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Encyclopedia > Proterozoic
Proterozoic eon
Geologic timescale of the Proterozoic
(millions of years ago)

(expand) The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. ...

The Proterozoic (IPA: /ˌprəʊt(ə)rəˈzəʊɪk/) is a geological eon representing a period before the first abundant complex life on Earth. The Proterozoic Eon extended from 2500 Ma to 542.0 ± 1.0 Ma (million years ago). The Proterozoic is the most recent part of the old informal Precambrian time. Not to be confused with the NATO phonetic alphabet, which has also informally been called the “International Phonetic Alphabet”. For information on how to read IPA transcriptions of English words, see IPA chart for English. ... In general usage, an eon (sometimes spelled aeon) is a very long period of time. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... Annum is a Latin noun meaning year. ... The Precambrian (or Pre-Cambrian) is an informal name for the eons of the geologic timescale that came before the current Phanerozoic eon. ...


The Proterozoic consists of 3 geologic eras, from oldest to youngest: A geologic era is a subdivision of geologic time that is a separate classification that divides the Phanerozoic Eon into three parts timeframes. ...

The well-identified events were:- The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between 2500 to 1600 million years ago. ... The Mesoproterozoic era is a geologic period that occurred between 1600 and 900 million years ago. ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ...

Contents

General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... The Mesoproterozoic era is a geologic period that occurred between 1600 and 900 million years ago. ... A glacier is a large, persistent body of ice, formed largely of compacted layers of snow, that slowly deforms and flows in response to gravity. ... The Snowball Earth hypothesis is a controversial hypothesis (Sankaran, 2003) that attempts to explain a number of phenomena noted in the geological record by proposing that an ice age that took place in the Neoproterozoic was so severe that the Earths oceans froze over completely, with only heat from... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ... The Ediacaran Period (from the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Era, just before the Cambrian. ...

The Proterozoic record

The geologic record of the Proterozoic is much better than that for the preceding Archean. In contrast to the deep-water deposits of the Archean, the Proterozoic features many strata that were laid down in extensive shallow epicontinental seas; furthermore, many of these rocks are less metamorphosed than Archean-age ones, and plenty are unaltered.[1] Study of these rocks show that the eon featured massive, rapid continental accretion (unique to the Proterozoic), supercontinent cycles, and wholly-modern orogenic activity.[2] The Archean is a geologic eon; it is a somewhat antiquated term for the time span between 2500 million years before the present and 3800 million years before the present. ... Strata is a comic science fiction novel by Terry Pratchett. ... An epeiric sea--also known as an epicontinental sea--is a large but shallow body of salt water that lies over a part of a continent. ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... Color-coded regions of the world based on the seven commonly reckoned continents Dymaxion map by Buckminster Fuller shows land masses with minimal distortion as nearly one continuous continent A continent is one of several large landmasses on Earth. ... The Supercontinent Cycle describes the quasi-periodic aggregration and dispersal of Earths continental crust. ... // Orogeny (Greek for mountain generating) is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within...


The first known glaciations occurred during the Proterozoic; one began shortly after the beginning of the eon, while there were at least four during the Neoproterozoic, climaxing with the "Snowball Earth" of the Varangian glaciation.[3] The Snowball Earth, also known as the Varangian glaciation, is a recent hypothesis, largely formulated by Paul F. Hoffman, Sturgis Hooper Professor of Geology at Harvard University. ...


The build-up of oxygen

One of the most important events of the Proterozoic was the gathering up of oxygen in the Earth's atmosphere. Though oxygen was undoubtedly released by photosynthesis well back in Archean times, it could not build up to any significant degree until chemical sinks--unoxidized sulfur and iron--had been filled; until roughly 2.3 billion years ago, oxygen was probably only 1% to 2% of its current level.[4] Banded iron formations, which provide most of the world's iron ore, were also a prominent chemical sink; most accumulation ceased after 1.9 billion years ago, either due to an increase in oxygen or a more thorough mixing of the oceanic water column.[5] The leaf is the primary site of photosynthesis in plants. ... The most fundamental reactions in chemistry are the redox processes. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... 2. ...


Red beds, which are colored by hematite, indicate an increase in atmospheric oxygen after 2 billion years ago; they are not found in older rocks.[5] The oxygen build-up was probably due to two factors: a filling of the chemical sinks, and an increase in carbon burial, which sequestered organic compounds that would have otherwise been oxidized by the atmosphere.[6] Red beds are strata of sedimentary rock that are red due to the presence of iron oxides. ... Hematite (AE) or haematite (BE) is the mineral form of Iron(III) oxide, (Fe2O3), one of several iron oxides. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Standard atomic weight 12. ... Benzene is the simplest of the arenes, a family of organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon and hydrogen; therefore, carbides, carbonates, carbon oxides and elementary carbon are not organic (see below for more on the definition controversy...


Proterozoic life

The first advanced single-celled and multi-cellular life roughly coincides with the oxygen accumulation; this may have been due to an increase in the oxidized nitrates that eukaryotes use, as opposed to cyanobacteria.[6] It was also during the Proterozoic that the first symbiotic relationships between mitochondria (for nearly all eukaryotes) and chloroplasts (for plants and some protists only) and their hosts evolved.[7] An electrostatic potential map of the nitrate ion. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Orders The taxonomy of the Cyanobacteria is currently under revision. ... Common Clownfish (Amphiprion ocellaris) in their Ritteri sea anemone (Heteractis magnifica) home. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Divisions Green algae Chlorophyta Charophyta Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta—liverworts Anthocerotophyta—hornworts Bryophyta—mosses Vascular plants (tracheophytes) †Rhyniophyta—rhyniophytes †Zosterophyllophyta—zosterophylls Lycopodiophyta—clubmosses †Trimerophytophyta—trimerophytes Pteridophyta—ferns and horsetails Seed plants (spermatophytes) †Pteridospermatophyta—seed ferns Pinophyta—conifers Cycadophyta—cycads Ginkgophyta—ginkgo Gnetophyta—gnetae Magnoliophyta—flowering plants... Typical phyla Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: ) are a diverse group of organisms, comprising those eukaryotes that are not animals...


The blossoming of eukaryotes such as acritarchs did not preclude the expansion of cyanobacteria; in fact, stromatolites reached their greatest abundance and diversity during the Proterozoic, peaking roughly 1.2 billion years ago.[8] Acritarchs are small organic structures found as fossils. ...


Classically, the boundary between the Proterozoic and the Phanerozoic eons was set at the base of the Cambrian period when the first fossils of animals known as trilobites and archeocyathids appeared. In the second half of the 20th century, a number of fossil forms have been found in Proterozoic rocks, but the upper boundary of the Proterozoic has remained fixed at the base of the Cambrian, which is currently placed at 542 Ma. The Phanerozoic (occasionally Phaenerozoic) Eon is the period of geologic time during which abundant animal life has existed. ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... A geologic period is a subdivision of geologic time that divides an era into smaller timeframes. ... Orders Agnostida Redlichiida Corynexochida Lichida Nektaspida? Phacopida Proetida Asaphida Harpetida Ptychopariida Trilobites are extinct arthropods in the class Trilobita. ... The Archeocyatha, also called Archaeocyathids, were sessile, reef-building marine organisms that lived during the Lower Cambrian period (500-600 million years ago). ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ...


See also

// This is a timeline of geological and relevant astronomical events on Earth before the Cambrian period started. ...

References

  1. ^ Stanley, Steven M. (1999). Earth System History. New York: W.H. Freeman and Company, 315. ISBN 0-7167-2882-6. 
  2. ^ Stanley, 315-18, 329-32
  3. ^ Stanley, 320-1, 325
  4. ^ Stanley, 323
  5. ^ a b Stanley, 324
  6. ^ a b Stanley, 325
  7. ^ Stanley 321-2
  8. ^ Stanley, 321-3
Precambrian  
(Hadean) Archean Proterozoic Phanerozoic
Proterozoic eon
Paleoproterozoic era Mesoproterozoic era Neoproterozoic era
Siderian Rhyacian Orosirian Statherian Calymmian Ectasian Stenian Tonian Cryogenian Ediacaran

  Results from FactBites:
 
Proterozoic - Wikipedia, the free encyclopedia (304 words)
In geology, the Proterozoic is an eon prior to the first abundant complex life on Earth.
The Proterozoic consists of 3 geologic eras, from oldest to youngest:
Classically, the boundary between the Proterozoic and the Paleozoic was set at the base of the Cambrian period when the first fossils of animals known as trilobites and archeocyathids appeared.
  More results at FactBites »

 
 

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