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Proterozoic eon
v • d • e
Geologic timescale of the Proterozoic
(millions of years ago)

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Lower Proterozoic Stromatolites from Bolivia, South America
Lower Proterozoic Stromatolites from Bolivia, South America

The Proterozoic (pronounced /ˌproʊtərəˈzoʊɪk/) is a geological eon representing a period before the first abundant complex life on Earth. The geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other Stromatolites (from Greek στρώμα strōma, mattress bed stratum and λιθος lithos, rock are layered accretionary Structures formed in EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The Proterozoic Eon extended from 2500 Ma to 542. Annum is one form of the Latin noun meaning Year, not a form normally used for derivatives in modern languages the accusative singular 0 ± 1. 0 Ma (million years ago), and is the most recent part of the old, informally named ‘Precambrian’ time. The Precambrian ( Pre-Cambrian) is an informal name for the supereon comprising the eons of the Geologic timescale that came before the current

The Proterozoic consists of 3 geologic eras, from oldest to youngest:

The well-identified events were:

Contents

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. In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes 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. Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change [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. A continent is one of several large Landmasses on Earth. They are generally identified by Convention rather than any strict criteria with seven regions The supercontinent cycle describes the quasi-periodic aggregration and dispersal of Earth 's Continental crust. Orogeny (Greek for "mountain generating" is the process of natural Mountain building and may be studied as a tectonic structural event as a geographical event and [2]

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. The Snowball Earth Hypothesis as it was originally proposed]] Evidence The Snowball Earth hypothesis was originally devised to explain the apparent presence of [3]

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. The Oxygen Catastrophe was a massive environmental change believed to have happened during the Siderian period at the beginning of the Paleoproterozoic 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. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 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. Banded iron formations (also known as banded ironstone formations or BIF s are a distinctive type of rock often found in primordial ( Precambrian) Sedimentary 9 billion years ago, either due to an increase in oxygen or a more thorough mixing of the oceanic water column. [5]

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. The term red beds usually refers to strata of reddish -colored sedimentary rocks such as Sandstone, Siltstone or Shale that Hematite, also spelt hæmatite, is the Mineral form of Iron(III oxide (Fe2O3 one of several Iron oxides [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. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. [6]

Paleogeography

The Mackenzie dike swarm in Canada's Canadian Shield is the largest known dike swarm on Earth, and was a source for significant massive flood basalt eruptions throughout the Proterozoic period. The Mackenzie dike swarm, also called the Mackenzie dikes, form a Large igneous province in the western Canadian Shield of Canada. The Canadian Shield &mdash also called the Laurentian Plateau, or Bouclier Canadien (French &mdash is a large geological shield covered by A dike swarm or dyke swarm in Geology is a major group of parallel linear or radially oriented dikes intruded within Continental crust A flood basalt or trap basalt is the result of a giant Volcanic eruption or series of Eruptions that coats large stretches of land or the Ocean floor The source for the Mackenzie dike swarm is thought to have been a mantle plume center called the Mackenzie hotspot. A mantle plume is an upwelling of abnormally hot rock within the Earth's mantle. The Mackenzie hotspot was a hotspot that existed about 1267 million years ago across Canada from the Northwest Territories and Nunavut. [7]


Proterozoic life

The first advanced single-celled and multi-cellular life roughly coincides with the start of the accumulation of free oxygen; this may have been due to an increase in the oxidized nitrates that eukaryotes use, as opposed to cyanobacteria. In Inorganic chemistry, a nitrate is a salt of Nitric acid with an Ion composed of one Nitrogen and three Oxygen atoms Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of Bacteria that obtain their energy [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. This article is about the biological phenomenon for other uses see Symbiosis (disambiguation The term symbiosis (from the Greek In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. Plants are living Organisms belonging to the kingdom Plantae. Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this [8]

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. Acritarchs are small organic Fossils present from approximately to the present 2 billion years ago. [9]

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. The Phanerozoic (occasionally Phanaerozoic) Eon is the current eon in the Geologic timescale, and the one during which abundant animal life has existed The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with Trilobites ("three-lobes" are extinct Arthropods that form the class Trilobita. The Archaeocyatha or archaeocyathids ("ancient cups" were Sessile 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 Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with

See also

References

  1. ^ Stanley, Steven M. This is a timeline of geological and relevant astronomical events on Earth before the Cambrian period started (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. ^ Lunar and Planetary Science XXVIII
  8. ^ Stanley 321-2
  9. ^ Stanley, 321-3

External links

Precambrian Phanerozoic  
(Hadean) Archean Proterozoic
Proterozoic eon
Paleoproterozoic era Mesoproterozoic era Neoproterozoic era
Siderian Rhyacian Orosirian Statherian Calymmian Ectasian Stenian Tonian Cryogenian Ediacaran
The Precambrian ( Pre-Cambrian) is an informal name for the supereon comprising the eons of the Geologic timescale that came before the current The Phanerozoic (occasionally Phanaerozoic) Eon is the current eon in the Geologic timescale, and the one during which abundant animal life has existed The Hadean (ˈheɪdiən is the geologic eon before the Archean. The Paleoproterozoic (ˌpeɪlɪoʊˌproʊtərəˈzoʊɪk also spelled Palaeoproterozoic) is the first of the three sub-divisions ( eras) of the The Mesoproterozoic Era is a geologic era that occurred between 1600 Ma and 1000 Ma (million years ago The Neoproterozoic Era is the unit of geologic time from 1000 to 542 +/- 0 The Siderian (saɪˈdɪəriən sideros meaning "iron" is the first Geologic period in the Paleoproterozoic Era and lasted from 2500 The Rhyacian (raɪˈeɪsiən Ρυαξ ( rhyax) meaning "stream of Lava " is the second Geologic period in the Paleoproterozoic The Orosirian (ˌɒroʊˈsɪəriən oroseira - ὀροσειρά, meaning "mountain range" is the third Geologic period in the The Statherian (stəˈθɪəriən statheros, meaning "stable firm" is the final Geologic period in the Paleoproterozoic Era The Calymmian (from Greek calymma, "cover" is the first Geologic period in the Mesoproterozoic Era and lasted The Ectasian (from Greek ectasis, "extension" is the second Geologic period in the Mesoproterozoic era and lasted The Stenian (from Greek stenos, "narrow" is the final Geologic period in the Mesoproterozoic Era and lasted The Tonian (from Greek tonas, "stretch" is the first Geologic period in the Neoproterozoic Era and lasted from The Cryogenian (from Greek cryos "cold" and genesis "birth" is a Geologic period that lasted from. The Ediacaran Period (ˌiːdiˈækərən named after the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic

Dictionary

Proterozoic

-adjective

  1. (geology) Of, or relating to the geologic eon from about 2,500 to 570 million years ago; comprises the Paleoproterozoic, Mesoproterozoic and Neoproterozoic eras; marked by the build up of oxygen in the atmosphere and the emergence of primitive multicellular life.

-proper noun

  1. (geology) The Proterozoic eon.
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