Earth:Mid-ocean ridge

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Short description: Basaltic underwater mountain system formed by plate tectonic spreading


Mid-ocean ridge cross-section (cut-away view)

A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about 2,600 meters (8,500 ft) and rises about 2,000 meters (6,600 ft) above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a divergent plate boundary. The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin.

The production of new seafloor and oceanic lithosphere results from mantle upwelling in response to plate separation. The melt rises as magma at the linear weakness between the separating plates, and emerges as lava, creating new oceanic crust and lithosphere upon cooling.

The first discovered mid-ocean ridge was the Mid-Atlantic Ridge, which is a spreading center that bisects the North and South Atlantic basins; hence the origin of the name 'mid-ocean ridge'. Most oceanic spreading centers are not in the middle of their hosting ocean basis but regardless, are traditionally called mid-ocean ridges. Mid-ocean ridges around the globe are linked by plate tectonic boundaries and the trace of the ridges across the ocean floor appears similar to the seam of a baseball. The mid-ocean ridge system thus is the longest mountain range on Earth, reaching about 65,000 km (40,000 mi).

Global system

World distribution of mid-oceanic ridges

The mid-ocean ridges of the world are connected and form the Ocean Ridge, a single global mid-oceanic ridge system that is part of every ocean, making it the longest mountain range in the world. The continuous mountain range is 65,000 km (40,400 mi) long (several times longer than the Andes, the longest continental mountain range), and the total length of the oceanic ridge system is 80,000 km (49,700 mi) long.[1]

Description

Map of Marie Tharp and Bruce Heezen, painted by Heinrich C. Berann (1977), showing the relief of the ocean floors with the system of mid-ocean ridges
A mid-ocean ridge, with magma rising from a chamber below, forming new oceanic lithosphere that spreads away from the ridge
Rift zone in Þingvellir National Park, Iceland. The island is a sub-aerial part of the Mid-Atlantic Ridge

Morphology

See also: Seafloor spreading#Seafloor global topography: cooling models and Seafloor depth versus ageAt the spreading center on a mid-ocean ridge, the depth of the seafloor is approximately 2,600 meters (8,500 ft).[2][3] On the ridge flanks, the depth of the seafloor (or the height of a location on a mid-ocean ridge above a base-level) is correlated with its age (age of the lithosphere where depth is measured). The depth-age relation can be modeled by the cooling of a lithosphere plate[4][5] or mantle half-space.[6] A good approximation is that the depth of the seafloor at a location on a spreading mid-ocean ridge is proportional to the square root of the age of the seafloor.[6] The overall shape of ridges results from Pratt isostacy: close to the ridge axis, there is a hot, low-density mantle supporting the oceanic crust. As the oceanic plate cools, away from the ridge axis, the oceanic mantle lithosphere (the colder, denser part of the mantle that, together with the crust, comprises the oceanic plates) thickens, and the density increases. Thus older seafloor is underlain by denser material and is deeper.[4][5]

Spreading rate is the rate at which an ocean basin widens due to seafloor spreading. Rates can be computed by mapping marine magnetic anomalies that span mid-ocean ridges. As crystallized basalt extruded at a ridge axis cools below Curie points of appropriate iron-titanium oxides, magnetic field directions parallel to the Earth's magnetic field are recorded in those oxides. The orientations of the field preserved in the oceanic crust comprise a record of directions of the Earth's magnetic field with time. Because the field has reversed directions at known intervals throughout its history, the pattern of geomagnetic reversals in the ocean crust can be used as an indicator of age; given the crustal age and distance from the ridge axis, spreading rates can be calculated.[2][3][7][8]

Spreading rates range from approximately 10–200 mm/yr.[2][3] Slow-spreading ridges such as the Mid-Atlantic Ridge have spread much less far (showing a steeper profile) than faster ridges such as the East Pacific Rise (gentle profile) for the same amount of time and cooling and consequent bathymetric deepening.[2] Slow-spreading ridges (less than 40 mm/yr) generally have large rift valleys, sometimes as wide as 10–20 km (6.2–12.4 mi), and very rugged terrain at the ridge crest that can have relief of up to 1,000 m (3,300 ft).[2][3][9][10] By contrast, fast-spreading ridges (greater than 90 mm/yr) such as the East Pacific Rise lack rift valleys. The spreading rate of the North Atlantic Ocean is ~ 25 mm/yr, while in the Pacific region, it is 80–145 mm/yr.[11] The highest known rate is over 200 mm/yr in the Miocene on the East Pacific Rise.[12] Ridges that spread at rates <20 mm/yr are referred to as ultraslow spreading ridges[3][13] (e.g., the Gakkel Ridge in the Arctic Ocean and the Southwest Indian Ridge).

The spreading center or axis commonly connects to a transform fault oriented at right angles to the axis. The flanks of mid-ocean ridges are in many places marked by the inactive scars of transform faults called fracture zones. At faster spreading rates the axes often display overlapping spreading centers that lack connecting transform faults.[2][14] The depth of the axis changes in a systematic way with shallower depths between offsets such as transform faults and overlapping spreading centers dividing the axis into segments. One hypothesis for different along-axis depths is variations in magma supply to the spreading center.[2] Ultra-slow spreading ridges form both magmatic and amagmatic (currently lack volcanic activity) ridge segments without transform faults.[13]

Volcanism

Mid-ocean ridges exhibit active volcanism and seismicity.[3] The oceanic crust is in a constant state of 'renewal' at the mid-ocean ridges by the processes of seafloor spreading and plate tectonics. New magma steadily emerges onto the ocean floor and intrudes into the existing ocean crust at and near rifts along the ridge axes. The rocks making up the crust below the seafloor are youngest along the axis of the ridge and age with increasing distance from that axis. New magma of basalt composition emerges at and near the axis because of decompression melting in the underlying Earth's mantle.[15] The isentropic upwelling solid mantle material exceeds the solidus temperature and melts.

The crystallized magma forms a new crust of basalt known as MORB for mid-ocean ridge basalt, and gabbro below it in the lower oceanic crust.[16] Mid-ocean ridge basalt is a tholeiitic basalt and is low in incompatible elements.[17][18] Hydrothermal vents fueled by magmatic and volcanic heat are a common feature at oceanic spreading centers.[19][20] A feature of the elevated ridges is their relatively high heat flow values, of about 1–10 μcal/cm2s,[21] or roughly 0.04–0.4 W/m2.

Most crust in the ocean basins is less than 200 million years old,[22][23] which is much younger than the 4.54 billion year age of Earth. This fact reflects the process of lithosphere recycling into the Earth's mantle during subduction. As the oceanic crust and lithosphere moves away from the ridge axis, the peridotite in the underlying mantle lithosphere cools and becomes more rigid. The crust and the relatively rigid peridotite below it make up the oceanic lithosphere, which sits above the less rigid and viscous asthenosphere.[3]

Age of oceanic crust. Red is most recent, and blue is the oldest.

Driving mechanisms

Further information: Earth:Plate tectonics
Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches.

The oceanic lithosphere is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at ocean trenches. Two processes, ridge-push and slab pull, are thought to be responsible for spreading at mid-ocean ridges.[24] Ridge push refers to the gravitation sliding of the ocean plate that is raised above the hotter asthenosphere, thus creating a body force causing sliding of the plate downslope.[25] In slab pull the weight of a tectonic plate being subducted (pulled) below an overlying plate at a subduction zone drags the rest of the plate along behind it. The slab pull mechanism is considered to be contributing more than the ridge push.[24][26]

A process previously proposed to contribute to plate motion and the formation of new oceanic crust at mid-ocean ridges is the "mantle conveyor" due to deep convection (see image).[27][28] However, some studies have shown that the upper mantle (asthenosphere) is too plastic (flexible) to generate enough friction to pull the tectonic plate along.[29][30] Moreover, mantle upwelling that causes magma to form beneath the ocean ridges appears to involve only its upper 400 km (250 mi), as deduced from seismic tomography and observations of the seismic discontinuity in the upper mantle at about 400 km (250 mi). On the other hand, some of the world's largest tectonic plates such as the North American Plate and South American plate are in motion, yet only are being subducted in restricted locations such as the Lesser Antilles Arc and Scotia Arc, pointing to action by the ridge push body force on these plates. Computer modeling of the plates and mantle motions suggest that plate motion and mantle convection are not connected, and the main plate driving force is slab pull.[31]

Impact on global sea level

Increased rates of seafloor spreading (i.e. the rate of expansion of the mid-ocean ridge) have caused the global (eustatic) sea level to rise over very long timescales (millions of years).[32][33] Increased seafloor spreading means that the mid-ocean ridge will then expand and form a broader ridge with decreased average depth, taking up more space in the ocean basin. This displaces the overlying ocean and causes sea levels to rise.[34]

Sealevel change can be attributed to other factors (thermal expansion, ice melting, and mantle convection creating dynamic topography[35]). Over very long timescales, however, it is the result of changes in the volume of the ocean basins which are, in turn, affected by rates of seafloor spreading along the mid-ocean ridges.[36]

The 100 to 170 meters higher sea level of the Cretaceous Period (144–65 Ma) is partly attributed to plate tectonics because thermal expansion and the absence of ice sheets only account for some of the extra sea level.[34]

Impact on seawater chemistry and carbonate deposition

Main page: Chemistry:Ocean chemistry
Magnesium/calcium ratio changes at mid-ocean ridges

Seafloor spreading on mid-ocean ridges is a global scale ion-exchange system.[37] Hydrothermal vents at spreading centers introduce various amounts of iron, sulfur, manganese, silicon, and other elements into the ocean, some of which are recycled into the ocean crust. Helium-3, an isotope that accompanies volcanism from the mantle, is emitted by hydrothermal vents and can be detected in plumes within the ocean.[38]

Fast spreading rates will expand the mid-ocean ridge causing basalt reactions with seawater to happen more rapidly. The magnesium/calcium ratio will be lower because more magnesium ions are being removed from seawater and consumed by the rock, and more calcium ions are being removed from the rock and released into seawater. Hydrothermal activity at the ridge crest is efficient in removing magnesium.[39] A lower Mg/Ca ratio favors the precipitation of low-Mg calcite polymorphs of calcium carbonate (calcite seas).[40][41]

Slow spreading at mid-ocean ridges has the opposite effect and will result in a higher Mg/Ca ratio favoring the precipitation of aragonite and high-Mg calcite polymorphs of calcium carbonate (aragonite seas).[41]

Experiments show that most modern high-Mg calcite organisms would have been low-Mg calcite in past calcite seas,[42] meaning that the Mg/Ca ratio in an organism's skeleton varies with the Mg/Ca ratio of the seawater in which it was grown.

The mineralogy of reef-building and sediment-producing organisms is thus regulated by chemical reactions occurring along the mid-ocean ridge, the rate of which is controlled by the rate of sea-floor spreading.[39][42]

History

Discovery

The first indications that a ridge bisects the Atlantic Ocean basin came from the results of the British Challenger expedition in the nineteenth century.[43] Soundings from lines dropped to the seafloor were analyzed by oceanographers Matthew Fontaine Maury and Charles Wyville Thomson and revealed a prominent rise in the seafloor that ran down the Atlantic basin from north to south. Sonar echo sounders confirmed this in the early twentieth century.[44]

It was not until after World War II, when the ocean floor was surveyed in more detail, that the full extent of mid-ocean ridges became known. The Vema, a ship of the Lamont–Doherty Earth Observatory of Columbia University, traversed the Atlantic Ocean, recording echo sounder data on the depth of the ocean floor. A team led by Marie Tharp and Bruce Heezen concluded that there was an enormous mountain chain with a rift valley at its crest, running up the middle of the Atlantic Ocean. Scientists named it the 'Mid-Atlantic Ridge'. Other research showed that the ridge crest was seismically active[45] and fresh lavas were found in the rift valley.[46] Also, crustal heat flow was higher here than elsewhere in the Atlantic Ocean basin.[47]

At first, the ridge was thought to be a feature specific to the Atlantic Ocean. However, as surveys of the ocean floor continued around the world, it was discovered that every ocean contains parts of the mid-ocean ridge system. The German Meteor expedition traced the mid-ocean ridge from the South Atlantic into the Indian Ocean early in the twentieth century. Although the first-discovered section of the ridge system runs down the middle of the Atlantic Ocean, it was found that most mid-ocean ridges are located away from the center of other ocean basins.[2][3]

Impact of discovery: seafloor spreading

Alfred Wegener proposed the theory of continental drift in 1912. He stated: "the Mid-Atlantic Ridge ... zone in which the floor of the Atlantic, as it keeps spreading, is continuously tearing open and making space for fresh, relatively fluid and hot sima [rising] from depth".[48] However, Wegener did not pursue this observation in his later works and his theory was dismissed by geologists because there was no mechanism to explain how continents could plow through ocean crust, and the theory became largely forgotten.

Following the discovery of the worldwide extent of the mid-ocean ridge in the 1950s, geologists faced a new task: explaining how such an enormous geological structure could have formed. In the 1960s, geologists discovered and began to propose mechanisms for seafloor spreading. The discovery of mid-ocean ridges and the process of seafloor spreading allowed for Wegener's theory to be expanded so that it included the movement of oceanic crust as well as the continents.[49] Plate tectonics was a suitable explanation for seafloor spreading, and the acceptance of plate tectonics by the majority of geologists resulted in a major paradigm shift in geological thinking.

It is estimated that along Earth's mid-ocean ridges every year 2.7 km2 (1.0 sq mi) of new seafloor is formed by this process.[50] With a crustal thickness of 7 km (4.3 mi), this amounts to about 19 km3 (4.6 cu mi) of new ocean crust formed every year.[50]

  • Oceanic ridge and deep sea vent chemistry

  • Plates in the crust of the earth, according to the plate tectonics theory

  • Seafloor magnetic striping

  • A demonstration of magnetic striping

List of mid-ocean ridges

List of ancient oceanic ridges

See also

References

  1. ↑ "What is the longest mountain range on earth?". NOAA. http://oceanservice.noaa.gov/facts/midoceanridge.html. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Macdonald, Ken C. (2019), "Mid-Ocean Ridge Tectonics, Volcanism, and Geomorphology" (in en), Encyclopedia of Ocean Sciences, Elsevier, pp. 405–419, doi:10.1016/b978-0-12-409548-9.11065-6, ISBN 9780128130827 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Searle, Roger (2013-09-19). Mid-ocean ridges. New York. ISBN 9781107017528. OCLC 842323181. 
  4. ↑ 4.0 4.1 Sclater, John G.; Anderson, Roger N.; Bell, M. Lee (1971-11-10). "Elevation of ridges and evolution of the central eastern Pacific". Journal of Geophysical Research 76 (32): 7888–7915. doi:10.1029/jb076i032p07888. ISSN 2156-2202. Bibcode: 1971JGR....76.7888S. 
  5. ↑ 5.0 5.1 Parsons, Barry; Sclater, John G. (1977-02-10). "An analysis of the variation of ocean floor bathymetry and heat flow with age". Journal of Geophysical Research 82 (5): 803–827. doi:10.1029/jb082i005p00803. ISSN 2156-2202. Bibcode: 1977JGR....82..803P. 
  6. ↑ 6.0 6.1 Davis, E.E; Lister, C. R. B. (1974). "Fundamentals of Ridge Crest Topography". Earth and Planetary Science Letters 21 (4): 405–413. doi:10.1016/0012-821X(74)90180-0. Bibcode: 1974E&PSL..21..405D. 
  7. ↑ Vine, F. J.; Matthews, D. H. (1963). "Magnetic Anomalies Over Oceanic Ridges" (in en). Nature 199 (4897): 947–949. doi:10.1038/199947a0. ISSN 0028-0836. Bibcode: 1963Natur.199..947V. 
  8. ↑ Vine, F. J. (1966-12-16). "Spreading of the Ocean Floor: New Evidence" (in en). Science 154 (3755): 1405–1415. doi:10.1126/science.154.3755.1405. ISSN 0036-8075. PMID 17821553. Bibcode: 1966Sci...154.1405V. 
  9. ↑ Macdonald, Ken C. (1977). "Near-bottom magnetic anomalies, asymmetric spreading, oblique spreading, and tectonics of the Mid-Atlantic Ridge near lat 37°N" (in en). Geological Society of America Bulletin 88 (4): 541. doi:10.1130/0016-7606(1977)88<541:NMAASO>2.0.CO;2. ISSN 0016-7606. Bibcode: 1977GSAB...88..541M. 
  10. ↑ Macdonald, K. C. (1982). "Mid-Ocean Ridges: Fine Scale Tectonic, Volcanic and Hydrothermal Processes Within the Plate Boundary Zone". Annual Review of Earth and Planetary Sciences 10 (1): 155–190. doi:10.1146/annurev.ea.10.050182.001103. Bibcode: 1982AREPS..10..155M. 
  11. ↑ Argus, Donald F.; Gordon, Richard G.; DeMets, Charles (2010-04-01). "Geologically current plate motions" (in en). Geophysical Journal International 181 (1): 1–80. doi:10.1111/j.1365-246X.2009.04491.x. ISSN 0956-540X. Bibcode: 2010GeoJI.181....1D. 
  12. ↑ Wilson, Douglas S. (1996). "Fastest known spreading on the Miocene Cocos-Pacific Plate Boundary" (in en). Geophysical Research Letters 23 (21): 3003–3006. doi:10.1029/96GL02893. ISSN 1944-8007. Bibcode: 1996GeoRL..23.3003W. 
  13. ↑ 13.0 13.1 Dick, Henry J. B.; Lin, Jian; Schouten, Hans (November 2003). "An ultraslow-spreading class of ocean ridge". Nature 426 (6965): 405–412. doi:10.1038/nature02128. ISSN 1476-4687. PMID 14647373. Bibcode: 2003Natur.426..405D. 
  14. ↑ Macdonald, Ken C.; Fox, P. J. (1983). "Overlapping spreading centres: new accretion geometry on the East Pacific Rise". Nature 302 (5903): 55–58. doi:10.1038/302055a0. ISSN 1476-4687. Bibcode: 1983Natur.302...55M. 
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  18. ↑ Blatt, Harvey; Robert Tracy (1996). Petrology (2nd ed.). Freeman. ISBN 978-0-7167-2438-4. 
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  20. ↑ Martin, William; Baross, John; Kelley, Deborah; Russell, Michael J. (2008-11-01). "Hydrothermal vents and the origin of life". Nature Reviews Microbiology 6 (11): 805–814. doi:10.1038/nrmicro1991. ISSN 1740-1526. PMID 18820700. 
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  25. ↑ Turcotte, Donald Lawson; Schubert, Gerald (2002). Geodynamics (2nd ed.). Cambridge. pp. 1–21. ISBN 0521661862. OCLC 48194722. https://archive.org/details/geodynamics00dltu. 
  26. ↑ Harff, Jan; Meschede, Martin; Petersen, Sven; Thiede, Jörn (2014). "Driving Forces: Slab Pull, Ridge Push". Encyclopedia of Marine Geosciences (2014 ed.). Springer Netherlands. pp. 1–6. doi:10.1007/978-94-007-6644-0_105-1. ISBN 978-94-007-6644-0. 
  27. ↑  , Wikidata Q61783012
  28. ↑ Hess, H. H. (1962), "History of Ocean Basins", in Engel, A. E. J.; James, Harold L.; Leonard, B. F. (in en), Petrologic Studies, Geological Society of America, pp. 599–620, doi:10.1130/petrologic.1962.599, ISBN 9780813770161, https://pubs.geoscienceworld.org/books/book/847/chapter/3918672/, retrieved 2019-09-11 
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  30. ↑ Richter, Frank M. (1973). "Convection and the large-scale circulation of the mantle" (in en). Journal of Geophysical Research 78 (35): 8735–8745. doi:10.1029/JB078i035p08735. ISSN 2156-2202. Bibcode: 1973JGR....78.8735R. 
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  32. ↑ Pitman, Walter C. (1978-09-01). "Relationship between eustacy and stratigraphic sequences of passive margins" (in en). GSA Bulletin 89 (9): 1389–1403. doi:10.1130/0016-7606(1978)89<1389:RBEASS>2.0.CO;2. ISSN 0016-7606. Bibcode: 1978GSAB...89.1389P. 
  33. ↑ Church, J.A.; Gregory, J.M. (2001). Encyclopedia of Ocean Sciences. pp. 2599–2604. doi:10.1006/rwos.2001.0268. ISBN 9780122274305. https://archive.org/details/encyclopediaofoc0000unse/page/2599. 
  34. ↑ 34.0 34.1 Miller, Kenneth G. (2009). "Sea Level Change, Last 250 Million Years". Encyclopedia of Paleoclimatology and Ancient Environments. Encyclopedia of Earth Sciences Series. Springer, Dordrecht. pp. 879–887. doi:10.1007/978-1-4020-4411-3_206. ISBN 978-1-4020-4551-6. 
  35. ↑ Muller, R. D.; Sdrolias, M.; Gaina, C.; Steinberger, B.; Heine, C. (2008-03-07). "Long-Term Sea-Level Fluctuations Driven by Ocean Basin Dynamics" (in en). Science 319 (5868): 1357–1362. doi:10.1126/science.1151540. ISSN 0036-8075. PMID 18323446. Bibcode: 2008Sci...319.1357M. 
  36. ↑ Kominz, M.A. (2001). "Sea Level Variations over Geologic Time". Encyclopedia of Ocean Sciences. San Diego : Academic Press. pp. 2605–2613. doi:10.1006/rwos.2001.0255. ISBN 9780122274305. http://linkinghub.elsevier.com/retrieve/pii/B012227430X002555. 
  37. ↑ Stanley, S.M. and Hardie, L.A., 1999. Hypercalcification: paleontology links plate tectonics and geochemistry to sedimentology. GSA today, 9(2), pp.1–7.
  38. ↑ Lupton, J., 1998. Hydrothermal helium plumes in the Pacific Ocean. Journal of Geophysical Research: Oceans, 103(C8), pp.15853-15868.
  39. ↑ 39.0 39.1 Coggon, R. M.; Teagle, D. A. H.; Smith-Duque, C. E.; Alt, J. C.; Cooper, M. J. (2010-02-26). "Reconstructing Past Seawater Mg/Ca and Sr/Ca from Mid-Ocean Ridge Flank Calcium Carbonate Veins" (in en). Science 327 (5969): 1114–1117. doi:10.1126/science.1182252. ISSN 0036-8075. PMID 20133522. Bibcode: 2010Sci...327.1114C. 
  40. ↑ Morse, John W.; Wang, Qiwei; Tsio, Mai Yin (1997). "Influences of temperature and Mg:Ca ratio on CaCO3 precipitates from seawater" (in en). Geology 25 (1): 85. doi:10.1130/0091-7613(1997)025<0085:IOTAMC>2.3.CO;2. ISSN 0091-7613. Bibcode: 1997Geo....25...85M. 
  41. ↑ 41.0 41.1 Hardie, Lawrence; Stanley, Steven (February 1999). "Hypercalcification: Paleontology Links Plate Tectonics and Geochemistry to Sedimentology". GSA Today 9 (2): 1–7. https://www.geosociety.org/gsatoday/archive/9/2/pdf/i1052-5173-9-2-1.pdf. 
  42. ↑ 42.0 42.1 Ries, Justin B. (2004-11-01). "Effect of ambient Mg/Ca ratio on Mg fractionation in calcareous marine invertebrates: A record of the oceanic Mg/Ca ratio over the Phanerozoic". Geology 32 (11): 981. doi:10.1130/g20851.1. ISSN 0091-7613. Bibcode: 2004Geo....32..981R. 
  43. ↑ Hsü, Kenneth J. (2014-07-14). Challenger at sea : a ship that revolutionized earth science. Princeton, New Jersey. ISBN 9781400863020. OCLC 889252330. 
  44. ↑ Bunch, Bryan H. (2004). The history of science and technology : a browser's guide to the great discoveries, inventions, and the people who made them, from the dawn of time to today. Hellemans, Alexander, 1946–. Boston: Houghton Mifflin. ISBN 0618221239. OCLC 54024134. https://archive.org/details/isbn_9780618221233. 
  45. ↑ Gutenberg, B.; Richter, C. F. (1954). Seismicity of the Earth and Associated Phenomena. Princeton Univ. Press. pp. 309. 
  46. ↑ Shand, S. J. (1949-01-01). "Rocks of the Mid-Atlantic Ridge". The Journal of Geology 57 (1): 89–92. doi:10.1086/625580. ISSN 0022-1376. Bibcode: 1949JG.....57...89S. 
  47. ↑ Day, A.; Bullard, E. C. (1961-12-01). "The Flow of Heat through the Floor of the Atlantic Ocean" (in en). Geophysical Journal International 4 (Supplement_1): 282–292. doi:10.1111/j.1365-246X.1961.tb06820.x. ISSN 0956-540X. Bibcode: 1961GeoJ....4..282B. 
  48. ↑ Jacoby, W. R. (January 1981). "Modern concepts of earth dynamics anticipated by Alfred Wegener in 1912". Geology 9 (1): 25–27. doi:10.1130/0091-7613(1981)9<25:MCOEDA>2.0.CO;2. Bibcode: 1981Geo.....9...25J. 
  49. ↑ "seafloor spreading". National Geographic Society. 2015-06-08. http://www.nationalgeographic.org/encyclopedia/seafloor-spreading/. 
  50. ↑ 50.0 50.1 Cogné, Jean-Pascal; Humler, Eric (2006). "Trends and rhythms in global seafloor generation rate: SEAFLOOR GENERATION RATE" (in en). Geochemistry, Geophysics, Geosystems 7 (3): n/a. doi:10.1029/2005GC001148. https://hal.archives-ouvertes.fr/hal-00149322/file/Cogn-_et_al-2006-Geochemistry%2C_Geophysics%2C_Geosystems.pdf. 

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