Jump to content

Paleoarchean: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous edit
Content deleted Content added
VisualWikitext
making all the archean period linking consistant
Open access status updates in citations with OAbot #oabot
 
(18 intermediate revisions by 13 users not shown)
Line 39: Line 39:
| timespan_formality = Formal
| timespan_formality = Formal
| lower_boundary_def = Defined Chronometrically
| lower_boundary_def = Defined Chronometrically
| lower_gssa_accept_date = 1991{{citation needed|date=February 2023|reason=Previously given Plumb 1991 reference was not about the Paleoarchean but only the introduction of the Archean Eon. It even said that further sub-division of the Archean was deferred to a later date.}}
| lower_gssa_accept_date = 1991<ref name = "episodes 1991">{{cite journal |last1=Plumb |first1=K. A. |title=New Precambrian time scale |journal=Episodes |date=June 1, 1991 |volume=14 |issue=2 |pages=139-140 |doi=10.18814/epiiugs/1991/v14i2/005 |url=https://www.episodes.org/journal/view.html?doi=10.18814/epiiugs/1991/v14i2/005 |access-date=16 January 2023}}</ref>
| upper_boundary_def = Defined Chronometrically
| upper_boundary_def = Defined Chronometrically
| upper_gssa_accept_date = 1991{{citation needed|date=February 2023|reason=Previously given Plumb 1991 reference was not about the Paleoarchean but only the introduction of the Archean Eon. It even said that further sub-division of the Archean was deferred to a later date.}}
| upper_gssa_accept_date = 1991<ref name = "episodes 1991"/>
}}
}}
The '''Paleoarchean''' ({{IPAc-en|ˌ|p|eɪ|l|i|oʊ|.|ɑːr|ˈ|k|iː|ə|n}}), also spelled '''Palaeoarchaean''' (formerly known as the '''early Archean'''), is a [[Geologic time scale#Terminology|geologic era]] within the [[Archean|Archean Eon]]. The name derives from Greek "Palaios" ''ancient''. It spans the period of time {{Ma|Paleoarchean|Mesoarchean}}. The era is defined [[Absolute dating|chronometrically]] and is not referenced to a specific level of a rock section on [[Earth]]. The [[Abiogenesis|earliest confirmed evidence of life]] comes from this era, and [[Vaalbara]], one of Earth's earliest [[Supercontinent|supercontinents]], may have formed during this era.<ref name=":1">{{Cite journal|last=Lepot|first=Kevin|date=2020|title=Signatures of early microbial life from the Archean (4 to 2.5 Ga) eon|url=https://www.sciencedirect.com/science/article/pii/S0012825220303421|journal=Earth-Science Reviews|language=en|volume=209|pages=103296|doi=10.1016/j.earscirev.2020.103296|bibcode=2020ESRv..20903296L|s2cid=225413847|issn=0012-8252}}</ref><ref name=":2">{{Cite journal|last1=Bradley|first1=Kyle|last2=Weiss|first2=Benjamin P.|last3=Buick|first3=Roger|date=2015|title=Records of geomagnetism, climate, and tectonics across a Paleoarchean erosion surface|url=https://www.sciencedirect.com/science/article/pii/S0012821X15001454|journal=Earth and Planetary Science Letters|language=en|volume=419|pages=1–13|doi=10.1016/j.epsl.2015.03.008|bibcode=2015E&PSL.419....1B|issn=0012-821X}}</ref>
The '''Paleoarchean''' ({{IPAc-en|ˌ|p|eɪ|l|i|oʊ|.|ɑːr|ˈ|k|iː|ə|n|,_|ˌ|p|æ|l|-}} {{respell|PAY|lee|oh|ar|KEE|ən|,_|PAL-}}), also spelled '''Palaeoarchaean''' (formerly known as the '''early Archean'''), is a [[Geologic time scale#Terminology|geologic era]] within the [[Archean|Archean Eon]]. The name derives from Greek "Palaios" ''ancient''. It spans the period of time {{Ma|Paleoarchean|Mesoarchean}}. The era is defined [[Absolute dating|chronometrically]] and is not referenced to a specific level of a rock section on [[Earth]]. The [[Abiogenesis|earliest confirmed evidence of life]] comes from this era, and [[Vaalbara]], one of Earth's earliest [[Supercontinent|supercontinents]], may have formed during this era.<ref name=Lepot2020>{{cite journal |last=Lepot |first=Kevin |date=2020 |title=Signatures of early microbial life from the Archean (4 to 2.5 Ga) eon |journal=Earth-Science Reviews |issn=0012-8252 |doi=10.1016/j.earscirev.2020.103296 |doi-access=free |bibcode=2020ESRv..20903296L |s2cid=225413847 |volume=209 |pages=103296 |hdl=20.500.12210/62415 |hdl-access=free }}</ref><ref name=Bradley2015>{{cite journal |last1=Bradley |first1=Kyle |last2=Weiss |first2=Benjamin P. |last3=Buick |first3=Roger |date=2015 |title=Records of geomagnetism, climate, and tectonics across a Paleoarchean erosion surface |journal=Earth and Planetary Science Letters |issn=0012-821X |doi=10.1016/j.epsl.2015.03.008 |bibcode=2015E&PSL.419....1B |volume=419 |pages=1–13 |url=https://www.sciencedirect.com/science/article/pii/S0012821X15001454|url-access=subscription }}</ref>


== Early life ==
== Early life ==
[[File:Stromatolithe_Paléoarchéen_-_MNHT.PAL.2009.10.1.jpg|thumb|left|upright 1.2| A [[stromatolite]] formed by Paleoarchean microbial mats, preserved as a [[fossil]], from [[Pilbara craton]], [[Western Australia]].]]
[[File:Stromatolithe_Paléoarchéen_-_MNHT.PAL.2009.10.1.jpg|thumb|left|upright 1.2| A [[stromatolite]] formed by Paleoarchean microbial mats, preserved as a [[fossil]], from [[Pilbara craton]], [[Western Australia]].]]
The geological record from the Paleoarchean era is very limited. Due to deformation and [[metamorphism]], most rocks from the Paleoarchean era cannot provide any useful information. There are only two locations in the world containing rock formations that are intact enough to preserve evidence of early life: the [[Kaapvaal Craton]] in [[Southern Africa]] and the [[Pilbara Craton]] in [[Western Australia]].<ref name=":02"/>
The geological record from the Paleoarchean era is very limited. Due to deformation and [[metamorphism]], most rocks from the Paleoarchean era cannot provide any useful information. There are only two locations in the world containing rock formations that are intact enough to preserve evidence of early life: the [[Kaapvaal Craton]] in [[Southern Africa]] and the [[Pilbara Craton]] in [[Western Australia]].<ref name=Homann2019>{{cite journal |last=Homann |first=Martin |year=2019 |title=Earliest life on Earth: Evidence from the Barberton Greenstone Belt, South Africa |journal=Earth-Science Reviews |issn=0012-8252 |doi=10.1016/j.earscirev.2019.102888 |bibcode=2019ESRv..19602888H |s2cid=198424907 |volume=196 |pages=102888 |url=https://archimer.ifremer.fr/doc/00637/74916/88260.pdf|url-access= |url-status= |archive-url= |archive-date= }}</ref>


The [[Pilbara Craton|Dresser Formation]], located in the [[Pilbara Craton]], contains samples of [[sedimentary rock]] from the Paleoarchean Era.<ref name=":02">{{Cite journal |last=Homann |first=Martin |year=2019| title=Earliest life on Earth: Evidence from the Barberton Greenstone Belt, South Africa |journal=Earth-Science Reviews |lang=en |volume=196 |pages=102888 |doi=10.1016/j.earscirev.2019.102888 |bibcode=2019ESRv..19602888H |s2cid=198424907 |issn=0012-8252 |url=https://www.sciencedirect.com/science/article/pii/S0012825219300741}}</ref> Inside the rocks, there are [[Microbial mat|microbial mats]] containing the [[Abiogenesis#Earliest biological evidence for life|oldest ascertained life form]], [[Fossil|fossilized]] bacteria estimated to be 3.48&nbsp;billion years old.<ref name=":1"/>
The [[Dresser Formation]] is located in the [[Pilbara Craton]], and contains [[sedimentary rock]] from the Paleoarchean Era. It is estimated to be 3.48&nbsp;billion years old.<ref name=Homann2019/> The Dresser Formation includes a great variety of structures caused by ancient life including stromatolites and MISS once formed by microbial mats. Such [[Microbial mat|microbial mats]] belong to the [[Abiogenesis#Earliest biological evidence for life|oldest ascertained life form]] and may include [[Fossil|fossilized]] bacteria.<ref name=Lepot2020/>
The [[Strelley Pool|Strelley Pool Chert]], also located in the Pilbara Craton, contains [[Stromatolite|stromatolites]] that may have been created by bacteria 3.4&nbsp;billion years ago. However, it is possible that these stromatolies are [[abiogenic]] and were actually formed through [[Evaporite|evaporitic precipitation]] then deposited on the sea floor.<ref>{{cite book |last=van Kranendonk |first=Martin J. |year=2007 |chapter=Chapter&nbsp;7.2 A review of the evidence for putative Paleoarchean life in the Pilbara craton, Western Australia |title=Developments in Precambrian Geology |pages=855–877 |editor1-last=van Kranendonk |editor1-first=Martin J. |editor2-last=Smithies |editor2-first=R. Hugh |editor3-last=Bennett |editor3-first=Vickie C. |series=Earth's Oldest Rocks |volume=15 |publisher=Elsevier |lang=en |doi=10.1016/s0166-2635(07)15072-6 |isbn=9780444528100 |chapter-url=https://www.sciencedirect.com/science/article/pii/S0166263507150726 |access-date=2021-11-26}}</ref>
The [[Strelley Pool|Strelley Pool Chert]], also located in the Pilbara Craton, contains [[Stromatolite|stromatolites]] that may have been created by bacteria 3.4&nbsp;billion years ago. However, it is possible that these stromatolies are [[abiogenic]] and were actually formed through [[Evaporite|evaporitic precipitation]] then deposited on the sea floor.<ref>{{cite book |last=van Kranendonk |first=Martin J. |editor1-last=van Kranendonk |editor1-first=Martin J. |editor2-last=Smithies |editor2-first=R. Hugh |editor3-last=Bennett |editor3-first=Vickie C. |year=2007 |title=Developments in Precambrian Geology |chapter=Chapter&nbsp;7.2 A review of the evidence for putative Paleoarchean life in the Pilbara craton, Western Australia |series=Earth's Oldest Rocks |volume=15 |pages=855–877 |publisher=Elsevier |doi=10.1016/s0166-2635(07)15072-6 |isbn=9780444528100 |chapter-url=https://www.sciencedirect.com/science/article/pii/S0166263507150726 |access-date=2021-11-26}}</ref>


The [[Barberton Greenstone Belt]], located in the Kaapvaal Craton, also contains evidence of life. It was created around 3.26 Ga when a large asteroid, about {{convert|37|to(-)|58|km}} wide, collided with the Earth.<ref>{{cite press release |url=http://news.agu.org/press-release/scientists-reconstruct-ancient-impact-that-dwarfs-dinosaur-extinction-blast/ |title=Scientists reconstruct ancient impact that dwarfs dinosaur-extinction blast |publisher=[[American Geophysical Union]] |date=9 April 2014}}</ref> The Buck Reef chert and the Josefsdal chert, two rock formations in the Barberton Greenstone Belt, both contain [[Microbial mat|microbial mats]] with fossilized bacteria from the Paleoarchean era.<ref name=":02"/> The Kromberg Formation, near the top of the Onverwacht Group which itself is a part of the Barberton Greenstone Belt, dates back to approximately 3.416–3.334 Ga and contains evidence of microbial life reproducing via [[multiple fission]] and binary fission.<ref>{{cite journal |last1=Kaźmierczak |first1=Józef |last2=Kremer |first2=Barbara |date=1 September 2019 |title=Pattern of cell division in ∼3.4 Ga-old microbes from South Africa |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926818304376 |journal=[[Precambrian Research]] |volume=331 |pages=1–9 |doi=10.1016/j.precamres.2019.105357 |s2cid=189977450 |access-date=17 December 2022}}</ref>
The [[Barberton Greenstone Belt]], located in the Kaapvaal Craton, also contains evidence of life. It was created around 3.26 Ga when a large asteroid, about {{convert|37|to(-)|58|km}} wide, collided with the Earth.<ref>{{cite press release |url=http://news.agu.org/press-release/scientists-reconstruct-ancient-impact-that-dwarfs-dinosaur-extinction-blast/ |title=Scientists reconstruct ancient impact that dwarfs dinosaur-extinction blast |publisher=[[American Geophysical Union]] |date=9 April 2014}}</ref> The Buck Reef chert and the Josefsdal chert, two rock formations in the Barberton Greenstone Belt, both contain [[Microbial mat|microbial mats]] with fossilized bacteria from the Paleoarchean era.<ref name=Homann2019/> The Kromberg Formation, near the top of the Onverwacht Group which itself is a part of the Barberton Greenstone Belt, dates back to approximately 3.416–3.334 Ga and contains evidence of microbial life reproducing via [[multiple fission]] and binary fission.<ref>{{cite journal |last1=Kaźmierczak |first1=Józef |last2=Kremer |first2=Barbara |date=1 September 2019 |title=Pattern of cell division in ~3.4 Ga-old microbes from South Africa |journal=[[Precambrian Research]] |doi=10.1016/j.precamres.2019.105357 |s2cid=189977450 |volume=331 |pages=1–9 |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926818304376 |access-date=17 December 2022|url-access=subscription }}</ref>


== Continental development ==
== Continental development ==
[[File:Vaalbara Continent.jpg|thumb|left|Artist's impression of what [[Vaalbara]] may have looked like.]][[File:Simplified geologic map of the Barberton greenstone belt.pdf|thumb|left|A map of the [[Barberton Greenstone Belt]] in [[southern Africa]].]]
[[File:Vaalbara Continent.jpg|thumb|left|Artist's impression of what [[Vaalbara]] may have looked like.]][[File:Simplified geologic map of the Barberton greenstone belt.pdf|thumb|left|A map of the [[Barberton Greenstone Belt]] in [[southern Africa]].]]
Similarities between the [[Barberton Greenstone Belt]] in the [[Kaapvaal Craton]] and the eastern part of the [[Pilbara Craton]] indicate that the two formations were once joined as part of the supercontinent [[Vaalbara]], one of Earth's earliest [[Supercontinent|supercontinents]].<ref name=":2"/> Both [[Craton|cratons]] formed at the beginning of the Paleoarchean era.<ref>{{cite journal |last1=van Kranendonk |first1=Martin J. |last2=Smithies |first2=R. Hugh |last3=Griffin |first3=William L. |last4=Huston |first4=David L. |last5=Hickman |first5=Arthur H. |last6=Champion |first6=David C. |last7=Anhaeusser |first7=Carl R. |last8=Pirajno |first8=Franco |year=2015 |title=Making it thick: a volcanic plateau origin of Palaeoarchean continental lithosphere of the Pilbara and Kaapvaal cratons |journal=Geological Society, London, Special Publications |lang=en |volume=389 |issue=1 |pages=83–111 |doi=10.1144/SP389.12 |bibcode=2015GSLSP.389...83V |s2cid=130084679 |issn=0305-8719 |url=http://sp.lyellcollection.org/lookup/doi/10.1144/SP389.12}}</ref> While some [[Paleomagnetism|paleomagnetic]] data suggests that they were connected during the Paleoarchean era, it is possible that Vaalbara did not form until the [[Mesoarchean]] or [[Neoarchean]] eras.<ref name=":2"/>
Similarities between the [[Barberton Greenstone Belt]] in the [[Kaapvaal Craton]] and the eastern part of the [[Pilbara Craton]] indicate that the two formations were once joined as part of the supercontinent [[Vaalbara]], one of Earth's earliest [[Supercontinent|supercontinents]].<ref name=Bradley2015/> Both [[Craton|cratons]] formed at the beginning of the Paleoarchean era.<ref>{{cite journal |last1=van Kranendonk |first1=Martin J. |last2=Smithies |first2=R. Hugh |last3=Griffin |first3=William L. |last4=Huston |first4=David L. |last5=Hickman |first5=Arthur H. |last6=Champion |first6=David C. |last7=Anhaeusser |first7=Carl R. |last8=Pirajno |first8=Franco |year=2015 |title=Making it thick: a volcanic plateau origin of Palaeoarchean continental lithosphere of the Pilbara and Kaapvaal cratons |journal=Geological Society, London, Special Publications |issn=0305-8719 |doi=10.1144/SP389.12 |bibcode=2015GSLSP.389...83V |s2cid=130084679 |volume=389 |issue=1 |pages=83–111 |url=http://sp.lyellcollection.org/lookup/doi/10.1144/SP389.12|url-access=subscription }}</ref> While some [[Paleomagnetism|paleomagnetic]] data suggests that they were connected during the Paleoarchean era, it is possible that Vaalbara did not form until the [[Mesoarchean]] or [[Neoarchean]] eras.<ref name=Bradley2015/>


It is also unclear whether there was any [[Land|exposed land]] during the Paleoarchean era. Although several Paleoarchean formations such as the [[Pilbara Craton|Dresser Formation]], the Josefsdal Chert, and the Mendon Formation show some evidence of being above the surface, over 90&nbsp;percent of [[Archean]] [[continental crust]] has been destroyed, making the existence of exposed land practically impossible to confirm or deny. It is likely that during the Paleoarchean era, there was a large amount of continental crust, but it was still underwater and would not emerge until later in the Archean era. [[Hotspot (geology)|Hotspot islands]] may have been the only exposed land at the time.<ref>{{cite journal |last=Korenaga |first=Jun |year=2021 |title=Was there land on the early Earth? |journal=[[Life (journal)|Life]] |lang=en |volume=11 |issue=11 |pages=1142 |doi=10.3390/life11111142 |pmid=34833018 |pmc=8623345 |doi-access=free}}</ref>
It is also unclear whether there was any [[Land|exposed land]] during the Paleoarchean era. Although several Paleoarchean formations such as the [[Pilbara Craton|Dresser Formation]], the Josefsdal Chert, and the Mendon Formation show some evidence of being above the surface, over 90&nbsp;percent of [[Archean]] [[continental crust]] has been destroyed, making the existence of exposed land practically impossible to confirm or deny. It is likely that during the Paleoarchean era, there was a large amount of continental crust, but it was still underwater and would not emerge until later in the Archean era. [[Hotspot (geology)|Hotspot islands]] may have been the only exposed land at the time.<ref>{{cite journal |last=Korenaga |first=Jun |year=2021 |title=Was there land on the early Earth? |journal=[[Life (journal)|Life]] |doi=10.3390/life11111142 |doi-access=free |pmid=34833018 |pmc=8623345 |volume=11 |issue=11 |pages=1142|bibcode=2021Life...11.1142K }}</ref>


Due to a much hotter mantle and an elevated oceanic geothermal gradient compared to the present day, plate tectonics in its modern form did not exist during the Paleoarchean. Instead, a model of "flake tectonics" has been proposed for this era of geologic time. According to this model, instead of normal subduction of oceanic plates, extensively silicified upper oceanic crust delaminated from lower oceanic crust and was deposited in a manner similar to [[ophiolites]] from the later [[Proterozoic]] and [[Phanerozoic]] eons.<ref>{{cite journal |last1=Grosch |first1=Eugene G. |last2=Viola |first2=Giulio |last3=Ndlela |first3=Sibusisiwe |date=15 August 2020 |title=Geological record of Paleoarchean oceanic flake tectonics preserved in the c. 3.3 Ga Kromberg volcanic type-section, Barberton greenstone belt, South Africa |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926820300346 |journal=[[Precambrian Research]] |volume=346 |page=105815 |doi=10.1016/j.precamres.2020.105815 |s2cid=225451582 |access-date=17 December 2022}}</ref>
Due to a much hotter mantle and an elevated oceanic geothermal gradient compared to the present day, plate tectonics in its modern form did not exist during the Paleoarchean. Instead, a model of "flake tectonics" has been proposed for this era of geologic time. According to this model, instead of normal subduction of oceanic plates, extensively silicified upper oceanic crust delaminated from lower oceanic crust and was deposited in a manner similar to [[ophiolites]] from the later [[Proterozoic]] and [[Phanerozoic]] eons.<ref>{{cite journal |last1=Grosch |first1=Eugene G. |last2=Viola |first2=Giulio |last3=Ndlela |first3=Sibusisiwe |date=15 August 2020 |title=Geological record of Paleoarchean oceanic flake tectonics preserved in the c. 3.3 Ga Kromberg volcanic type-section, Barberton greenstone belt, South Africa |journal=[[Precambrian Research]] |doi=10.1016/j.precamres.2020.105815 |s2cid=225451582 |volume=346 |page=105815 |url=https://www.sciencedirect.com/science/article/abs/pii/S0301926820300346 |access-date=17 December 2022|url-access=subscription }}</ref>


{{clear}}
{{clear}}
Line 68: Line 68:


==External links==
==External links==
⚫
{{Commons category|Paleoarchean|Paleoarchean}}
* [https://ghkclass.com/ghkC.html?paleoarchean Paleoarchean (chronostratigraphy scale)]
* [https://ghkclass.com/ghkC.html?paleoarchean Paleoarchean (chronostratigraphy scale)]
⚫
{{Commons category|Paleoarchean|<br>Paleoarchean|position=left}}


{{Clear}}
{{Archean Footer}}
{{Archean Footer}}
{{Geological history|c}}
{{Geological history|c}}

Latest revision as of 11:07, 3 March 2024

Paleoarchean
3600 – 3200 Ma
The Vaalbara continent, a continent dating from 2.7 to 3.6 billion years ago
Chronology
Proposed redefinition(s)4031–3490 Ma
Gradstein et al., 2012
Proposed subdivisionsAcastan Period, 4031–3810 Ma

Gradstein et al., 2012
Isuan Period, 3810–3490 Ma

Gradstein et al., 2012
Etymology
Name formalityFormal
Alternate spelling(s)Palaeoarchaean
Synonym(s)Early Archean
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitEra
Stratigraphic unitErathem
Time span formalityFormal
Lower boundary definitionDefined Chronometrically
Lower GSSA ratified1991[citation needed]
Upper boundary definitionDefined Chronometrically
Upper GSSA ratified1991[citation needed]

The Paleoarchean (/ˌpeɪlioʊ.ɑːrˈkiːən, ˌpæl-/ PAY-lee-oh-ar-KEE-ən, PAL-), also spelled Palaeoarchaean (formerly known as the early Archean), is a geologic era within the Archean Eon. The name derives from Greek "Palaios" ancient. It spans the period of time 3,600 to 3,200 million years ago. The era is defined chronometrically and is not referenced to a specific level of a rock section on Earth. The earliest confirmed evidence of life comes from this era, and Vaalbara, one of Earth's earliest supercontinents, may have formed during this era.[2][3]

Early life

[edit]
A stromatolite formed by Paleoarchean microbial mats, preserved as a fossil, from Pilbara craton, Western Australia.

The geological record from the Paleoarchean era is very limited. Due to deformation and metamorphism, most rocks from the Paleoarchean era cannot provide any useful information. There are only two locations in the world containing rock formations that are intact enough to preserve evidence of early life: the Kaapvaal Craton in Southern Africa and the Pilbara Craton in Western Australia.[4]

The Dresser Formation is located in the Pilbara Craton, and contains sedimentary rock from the Paleoarchean Era. It is estimated to be 3.48 billion years old.[4] The Dresser Formation includes a great variety of structures caused by ancient life including stromatolites and MISS once formed by microbial mats. Such microbial mats belong to the oldest ascertained life form and may include fossilized bacteria.[2] The Strelley Pool Chert, also located in the Pilbara Craton, contains stromatolites that may have been created by bacteria 3.4 billion years ago. However, it is possible that these stromatolies are abiogenic and were actually formed through evaporitic precipitation then deposited on the sea floor.[5]

The Barberton Greenstone Belt, located in the Kaapvaal Craton, also contains evidence of life. It was created around 3.26 Ga when a large asteroid, about 37 to 58 kilometres (23–36 mi) wide, collided with the Earth.[6] The Buck Reef chert and the Josefsdal chert, two rock formations in the Barberton Greenstone Belt, both contain microbial mats with fossilized bacteria from the Paleoarchean era.[4] The Kromberg Formation, near the top of the Onverwacht Group which itself is a part of the Barberton Greenstone Belt, dates back to approximately 3.416–3.334 Ga and contains evidence of microbial life reproducing via multiple fission and binary fission.[7]

Continental development

[edit]
Artist's impression of what Vaalbara may have looked like.
A map of the Barberton Greenstone Belt in southern Africa.

Similarities between the Barberton Greenstone Belt in the Kaapvaal Craton and the eastern part of the Pilbara Craton indicate that the two formations were once joined as part of the supercontinent Vaalbara, one of Earth's earliest supercontinents.[3] Both cratons formed at the beginning of the Paleoarchean era.[8] While some paleomagnetic data suggests that they were connected during the Paleoarchean era, it is possible that Vaalbara did not form until the Mesoarchean or Neoarchean eras.[3]

It is also unclear whether there was any exposed land during the Paleoarchean era. Although several Paleoarchean formations such as the Dresser Formation, the Josefsdal Chert, and the Mendon Formation show some evidence of being above the surface, over 90 percent of Archean continental crust has been destroyed, making the existence of exposed land practically impossible to confirm or deny. It is likely that during the Paleoarchean era, there was a large amount of continental crust, but it was still underwater and would not emerge until later in the Archean era. Hotspot islands may have been the only exposed land at the time.[9]

Due to a much hotter mantle and an elevated oceanic geothermal gradient compared to the present day, plate tectonics in its modern form did not exist during the Paleoarchean. Instead, a model of "flake tectonics" has been proposed for this era of geologic time. According to this model, instead of normal subduction of oceanic plates, extensively silicified upper oceanic crust delaminated from lower oceanic crust and was deposited in a manner similar to ophiolites from the later Proterozoic and Phanerozoic eons.[10]

References

[edit]
  1. ^ Caredona, Tanai (6 March 2018). "Early Archean origin of heterodimeric Photosystem I". Heliyon. 4 (3): e00548. doi:10.1016/j.heliyon.2018.e00548. PMC 5857716. PMID 29560463. Retrieved 25 February 2021.
  2. ^ a b Lepot, Kevin (2020). "Signatures of early microbial life from the Archean (4 to 2.5 Ga) eon". Earth-Science Reviews. 209: 103296. Bibcode:2020ESRv..20903296L. doi:10.1016/j.earscirev.2020.103296. hdl:20.500.12210/62415. ISSN 0012-8252. S2CID 225413847.
  3. ^ a b c Bradley, Kyle; Weiss, Benjamin P.; Buick, Roger (2015). "Records of geomagnetism, climate, and tectonics across a Paleoarchean erosion surface". Earth and Planetary Science Letters. 419: 1–13. Bibcode:2015E&PSL.419....1B. doi:10.1016/j.epsl.2015.03.008. ISSN 0012-821X.
  4. ^ a b c Homann, Martin (2019). "Earliest life on Earth: Evidence from the Barberton Greenstone Belt, South Africa" (PDF). Earth-Science Reviews. 196: 102888. Bibcode:2019ESRv..19602888H. doi:10.1016/j.earscirev.2019.102888. ISSN 0012-8252. S2CID 198424907.
  5. ^ van Kranendonk, Martin J. (2007). "Chapter 7.2 A review of the evidence for putative Paleoarchean life in the Pilbara craton, Western Australia". In van Kranendonk, Martin J.; Smithies, R. Hugh; Bennett, Vickie C. (eds.). Developments in Precambrian Geology. Earth's Oldest Rocks. Vol. 15. Elsevier. pp. 855–877. doi:10.1016/s0166-2635(07)15072-6. ISBN 9780444528100. Retrieved 2021-11-26.
  6. ^ "Scientists reconstruct ancient impact that dwarfs dinosaur-extinction blast" (Press release). American Geophysical Union. 9 April 2014.
  7. ^ Kaźmierczak, Józef; Kremer, Barbara (1 September 2019). "Pattern of cell division in ~3.4 Ga-old microbes from South Africa". Precambrian Research. 331: 1–9. doi:10.1016/j.precamres.2019.105357. S2CID 189977450. Retrieved 17 December 2022.
  8. ^ van Kranendonk, Martin J.; Smithies, R. Hugh; Griffin, William L.; Huston, David L.; Hickman, Arthur H.; Champion, David C.; Anhaeusser, Carl R.; Pirajno, Franco (2015). "Making it thick: a volcanic plateau origin of Palaeoarchean continental lithosphere of the Pilbara and Kaapvaal cratons". Geological Society, London, Special Publications. 389 (1): 83–111. Bibcode:2015GSLSP.389...83V. doi:10.1144/SP389.12. ISSN 0305-8719. S2CID 130084679.
  9. ^ Korenaga, Jun (2021). "Was there land on the early Earth?". Life. 11 (11): 1142. Bibcode:2021Life...11.1142K. doi:10.3390/life11111142. PMC 8623345. PMID 34833018.
  10. ^ Grosch, Eugene G.; Viola, Giulio; Ndlela, Sibusisiwe (15 August 2020). "Geological record of Paleoarchean oceanic flake tectonics preserved in the c. 3.3 Ga Kromberg volcanic type-section, Barberton greenstone belt, South Africa". Precambrian Research. 346: 105815. doi:10.1016/j.precamres.2020.105815. S2CID 225451582. Retrieved 17 December 2022.
[edit]
Wikimedia Commons has media related to Paleoarchean.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Paleoarchean&oldid=1211596268"