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The Proterozoic
Proterozoic
( /ˌproʊtərəˈzoʊɪk, prɔː-, -trə-/[1][2]) is a geological eon representing the time just before the proliferation of complex life on Earth. The name Proterozoic
Proterozoic
comes from Greek and means "earlier life": the Greek root "protero-" means "former, earlier" and "zoic-" means "animal, living being".[3] The Proterozoic Eon extended from 7016788940000000000♠2500 Ma to 7016170726616000000♠541 Ma (million years ago), and is the most recent part of the Precambrian
Precambrian
Supereon. It can be also described as the time range between the appearance of oxygen in Earth's atmosphere and the appearance of first complex life forms (like trilobites or corals). It is subdivided into three geologic eras (from oldest to youngest): the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic. [4] 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
Earth
during the Cryogenian Period in the late Neoproterozoic Era; and the Ediacaran Period (635 to 541 Ma) which is characterized by the evolution of abundant soft-bodied multicellular organisms and provides us with the first obvious fossil evidence of life on earth.

Contents

1 The Proterozoic
Proterozoic
record 2 The accumulation of oxygen 3 Subduction
Subduction
processes 4 Tectonic history (supercontinents) 5 Life 6 See also 7 References 8 External links

The Proterozoic
Proterozoic
record[edit]

Life
Life
timeline

view • discuss • edit

-4500 — – -4000 — – -3500 — – -3000 — – -2500 — – -2000 — – -1500 — – -1000 — – -500 — – 0 —

water

Single-celled life

photosynthesis

Eukaryotes

Multicellular life

Land life

Dinosaurs    

Mammals

Flowers

 

Earliest Earth
Earth
(−4540)

Earliest water

Earliest life

LHB meteorites

Earliest oxygen

Atmospheric oxygen

Oxygen
Oxygen
crisis

Earliest sexual reproduction

Ediacara biota

Cambrian
Cambrian
explosion

Earliest humans

P h a n e r o z o i c

P r o t e r o z o i c

A r c h e a n

H a d e a n

Pongola

Huronian

Cryogenian

Andean

Karoo

Quaternary

Axis scale: million years Orange labels: ice ages. Also see: Human
Human
timeline and Nature timeline

The geologic record of the Proterozoic
Proterozoic
Eon is more complete than that for the preceding Archean
Archean
Eon. In contrast to the deep-water deposits of the Archean, the Proterozoic
Proterozoic
features many strata that were laid down in extensive shallow epicontinental seas; furthermore, many of those rocks are less metamorphosed than are Archean
Archean
ones, and many are unaltered.[5]:315 Studies of these rocks have shown that the eon continued the massive continental accretion that had begun late in the Archean
Archean
Eon. The Proterozoic
Proterozoic
Eon also featured the first definitive supercontinent cycles and wholly modern mountain building activity (orogeny).[5]:315–18, 329–32 There is evidence that the first known glaciations occurred during the Proterozoic. The first began shortly after the beginning of the Proterozoic
Proterozoic
Eon, and evidence of at least four during the Neoproterozoic Era at the end of the Proterozoic
Proterozoic
Eon, possibly climaxing with the hypothesized Snowball Earth
Earth
of the Sturtian and Marinoan
Marinoan
glaciations.[5]:320–1, 325 The accumulation of oxygen[edit] One of the most important events of the Proterozoic
Proterozoic
was the accumulation of oxygen in the Earth's atmosphere. Though oxygen is believed to have been released by photosynthesis as far back as Archean
Archean
Eon, it could not build up to any significant degree until mineral sinks of 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.[5]:323 The Banded iron formations, which provide most of the world's iron ore, are one mark of that mineral sink process. Their accumulation ceased after 1.9 billion years ago, after the iron in the oceans had all been oxidized.[5]:324 Red beds, which are colored by hematite, indicate an increase in atmospheric oxygen 2 billion years ago. Such massive iron oxide formations are not found in older rocks.[5]:324 The oxygen buildup 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.[5]:325 Subduction
Subduction
processes[edit] The Proterozoic
Proterozoic
Eon was a very tectonically active period in the Earth’s history. The late Archean
Archean
Eon to Early Proterozoic
Proterozoic
Eon corresponds to a period of increasing crustal recycling, suggesting subduction. Evidence for this increased subduction activity comes from the abundance of old granites originating mostly after 2.6 Ga.[6] The appearance of eclogites, which metamorphic rocks created by high pressure (>1 GPa), are explained using a model that incorporates subduction. The lack of eclogites that date to the Archean
Archean
Eon suggests that conditions at that time did not favor the formation of high grade metamorphism and therefore did not achieve the same levels of subduction as was occurring in the Proterozoic
Proterozoic
Eon.[7] As a result of remelting of basaltic oceanic crust due to subduction, the cores of the first continents grew large enough to withstand the crustal recycling processes. The long-term tectonic stability of those cratons is why we find continental crust ranging up to a few billion years in age.[8] It is believed that 43% of modern continental crust was formed in the Proterozoic, 39% formed in the Archean, and only 18% in the Phanerozoic.[6] Studies by Condie 2000[citation needed] and Rino et al. 2004[citation needed] suggest that crust production happened episodically. By isotopically calculating the ages of Proterozoic
Proterozoic
granitoids it was determined that there were several episodes of rapid increase in continental crust production. The reason for these pulses is unknown, but they seemed to have decreased in magnitude after every period.[6] Tectonic history (supercontinents)[edit] Evidence of collision and rifting between continents raises the question as to what exactly were the movements of the Archean
Archean
cratons composing Proterozoic
Proterozoic
continents. Paleomagnetic and geochronological dating mechanisms have allowed the deciphering of Precambrian
Precambrian
Supereon tectonics. It is known that tectonic processes of the Proterozoic
Proterozoic
Eon resemble greatly the evidence of tectonic activity, such as orogenic belts or ophiolite complexes, we see today. Hence, most geologists would conclude that the Earth
Earth
was active at that time. It is also commonly accepted that during the Precambrian, the Earth
Earth
went through several supercontinent breakup and rebuilding cycles (Wilson cycle).[6] In the late Proterozoic
Proterozoic
(most recent), the dominant supercontinent was Rodinia
Rodinia
(~1000–750 Ma). It consisted of a series of continents attached to a central craton that forms the core of the North American Continent
Continent
called Laurentia. An example of an orogeny (mountain building processes) associated with the construction of Rodinia
Rodinia
is the Grenville orogeny
Grenville orogeny
located in Eastern North America. Rodinia
Rodinia
formed after the breakup of the supercontinent Columbia and prior to the assemblage of the supercontinent Gondwana (~500 Ma).[9] The defining orogenic event associated with the formation of Gondwana
Gondwana
was the collision of Africa, South America, Antarctica and Australia forming the Pan-African orogeny.[10] Columbia was dominant in the early-mid Proterozoic
Proterozoic
and not much is known about continental assemblages before then. There are a few plausible models that explain tectonics of the early Earth pre-Columbia, but the current most plausible theory is that prior to Columbia, there were only a few independent craton formations scattered around the Earth
Earth
(not necessarily a supercontinent formation like Rodinia
Rodinia
or Columbia).[6] Life[edit]

Stromatolites

South America

Western Namibia

The first advanced single-celled, eukaryotes and multi-cellular life, Francevillian Group Fossils, roughly coincides with the start of the accumulation of free oxygen.[11] This may have been due to an increase in the oxidized nitrates that eukaryotes use, as opposed to cyanobacteria.[5]:325 It was also during the Proterozoic
Proterozoic
that the first symbiotic relationships between mitochondria (found in nearly all eukaryotes) and chloroplasts (found in plants and some protists only) and their hosts evolved.[5]:321–2 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 1200 million years ago.[5]:321–3 Classically, the boundary between the Proterozoic
Proterozoic
and the Phanerozoic eons was set at the base of the Cambrian
Cambrian
Period when the first fossils of animals including trilobites and archeocyathids appeared. In the second half of the 20th century, a number of fossil forms have been found in Proterozoic
Proterozoic
rocks, but the upper boundary of the Proterozoic has remained fixed at the base of the Cambrian, which is currently placed at 541 Ma.

See also[edit]

Timeline of natural history

References[edit]

^ " Proterozoic
Proterozoic
– definition of Proterozoic
Proterozoic
in English from the Oxford dictionary". OxfordDictionaries.com. Retrieved 2016-01-20.  ^ "Proterozoic". Merriam-Webster
Merriam-Webster
Dictionary.  ^ "Online Etymology Dictionary". www.etymonline.com. Retrieved 2015-12-16.  ^ Speer, Brian. "The Proterozoic
Proterozoic
Eon". University of California Museum of Paleontology.  ^ a b c d e f g h i j Stanley, Steven M. (1999). Earth
Earth
System History. New York: W.H. Freeman and Company. ISBN 0-7167-2882-6.  ^ a b c d e Kearey, P., Klepeis, K., Vine, F., Precambrian
Precambrian
Tectonics and the Supercontinent Cycle, Global Tectonics, Third Edition, pp. 361–377, 2008. ^ Bird, P. (2003). "An updated digital model of plate boundaries". Geochemistry, Geophysics, Geosystems. 4 (3). Bibcode:2003GGG.....4.1027B. doi:10.1029/2001GC000252.  ^ Mengel, F., Proterozoic
Proterozoic
History, Earth
Earth
System: History and Variablility, volume 2, 1998. ^ Condie, K. C.; O'Neill, C. (2011). "The Archean-Proterozoic boundary: 500 my of tectonic transition in Earth
Earth
history". American Journal of Science. 310 (9): 775–790. Bibcode:2010AmJS..310..775C. doi:10.2475/09.2010.01.  ^ Huntly, C., The Mozambique Belt, Eastern Africa: Tectonic Evolution of the Mozambique Ocean and Gondwana
Gondwana
Amalgamation. The Geological Society of America. 2002. ^ El Albani, A.; Bengtson, S.; Canfield, D. E.; Bekker, A.; Macchiarelli, R.; Mazurier, A.; Hammarlund, E. U.; Boulvais, P.; Dupuy, J.-J.; Fontaine, C.; Fürsich, F. T.; Gauthier-Lafaye, F.; Janvier, P.; Javaux, E.; Ossa, F. O.; Pierson-Wickmann, A.-C.; Riboulleau, A.; Sardini, P.; Vachard, D.; Whitehouse, M.; Meunier, A. (2010). "Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago". Nature. 466 (7302): 100–104. Bibcode:2010Natur.466..100A. doi:10.1038/nature09166. PMID 20596019. 

External links[edit]

Wikimedia Commons has media related to Proterozoic.

Palaeos.com: Proterozoic
Proterozoic
eon

v t e

Geologic history of Earth

Cenozoic
Cenozoic
era¹ (present–66.0 Mya)

Quaternary
Quaternary
(present–2.588 Mya)

Holocene
Holocene
(present–11.784 kya) Pleistocene
Pleistocene
(11.784 kya–2.588 Mya)

Neogene
Neogene
(2.588–23.03 Mya)

Pliocene
Pliocene
(2.588–5.333 Mya) Miocene
Miocene
(5.333–23.03 Mya)

Paleogene (23.03–66.0 Mya)

Oligocene
Oligocene
(23.03–33.9 Mya) Eocene
Eocene
(33.9–56.0 Mya) Paleocene
Paleocene
(56.0–66.0 Mya)

Mesozoic
Mesozoic
era¹ (66.0–251.902 Mya)

Cretaceous
Cretaceous
(66.0–145.0 Mya)

Late (66.0–100.5 Mya) Early (100.5–145.0 Mya)

Jurassic
Jurassic
(145.0–201.3 Mya)

Late (145.0–163.5 Mya) Middle (163.5–174.1 Mya) Early (174.1–201.3 Mya)

Triassic
Triassic
(201.3–251.902 Mya)

Late (201.3–237 Mya) Middle (237–247.2 Mya) Early (247.2–251.902 Mya)

Paleozoic
Paleozoic
era¹ (251.902–541.0 Mya)

Permian
Permian
(251.902–298.9 Mya)

Lopingian
Lopingian
(251.902–259.8 Mya) Guadalupian
Guadalupian
(259.8–272.3 Mya) Cisuralian
Cisuralian
(272.3–298.9 Mya)

Carboniferous
Carboniferous
(298.9–358.9 Mya)

Pennsylvanian (298.9–323.2 Mya) Mississippian (323.2–358.9 Mya)

Devonian
Devonian
(358.9–419.2 Mya)

Late (358.9–382.7 Mya) Middle (382.7–393.3 Mya) Early (393.3–419.2 Mya)

Silurian
Silurian
(419.2–443.8 Mya)

Pridoli (419.2–423.0 Mya) Ludlow (423.0–427.4 Mya) Wenlock (427.4–433.4 Mya) Llandovery (433.4–443.8 Mya)

Ordovician
Ordovician
(443.8–485.4 Mya)

Late (443.8–458.4 Mya) Middle (458.4–470.0 Mya) Early (470.0–485.4 Mya)

Cambrian
Cambrian
(485.4–541.0 Mya)

Furongian (485.4–497 Mya) Series 3 (497–509 Mya) Series 2 (509–521 Mya) Terreneuvian
Terreneuvian
(521–541.0 Mya)

Proterozoic
Proterozoic
eon² (541.0 Mya–2.5 Gya)

Neoproterozoic era (541.0 Mya–1 Gya)

Ediacaran
Ediacaran
(541.0-~635 Mya) Cryogenian (~635-~720 Mya) Tonian (~720 Mya-1 Gya)

Mesoproterozoic era (1–1.6 Gya)

Stenian (1-1.2 Gya) Ectasian (1.2-1.4 Gya) Calymmian (1.4-1.6 Gya)

Paleoproterozoic era (1.6–2.5 Gya)

Statherian (1.6-1.8 Gya) Orosirian
Orosirian
(1.8-2.05 Gya) Rhyacian (2.05-2.3 Gya) Siderian
Siderian
(2.3-2.5 Gya)

Archean
Archean
eon² (2.5–4 Gya)

Eras

Neoarchean (2.5–2.8 Gya) Mesoarchean (2.8–3.2 Gya) Paleoarchean
Paleoarchean
(3.2–3.6 Gya) Eoarchean
Eoarchean
(3.6–4 Gya)

Hadean
Hadean
eon² (4–4.6 Gya)

 

 

kya = thousands years ago. Mya = millions years ago. Gya = billions years ago.¹ = Phanerozoic
Phanerozoic
eon. ² = Precambrian
Precambrian
supereon. Source: (2017/02). International Commission on Stratigraphy. Retrieved 13 July 2015. Divisions of Geologic Time—Major Chronostratigraphic and Geochronologic Units USGS Retrieved 10 March 2013.

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