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Encyclopedia > Acritarch

Acritarchs are small organic structures found as fossils. In general, any small, non-acid soluble (i.e. non carbonate, non-silicate) organic structure that can not otherwise be accounted for is an acritarch. Most acritarchs are surely remains of single celled lifeforms. They are found in sedimentary rocks from the present back into the Precambrian. They are easily isolated from limestones with hydrochloric acid, and can also be isolated from silica rich rocks using hydrofluoric acid. They are excellent candidates for index fossils to be used for formation dating in the Palaeozoic and when other fossils are not available. They are also useful for palaeoenvironmental interpretation. Acritarchs include the remains of several quite different kinds of organisms including bacteria and dinoflagellates. The nature of the creatures associated with older acritarchs is generally not clear, though many are probably related to unicellular marine algae. Tentaculites found in a State Park in Albany, New York, believed to have existed over 360 million years ago. ... An acid (often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... The Precambrian or Cryptozoic is the period of the geologic timescale from the formation of Earth (around 4500 million years before the present [BP]) to the evolution of abundant macroscopic hard-shelled fossils, which marked the beginning of the Cambrian, some 542 million years BP. Remarkably little is known about... The chemical substance hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride (HCl) gas. ... Hydrofluoric acid is a highly corrosive solution of the chemical compound hydrogen fluoride in water. ... The Palaeozoic is a major division of the geologic timescale, one of four geologic eras. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Classes Dinophyceae Noctiluciphyceae Syndiniophyceae The dinoflagellates are a large group of flagellate protists. ...


Acritarchs are known from 1400Ma and had achieved considerable diversity by 1300Ma. Diversity crashed during the Sturtian-Varanger glacial event around 800Ma. Diversity increased again during the Ediacaran period. Diversity declined suddenly at the end of the Precambrian. The acritarchs show their greatest diversity during the Cambrian, Ordovician, Silurian and Devonian. The nature of some Acritarchs can be identified by their structure. A few can be tentatively identified by the presence of specific chemicals associated with the fossils. Mega-annum, usually abbreviated as Ma, is a unit of time equal to one million years. ... // Generalità Il Periodo Cryogeniano (dal Greco cryos ghiaccio e genesi, nascita) è il secondo periodo geologico dell Era Neoprotozoica seguito poi dal periodo Ediacarano. ... The Ediacaran period is the last geologic period of the Neoproterozoic age, just before the Cambrian. ... The Precambrian or Cryptozoic is the period of the geologic timescale from the formation of Earth (around 4500 million years before the present [BP]) to the evolution of abundant macroscopic hard-shelled fossils, which marked the beginning of the Cambrian, some 542 million years BP. Remarkably little is known about... The Cambrian is a major division of the geologic timescale that begins about 542 million years before the present (BP) at the end of the Proterozoic eon and ended about 490 million years BP with the beginning of the Ordovician period. ... The Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era. ... The Silurian is a major division of the geologic timescale that extends from the end of the Ordovician period, about 439 million years ago (mega years ago, mya), to the beginning of the Devonian period, about 408. ... The Devonian is a major division of the geologic timescale that extends from the end of the Silurian period (360 million years ago (mya)) to the beginning of the Mississippian subperiod of the Carboniferous (408. ...


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  Results from FactBites:
 
Acritarch - Wikipedia, the free encyclopedia (234 words)
Acritarchs include the remains of several quite different kinds of organisms including bacteria and dinoflagellates.
The nature of the creatures associated with older acritarchs is generally not clear, though many are probably related to unicellular marine algae.
Acritarchs are known from 1400Ma and had achieved considerable diversity by 1300Ma.
Ordovician acritarchs from northwestern Argentina (2133 words)
In this new scenario, diversified acritarch assemblages from the Cordillera Oriental correspond to the platform facies of the foreland basin.
Identification of the Ordovician–Silurian boundary on the basis of acritarchs is complicated because of the extinction caused by the Hirnantian glaciation.
Acritarchs from both formations are middle Arenig in age and independently dated by conodonts from the upper part of the Oepikodus evae Zone (Rubinstein and Astini, 2000; Rubinstein 2001a, 2001b and unpublished data).
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