, which refers to the network of veins on the insects wings. Another fine fossil specimen was found in 1979 at Bolsover in Derbyshire, the holotype is housed in the Muséum national dhistoire naturelle, Paris. There has been controversy as to how insects of the Carboniferous period were able to grow so large. The way oxygen is diffused through the body via its tracheal breathing system puts an upper limit on body size. It was originally proposed that Meganeura was able to fly only because the atmosphere at that time contained more oxygen than the present 20% and this hypothesis was initially dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability. If this hypothesis is correct, these insects would have been susceptible to falling oxygen levels, other research indicates that insects really do breathe, with rapid cycles of tracheal compression and expansion. Recent analysis of the energetics of modern insects and birds suggests that both the oxygen levels and air density provide an upper bound on size. Other explanations for the size of meganeurids compared to living relatives are warranted. Another theory suggests that insects that developed in water before becoming terrestrial as adults grew bigger as a way to protect themselves against the high levels of oxygen, media related to Meganeura at Wikimedia Commons Picture of life sized model of Meganeura monyi made for Denver Museum of Natural History
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Geological history of Earth
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The geological history of Earth follows the major events in Earths past based on the geologic time scale, a system of chronological measurement based on the study of the planets rock layers. Earth was initially due to extreme volcanism and frequent collisions with other bodies. Eventually, the layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards, possibly as a result of the impact of a planetoid with the Earth, outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans, as the surface continually reshaped itself over hundreds of millions of years, continents formed and broke apart. They migrated across the surface, occasionally combining to form a supercontinent, roughly 750 million years ago, the earliest-known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia,600 to 540 million years ago, then finally Pangaea, the present pattern of ice ages began about 40 million years ago, then intensified at the end of the Pliocene. The polar regions have undergone repeated cycles of glaciation and thaw, repeating every 40. The last glacial period of the current ice age ended about 10,000 years ago, the Precambrian includes approximately 90% of geologic time. It extends from 4.6 billion years ago to the beginning of the Cambrian Period and it includes three eons, the Hadean, Archean, and Proterozoic. Major volcanic events altering the Earths environment and causing extinctions may have occurred 10 times in the past 3 billion years. During Hadean time, the Solar System was forming, probably within a cloud of gas and dust around the sun. The Hadean Eon is not formally recognized, but it marks the era before we have adequate record of significant solid rocks. The oldest dated zircons date from about 4,400 million years ago, Earth was initially molten due to extreme volcanism and frequent collisions with other bodies. Eventually, the layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards, possibly as a result of the impact of a planetoid with the Earth. Some of this objects mass merged with the Earth, significantly altering its composition. Some of the material survived to form an orbiting moon, more recent potassium isotopic studies suggest that the Moon was formed by a smaller, high-energy, high-angular-momentum giant impact cleaving off a significant portion of the Earth
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Glacial period
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A glacial period is an interval of time within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the hand, are periods of warmer climate between glacial periods. The last glacial period ended about 15,000 years ago, the Holocene epoch is the current interglacial. A time when there are no glaciers on Earth is considered a greenhouse climate state, within the Quaternary glaciation, there have been a number of glacials and interglacials. The last glacial period was the most recent glacial period within the current ice age, occurring in the Pleistocene epoch, the glacial advance reached its maximum extent about 18,000 BP. In Europe, the ice sheet reached northern Germany, since orbital variations are predictable, computer models that relate orbital variations to climate can predict future climate possibilities. Work by Berger and Loutre suggests that the current warm climate may last another 50,000 years
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Mountain formation
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Mountain formation refers to the geological processes that underlie the formation of mountains. These processes are associated with movements of the Earths crust. Folding, faulting, volcanic activity, igneous intrusion and metamorphism can all be parts of the process of mountain building. The formation of mountains is not necessarily related to the structures found on it. There are three types of mountains, volcanic, fold, and block. A more detailed classification useful on a local scale predates plate tectonics, movements of tectonic plates create volcanoes along the plate boundaries, which erupt and form mountains. A volcanic arc system is a series of volcanoes that form near a subduction zone where the crust of an oceanic plate melts. Most volcanoes occur in a band encircling the Pacific Ocean, the most important types of volcanic mountain are composite cones or stratovolcanoes and shield volcanoes. A shield volcano has a gently sloping cone due to the low viscosity of the emitted material, mauna Loa is the classic example, with a slope of 4°-6°. The composite volcano or stratovolcano has a steeply rising cone, due to the higher viscosity of the emitted material. Besides the examples already mentioned are Mount Shasta, Mount Hood, when plates collide or undergo subduction, the plates tend to buckle and fold, forming mountains. Most of the major mountain ranges are associated with thrusting and folding or orogenesis. Examples are the Jura and the Zagros mountains, when a fault block is raised or tilted, block mountains can result. Higher blocks are called horsts and troughs are called grabens, a spreading apart of the surface causes tensional forces. When the tensional forces are enough to cause a plate to split apart. Hotspots are supplied by a source in the Earths mantle called a mantle plume. Although originally attributed to a melting of subducted oceanic crust, recent evidence belies this connection, the mechanism for plume formation remains a research topic. Several movements of the earths crust that lead to mountains are associated with faults, early bent plate models predicting fractures and fault movements have evolved into todays kinematic and flexural models
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Pangaea
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Pangaea or Pangea was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from earlier continental units approximately 335 million years ago, in contrast to the present Earth and its distribution of continental mass, much of Pangaea was in the southern hemisphere and surrounded by a superocean, Panthalassa. Pangaea was the most recent supercontinent to have existed and the first to be reconstructed by geologists, the name Pangaea/Pangea is derived from Ancient Greek pan and Gaia. The name Pangea occurs in the 1920 edition of Die Entstehung der Kontinente und Ozeane, but only once, the forming of supercontinents and their breaking up appears to have been cyclical through Earths history. There may have many others before Pangaea. When Rodinia broke up, it split into three pieces, the supercontinent of Proto-Laurasia, the supercontinent of Proto-Gondwana, and the smaller Congo craton, Proto-Laurasia and Proto-Gondwana were separated by the Proto-Tethys Ocean. Next Proto-Laurasia itself split apart to form the continents of Laurentia, Siberia, Baltica moved to the east of Laurentia, and Siberia moved northeast of Laurentia. The splitting also created two new oceans, the Iapetus Ocean and Paleoasian Ocean, most of the above masses coalesced again to form the relatively short-lived supercontinent of Pannotia. This supercontinent included large amounts of land near the poles and, near the equator, Pannotia lasted until 540 Ma, near the beginning of the Cambrian period and then broke up, giving rise to the continents of Laurentia, Baltica, and the southern supercontinent of Gondwana. Baltica, Laurentia, and Avalonia all came together by the end of the Ordovician to form a supercontinent called Euramerica or Laurussia. The collision also resulted in the formation of the northern Appalachians, Siberia sat near Euramerica, with the Khanty Ocean between the two continents. While all this was happening, Gondwana drifted slowly towards the South Pole and this was the first step of the formation of Pangaea. The second step in the formation of Pangaea was the collision of Gondwana with Euramerica, by Silurian time,440 Ma, Baltica had already collided with Laurentia, forming Euramerica. Avalonia had not yet collided with Laurentia, but as Avalonia inched towards Laurentia, meanwhile, southern Europe broke off from Gondwana and began to move towards Euramerica across the newly formed Rheic Ocean. It collided with southern Baltica in the Devonian, though this microcontinent was an underwater plate, the Iapetus Oceans sister ocean, the Khanty Ocean, shrank as an island arc from Siberia collided with eastern Baltica. Behind this island arc was a new ocean, the Ural Ocean, by late Silurian time, North and South China split from Gondwana and started to head northward, shrinking the Proto-Tethys Ocean in their path and opening the new Paleo-Tethys Ocean to their south. In the Devonian Period, Gondwana itself headed towards Euramerica, causing the Rheic Ocean to shrink, South America moved northward to southern Euramerica, while the eastern portion of Gondwana headed toward the South Pole from the equator. North and South China were on independent continents, the Kazakhstania microcontinent had collided with Siberia
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United States
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Forty-eight of the fifty states and the federal district are contiguous and located in North America between Canada and Mexico. The state of Alaska is in the northwest corner of North America, bordered by Canada to the east, the state of Hawaii is an archipelago in the mid-Pacific Ocean. The U. S. territories are scattered about the Pacific Ocean, the geography, climate and wildlife of the country are extremely diverse. At 3.8 million square miles and with over 324 million people, the United States is the worlds third- or fourth-largest country by area, third-largest by land area. It is one of the worlds most ethnically diverse and multicultural nations, paleo-Indians migrated from Asia to the North American mainland at least 15,000 years ago. European colonization began in the 16th century, the United States emerged from 13 British colonies along the East Coast. Numerous disputes between Great Britain and the following the Seven Years War led to the American Revolution. On July 4,1776, during the course of the American Revolutionary War, the war ended in 1783 with recognition of the independence of the United States by Great Britain, representing the first successful war of independence against a European power. The current constitution was adopted in 1788, after the Articles of Confederation, the first ten amendments, collectively named the Bill of Rights, were ratified in 1791 and designed to guarantee many fundamental civil liberties. During the second half of the 19th century, the American Civil War led to the end of slavery in the country. By the end of century, the United States extended into the Pacific Ocean. The Spanish–American War and World War I confirmed the status as a global military power. The end of the Cold War and the dissolution of the Soviet Union in 1991 left the United States as the sole superpower. The U. S. is a member of the United Nations, World Bank, International Monetary Fund, Organization of American States. The United States is a developed country, with the worlds largest economy by nominal GDP. It ranks highly in several measures of performance, including average wage, human development, per capita GDP. While the U. S. economy is considered post-industrial, characterized by the dominance of services and knowledge economy, the United States is a prominent political and cultural force internationally, and a leader in scientific research and technological innovations. In 1507, the German cartographer Martin Waldseemüller produced a map on which he named the lands of the Western Hemisphere America after the Italian explorer and cartographer Amerigo Vespucci
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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
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. PMID 20392720. Archived from the original on August 9, 2016. Retrieved June 9, 2015.
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Carboniferous System". Encyclopædia Britannica (11th ed.). Cambridge University Press.
