Structure of the Earth
The crust ranges from 5 to 70 km in depth. The thin parts are oceanic crust composed of dense (mafic) iron magnesium silicate rocks and underlie the ocean basins. The thicker crust is continental crust, which is less dense and composed of (felsic) sodium potassium aluminium silicate rocks. The crust-mantle boundary occurs as two physically different events. First, there is a discontinuity in the seismic velocity, which is known as the Mohorovičić discontinuity or Moho. The cause of the Moho is thought to be a change in rock composition from rocks containing plagioclase feldspar (above) to rocks that contain no feldspars (below). Second, there is a chemical discontinuity between ultramafic cumulates and tectonized harzburgites, which has been observed from deep parts of the oceanic crust that have been obducted into the continental crust and preserved as ophiolite sequences.
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Historical development of alternative conceptions
In 1692 Edmund Halley (in a paper printed in Philosophical Transactions of Royal Society of London) put forth the idea of Earth consisting of a hollow shell about 500 miles thick, with two inner concentric shells around an innermost core, corresponding to the diameters of the planets Venus, Mars, and Mercury respectively.[12] Halley's construct was a method of accounting for the (flawed) values of the relative density of the Earth and the Moon that had been given by Sir Isaac Newton, in Principia (1687).“Sir Isaac Newton has demonstrated the Moon to be more solid than our Earth, as 9 to 5" Halley remarked; "why may we not then suppose four ninths of our globe to be cavity?”[12]
In 1818, John Cleves Symmes, Jr. suggested that the Earth consisted of a hollow shell about 800 miles (1,300 km) thick, with openings about 1400 miles (2,300 km) across at both poles with 4 inner shells each open at the poles. Jules Verne, in Journey to the Center of the Earth imagined vast interior caverns, and William Reed, in Phantom of the Poles (1906) imagined a hollow earth.
Some Christian writers resisted the idea of a spherical Earth on theological grounds, without gaining widespread acceptance. The Flat Earth Society continue to oppose the concept of a spherical Earth.[13]
It has been also suggested that the earth's core consists of metallic hydrogen.[14]
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See also
- Rain-out model
- Mohorovičić discontinuity, boundary crust and mantle.
- Core-mantle boundary
- Lehmann discontinuity
- Hydridic Earth theory
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Notes
- ^ Spaceflight Now | Breaking News | Oldest rock shows Earth was a hospitable young planet
- ^ T. H. Jordan, "Structural Geology of the Earth's Interior", Proceedings of the National Academy of Science, 1979, Sept., 76(9): 4192–4200.
- ^ Cohen, Ronald; Stixrude, Lars. Crystal at the Center of the Earth. Retrieved on 2007-02-05.
- ^ Lars Stixrude and R. E. Cohen, "High-Pressure Elasticity of Iron and Anisotropy of Earth's Inner Core", Science 31 March 1995: Vol. 267. no. 5206, pp. 1972 - 1975 DOI: 10.1126/science.267.5206.1972
- ^ Wootton, Anne (September 2006) "Earth's Inner Fort Knox" Discover 27(9): p.18;
- ^ Herndon, J. M., The chemical composition of the interior shells of the Earth. Proc. R. Soc. Lond, 1980, A372, 149-154.
- ^ Herndon, J. M., Scientific basis of knowledge on Earth's composition. Curr.Sci., 2005, 88(7), 1034-1037.
- ^ Earth's Core Spins Faster Than the Rest of the Planet - New York Times
- ^ Kerr, Richard A. (26 August 2005) "Earth's Inner Core Is Running a Tad Faster Than the Rest of the Planet" Science 309(5739): p.1313;
- ^ Chang, Kenneth (26 August 2005) "Scientists Say Earth's Center Rotates Faster Than Surface" The New York Times Sec. A, Col. 1, p.13;
- ^ http://www2.uni-jena.de/chemie/geowiss/geodyn/poster2.html
- ^ a b N. Kollerstrom, 1992. "The hollow world of Edmond Halley" from Journal for History of Astronomy 23, 185-192
- ^ Documenting the Existence of "The International Flat Earth Society"
- ^ Christianson, Neil B. (1989). Earth has a cold heart. ne-do Press. ISBN 0962724009.
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References
- Herndon, J. Marvin (1994) Planetary and Protostellar Nuclear Fission: Implications for Planetary Change, Stellar Ignition and Dark Matter Proceedings: Mathematical and Physical Sciences, Vol. 445, No. 1924 (May 9, 1994) , pp. 453-461
- Herndon, J. Marvin (1996) Substructure of the inner core of the Earth Vol. 93, Issue 2, 646-648, January 23, 1996, PNAS
- Hollenbach, D. F. ,dagger and J. M. HerndonDagger (2001) Deep-Earth reactor: Nuclear fission, helium, and the geomagnetic field Published online before print September 18, 2001, 10.1073/pnas.201393998, September 25, 2001, vol. 98, no. 20, PNAS
- Lehmann, I. (1936) Inner Earth, Bur. Cent. Seismol. Int. 14, 3-31
- Schneider, David (Oct 1996) A Spinning Crystal Ball, Scientific American
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