Continental drift

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The continental drift of the last 250 million years
Antonio Snider-Pellegrini's Illustration of the closed and opened Atlantic Ocean (1858).[1]

Continental drift is the theory that the Earth's continents have moved over geologic time relative to each other, thus appearing to have "drifted" across the ocean bed.[2] The speculation that continents might have 'drifted' was first put forward by Abraham Ortelius in 1596. The concept was independently and more fully developed by Alfred Wegener in 1912, but his theory was rejected by many for lack of any motive mechanism. Arthur Holmes later proposed mantle convection for that mechanism. The idea of continental drift has since been subsumed by the theory of plate tectonics, which explains that the continents move by riding on plates of the Earth's lithosphere.[3]

History[edit]

Early history[edit]

Abraham Ortelius (Ortelius 1596),[4] Theodor Christoph Lilienthal (1756),[5] Alexander von Humboldt (1801 and 1845),[5] Antonio Snider-Pellegrini (Snider-Pellegrini 1858), and others had noted earlier that the shapes of continents on opposite sides of the Atlantic Ocean (most notably, Africa and South America) seem to fit together.[6] W. J. Kious described Ortelius' thoughts in this way:[7]

Abraham Ortelius in his work Thesaurus Geographicus ... suggested that the Americas were "torn away from Europe and Africa ... by earthquakes and floods" and went on to say: "The vestiges of the rupture reveal themselves if someone brings forward a map of the world and considers carefully the coasts of the three [continents]."

In 1889, Alfred Russel Wallace remarked, "It was formerly a very general belief, even amongst geologists, that the great features of the earth's surface, no less than the smaller ones, were subject to continual mutations, and that during the course of known geological time the continents and great oceans had, again and again, changed places with each other."[8] He quotes Charles Lyell as saying, "Continents, therefore, although permanent for whole geological epochs, shift their positions entirely in the course of ages."[9] and claims that the first to throw doubt on this was James Dwight Dana in 1849.

In his Manual of Geology (1863), Dana wrote, "The continents and oceans had their general outline or form defined in earliest time. This has been proved with respect to North America from the position and distribution of the first beds of the Silurian – those of the Potsdam epoch. … and this will probably prove to the case in Primordial time with the other continents also".[10] Dana was enormously influential in America – his Manual of Mineralogy is still in print in revised form – and the theory became known as Permanence theory.[11]

This appeared to be confirmed by the exploration of the deep sea beds conducted by the Challenger expedition, 1872-6, which showed that contrary to expectation, land debris brought down by rivers to the ocean is deposited comparatively close to the shore on what is now known as the continental shelf. This suggested that the oceans were a permanent feature of the Earth's surface, and did not change places[clarification needed] with the continents.[8]

Wegener and his predecessors[edit]

Alfred Wegener

Apart from the earlier speculations mentioned in the previous section, the idea that the American continents had once formed a single landmass together with Europe and Asia before assuming their present shapes and positions was speculated by several scientists before Alfred Wegener's 1912 paper.[12] Although Wegener's theory was formed independently and was more complete than those of his predecessors, Wegener later credited a number of past authors with similar ideas:[13][14] Franklin Coxworthy (between 1848 and 1890),[15] Roberto Mantovani (between 1889 and 1909), William Henry Pickering (1907)[16] and Frank Bursley Taylor (1908).[17] In addition, Eduard Suess had proposed a supercontinent Gondwana in 1885[18] and the Tethys Ocean in 1893,[19] assuming a land-bridge between the present continents submerged in the form of a geosyncline, and John Perry had written an 1895 paper proposing that the earth's interior was fluid, and disagreeing with Lord Kelvin on the age of the earth.[20]

For example: the similarity of southern continent geological formations had led Roberto Mantovani to conjecture in 1889 and 1909 that all the continents had once been joined into a supercontinent; Wegener noted the similarity of Mantovani's and his own maps of the former positions of the southern continents. In Mantovani's conjecture, this continent broke due to volcanic activity caused by thermal expansion, and the new continents drifted away from each other because of further expansion of the rip-zones, where the oceans now lie. This led Mantovani to propose an Expanding Earth theory which has since been shown to be incorrect.[21][22][23]

Continental drift without expansion was proposed by Frank Bursley Taylor,[24] who suggested in 1908 (published in 1910) that the continents were moved into their present positions by a process of "continental creep".[25][26] In a later paper he proposed that this occurred by their being dragged towards the equator by tidal forces during the hypothesized capture of the moon in the Cretaceous, resulting in "general crustal creep" toward the equator. Although his proposed mechanism was wrong, he was the first to realize the insight that one of the effects of continental motion would be the formation of mountains, and attributed the formation of the Himalayas to the collision between the Indian subcontinent with Asia.[27] Wegener said that of all those theories, Taylor's, although not fully developed, had the most similarities to his own. In the mid-20th century, the theory of continental drift was referred to as the "Taylor-Wegener hypothesis",[24][27][28] although this terminology eventually fell out of common use.[29]

Alfred Wegener first presented his hypothesis to the German Geological Society on 6 January 1912.[12] His hypothesis was that the continents had once formed a single landmass, called Pangaea, before breaking apart and drifting to their present locations.

Wegener was the first to use the phrase "continental drift" (1912, 1915)[12][13] (in German "die Verschiebung der Kontinente" – translated into English in 1922) and formally publish the hypothesis that the continents had somehow "drifted" apart. Although he presented much evidence for continental drift, he was unable to provide a convincing explanation for the physical processes which might have caused this drift. His suggestion that the continents had been pulled apart by the centrifugal pseudoforce (Polflucht) of the Earth's rotation or by a small component of astronomical precession was rejected, as calculations showed that the force was not sufficient.[30] The Polflucht hypothesis was also studied by Paul Sophus Epstein in 1920 and found to be implausible.

Rejection of Wegener's theory, 1910s–1950s[edit]

The theory of continental drift was not accepted for many years. One problem was that a plausible driving force was missing.[2] A second problem was that Wegener's estimate of the velocity of continental motion, 250  cm/year, was implausibly high.[31] (The currently accepted rate for the separation of the Americas from Europe and Africa is about 2.5  cm/year).[32] It also did not help that Wegener was not a geologist. Other geologists also believed that the evidence that Wegener had provided was not sufficient. It is now accepted that the plates carrying the continents do move across the Earth's surface, although not as fast as Wegener believed; ironically one of the chief outstanding questions is the one Wegener failed to resolve: what is the nature of the forces propelling the plates?[2]

The British geologist Arthur Holmes championed the theory of continental drift at a time when it was deeply unfashionable. He proposed in 1931 that the Earth's mantle contained convection cells which dissipated radioactive heat and moved the crust at the surface.[33] His Principles of Physical Geology, ending with a chapter on continental drift, was published in 1944.[34]

Geological maps of the time showed huge land bridges spanning the Atlantic and Indian oceans to account for the similarities of fauna and flora and the divisions of the Asian continent in the Permian era but failing to account for glaciation in India, Australia and South Africa.[35]

Geophysicist Jack Oliver is credited with providing seismologic evidence supporting plate tectonics which encompassed and superseded continental drift with the article "Seismology and the New Global Tectonics", published in 1968, using data collected from seismologic stations, including those he set up in the South Pacific.[36][37]

It is now known that there are two kinds of crust: continental crust and oceanic crust. Continental crust is inherently lighter and its composition is different from oceanic crust, but both kinds reside above a much deeper "plastic" mantle. Oceanic crust is created at spreading centers, and this, along with subduction, drives the system of plates in a chaotic manner, resulting in continuous orogeny and areas of isostatic imbalance. The theory of plate tectonics explains all this, including the movement of the continents, better than Wegener's theory.

The fixists[edit]

Hans Stille and Leopold Kober opposed the idea of continental drift and worked on a "fixist"[38] geosyncline model with Earth contraction playing a key role in the formation of orogens.[39][40] Other geologists who opposed continental drift were Bailey Willis, Charles Schuchert, Rollin Chamberlin and Walther Bucher.[41] In 1939 an international geological conference was held in Frankfurt.[42] This conference came to be dominated by the fixists, especially as those geologists specializing in tectonics were all fixists except Willem van der Gracht.[42] Criticism of continental drift and mobilism was abundant at the conference not only from tectonicists but also from sedimentological (Nölke), paleontological (Nölke), mechanical (Lehmann) and oceanographic (Troll, Wüst) perspectives.[42][43] Hans Cloos, the organizer of the conference, was also a fixist[42] who together with Troll held the view that excepting the Pacific Ocean continents were not radically different from oceans in their behaviour.[43] The mobilist theory of Émile Argand for the Alpine orogeny was criticized by Kurt Leuchs.[42] The few drifters and mobilists at the conference appealed to biogeography (Kirsch, Wittmann), paleoclimatology (Wegener, K), paleontology (Gerth) and geodetic measurements (Wegener, K).[44] F. Bernauer correctly equated Reykjanes in Iceland with the Mid-Atlantic Ridge arguing with this that the floor of the Atlantic Ocean was undergoing extension just like Reykjanes. Bernauer thought this extension had drifted the continents only 100–200 km apart, the approximate width of the volcanic zone in Iceland.[45]

David Attenborough, who attended university in the second half of the 1940s, recounted an incident illustrating its lack of acceptance then: "I once asked one of my lecturers why he was not talking to us about continental drift and I was told, sneeringly, that if I could prove there was a force that could move continents, then he might think about it. The idea was moonshine, I was informed."[46]

As late as 1953 – just five years before Carey[47] introduced the theory of plate tectonics – the theory of continental drift was rejected by the physicist Scheidegger on the following grounds.[48]

  • First, it had been shown that floating masses on a rotating geoid would collect at the equator, and stay there. This would explain one, but only one, mountain building episode between any pair of continents; it failed to account for earlier orogenic episodes.
  • Second, masses floating freely in a fluid substratum, like icebergs in the ocean, should be in isostatic equilibrium (in which the forces of gravity and buoyancy are in balance). But gravitational measurements showed that many areas are not in isostatic equilibrium.
  • Third, there was the problem of why some parts of the Earth's surface (crust) should have solidified while other parts were still fluid. Various attempts to explain this foundered on other difficulties.

Road to acceptance[edit]

From the 1930s to the late 1950s, works by Vening-Meinesz, Holmes, Umbgrove, and numerous others outlined concepts that were close or nearly identical to modern plate tectonics theory. In particular, the English geologist Arthur Holmes proposed in 1920 that plate junctions might lie beneath the sea, and in 1928 that convection currents within the mantle might be the driving force.[49] Holmes' views were particularly influential: in his bestselling textbook, Principles of Physical Geology, he included a chapter on continental drift, proposing that Earth's mantle contained convection cells which dissipated radioactive heat and moved the crust at the surface.[50][51]  Holmes' proposal resolved the phase disequilibrium objection (the underlying fluid was kept from solidifying by radioactive heating from the core).  However, scientific communication in the '30 and '40s was inhibited by the war, and the theory still required work to avoid foundering on the orogeny and isostasy objections.  Worse, the most viable forms of the theory predicted the existence of convection cell boundaries reaching deep into the earth that had yet to be observed.[citation needed]

In 1947, a team of scientists led by Maurice Ewing confirmed the existence of a rise in the central Atlantic Ocean, and found that the floor of the seabed beneath the sediments was chemically and physically different from continental crust.[52][53]  As oceanographers continued to bathymeter the ocean basins, a system of mid-oceanic ridges was detected.  An important conclusion was that along this system, new ocean floor was being created, which led to the concept of the "Great Global Rift".[54]

Meanwhile, scientists began recognizing odd magnetic variations across the ocean floor using devices developed during World War II to detect submarines.[55]  Over the next decade, it became increasingly clear that the magnetization patterns were not anomalies, as had been originally supposed. In a series of papers in 1959-1963, Heezen, Dietz, Hess, Mason, Vine, Matthews, and Morley collectively realized that the magnetization of the ocean floor formed extensive, zebra-like patterns: one stripe would exhibit normal polarity and the adjoining stripes reversed polarity.[56][57][58]  The best explanation was the "conveyor belt" or Vine–Matthews–Morley hypothesis.  New magma from deep within the Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust.  The new crust is magnetized by the earth's magnetic field, which undergoes occasional reversals.  Formation of new crust then displaces the magnetized crust apart, akin to a conveyor belt — hence the name.[59]

Without workable alternatives to explain the stripes, geophysicists were forced to conclude that Holmes had been right: ocean rifts were sites of perpetual orogeny at the boundaries of convection cells.[60][61] By 1967, barely two decades after discovery of the mid-oceanic rifts, and a decade after discovery of the striping, plate tectonics had become axiomatic to modern geophysics.

In addition, Marie Tharp, in collaboration with Bruce Heezen, (who initially ridiculed Marie's observations that her maps confirmed continental drift theory), provided essential corroboration, using her skills in cartography and seismographic data, to confirm the theory.[62][63][64][65][66]

Modern evidence[edit]

Fossil patterns across continents (Gondwanaland).
Mesosaurus skeleton, MacGregor, 1908.

Evidence for the movement of continents on tectonic plates is now extensive. Similar plant and animal fossils are found around the shores of different continents, suggesting that they were once joined. The fossils of Mesosaurus, a freshwater reptile rather like a small crocodile, found both in Brazil and South Africa, are one example; another is the discovery of fossils of the land reptile Lystrosaurus in rocks of the same age at locations in Africa, India, and Antarctica.[67] There is also living evidence, with the same animals being found on two continents. Some earthworm families (such as Ocnerodrilidae, Acanthodrilidae, Octochaetidae) are found in South America and Africa.

The complementary arrangement of the facing sides of South America and Africa is obvious but a temporary coincidence. In millions of years, slab pull, ridge-push, and other forces of tectonophysics will further separate and rotate those two continents. It was that temporary feature that inspired Wegener to study what he defined as continental drift although he did not live to see his hypothesis generally accepted.

The widespread distribution of Permo-Carboniferous glacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia was one of the major pieces of evidence for the theory of continental drift. The continuity of glaciers, inferred from oriented glacial striations and deposits called tillites, suggested the existence of the supercontinent of Gondwana, which became a central element of the concept of continental drift. Striations indicated glacial flow away from the equator and toward the poles, based on continents' current positions and orientations, and supported the idea that the southern continents had previously been in dramatically different locations that were contiguous with one another.[13]

See also[edit]

Works cited[edit]

Notes
  1. ^ Antonio Snider-Pellegrini, La Création et ses mystères dévoilés (Creation and its mysteries revealed) (Paris, France: Frank et Dentu, 1858), plates 9 and 10 (between pages 314 and 315).
  2. ^ a b c "Historical perspective [This Dynamic Earth, USGS]". pubs.usgs.gov.
  3. ^ Oreskes 2002, p. 324.
  4. ^ Romm, James (3 February 1994), "A New Forerunner for Continental Drift", Nature, 367 (6462): 407–408, Bibcode:1994Natur.367..407R, doi:10.1038/367407a0.
  5. ^ a b Schmeling, Harro (2004). "Geodynamik" (PDF) (in German). University of Frankfurt.
  6. ^ Brusatte, Stephen, Continents Adrift and Sea-Floors Spreading: The Revolution of Plate Tectonics (PDF)
  7. ^ Kious, W. J.; Tilling, R. I. (February 2001) [1996], "Historical perspective", This Dynamic Earth: the Story of Plate Tectonics (Online ed.), U.S. Geological Survey, ISBN 0-16-048220-8, retrieved 29 January 2008
  8. ^ a b Wallace, Alfred Russel (1889), "12", Darwinism …, Macmillan, p. 341
  9. ^ Lyell, Charles (1872), Principles of Geology ... (11 ed.), John Murray, p. 258
  10. ^ Dana, James D. (1863), Manual of Geology, Theodore Bliss & Co, Philadelphia, p. 732
  11. ^ Oreskes, Naomi (2002), Continental Drift (PDF), archived from the original (PDF) on 4 February 2012
  12. ^ a b c Wegener, Alfred (6 January 1912), "Die Herausbildung der Grossformen der Erdrinde (Kontinente und Ozeane), auf geophysikalischer Grundlage" (PDF), Petermanns Geographische Mitteilungen, 63: 185–195, 253–256, 305–309, archived from the original (PDF) on 4 October 2011.
  13. ^ a b c Wegener, A. (1966) [1929], The Origin of Continents and Oceans, Courier Dover Publications, ISBN 0-486-61708-4
  14. ^ Wegener, A. (1929), Die Entstehung der Kontinente und Ozeane (4 ed.), Braunschweig: Friedrich Vieweg & Sohn Akt. Ges.
  15. ^ Coxworthy, Franklin (1924). Electrical Condition; Or, How and where Our Earth was Created. J.S. Phillips. Retrieved 6 December 2014.
  16. ^ Pickering, W.H (1907), "The Place of Origin of the Moon – The Volcani Problems", Popular Astronomy, 15: 274–287, Bibcode:1907PA.....15..274P
  17. ^ Frank Bursley Taylor (3 June 1910) "Bearing of the Tertiary mountain belt on the origin of the earth’s plan", Bulletin of the Geological Society of America, 21 : 179–226.
  18. ^ Eduard Suess, Das Antlitz der Erde (The Face of the Earth), vol. 1 (Leipzig, (Germany): G. Freytag, 1885), page 768. From p. 768: "Wir nennen es Gondwána-Land, nach der gemeinsamen alten Gondwána-Flora, ... " (We name it Gondwána-Land, after the common ancient flora of Gondwána ... )
  19. ^ Edward Suess (March 1893) "Are ocean depths permanent?", Natural Science: A Monthly Review of Scientific Progress (London), 2 : 180- 187. From page 183: "This ocean we designate by the name "Tethys", after the sister and consort of Oceanus. The latest successor of the Tethyan Sea is the present Mediterranean."
  20. ^ Perry, John (1895) "On the age of the earth", Nature, 51 : 224–227, 341–342, 582–585.
  21. ^ Mantovani, R. (1889), "Les fractures de l'écorce terrestre et la théorie de Laplace", Bull. Soc. Sc. Et Arts Réunion: 41–53
  22. ^ Mantovani, R. (1909), "L'Antarctide", Je m'instruis. La science pour tous, 38: 595–597
  23. ^ Scalera, G. (2003), "Roberto Mantovani an Italian defender of the continental drift and planetary expansion", in Scalera, G.; Jacob, K.-H., Why expanding Earth? – A book in honour of O.C. Hilgenberg, Rome: Istituto Nazionale di Geofisica e Vulcanologia, pp. 71–74
  24. ^ a b Obituary: Frank Bursley Taylor (1860–1938), Proceedings of the American Academy, Vol. 75, No. 6 (Dec. 1944), American Academy of Arts and Sciences, pp. 176–178 (retrieved 20 October 2015)
  25. ^ Taylor, F.B. (1910), "Bearing of the tertiary mountain belt on the origin of the earth's plan", GSA Bulletin, 21 (2): 179–226, doi:10.1130/1052-5173(2005)015[29b:WTCCA]2.0.CO;2
  26. ^ Henry R. Frankel, "Wegener and Taylor develop their theories of continental drift", in The Continental Drift Controversy: Wegener and the Early Debate Volume 1, Wegener and the Early Debate, pp. 38–80, Cambridge University Press, 2012. ISBN 9780521875042 doi:10.1017/CBO9780511842368.004
  27. ^ a b Powell, James Lawrence (2015). Four Revolutions in the Earth Sciences: From Heresy to Truth. Columbia University Press. pp. 69–70. ISBN 978-0-231-53845-9. Retrieved 20 October 2015.
  28. ^ Hansen, L. T., Some considerations of, and additions to the Taylor-Wegener hypothesis of continental displacement, Los Angeles, 1946. OCLC 1247437 OCLC
  29. ^ R. M. Wood, Coming Apart at the Seams, New Scientist, 24 January 1980
  30. ^ "Plate Tectonics: The Rocky History of an Idea". Wegener's inability to provide an adequate explanation of the forces responsible for continental drift and the prevailing belief that the earth was solid and immovable resulted in the scientific dismissal of his theories.
  31. ^ University of California Museum of Paleontology, Alfred Wegener (1880–1930) (accessed 30 April 2015).
  32. ^ Unavco Plate Motion Calculator (accessed 30 April 2015).
  33. ^ Holmes, Arthur (1931). "Radioactivity and Earth Movements" (PDF). Transactions of the Geological Society of Glasgow. Geological Society of Glasgow: 559–606.
  34. ^ Holmes, Arthur (1944). Principles of Physical Geology (1st ed.). Edinburgh: Thomas Nelson & Sons. ISBN 0-17-448020-2.
  35. ^ See map based on the work of the American paleontologist Charles Schuchert in Wells, H. G.; Huxley, Julian; Wells, G. P. (1931), The Science of life, p. 734
  36. ^ "Jack Oliver, Who Proved Continental Drift, Dies at 87". The New York Times. 12 January 2011. p. A16. Retrieved 6 June 2013.
  37. ^ Isacks, Bryan; Oliver, Jack; Sykes, Lynn R. (15 September 1968). "Seismology and the New Global Tectonics". Journal of Geophysical Research. 73 (18): 5855–5899. Bibcode:1968JGR....73.5855I. doi:10.1029/JB073i018p05855. Retrieved 6 June 2013.
  38. ^ Şengör (1982), p. 30
  39. ^ Şengör (1982), p. 28
  40. ^ Şengör (1982), p. 29
  41. ^ Şengör (1982), p. 31
  42. ^ a b c d e Frankel (2012), p. 403
  43. ^ a b Frankel (2012), p. 405
  44. ^ Frankel (2012), p. 407
  45. ^ Frankel (2012), p. 409
  46. ^ McKie, Robin (28 October 2012). "David Attenborough: force of nature". The Observer. London. Retrieved 29 October 2012.
  47. ^ Carey, S. W. (1958). Carey, S. W., ed. "Continental Drift—A symposium". Hobart: Univ. of Tasmania: 177–363.
  48. ^ Scheidegger, Adrian E. (1953), "Examination of the physics of theories of orogenesis", GSA Bulletin, 64 (2): 127–150, Bibcode:1953GSAB...64..127S, doi:10.1130/0016-7606(1953)64[127:EOTPOT]2.0.CO;2
  49. ^ Holmes, Arthur (1928). "Radioactivity and Earth movements". Transactions of the Geological Society of Glasgow. 18: 559–606.; see also Holmes, Arthur (1978). Principles of Physical Geology (3 ed.). Wiley. pp. 640–41. ISBN 0-471-07251-6. and Frankel, Henry (July 1978). "Arthur Holmes and continental drift". The British Journal for the History of Science. 11 (2): 130–50. doi:10.1017/S0007087400016551. JSTOR 4025726..
  50. ^ Wessel, P.; Müller, R. D. (2007), "Plate Tectonics", Treatise on Geophysics, 6, Elsevier, pp. 49–98
  51. ^ Vine, F. J. (1966). "Spreading of the Ocean Floor: New Evidence". Science. 154 (3755): 1405–1415. Bibcode:1966Sci...154.1405V. doi:10.1126/science.154.3755.1405. PMID 17821553.
  52. ^ Lippsett, Laurence (2001). "Maurice Ewing and the Lamont-Doherty Earth Observatory". Living Legacies. Retrieved 2008-03-04.
  53. ^ Lippsett, Laurence (2006). "Maurice Ewing and the Lamont-Doherty Earth Observatory". In William Theodore De Bary; Jerry Kisslinger; Tom Mathewson. Living Legacies at Columbia. Columbia University Press. pp. 277–97. ISBN 0-231-13884-9. Retrieved 2010-06-22.
  54. ^ Heezen, B. (1960). "The rift in the ocean floor". Scientific American. 203 (4): 98–110. Bibcode:1960SciAm.203d..98H. doi:10.1038/scientificamerican1060-98.
  55. ^ "Victor Vacquier Sr., 1907–2009: Geophysicist was a master of magnetics", Los Angeles Times: B24, January 24, 2009.
  56. ^ Mason, Ronald G.; Raff, Arthur D. (1961). "Magnetic survey off the west coast of the United States between 32°N latitude and 42°N latitude". Bulletin of the Geological Society of America. 72 (8): 1259–66. Bibcode:1961GSAB...72.1259M. doi:10.1130/0016-7606(1961)72[1259:MSOTWC]2.0.CO;2. ISSN 0016-7606.
  57. ^ Korgen, Ben J. (1995). "A voice from the past: John Lyman and the plate tectonics story" (PDF). Oceanography. The Oceanography Society. 8 (1): 19–20. doi:10.5670/oceanog.1995.29. Archived from the original (PDF) on 2007-09-26.
  58. ^ Spiess, Fred; Kuperman, William (2003). "The Marine Physical Laboratory at Scripps" (PDF). Oceanography. The Oceanography Society. 16 (3): 45–54. doi:10.5670/oceanog.2003.30. Archived from the original (PDF) on 2007-09-26.
  59. ^ See summary in Heirtzler, James R.; Le Pichon, Xavier; Baron, J. Gregory (1966). "Magnetic anomalies over the Reykjanes Ridge". Deep-Sea Research. 13 (3): 427–32. Bibcode:1966DSROA..13..427H. doi:10.1016/0011-7471(66)91078-3.
  60. ^ Le Pichon, Xavier (15 June 1968). "Sea-floor spreading and continental drift". Journal of Geophysical Research. 73 (12): 3661–97. Bibcode:1968JGR....73.3661L. doi:10.1029/JB073i012p03661.
  61. ^ Mc Kenzie, D.; Parker, R.L. (1967). "The North Pacific: an example of tectonics on a sphere". Nature. 216 (5122): 1276–1280. Bibcode:1967Natur.216.1276M. doi:10.1038/2161276a0.
  62. ^ Barton, Cathy (2002). "Marie Tharp, oceanographic cartographer, and her contributions to the revolution in the Earth sciences". Geological Society, London, Special Publications. 192 (1): 215–228. Bibcode:2002GSLSP.192..215B. doi:10.1144/gsl.sp.2002.192.01.11.
  63. ^ Blakemore, Erin (2016-08-30). "Seeing Is Believing: How Marie Tharp Changed Geology Forever". Smithsonian.
  64. ^ Evans, R. (November 2002). "Plumbing Depths to Reach New Heights". Retrieved 2008-06-02.
  65. ^ Doel, R.E.; Levin, T.J.; Marker, M.K. (2006). "Extending modern cartography to the ocean depths: military patronage, Cold War priorities, and the Heezen-Tharp mapping project, 1952–1959". Journal of Historical Geography. 32 (3): 605–626. doi:10.1016/j.jhg.2005.10.011.
  66. ^ Wills, Matthew (2016-10-08). "The Mother of Ocean Floor Cartography". JSTOR. Retrieved 2016-10-14. While working with the North Atlantic data, she noted what must have been a rift between high undersea mountains. This suggested earthquake activity, which then [was] only associated with [the] fringe theory of continental drift. Heezen infamously dismissed his assistant's idea as "girl talk." But she was right, and her thinking helped to vindicate Alfred Wegener's 1912 theory of moving continents. Yet Tharp's name isn't on any of the key papers that Heezen and others published about plate tectonics between 1959–1963, which brought this once-controversial idea to the mainstream of earth sciences.
  67. ^ "Rejoined continents [This Dynamic Earth, USGS]". USGS.
References

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