Earth's crustal evolution: Difference between revisions
Georgealee (talk | contribs) mNo edit summary |
Georgealee (talk | contribs) mNo edit summary |
||
| Line 8: | Line 8: | ||
=== Mechanism of formation === |
=== Mechanism of formation === |
||
The Proto-Earth was entirely molten due to high temperatures created and maintained by compression of the early atmosphere, rapid axial rotation and regular impacts with neighbouring planetesimals.<ref>{{Cite book|url=https://books.google.co.uk/books/about/Historical_Geology.html?id=EIrwxgpc9GsC&redir_esc=y|title=Historical Geology: Understanding Our Planet's Past|last=Erickson|first=Jon|date=2014-05-14|publisher=Infobase Publishing|isbn=9781438109640|language=en}}</ref> However, over time the Earth began to cool as the frequency of planetary accretion slowed and heat stored within the magma ocean is lost to space through radiation. Once cool enough, the magma crystallises, starting from the base of the ocean, as this would cool more rapidly due to the lowering of the solidus nearer the surface where pressures are less than 25GPa.<ref>{{Cite journal|date=2004-09-15|title=Early Earth differentiation|url=https://www.sciencedirect.com/science/article/pii/S0012821X04004285|journal=Earth and Planetary Science Letters|language=en|volume=225|issue=3-4|pages=253–269|doi=10.1016/j.epsl.2004.07.008|issn=0012-821X}}</ref> The formation of a thin 'chill-crust' at the extreme surface would provide thermal insulation to the shallow sub surface, reinforcing a mechanism of deep magma ocean crystallisation. |
The Proto-Earth was entirely molten due to high temperatures created and maintained by compression of the early atmosphere, rapid axial rotation and regular impacts with neighbouring planetesimals.<ref>{{Cite book|url=https://books.google.co.uk/books/about/Historical_Geology.html?id=EIrwxgpc9GsC&redir_esc=y|title=Historical Geology: Understanding Our Planet's Past|last=Erickson|first=Jon|date=2014-05-14|publisher=Infobase Publishing|isbn=9781438109640|language=en}}</ref> The mantle remained hotter than modern day temperatures throughout the Archean.<ref>{{Cite journal|date=2016-07-01|title=A great thermal divergence in the mantle beginning 2.5 Ga: Geochemical constraints from greenstone basalts and komatiites|url=https://www.sciencedirect.com/science/article/pii/S1674987116000311|journal=Geoscience Frontiers|language=en|volume=7|issue=4|pages=543–553|doi=10.1016/j.gsf.2016.01.006|issn=1674-9871}}</ref> However, over time the Earth began to cool as the frequency of planetary accretion slowed and heat stored within the magma ocean is lost to space through radiation. Once cool enough, the magma crystallises, starting from the base of the ocean, as this would cool more rapidly due to the lowering of the solidus nearer the surface where pressures are less than 25GPa.<ref>{{Cite journal|date=2004-09-15|title=Early Earth differentiation|url=https://www.sciencedirect.com/science/article/pii/S0012821X04004285|journal=Earth and Planetary Science Letters|language=en|volume=225|issue=3-4|pages=253–269|doi=10.1016/j.epsl.2004.07.008|issn=0012-821X}}</ref> The formation of a thin 'chill-crust' at the extreme surface would provide thermal insulation to the shallow sub surface, reinforcing a mechanism of deep magma ocean crystallisation. |
||
The composition of early magma ocean crystallisation varies with depth. Experiments involving the melting of peridotite magma show that deep in the ocean (> |
The composition of early magma ocean crystallisation varies with depth. Experiments involving the melting of peridotite magma show that deep in the ocean (>≈700m), the main mineral present would be Mg-perovskite. Whereas olivine would dominate in the shallower areas along with it's high pressure polymorphs e.g. garnet and majorite.<ref>{{Cite journal|date=2004-06-15|title=Melting experiments of mantle materials under lower mantle conditions with implications for magma ocean differentiation|url=https://www.sciencedirect.com/science/article/pii/S0031920104000718|journal=Physics of the Earth and Planetary Interiors|language=en|volume=143-144|pages=397–406|doi=10.1016/j.pepi.2003.09.016|issn=0031-9201}}</ref> |
||
Heat pipe volcanism is a model for early Earth thermodynamics and in turn contributes to the process by which a cooler, solid lithosphere formed from a molten ocean. Convection is initiated when melt, extracted form the mantle, rises towards the surface due to it's higher temperature compared to that of the surrounding mantle . The section of the mantle removed where the melt was produced is advected downwards, meanwhile the rising melt loses heat and is deposited or erupted. A cold lithosphere is able to be created from this process as the rising and eruption of melt overlays cooler surface mantle causing the continual transfer of cooler temperatures downwards.<ref>{{Cite journal|last=Moore|first=William B.|last2=Webb|first2=A. Alexander G.|date=2013-09-26|title=Heat-pipe Earth|url=https://www.ncbi.nlm.nih.gov/pubmed/24067709|journal=Nature|volume=501|issue=7468|pages=501–505|doi=10.1038/nature12473|issn=1476-4687|pmid=24067709}}</ref> |
Heat pipe volcanism is a model for early Earth thermodynamics and in turn contributes to the process by which a cooler, solid lithosphere formed from a molten ocean. Convection is initiated when melt, extracted form the mantle, rises towards the surface due to it's higher temperature compared to that of the surrounding mantle . The section of the mantle removed where the melt was produced is advected downwards, meanwhile the rising melt loses heat and is deposited or erupted. A cold lithosphere is able to be created from this process as the rising and eruption of melt overlays cooler surface mantle causing the continual transfer of cooler temperatures downwards.<ref>{{Cite journal|last=Moore|first=William B.|last2=Webb|first2=A. Alexander G.|date=2013-09-26|title=Heat-pipe Earth|url=https://www.ncbi.nlm.nih.gov/pubmed/24067709|journal=Nature|volume=501|issue=7468|pages=501–505|doi=10.1038/nature12473|issn=1476-4687|pmid=24067709}}</ref> |
||
A further contribution to the formation of the first continental crust is also through volcanism, this time intrusive. This model proposes much of the early crust was formed through plutonic volcanism,<ref name=":0">{{Cite journal|date=2016-10-01|title=Early Earth plume-lid tectonics: A high-resolution 3D numerical modelling approach|url=https://www.sciencedirect.com/science/article/pii/S0264370716300503|journal=Journal of Geodynamics|language=en|volume=100|pages=198–214|doi=10.1016/j.jog.2016.03.004|issn=0264-3707}}</ref> forming hotter and thicker lithosphere which underwent regular cycling with the mantle.<ref>{{Cite journal|date=2015-12-01|title=Generation of felsic crust in the Archean: A geodynamic modeling perspective|url=https://www.sciencedirect.com/science/article/pii/S030192681500337X|journal=Precambrian Research|language=en|volume=271|pages=198–224|doi=10.1016/j.precamres.2015.10.005|issn=0301-9268}}</ref> The heat released by this form of volcanism, as well as assisting mantle convection, increased the geothermal gradient of the early crust.<ref name=":0" /> Where heat pipe volcanism would produce a crust too cold to sustain, a combination of these two mechanisms produces a early lithosphere with a geothermal gradient, as well as a composition, that is fitting with that of Earth-like proto-crust.<ref>{{Cite journal|last=Rozel|first=A. B.|last2=Golabek|first2=G. J.|last3=Jain|first3=C.|last4=Tackley|first4=P. J.|last5=Gerya|first5=T.|date=2017-05-08|title=Continental crust formation on early Earth controlled by intrusive magmatism|url=https://www.nature.com/articles/nature22042#ref10|journal=Nature|language=En|volume=545|issue=7654|pages=332–335|doi=10.1038/nature22042|issn=0028-0836}}</ref> |
|||
=== Types of crust === |
=== Types of crust === |
||
==== Primordial crust ==== |
==== Primordial crust ==== |
||
The result of initial crystallisation from the magma ocean forms the primordial crust. This solidification of the mantle edge at approximately 4.53Ga produced continents with komatiite, an ultramafic rock rich in magnesium with a high melting point and low dynamic viscosity.<ref>{{Cite journal|last=Nna-Mvondo|first=Delphine|last2=Martinez-Frias|first2=Jesus|date=2007-02-15|title=Review komatiites: from Earth’s geological settings to planetary and astrobiological contexts|url=https://link.springer.com/article/10.1007/s11038-007-9135-9|journal=Earth, Moon, and Planets|language=en|volume=100|issue=3-4|pages=157–179|doi=10.1007/s11038-007-9135-9|issn=0167-9295}}</ref> Initial internal differentiation dictated that the upper crust was largely composed of fractionated gabbros, the middle of anorthosite with the base of the crust reaching ≈ 60km in depth. <ref>{{Cite journal|date=2017-03-01|title=Hadean Earth and primordial continents: The cradle of prebiotic life|url=https://www.sciencedirect.com/science/article/pii/S1674987116300834|journal=Geoscience Frontiers|language=en|volume=8|issue=2|pages=309–327|doi=10.1016/j.gsf.2016.07.005|issn=1674-9871}}</ref> |
|||
The result of crystalisation from |
|||
== Crustal dichotomy == |
== Crustal dichotomy == |
||
=== Impact cratering === |
=== Impact cratering === |
||
== Initiation of plate tectonics == |
|||
== Lifespan == |
== Lifespan == |
||
Revision as of 05:43, 1 October 2018
Crustal evolution regards the formation, existence, destruction and eventual renewal of the rocky crust found on the surface of the Earth.
Evolution on this scale can take place through the unique composition of Earth's crust in comparison to other terrestrial planets. Mars, Venus, Mercury and other planetary bodies possess compositionally uniform crusts unlike that of the Earth where both oceanic and continental plates make up the overall outermost shell. In particular, crustal evolution represents the growth and destruction rates of both types of crust.
Early crust
Mechanism of formation
The Proto-Earth was entirely molten due to high temperatures created and maintained by compression of the early atmosphere, rapid axial rotation and regular impacts with neighbouring planetesimals.[1] The mantle remained hotter than modern day temperatures throughout the Archean.[2] However, over time the Earth began to cool as the frequency of planetary accretion slowed and heat stored within the magma ocean is lost to space through radiation. Once cool enough, the magma crystallises, starting from the base of the ocean, as this would cool more rapidly due to the lowering of the solidus nearer the surface where pressures are less than 25GPa.[3] The formation of a thin 'chill-crust' at the extreme surface would provide thermal insulation to the shallow sub surface, reinforcing a mechanism of deep magma ocean crystallisation.
The composition of early magma ocean crystallisation varies with depth. Experiments involving the melting of peridotite magma show that deep in the ocean (>≈700m), the main mineral present would be Mg-perovskite. Whereas olivine would dominate in the shallower areas along with it's high pressure polymorphs e.g. garnet and majorite.[4]
Heat pipe volcanism is a model for early Earth thermodynamics and in turn contributes to the process by which a cooler, solid lithosphere formed from a molten ocean. Convection is initiated when melt, extracted form the mantle, rises towards the surface due to it's higher temperature compared to that of the surrounding mantle . The section of the mantle removed where the melt was produced is advected downwards, meanwhile the rising melt loses heat and is deposited or erupted. A cold lithosphere is able to be created from this process as the rising and eruption of melt overlays cooler surface mantle causing the continual transfer of cooler temperatures downwards.[5]
A further contribution to the formation of the first continental crust is also through volcanism, this time intrusive. This model proposes much of the early crust was formed through plutonic volcanism,[6] forming hotter and thicker lithosphere which underwent regular cycling with the mantle.[7] The heat released by this form of volcanism, as well as assisting mantle convection, increased the geothermal gradient of the early crust.[6] Where heat pipe volcanism would produce a crust too cold to sustain, a combination of these two mechanisms produces a early lithosphere with a geothermal gradient, as well as a composition, that is fitting with that of Earth-like proto-crust.[8]
Types of crust
Primordial crust
The result of initial crystallisation from the magma ocean forms the primordial crust. This solidification of the mantle edge at approximately 4.53Ga produced continents with komatiite, an ultramafic rock rich in magnesium with a high melting point and low dynamic viscosity.[9] Initial internal differentiation dictated that the upper crust was largely composed of fractionated gabbros, the middle of anorthosite with the base of the crust reaching ≈ 60km in depth. [10]
Crustal dichotomy
Impact cratering
Initiation of plate tectonics
Lifespan
Relative ages
Destruction
References
- ^ Erickson, Jon (2014-05-14). Historical Geology: Understanding Our Planet's Past. Infobase Publishing. ISBN 9781438109640.
- ^ "A great thermal divergence in the mantle beginning 2.5 Ga: Geochemical constraints from greenstone basalts and komatiites". Geoscience Frontiers. 7 (4): 543–553. 2016-07-01. doi:10.1016/j.gsf.2016.01.006. ISSN 1674-9871.
- ^ "Early Earth differentiation". Earth and Planetary Science Letters. 225 (3–4): 253–269. 2004-09-15. doi:10.1016/j.epsl.2004.07.008. ISSN 0012-821X.
- ^ "Melting experiments of mantle materials under lower mantle conditions with implications for magma ocean differentiation". Physics of the Earth and Planetary Interiors. 143–144: 397–406. 2004-06-15. doi:10.1016/j.pepi.2003.09.016. ISSN 0031-9201.
- ^ Moore, William B.; Webb, A. Alexander G. (2013-09-26). "Heat-pipe Earth". Nature. 501 (7468): 501–505. doi:10.1038/nature12473. ISSN 1476-4687. PMID 24067709.
- ^ a b "Early Earth plume-lid tectonics: A high-resolution 3D numerical modelling approach". Journal of Geodynamics. 100: 198–214. 2016-10-01. doi:10.1016/j.jog.2016.03.004. ISSN 0264-3707.
- ^ "Generation of felsic crust in the Archean: A geodynamic modeling perspective". Precambrian Research. 271: 198–224. 2015-12-01. doi:10.1016/j.precamres.2015.10.005. ISSN 0301-9268.
- ^ Rozel, A. B.; Golabek, G. J.; Jain, C.; Tackley, P. J.; Gerya, T. (2017-05-08). "Continental crust formation on early Earth controlled by intrusive magmatism". Nature. 545 (7654): 332–335. doi:10.1038/nature22042. ISSN 0028-0836.
- ^ Nna-Mvondo, Delphine; Martinez-Frias, Jesus (2007-02-15). "Review komatiites: from Earth's geological settings to planetary and astrobiological contexts". Earth, Moon, and Planets. 100 (3–4): 157–179. doi:10.1007/s11038-007-9135-9. ISSN 0167-9295.
- ^ "Hadean Earth and primordial continents: The cradle of prebiotic life". Geoscience Frontiers. 8 (2): 309–327. 2017-03-01. doi:10.1016/j.gsf.2016.07.005. ISSN 1674-9871.