Internal structure of Earth
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The internal structure of Earth is the layers of the
Scientific understanding of the internal structure of Earth is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through Earth, measurements of the gravitational and magnetic fields of Earth, and experiments with crystalline solids at pressures and temperatures characteristic of Earth's deep interior.
Global properties
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Chemical composition and other | Continental crust | Upper mantle | Pyrolite model | Chondrite model (1) | Chondrite model (2) |
---|---|---|---|---|---|
MgO | 4.4 | 36.6 | 38.1 | 26.3 | 38.1 |
Al2O3 | 15.8 | 4.6 | 4.6 | 2.7 | 3.9 |
SiO2 | 59.1 | 45.4 | 45.1 | 29.8 | 43.2 |
CaO | 6.4 | 3.7 | 3.1 | 2.6 | 3.9 |
FeO | 6.6 | 8.1 | 7.9 | 6.4 | 9.3 |
other oxides | 7.7 | 1.4 | 1.2 | N/A | 5.5 |
Fe | N/A | N/A | N/A | 25.8 | N/A |
Ni | N/A | N/A | N/A | 1.7 | N/A |
Si | N/A | N/A | N/A | 3.5 | N/A |
"Note: In chondrite model (1), the light element in the core is assumed to be Si. Chondrite model (2) is a model of chemical composition of the mantle corresponding to the model of core shown in chondrite model (1)."
Layers
The structure of Earth can be defined in two ways: by mechanical properties such as
Crust and lithosphere
Earth's crust ranges from 5–70 kilometres (3.1–43.5 mi)[7] in depth and is the outermost layer.[8] The thin parts are the oceanic crust, which underlie the ocean basins (5–10 km) and is mafic-rich[9] (dense iron-magnesium silicate mineral or igneous rock).[10] The thicker crust is the continental crust, which is less dense[11] and is felsic-rich (igneous rocks rich in elements that form feldspar and quartz).[12] The rocks of the crust fall into two major categories – sial (aluminium silicate) and sima (magnesium silicate).[13] It is estimated that sima starts about 11 km below the Conrad discontinuity,[14] though the discontinuity is not distinct and can be absent in some continental regions.[15]
Earth's lithosphere consists of the crust and the uppermost
Many rocks making up Earth's crust formed less than 100
Mantle
Earth's mantle extends to a depth of 2,890 km (1,800 mi), making it the planet's thickest layer.[20] [This is 45% of the 6,371 km (3,959 mi) radius, and 83.7% of the volume - 0.6% of the volume is the crust]. The mantle is divided into
Due to increasing pressure deeper in the mantle, the lower part flows less easily, though chemical changes within the mantle may also be important. The viscosity of the mantle ranges between 1021 and 1024
Core
Earth's outer core is a fluid layer about 2,260 km (1,400 mi) in height (i.e. distance from the highest point to the lowest point at the edge of the inner core) [36% of the Earth's radius, 15.6% of the volume] and composed of mostly
The inner core was discovered in 1936 by Inge Lehmann and is generally composed primarily of iron and some nickel. Since this layer is able to transmit shear waves (transverse seismic waves), it must be solid. Experimental evidence has at times been inconsistent with current crystal models of the core.[34] Other experimental studies show a discrepancy under high pressure: diamond anvil (static) studies at core pressures yield melting temperatures that are approximately 2000 K below those from shock laser (dynamic) studies.[35][36] The laser studies create plasma,[37] and the results are suggestive that constraining inner core conditions will depend on whether the inner core is a solid or is a plasma with the density of a solid. This is an area of active research.
In early stages of Earth's formation about 4.6 billion years ago, melting would have caused denser substances to sink toward the center in a process called planetary differentiation (see also the iron catastrophe), while less-dense materials would have migrated to the crust. The core is thus believed to largely be composed of iron (80%), along with nickel and one or more light elements, whereas other dense elements, such as lead and uranium, either are too rare to be significant or tend to bind to lighter elements and thus remain in the crust (see felsic materials). Some have argued that the inner core may be in the form of a single iron crystal.[38][39]
Under laboratory conditions a sample of iron–nickel alloy was subjected to the corelike pressures by gripping it in a vise between 2 diamond tips (diamond anvil cell), and then heating to approximately 4000 K. The sample was observed with x-rays, and strongly supported the theory that Earth's inner core was made of giant crystals running north to south.[40][41]
The composition of Earth bears strong similarities to that of certain chondrite meteorites, and even to some elements in the outer portion of the Sun.[42][43] Beginning as early as 1940, scientists, including Francis Birch, built geophysics upon the premise that Earth is like ordinary chondrites, the most common type of meteorite observed impacting Earth. This ignores the less abundant enstatite chondrites, which formed under extremely limited available oxygen, leading to certain normally oxyphile elements existing either partially or wholly in the alloy portion that corresponds to the core of Earth.[citation needed]
Seismology
The layering of Earth has been inferred indirectly using the time of travel of refracted and reflected seismic waves created by earthquakes. The core does not allow shear waves to pass through it, while the speed of travel (
See also
- Hollow Earth
- Geological history of Earth
- Lehmann discontinuity
- Rain-out model
- Travel to the Earth's center
- Solid earth
References
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- ^ ME = 5·9722×1024 kg ± 6×1020 kg. "2016 Selected Astronomical Constants Archived 2016-02-15 at the Wayback Machine" in The Astronomical Almanac Online, USNO–UKHO, archived (PDF) from the original on 2016-12-24, retrieved 2016-02-18
- ^ "Planetary Fact Sheet". Lunar and Planetary Science. NASA. Archived from the original on 24 March 2016. Retrieved 2 January 2009.
- ^ ISBN 9789048187010.
- ^ Andrei, Mihai (21 August 2018). "What are the layers of the Earth?". ZME Science. Archived from the original on 12 May 2020. Retrieved 28 June 2019.
- ^ Chinn, Lisa (25 April 2017). "Earth's Structure From the Crust to the Inner Core". Sciencing. Leaf Group Media. Archived from the original on 30 July 2020. Retrieved 28 June 2019.
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- ^ Britannica, The Editors of Encyclopaedia. "continental crust". Encyclopedia Britannica, 5 Sep. 2023, https://www.britannica.com/science/continental-crust. |access-date=12 October 2023 |url-status=live
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- ^ Hess, H. (1955-01-01). "The oceanic crust". Journal of Marine Research. 14 (4): 424.
It has been common practice to subdivide the crust into sial and sima. These terms refer to generalized compositions, sial being those rocks rich in Si and Al and sima those rich in Si and Mg.
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- ^ Breaking News | Oldest rock shows Earth was a hospitable young planet Archived 2009-06-28 at the Wayback Machine. Spaceflight Now (2001-01-14). Retrieved on 2012-01-27.
- ^ Nace, Trevor (16 January 2016). "Layers Of The Earth: What Lies Beneath Earth's Crust". Forbes. Archived from the original on 5 March 2020. Retrieved 28 June 2019.
- ^ Evers, Jeannie (11 August 2015). "Mantle". National Geographic. National Geographic Society. Archived from the original on 12 May 2016. Retrieved 28 June 2019.
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- ^ Krieger, Kim (24 March 2004). "D Layer Demystified". Science News. American Association for the Advancement of Science. Archived from the original on 10 July 2022. Retrieved 5 November 2016.
- W. M. Keck Earth Science and Mineral Engineering Museum. University of Nevada, Reno: 5. Archived from the original(PDF) on 7 September 2015. Retrieved 28 June 2019.
- ^ Cain, Fraser (26 March 2016). "What is the Earth's Mantle Made Of?". Universe Today. Archived from the original on 6 November 2010. Retrieved 28 June 2019.
- ^ Shaw, Ethan (22 October 2018). "The Different Properties of the Asthenosphere & the Lithosphere". Sciencing. Leaf Group Media. Archived from the original on 30 July 2020. Retrieved 28 June 2019.
- ^ Preuss, Paul (July 17, 2011). "What Keeps the Earth Cooking?". Lawrence Berkeley National Laboratory. University of California, Berkeley. Archived from the original on 21 January 2022. Retrieved 28 June 2019.
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- ^ Edgeworth, R.; Dalton, B.J.; Parnell, T. "The Pitch Drop Experiment". The University of Queensland Australia. Archived from the original on 28 March 2013. Retrieved 15 October 2007.
- ^ "Earth's Interior". Science & Innovation. National Geographic. 18 January 2017. Archived from the original on 18 January 2019. Retrieved 14 November 2018.
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- ^ Engdahl, E.R.; Flinn, E.A.; Massé, R.P. (1974). "Differential PKiKP travel times and the radius of the inner core". Geophysical Journal International. 39 (3): 457–463. .
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- ^ Schneider, Michael (1996). "Crystal at the Center of the Earth". Projects in Scientific Computing, 1996. Pittsburgh Supercomputing Center. Archived from the original on 5 February 2007. Retrieved 8 March 2019.
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Further reading
- Drollette, Daniel (October 1996). "A Spinning Crystal Ball". Scientific American. 275 (4): 28–33. .
- Kruglinski, Susan (June 2007). "Journey to the Center of the Earth". Discover. Archived from the original on 26 May 2016. Retrieved 9 July 2016.
- Lehmann, I (1936). "Inner Earth". Bur. Cent. Seismol. Int. 14: 3–31.
- Wegener, Alfred (1966). The origin of continents and oceans. New York: Dover Publications. ISBN 978-0-486-61708-4.
External links
- Media related to Structure of the Earth at Wikimedia Commons