Difference between revisions of "Lithosphere" - New World Encyclopedia

Latest revision as of 00:35, 3 November 2022

The tectonic plates of the Earth's lithosphere.

The lithosphere (from the Greek for "rocky" sphere) is the solid, outermost shell of a rocky planet. In the case of the Earth, the lithosphere includes the crust and the upper layer of the mantle that is joined to the crust. The lithosphere contains a rich variety of minerals. In addition, it continually interacts with the atmosphere and hydrosphere.

The Earth's lithosphere provides us with the "terra firma" on which we live. To sustain our lives, we need access to air, water, soil, and sunlight, and we need the ecosystems created by plants and animals. The lithosphere gives us access to all of these simultaneously. While dwelling on the lithosphere, we are surrounded by air, receive the Sun's heat and light, and have access to freshwater and various minerals that we use for our domestic, agricultural, and industrial activities.

Plate tectonics

Main article: Plate tectonics

In forming the lithosphere, the Earth's crust and upper mantle are attached to each other, but they differ in chemical composition. The boundary that marks this change in chemical composition is known as the Mohorovičić discontinuity (or the Moho discontinuity).

Thus the distinguishing characteristic of the lithosphere is not its composition but its flow properties. It floats on the asthenosphere, which is the heat-softened layer of the mantle below the lithosphere. The lithosphere is fragmented into relatively strong pieces called tectonic plates, which move independently relative to one another. This movement of lithospheric plates over the asthenosphere is described as plate tectonics.

Oceanic / Continental

Continental / Continental

Oceanic / Oceanic

Two types of lithosphere

There are two types of lithosphere: the oceanic lithosphere, or oceanic crust, and the continental lithosphere, or continental crust. The oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. The continental crust is the layer of rocks that form the continents and areas of shallow seabed close to their shores, known as continental shelves. The two types of crust differ in composition, density, and thickness. As a whole, the oceanic crust is thinner but denser than the continental crust.

The oceanic crust is generally less than 10 kilometers (km) thick, and its mean density is about 3.3 grams per cubic centimeter (g/cm³). The thickness of the continental crust ranges from 20 to 80 km, and its density is less than 3 g/cm³.

The oceanic crust. The increase in estimated age of the material is indicated by a progression of colors, from red to yellow to green to blue. Dark red represents newly formed material; dark blue represents crust that is 180 million years old. (Dark gray areas represent landmasses; light gray areas indicate sediment-covered continental shelves.)

As a consequence of the density difference, when active margins of continental crust meet oceanic crust in regions known as subduction zones, the oceanic crust typically sinks beneath the continental crust and is recycled back into the mantle. At the same time, new oceanic crust is continually being produced at mid-ocean ridges from mantle material. In addition, as the oceanic lithosphere grows older, it gets cooler and denser, with the result that if two oceanic plates converge, the older one will subduct below the younger one. As a consequence of these processes, most of the present-day oceanic crust is less than 200 million years old.

By contrast, the continental crust is rarely subducted or recycled back into the mantle. For this reason, the oldest rocks on Earth are within the stable "cratons" of the continents, rather than in repeatedly recycled oceanic crust. (A craton is a stable part of the continental crust that has survived continental merging and splitting for 500 million years or more.) The oldest continental rock is the Acasta Gneiss, with an estimated age of 4.01 billion (4.01x10⁹) years.

Composition of oceanic crust

The oceanic crust is composed mainly of mafic rocks. The term mafic is applied to silicate minerals and rocks that have high concentrations of relatively heavy elements, particularly magnesium and iron. The word "mafic" is derived by combining letters from magnesium and ferrum, the Latin word for iron [1].

Mafic minerals are usually dark in color. Common rock-forming mafic minerals include olivine, pyroxene, amphibole, biotite and other micas, augite and calcium-rich plagioclase feldspars. Common mafic rocks include basalt and gabbro.

Composition of continental crust

The North American craton.

The continental crust consists predominantly of felsic rocks. The term felsic is used in referring to silicate minerals, magmas, and rocks that are enriched in silica and light elements such as oxygen, aluminium, sodium, and potassium. The word "felsic" combines letters from the words feldspar and silica. Felsic minerals are usually light in color. Common felsic minerals include quartz, biotite, muscovite, hornblende, orthoclase, and sodium-rich plagioclase feldspars. The most common felsic rock is granite.

It is a matter of debate whether the amount of continental crust has been increasing, decreasing, or remaining constant over geological time. One model suggests that prior to 3.7 billion years ago, the continental crust constituted less than 10 percent of the present amount. By 3.0 billion years ago, that figure rose to about 25 percent, and by about 2.6 billion years ago, it was about 60 percent of the current amount (Taylor and McLennan 1995). The growth of continental crust is thought to have occurred in "spurts" of activity, corresponding to five episodes of increased production through geologic time (see graphic at Butler).

References
ISBN links support NWE through referral fees

Butler, Rob. Making new continents. http://earth.leeds.ac.uk/assyntgeology/extra_info/ehistory.htm Accessed 01/29/2006
Earth's Crust, Lithosphere and Asthenosphere
Crust and Lithosphere
Stanley Chernicoff and Donna Whitney. Geology. An Introduction to Physical Geology, 4th ed., Pearson 2007
Saal, A.L., Rudnick R.L., Ravizza G.E. & Hart S.R. 1998. Re-Os isotope evidence for the composition, formation and age of the lower crust. Nature 39317, 1998.
Taylor and McLennan. 1995. Model of growth of continental crust through time in John Victor Walther 2005, Essentials Of Geochemistry. ones & Bartlett. ISBN 0763726427
von Huene, R. and D.W. Scholl, 1991. "Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust." Reviews of Geophysics 29: 279-316.

External links

All links retrieved November 2, 2022.

Composition of Continental Crust

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

The history of this article since it was imported to New World Encyclopedia:

History of "Lithosphere"

Note: Some restrictions may apply to use of individual images which are separately licensed.

@@ Line 1: / Line 1: @@
+{{Copyedited}}{{Paid}}{{Submitted}}{{Images OK}}{{Approved}}
+[[Category:Public]]
 [[Image:Tectonic plates.png|thumb|right|300px|The tectonic plates of the Earth's lithosphere.]]
-The '''lithosphere''' (from the [[Greek language|Greek]] for "rocky" sphere) is the solid, outermost shell of a rocky [[planet]]. In the case of the [[Earth]], the lithosphere includes the [[Crust (geology)|crust]] and the upper layer of the [[Mantle (geology)|mantle]] that is joined to the crust. As the cooling surface of the Earth's internal convection system, the lithosphere thickens over time.
+The '''lithosphere''' (from the [[Greek language|Greek]] for "rocky" sphere) is the solid, outermost shell of a rocky [[planet]]. In the case of the [[Earth]], the lithosphere includes the [[Crust (geology)|crust]] and the upper layer of the [[Mantle (geology)|mantle]] that is joined to the crust. The lithosphere contains a rich variety of minerals. In addition, it continually interacts with the [[Earth's atmosphere|atmosphere]] and [[hydrosphere]].
+{{toc}}
+The Earth's lithosphere provides us with the "terra firma" on which we live. To sustain our lives, we need access to air, water, soil, and sunlight, and we need the ecosystems created by plants and animals. The lithosphere gives us access to all of these simultaneously. While dwelling on the lithosphere, we are surrounded by air, receive the Sun's heat and light, and have access to freshwater and various minerals that we use for our domestic, agricultural, and industrial activities.
 == Plate tectonics ==
+:{{main|Plate tectonics}}
-The distinguishing characteristic of the lithosphere is not its composition but its flow properties. It floats on the [[asthenosphere]], which is the heat-softened layer of the mantle below the lithosphere. Under the influence of low-intensity, long-term stresses, the lithosphere responds essentially as a rigid shell and deforms primarily through brittle failure. Thus it is fragmented into relatively strong pieces called ''tectonic plates'', which move independently relative to one another. This movement of lithospheric plates is described as [[plate tectonics]]. The asthenosphere, by contrast, accommodates strain through [[Plasticity (physics)|plastic]] deformation.
+In forming the lithosphere, the Earth's crust and upper mantle are attached to each other, but they differ in chemical composition. The boundary that marks this change in chemical composition is known as the '''Mohorovi&#269;i&#263; discontinuity''' (or the Moho discontinuity).
-The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the [[Moho discontinuity]].
+Thus the distinguishing characteristic of the lithosphere is not its composition but its flow properties. It floats on the [[asthenosphere]], which is the heat-softened layer of the mantle below the lithosphere. The lithosphere is fragmented into relatively strong pieces called ''tectonic plates'', which move independently relative to one another. This movement of lithospheric plates over the asthenosphere is described as '''[[plate tectonics]]'''.
-There are two types of lithosphere:
+<br clear="all">
-* [[Oceanic crust|oceanic lithosphere]]
+{|align="center"
-* [[Continental crust|continental lithosphere]]
+|[[Image:Oceanic-continental convergence Fig21oceancont.gif|thumb|Oceanic / Continental]]
-Oceanic lithosphere is about 70 km thick (but can be as thin as 1.6 km at the [[mid-ocean ridge]]s), while continental lithosphere is about 150 km thick (and can be considerably thicker at continental collision zones). Oceanic lithosphere consists mainly of [[mafic]] and [[ultramafic]] rocks and is denser than continental lithosphere, which consists predominantly of [[felsic]] rocks. This higher density has the effect that at [[subduction zone]]s the oceanic plate will invariably sink underneath the continental plate. New oceanic lithosphere is constantly being produced at mid-ocean ridges from mantle material and is recycled back to the mantle at subduction zones. As a result, oceanic lithosphere is much younger than continental lithosphere: the oldest oceanic lithosphere is about 200 million years old, while parts of the continental lithosphere are billions of years old. As oceanic lithosphere grows older, it gets cooler and denser, with the result that if two oceanic plates converge, the older one will subduct below the younger one.
+|[[Image:Continental-continental convergence Fig21contcont.gif|thumb|Continental / Continental]]
+|[[Image:Oceanic-oceanic convergence Fig21oceanocean.gif|thumb|Oceanic / Oceanic]]
+|}
-==Oceanic lithosphere (Oceanic crust)==
+== Two types of lithosphere ==
-[[Image:Earth seafloor crust age 1996.gif|thumb|300px|Age of oceanic crust]]
-'''Oceanic crust''' is the part of Earth's [[lithosphere]] which surfaces in the [[ocean]] basins. Oceanic crust is composed of [[mafic]] [[basalt]]ic rocks, or [[Sima (geology)|sima]]. It is thinner, generally less than 10 [[kilometre]]s thick, but more [[density|dense]] than the [[continental crust]], or [[sial]], having a mean density of about 3.3 [[gram]]s per [[cubic centimeter]].
+There are two types of lithosphere: the '''oceanic lithosphere''', or '''oceanic crust''', and the '''continental lithosphere''', or '''continental crust'''. The oceanic crust is the part of Earth's lithosphere that surfaces in the [[ocean]] basins. The continental crust is the layer of rocks that form the [[continent]]s and areas of shallow seabed close to their shores, known as ''[[Continental shelf|continental shelves]]''. The two types of crust differ in composition, density, and thickness. As a whole, the oceanic crust is thinner but denser than the continental crust.
-Most of the present day oceanic crust is less than 200 million years old because it is continuously being created at [[oceanic ridge]]s and destroyed by being pulled back under the continental crust in [[subduction zone]]s by the convection currents in the lower [[Mantle (geology)|mantle]].  [[Plate tectonics]] is the study of these processes.
+The oceanic crust is generally less than 10 [[kilometer]]s (km) thick, and its mean density is about 3.3 [[gram]]s per [[cubic centimeter]] (g/cm<sup>3</sup>). The thickness of the continental crust ranges from 20 to 80 km, and its density is less than 3 g/cm<sup>3</sup>.
-==Continental lithosphere (Continental crust)==
+[[Image:Earth seafloor crust age 1996.gif|thumb|300px|The oceanic crust. The increase in estimated age of the material is indicated by a progression of colors, from red to yellow to green to blue. Dark red represents newly formed material; dark blue represents crust that is 180 million years old. (Dark gray areas represent landmasses; light gray areas indicate sediment-covered continental shelves.)]]
-[[Image:North america craton nps.gif|right|250px|thumb|North American craton.]]
-The '''continental crust''' is the layer of [[granite|granitic]], [[sedimentary]] and [[metamorphic rocks]] which form the [[continent]]s and the areas of shallow seabed close to their shores, known as [[Continental shelf|continental shelves]].  It is less [[dense]] than the material of the Earth's [[Mantle (geology)|mantle]] and thus "floats" on top of it. Continental crust is also less dense than [[oceanic crust]], though it is considerably thicker; 20 to 80 km versus the average oceanic thickness of around 5-10 km. About 40% of the Earth's surface is now underlain by continental crust.
+As a consequence of the density difference, when active margins of continental crust meet oceanic crust in regions known as ''subduction zones'', the oceanic crust typically sinks beneath the continental crust and is recycled back into the mantle. At the same time, new oceanic crust is continually being produced at mid-ocean ridges from mantle material. In addition, as the oceanic lithosphere grows older, it gets cooler and denser, with the result that if two oceanic plates converge, the older one will subduct below the younger one. As a consequence of these processes, most of the present-day oceanic crust is less than 200 million years old.
-As a consequence of the density difference, when active margins of continental crust meet oceanic crust in [[subduction zone]]s, the oceanic crust is typically [[subducted]] back into the mantle. Because of its relative low density, continental crust is only rarely subducted or re-cycled back into the mantle (for instance, where continental crustal blocks collide and overthicken, causing deep melting). For this reason the oldest rocks on Earth are within the ''[[craton]]s'' or cores of the continents, rather than in repeatedly recycled [[oceanic crust]]; the oldest continental rock is the [[Acasta Gneiss]] at 4.01 [[Annum|Ga]], while the oldest oceanic crust is of [[Jurassic]] age.
+By contrast, the continental crust is rarely subducted or recycled back into the mantle. For this reason, the oldest rocks on Earth are within the stable "cratons" of the continents, rather than in repeatedly recycled oceanic crust. (A craton is a stable part of the continental crust that has survived continental merging and splitting for 500 million years or more.) The oldest continental rock is the [[Acasta Gneiss]], with an estimated age of 4.01 billion (4.01x10<sup>9</sup>) years.
-The height of mountain ranges is usually related to the thickness of crust. This results from the [[isostasy]] associated with [[orogeny]] (mountain formation). The crust is thickened by the compressive forces related to [[subduction]] or continental collision. The buoyancy of the crust forces it upwards, the forces of the collisional stress balanced by gravity and erosion. This forms a keel or mountain root beneath the mountain range, which is where the thickest crust is found.
+===Composition of oceanic crust===
-The thinnest continental crust is found in [[rift]] zones, where the crust is thinned by  [[fault (geology)|detachment faulting]] and eventually severed, replaced by [[oceanic crust]]. The edges of continental fragments formed this way (both sides of the [[Atlantic Ocean]], for example) are termed [[passive margin]]s.
+The oceanic crust is composed mainly of '''mafic''' rocks. The term ''mafic'' is applied to silicate minerals and rocks that have high concentrations of relatively heavy [[Chemical element|element]]s, particularly [[magnesium]] and [[iron]]. The word "mafic" is derived by combining letters from ''[[magnesium]]'' and ''ferrum'', the [[Latin]] word for [[iron]] [http://dictionary.reference.com/search?q=mafic].
-It is a matter of debate whether the amount of continental crust has been increasing, decreasing, or remaining constant over geological time. One model indicates that at prior to 3.7 Bya continental crust contituted less than 10% of the present amount. By 3.0 Bya the amount was about 25% and following a period of rapid crustal evolution it was about 60% of the current amount by 2.6 Bya (Taylor and McLennan, 1995). The growth of continental crust appears to have occurred in ''spurts'' of increased activity corresponding to five episodes of increased production through geologic time (see graphic at [http://earth.leeds.ac.uk/assyntgeology/extra_info/ehistory.htm Butler]).
+Mafic minerals are usually dark in color. Common rock-forming mafic minerals include [[olivine]], [[pyroxene]], [[amphibole]], [[biotite]] and other [[mica]]s, [[augite]] and calcium-rich [[plagioclase]] [[feldspar|feldspars]]. Common mafic rocks include [[basalt]] and [[gabbro]].
-== References ==
+===Composition of continental crust===
+[[Image:North america craton nps.gif|right|250px|thumb|The North American craton.]]
-* [http://www.windows.ucar.edu/cgi-bin/tour_def/earth/interior/earths_crust.html Earth's Crust, Lithosphere and Asthenosphere]
-* [http://www.geolsoc.org.uk/template.cfm?name=lithosphere Crust and Lithosphere]
-* Stanley Chernicoff and Donna Whitney. ''Geology. An Introduction to Physical Geology'', 4th ed., Pearson 2007
-*Butler, Rob, ''Making new continents'', http://earth.leeds.ac.uk/assyntgeology/extra_info/ehistory.htm Accessed 01/29/2006
-*Saal, A.L., Rudnick R.L., Ravizza G.E. & Hart S.R., 1998. ''Re-Os [[isotope geochemistry|isotope]] evdence for the composition, formation and age of the lower crust.'' Nature, 39317, 1998.
-*Taylor and McLennan, 1995, ''Model of growth of continental crust through time'' in John Victor Walther, 2005, ''Essentials Of Geochemistry'', Jones & Bartlett, ISBN 0763726427
-*von Huene, R. and D.W. Scholl, 1991. "Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust." Reviews of Geophysics, 29, 279-316.
-==External links==
+The continental crust consists predominantly of '''felsic''' rocks. The term ''felsic'' is used in referring to silicate minerals, magmas, and rocks that are enriched in [[silica]] and light elements such as [[oxygen]], [[aluminium]], [[sodium]], and [[potassium]]. The word "felsic" combines letters from the words ''[[feldspar]]'' and ''silica''. Felsic minerals are usually light in color. Common felsic minerals include [[quartz]], [[biotite]], [[muscovite]], [[hornblende]], [[orthoclase]], and sodium-rich [[plagioclase]] feldspars. The most common felsic rock is [[granite]].
-*[http://www.geo.cornell.edu/geology/classes/geochemdata/CrustalAbundances.html Average composition of Continental Crust]
+It is a matter of debate whether the amount of continental crust has been increasing, decreasing, or remaining constant over geological time. One model suggests that prior to 3.7 billion years ago, the continental crust constituted less than 10 percent of the present amount. By 3.0 billion years ago, that figure rose to about 25 percent, and by about 2.6 billion years ago, it was about 60 percent of the current amount (Taylor and McLennan 1995). The growth of continental crust is thought to have occurred in "spurts" of activity, corresponding to five episodes of increased production through geologic time (see graphic at [http://earth.leeds.ac.uk/assyntgeology/extra_info/ehistory.htm Butler]).
-*[http://quake.wr.usgs.gov/research/structure/CrustalStructure Crust 5.1]
 ==See also==
@@ Line 58: / Line 54: @@
 *[[Cryosphere]]
 *[[Hydrosphere]]
-*[[Pedosphere]]
 *[[Plate tectonics]]
+== References ==
+*Butler, Rob. ''Making new continents''. http://earth.leeds.ac.uk/assyntgeology/extra_info/ehistory.htm Accessed 01/29/2006
+* [http://www.windows.ucar.edu/cgi-bin/tour_def/earth/interior/earths_crust.html Earth's Crust, Lithosphere and Asthenosphere]
+* [http://www.geolsoc.org.uk/template.cfm?name=lithosphere Crust and Lithosphere]
+* Stanley Chernicoff and Donna Whitney. ''Geology. An Introduction to Physical Geology'', 4th ed., Pearson 2007
+*Saal, A.L., Rudnick R.L., Ravizza G.E. & Hart S.R. 1998. ''Re-Os [[isotope geochemistry|isotope]] evidence for the composition, formation and age of the lower crust.'' Nature 39317, 1998.
+*Taylor and McLennan. 1995. ''Model of growth of continental crust through time'' in John Victor Walther 2005, ''Essentials Of Geochemistry''. ones & Bartlett. ISBN 0763726427
+*von Huene, R. and D.W. Scholl, 1991. "Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust." Reviews of Geophysics 29: 279-316.
+==External links==
+All links retrieved November 2, 2022.
+*[http://www.geo.cornell.edu/geology/classes/geochemdata/CrustalAbundances.html Composition of Continental Crust]
 [[Category:Physical sciences]]
 [[Category:Earth sciences]]
 [[Category:Geology]]
-[[Category:Plate tectonics]]
-[[Category:Physical geography]]
-{{credit3|Lithosphere|56979503|Oceanic_crust|57958902|Continental_crust|54702418}}
+{{credit5|Lithosphere|56979503|Oceanic_crust|57958902|Continental_crust|54702418|Felsic|57590810|Mafic|50956225}}