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Neoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1,000 million to 541 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran Periods. It is preceded by the Mesoproterozoic era and succeeded by the Paleozoic era of the Phanerozoic eon. The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets may have reached the equator and formed a "Snowball Earth". The earliest fossils of complex multicellular life are found in the Ediacaran period. These organisms make up the Ediacaran biota, including the oldest definitive animals in the fossil record. According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust. Geology At the onset of the Neoproterozoic the supercontinent Rodinia, ...
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Snowball Earth
The Snowball Earth hypothesis proposes that during one or more of Earth's icehouse climates, Earth's surface became entirely or nearly entirely frozen, sometime earlier than 650 Mya (million years ago) during the Cryogenian period. Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical palaeolatitudes and other enigmatic features in the geological record. Opponents of the hypothesis contest the implications of the geological evidence for global glaciation and the geophysical feasibility of an ice- or slush-covered ocean and emphasize the difficulty of escaping an all-frozen condition. A number of unanswered questions remain, including whether the Earth was a full snowball, or a "slushball" with a thin equatorial band of open (or seasonally open) water. The snowball-Earth episodes are proposed to have occurred before the sudden radiation of multicellular bioforms known as the Cambrian explosion. The most rec ...
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Marinoan
The Marinoan glaciation was a period of worldwide glaciation that lasted from approximately 650 to 635 Ma (million years ago) during the Cryogenian period. The glaciation may have covered the entire planet, in an event called the Snowball Earth. The end of the glaciation may have been sped by the release of methane from equatorial permafrost. Origin of name and history of terminology The name is derived from the stratigraphic terminology of the Adelaide Geosyncline (Adelaide Rift Complex) in South Australia and is taken from the Adelaide suburb of Marino. The term Marinoan Series was first used in a 1950 paper by Douglas Mawson and Reg Sprigg to subdivide the Neoproterozoic rocks of the Adelaide area and encompassed all strata from the top of the Brighton Limestone to the base of the Cambrian. The corresponding time period, referred to as the Marinoan Epoch, spanned from the middle Cryogenian to the top of the Ediacaran in modern terminology. Mawson recognised a glacial episode w ...
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Pan-African Orogeny
The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Orogeny. The Pan-African orogeny and the Grenville orogeny are the largest known systems of orogenies on Earth. The sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust. History and terminology The term ''Pan-African'' was coined by for a tectono-thermal event at about 500 Ma when a series of mobile belts in Africa formed between much older African cratons. At the time, other terms were used for similar orogenic events on other continents, i.e. ''Brasiliano'' in South America; ''Adelaidean'' in Australia; and ''Beardmore'' in Antarctica. Later, when plate tectonics became generally accepted, the term ''Pan-Afri ...
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Rodinia
Rodinia (from the Russian родить, ''rodit'', meaning "to beget, to give birth", or родина, ''rodina'', meaning "motherland, birthplace") was a Neoproterozoic supercontinent that assembled 1.1–0.9 billion years ago and broke up 750–633 million years ago. were probably the first to recognise a Precambrian supercontinent, which they named 'Pangaea I'. It was renamed 'Rodinia' by who also were the first to produce a reconstruction and propose a temporal framework for the supercontinent. Rodinia formed at c. 1.23 Ga by accretion and collision of fragments produced by breakup of an older supercontinent, Columbia, assembled by global-scale 2.0–1.8 Ga collisional events.; Rodinia broke up in the Neoproterozoic with its continental fragments reassembled to form Pannotia 633–573 million years ago. In contrast with Pannotia, little is known yet about the exact configuration and geodynamic history of Rodinia. Paleomagnetic evidence provides some clues to the paleolati ...
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Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time. The Precambrian (colored red in the timeline figure) is an informal unit of geologic time, subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale. It spans from the formation of Earth about 4.6 billion years ago (Ga) to the beginning of the Cambrian Period, about million years ago (Ma), when hard-shelled creatures first appeared in abundance. Overview Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history, and what is known has largely been discovered from the 1960s o ...
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Ediacaran Biota
The Ediacaran (; formerly Vendian) biota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (c. 635–541 Mya). These were composed of enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms.Simple multicellular organisms such as red algae evolved at least . The status of the Francevillian biota of is unclear, but they may represent earlier multicellular forms of a more complex nature. The Ediacaran biota may have undergone evolutionary radiation in a proposed event called the Avalon explosion, . This was after the Earth had thawed from the Cryogenian period's extensive glaciation. This biota largely disappeared with the rapid increase in biodiversity known as the Cambrian explosion. Most of the currently existing body plans of animals first appeared in the fossil record of t ...
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Ediacaran
The Ediacaran Period ( ) is a geological period that spans 94 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 541 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia. The Ediacaran Period's status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years. Although the period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous Ediacara biota in 1946, the type section is located in the bed of the Enorama Creek within Brachina Gorge in the Flinders Ranges of South Australia, at . Ediacaran and Vendian The Ediacaran Period overlaps, but is shorter than the Vendian Period, a name that was earlier, in 1952, proposed by Russian geologist and paleontol ...
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Cryogenian
The Cryogenian (, from Greek κρύος ''(krýos)'', meaning "cold" and γένεσις ''(génesis)'', meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran. The Sturtian and Marinoan glaciations occurred during the Cryogenian period, which are the greatest ice ages known to have occurred on Earth. These events are the subject of much scientific controversy. The main debate contests whether these glaciations covered the entire planet (the so-called "Snowball Earth") or a band of open sea survived near the equator (termed "slushball Earth"). Ratification The Cryogenian period was ratified in 1990 by the International Commission on Stratigraphy. In contrast to most other time periods, the beginning of the Cryogenian is not linked to a globally observable and documented event. Instead, the base of the period is defined by a fixed rock age, that was originally ...
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Sturtian
The Sturtian glaciation was a glaciation, or perhaps multiple glaciations, during the Cryogenian Period when the Earth experienced repeated large-scale glaciations. The duration of the Sturtian glaciation has been variously defined,with dates ranging from 717 to 643 Ma. Stern ''et al.'' place the period at 715 to 680 Ma. According to Eyles and Young, "Glaciogenic rocks figure prominently in the Neoproterozoic stratigraphy of southeastern Australia and the northern Canadian Cordillera. The Sturtian glaciogenic succession (c. 740 Ma) unconformably overlies rocks of the Burra Group." The Sturtian succession includes two major diamictite-mudstone sequences which represent glacial advance and retreat cycles. It is stratigraphically correlated with the Rapitan Group of North America. The Sturtian is named after the Sturt Tillite, exposed in the Sturt River Gorge, near Bellevue Heights, South Australia. Reusch's Moraine in northern Norway may have been deposited during this period. See ...
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Geologic Time Scale
The geologic time scale (GTS) is a system of chronological dating that classifies geological strata (stratigraphy) in time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history. The time scale was developed through the study of physical rock layers and relationships as well as the times when different organisms appeared, evolved and became extinct through the study of fossilized remains and imprints. The table of geologic time spans, presented here, agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS). Terminology The primary and largest catalogued divisions of time are periods called ''eons''. The first eon was the Hadean, starting with the formation of the Earth and lasting over 600 million years until the Archean, which is when the Earth had cooled enough for continents and the earliest known life to emerge. After about ...
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Paleozoic
The Paleozoic (or Palaeozoic) Era ( ; from the Greek ''palaiós'' (), "old" and ''zōḗ'' (), "life", meaning "ancient life") is the earliest of three geologic eras of the Phanerozoic Eon. It is the longest of the Phanerozoic eras, lasting from , and is subdivided into six geologic periods (from oldest to youngest): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic comes after the Neoproterozoic Era of the Proterozoic Eon and is followed by the Mesozoic Era. The Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earth's history, known as the Cambrian explosion, in which most modern phyla first appeared. Arthropods, molluscs, fish, amphibians, synapsids and diapsids all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, it was dominated by various forms of organisms. G ...
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Proterozoic
The Proterozoic () is a geological eon spanning the time from the appearance of oxygen in Earth's atmosphere to just before the proliferation of complex life (such as trilobites or corals) on the Earth. The name Proterozoic combines the two forms of ultimately Greek origin: ''protero-'' meaning "former, earlier", and ''-zoic'', a suffix related to ''zoe'' "life". The Proterozoic Eon extended from 2500 mya to 541 mya (million years ago), and is the most recent part of the Precambrian "supereon." The Proterozoic is the longest eon of the Earth's geologic time scale and it is subdivided into three geologic eras (from oldest to youngest): the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic. The well-identified events of this eon were the transition to an oxygenated atmosphere during the Paleoproterozoic; several glaciations, which produced the hypothesized Snowball Earth during the Cryogenian Period in the late Neoproterozoic Era; and the Ediacaran Period (635 to 541 Ma) which is ...
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Tonian
The Tonian (from Greek τόνος ''(tónos)'', meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry. The Tonian is preceded by the Stenian Period of the Mesoproterozoic era and followed by the Cryogenian. Rifting leading to the breakup of supercontinent Rodinia, which had formed in the mid-Stenian, occurred during this period, starting from 900 to 850 Mya. Biology The first large evolutionary radiation of acritarchs occurred during the Tonian. The first putative metazoans (animal) fossils dated to the late Tonian (c. 800 Mya). A notable example of this is the ''Otavia antiqua'', which has been described as a sponge by its discoverers and numerous other scholars. This dating is consistent with molecular data recovered through genetic studies on modern metazoan species; more recent studies have concluded ...
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Mesoproterozoic
The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first period of Earth's history of which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), but little is known about them. The continental masses of the Mesoproterozoic were more or less the same ones that exist today. Major events and characteristics The major events of this era are the breakup of the Columbia supercontinent, the formation of the Rodinia supercontinent, and the evolution of sexual reproduction. This era is marked by the further development of continental plates and plate tectonics. The first large-scale mountain building episode, the Grenville Orogeny, for which extensive evidence still survives, happened in this period. This era was the high point of the Stromatolites before they declined in the Neoproterozoic. The era saw the development of sexual reproduction, which greatly increased the complexity of l ...
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Grenville Orogeny
The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, from Labrador to Mexico, as well as to Scotland. Grenville orogenic crust of mid-late Mesoproterozoic age (c. 1250–980 Ma) is found worldwide, but generally only events which occurred on the southern and eastern margins of Laurentia are recognized under the "Grenville" name. These orogenic events are also known as the Kibaran orogeny in Africa and the Dalslandian orogeny in Western Europe. Timescale The problem of timing the Grenville orogeny is an area of some contention today. The timescale outlined by Toby Rivers in 2008 is derived from the well-preserved Grenville Province and represents one of the most detailed records of the orogeny. This classification considers the classical Grenville designation to cover two separate orogeni ...
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