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[[Image:EarthGrowth.jpg|thumb|180px|Movements of the continents as the Earth expands. Left: [[Atlantic Ocean]] centered; right: [[Pacific Ocean]] centered.]]
[[Image:EarthGrowth.jpg|thumb|180px|Movements of the continents as the Earth expands. Left: [[Atlantic Ocean]] centered; right: [[Pacific Ocean]] centered.]]
'''Expanding Earth''' hypotheses are widely regarded as obsolete scientific models which are opposed to the [[scientific consensus]] of [[continental drift]] theory. They claim that the explanation for the position and movement of [[continents]] and the appearance of new crustal material at [[mid-ocean ridge]]s is that Earth's volume is increasing. In expanding Earth models, the continents drifted away from each other because of further expansion at the rip-zones, where oceans currently lie, and that significant [[Convergent boundary|destructive plate boundaries]] do not exist. Various forms of these hypotheses include models which suppose Earth's mass has remained constant (and thus the gravitational pull at the surface has decreased over time), that Earth's mass has grown with its volume over time (allowing for a constant gravitational pull at the surface), or that the gravitational constant of the universe has changed over time (a hypothesis used to explain how the mass ''and'' gravitational pull of the earth could remain constant during growth).
'''Expanding Earth''' hypotheses are models which explain continental drift as being caused by expansion at the rip-zones, where oceans currently lie, and which maintain that significant [[Convergent boundary|destructive plate boundaries]] do not exist. The hypothesis claims that the explanation for the position and movement of [[continents]] and the appearance of new crustal material at [[mid-ocean ridge]]s is that Earth's volume is increasing. There are various forms of this hypothesis, including models in which Earth's mass has remained constant (and thus the gravitational pull at the surface has decreased over time), or models which assume that Earth's mass has grown with its volume over time (allowing for a constant gravitational pull at the surface), or that the gravitational constant of the universe has changed over time (a hypothesis used to explain how the mass ''and'' gravitational pull of the earth could remain constant during growth). Many of those who currently believe in the expanding Earth hypothesis are proponents of the ideas of the late [[Australia]]n geologist [[Samuel Warren Carey|S. Warren Carey]], whose ideas were popular for a time in the 1950s and 60s.


Today the theory of [[plate tectonics]] is almost universally accepted as correct. The primary objections to expanding Earth center around the lack of an accepted process by which the Earth's radius could increase and on the inability to find an actual increase of earth's radius by modern measurements. Another reason expanding Earth ideas are considered to be discredited by mainstream geologists is that these ideas regard the process of [[subduction]] and other [[Convergent boundary|destructive plate boundaries]] as non-existent, when in fact subduction is observed at [[oceanic trench]]es, such as the [[Mariana Trench]].
The [[scientific consensus]] is that expanding earth hypotheses are obsolete, having been replaced with the [[continental drift]] theory. The primary objections to expanding Earth center around the lack of an accepted process by which the Earth's radius could increase and on the inability to find an actual increase of earth's radius by modern measurements. Another reason expanding Earth ideas are considered to be discredited is that these ideas regard the process of [[subduction]] and other [[Convergent boundary|destructive plate boundaries]] as non-existent, when in fact subduction has been observed at [[oceanic trench]]es, such as the [[Mariana Trench]].

Many of the remaining expanding Earth adherents are proponents of the ideas of the late [[Australia]]n geologist [[Samuel Warren Carey|S. Warren Carey]], whose ideas were popular for a time in the 1950s and 60s.


== Current status of the concept ==
== Current status of the concept ==

Revision as of 02:32, 27 October 2008

Movements of the continents as the Earth expands. Left: Atlantic Ocean centered; right: Pacific Ocean centered.

Expanding Earth hypotheses are models which explain continental drift as being caused by expansion at the rip-zones, where oceans currently lie, and which maintain that significant destructive plate boundaries do not exist. The hypothesis claims that the explanation for the position and movement of continents and the appearance of new crustal material at mid-ocean ridges is that Earth's volume is increasing. There are various forms of this hypothesis, including models in which Earth's mass has remained constant (and thus the gravitational pull at the surface has decreased over time), or models which assume that Earth's mass has grown with its volume over time (allowing for a constant gravitational pull at the surface), or that the gravitational constant of the universe has changed over time (a hypothesis used to explain how the mass and gravitational pull of the earth could remain constant during growth). Many of those who currently believe in the expanding Earth hypothesis are proponents of the ideas of the late Australian geologist S. Warren Carey, whose ideas were popular for a time in the 1950s and 60s.

The scientific consensus is that expanding earth hypotheses are obsolete, having been replaced with the continental drift theory. The primary objections to expanding Earth center around the lack of an accepted process by which the Earth's radius could increase and on the inability to find an actual increase of earth's radius by modern measurements. Another reason expanding Earth ideas are considered to be discredited is that these ideas regard the process of subduction and other destructive plate boundaries as non-existent, when in fact subduction has been observed at oceanic trenches, such as the Mariana Trench.

Current status of the concept

Modern measurements have established very stringent upper bound limits for the expansion rate, which very much reduces the possibility of an expanding Earth. For example, paleomagnetic data has been used to calculate that the radius of the Earth 400 million years ago was 102 ± 2.8% of today's radius.[1] Furthermore, examinations of earth's moment of inertia suggest that no significant change of earth's radius in the last 620 Million years could have taken place and therefore earth expansion is untenable.[2]

The primary objections to an expanding Earth have centered around the lack of an accepted process by which the Earth's radius could increase and on the inability to find an actual increase of earth's radius by modern measurements. This issue, along with the evidence for the process of subduction, caused the scientific community to dismiss the theory of an expanding Earth.

History and explanations

Expansion with constant mass

During the second voyage of HMS Beagle, in 1834 – 1835 Charles Darwin theorised that an expanding earth could explain the elevation of the landmass of South America as shown by mountain building in the Andes and stepped plains featuring raised beaches in Patagonia. Later in 1835 he abandoned this idea, and proposed that as mountains rose, the ocean floor subsided.[3]

In 1889 and 1909 Roberto Mantovani published a theory of earth expansion and continental drift. He assumed that a closed continent covered the entire surface of a smaller earth. Thermal expansion led to volcanic activity, which broke the land mass into smaller continents. These continents drifted away from each other because of further expansion at the rip-zones, where oceans currently lie. [4] [5] Although Alfred Wegener noticed some similarities to his own theory, he did not mention earth expansion as the cause of drift in Mantovani's theory. [6]

A compromise between earth-expansion and earth-contraction is the "theory of thermal cycles" by Irish physicist John Joly. He assumed that heat flow from radioactive decay inside the Earth surpasses the cooling of the Earth's exterior. Together with British geologist Arthur Holmes, Joly proposed a theory in which the Earth loses its heat by cyclic periods of expansion. In their theory, expansion led to cracks and joints in the Earth's interior, that could fill with magma. This was followed by a cooling phase, where the magma would freeze and become solid rock again, causing the Earth to shrink. [7]

On the other hand, Lindemann (1927), [8] Halm (1935), [9] László Egyed (1956), [10] [11] and Owen (1983) [12] [13] explained the expansion through phase transitions in earth's core. The super-dense core material changes into a less dense form and therefore causes the earth to expand. On that occasion Egyed connected his theory with a possible decrease of the gravitational constant.

The theories based on thermal expansion contradict most modern principles from rheology and an acceptable explanation for phase transitions is missing as well. And Stewart remarked that expansion from half the present radius implies surface gravity g would have been four times its present value. However, this was excluded by Stewart, who set an upper limit on surface gravity of ~2g.[14][15]

Mass accretion

In 1888 Ivan Osipovich Yarkovsky suggested that some sort of aether is absorbed within the earth and transformed into new chemical elements, forcing the celestial bodies to expand. This was connected with his mechanical explanation of gravitation. [16] Also the system of Ott Christoph Hilgenberg (1933, 1974) is based on absorption and transformation of aether-energy into normal matter. However, modern physics does not support the idea of an aether which is absorbed by matter or is transformed into new matter. [17] [18]

The most well known proponent of expanding Earth, S. Warren Carey (1956, 1976, 1997), also proposed some sort of mass increase in planets and said that a final solution to the problem is only possible in a cosmological perspective in connection with the expansion of the universe. As Carey points out, this model is not affected by the criticism of Stewart: Because if the smaller radius in the past is accompanied with a smaller mass, both effects compensate each other and gravity at earth's surface remains nearly constant, or if the latter effect is greater, surface gravity would be less than today, which might be an explanation of the great size of the dinosaurs. [19] [20] [21]

Decrease of the gravitational constant

Paul Dirac suggested in 1938 that the universal gravitational constant had decreased in the billions of years of its existence. This led German physicist Pascual Jordan to a modification of general relativity and to propose in 1964 that all planets slowly expand. Contrary to most of the other explanations this one was at least within the framework of physics considered as a viable hypothesis. [22]

Like the theories with constant mass this hypothesis causes problems with the great size of the dinosaurs. The gravity at the surface was higher not only because of the smaller radius but also because of the higher gravitational constant. Recent measurements of a possible variation of the gravitational constant showed an upper limit for a relative change of 5•10-12, while Jordan's theory needs a variation ten times higher than that measured. [23]

Nikola Tesla

Nikola Tesla had the view that all planets grow. In 1935 he wrote this in the New York Herald Tribune: "Condensation of the primary substance is going on continuously, this being in a measure proved, for I have established by experiments which admit of no doubt that the sun and other celestial bodies steadily increase in mass and energy and ultimately must explode, reverting to the primary substance." [24]

Concepts

Comparison to contentental drift theory

There are a number of observations and partial interpretations on which expanding Earth theories and tectonic theories agree. One is that there are real similarities in shape and other features along the Atlantic coastlines of the continents, indicating that the continents were once joined there. Whereas tectonic theory concludes that a super-continent Pangaea once existed, most expanding Earth theories go farther and claim that such similarities also exist along the Pacific coastlines and that at one time there were no ocean basins at all. Another is that the oldest oceanic crusts are 200 million years old (Continental crusts are nearly 20 times older.), and that the oceanic crust near the mid-ocean ridges is much younger, indicating that new ocean crust has been continuously created for at least the last 200 million years. Most expanding Earth theories contend that ocean crust is not being destroyed, so that the Earth's surface must have been increasing for the last 200 million years, whereas tectonic theory sees oceanic crust being destroyed and recycled in subduction zones.

Geologic activity

Carey, Prof. Geol University of Tasmania 1946-76

Expansion contra subduction: The main difference between the geology of an expanding Earth and that of an Earth with a volume held fixed by plate tectonics is the existence of subduction in the latter. Both models assume new crust is created by oceanic spreading at mid oceanic ridges. Subduction is the process by which (in plate tectonic theory) crustal material disappears into the mantle, thus keeping the size of the planet the same. Most proponents of an expanding Earth like Carey deny the existence of subduction, so seafloor spreading is uncompensated, leading to expansion. [21] An exception is Owen, who combines Earth expansion with subduction. [13]

Shape of the continents: In expanding Earth models a supercontinent is supposed to have covered the surface of the earth practically completely. Proponents argued that, if the oceans were removed and Earth's radius decreased, the continents would fit together better than they do in reconstructions of Pangaea at a constant radius. Most proponents argue that in the mesozoic, 250 million years ago, the Earth's radius was only 50-60% of the current radius, entailing a continental matching on the Pacific facing sides of the continents as well as on the Atlantic sides. [25] Again, Owen is an exception because he assumes a radius of 80% of the current value, and his model doesn't predict a continental matching of the pacific facing sides. [13]

Mountain building : Following some models of German and Italian geologists in the 19th century, Carey explained orogeny as a consequence from the uplift of light material (diapir) because of phase transitions, thermal expansion and gravitation. [21] In plate tectonics, however, orogeny is explained by collisions of continental plates. An illustrative example for plate tectonics is the Indian subcontinent, which broke away from Africa, drifted for a long time in the Indian Ocean, and then collided with Asia, causing the Himalayas to pile up.

Formation of the oceans: Bailey/Stewart argue that with elimination of all oceans all continents would be drowned under 8 km of water, assuming the same amount of water as exists today. [26] During expansion the continents emerged out of this ocean, the water was collected in the expansion zones and formed the oceans in their present form. Carey, in contrast, rejected this scenario and proposed that the present atmosphere and hydrosphere were outgassed from the interior over a long period. [21] The oldest oceanic crusts are 200 million years old, but the continental crusts are nearly 20 times older. To explain this fact, those believing in an expanding Earth propose that the formation of the oceans did not begin until the mesozoic, whereas plate tectonics invokes recycling of the seafloor through spreading and subduction.

Rate of expansion: Some proponents like Jordan or Egyed assume constant and slow expansion. Egyed, for example, set the annual increase of Earth's radius at 0,5 mm. [11] Such an expansion rate by itself, however, is much too small to explain the continental drift that has occurred since the mesozoic 250 million years ago. Owen therefore included some subduction in his model, allowing both a small expansion rate and sufficient velocity of continental drift. [13] Carey and most other proponents of Earth expansion, in contrast, reject any form of subduction and therefore assume fast expansion. This leads to the question of what was happening in the billions of years before the mesozoic, when Pangaea broke up. Carey answered this question by assuming - with no further justification - that the expansion rate was initially very slow and then increased exponentially.[21]

Subduction

Believers in an expanding Earth question the existence, or at least the extent, of subduction in global tectonic theory. Proponents contend that in order for subduction to cause the Earth's size to remain fixed, the exact same amount of crustal material appearing at the mid-ocean ridges must be subducted. This balance is required by conservation of mass as the the Earth has not been observed to be lessening in density.

  1. Proponents of an expanding Earth argue that the mid-ocean ridges are greater in length and area than the known subduction zones and circle the entire globe in several configurations. They claim that the entire ocean floor is smoothly surfaced, free of oceanic slab irregularities, which they believe indicates harmonious spreading unencumbered by such a process.
  2. Subduction only occurs on one side of subduction zones, so the "other side" should show evidence of being much older. In some cases (where two oceanic plates come together), expanding Earth believers see no such evidence. However, this is explained in plate tectonics by the assumption that in some cases, the direction of subduction can change.

Evidence for subduction

Since the 1970s, a vast amount of evidence was found in structural geology, seismology, petrology and isotope geochemistry that subduction is taking place. Observations seen as evidence for subduction include:

  1. The existence of Wadati-Benioff zones, elongated regions of high seismic activity within the crust and mantle that are explained as huge shear zones. These zones are located beneath oceanic trenches and seem to indicate a slice of crustal material is moving downward through the mantle. They form one of the best arguments for subduction.
  2. 3D models of the mantle made with seismic tomography show cold zones of sinking material exactly in the regions where plate tectonics predicts slabs of crust are subducting into the mantle.
  3. Petrologic research of rocks from mountain belts has yielded countless pressure-temperature-time paths. Paths for the axial zones of mountain belts (the metamorphic core) show many mountain chains went through a period of "deep burial". This is explained by plate tectonics (subduction followed by obduction). The existence of eclogite in many mountainbelts indicates material was "pushed" to depths far into the mantle (depths up to over 200 km are found). In plate tectonics this is explained by the slab pull force which occurs at mid-ocean ridges.
  4. The existence of major geologic shearzones (sutures) in most mountain belts. Paleomagnetic and mineralogic studies show the rocks that are now lying next to each other were originally thousands of kilometers apart. In other words: a piece of the crust is missing. Structural geology has shown these missing pieces of crust are not located directly underneath the shearzones or laterally. Instead, they seem to have moved along the sutures into the mantle (this is supported by shear indicators in the shear zones). This is again strong evidence that subduction took place and mountains form by the "continental collision" of tectonic plates.
  5. Rare earth isotope compositions of volcanic rocks that formed above subduction zones are similar to those of sediments on top of the subducting plate. If there are lateral differences in the isotope composition of sediments on subducting plates, these lateral differences are also found back in the composition of the magma that rose from the deeper part of the subduction zone.

Present day advocates

The hypothesized spreading apart of continental masses as Earth's size increases by the creation of new ocean floor material.

One prominent present day advocate of an expanding Earth is comics artist Neal Adams [27], who calls his ideas "Growing Earth Theory". He believes that an Earth with half its present radius would allow the continents to fit together perfectly, completely closing both the Atlantic and Pacific oceans. Adams has made video animations that graphically illustrate his hypothesis. His divergence from older versions of Expanded Earth is his proposed mechanism of expansion, in which new mass is created by some sort of electron/positron pair production within the core of the Earth.[28][29][30]

Some additional current advocates[31] of similar hypotheses are James Maxlow,[32][33][34] Stavros Tassos,[35] Weijermars,[36] Michihei,[37] Scalera,[38] and Edwards.[39]

See also

References

  1. ^ McElhinney, M. W., Taylor, S. R., and Stevenson, D. J. (1978), "Limits to the expansion of Earth, Moon, Mars, and Mercury and to changes in the gravitational constant", Nature, 271: 316–321{{citation}}: CS1 maint: multiple names: authors list (link)
  2. ^ Williams, G.E. (2000), "Geological constraints on the Precambrian history of the Earth's rotation and the moon's orbit", Reviews of Geophysics, 38 (1): 37–59 {{citation}}: Cite has empty unknown parameter: |1= (help); External link in |title= (help)
  3. ^ Herbert, Sandra (1991), "Charles Darwin as a prospective geological author", British Journal for the History of Science, no. 24, pp. 184–188, retrieved 2008-10-24
  4. ^ Mantovani, R. (1889), "Les fractures de l'écorce terrestre et la théorie de Laplace", Bull. Soc. Sc. et Arts Réunion: 41–53
  5. ^ Mantovani, R. (1909), "L'Antarctide", Je m’instruis. La science pour tous, 38: 595–597
  6. ^ Wegener, A. (1929/1966), The Origin of Continents and Oceans, Courier Dover Publications, ISBN 0486617084 {{citation}}: Check date values in: |year= (help) See Online version in German.
  7. ^ Hohl, R. (1970), "Geotektonische Hypothesen", Die Entwicklungsgeschichte der Erde. Brockhaus Nachschlagewerk Geologie mit einem ABC der Geologie, Bd. 1: 279–321 {{citation}}: Unknown parameter |Auflage= ignored (|edition= suggested) (help)
  8. ^ Lindemann, B. (1927), Kettengebirge, kontinentale Zerspaltung und Erdexpansion, Jena{{citation}}: CS1 maint: location missing publisher (link)
  9. ^ Halm, J.K.E. (1935), "An astronomical aspect of the evolution of the earth", Astron. Soc. S. Afr., 4 (1): 1–28 {{citation}}: Cite has empty unknown parameter: |1= (help)
  10. ^ Egyed, L. (1956), "The change of the Earth's dimensions determined from palaeo-geographical data", Geofisica Pura e Applicata, 33: 42–48
  11. ^ a b Egyed, L. (1969), Physik der festen Erde, Budapest: Akadémiai Kiadó
  12. ^ Owen, H.G. (1983), Atlas of continental displacement, Cambridge: Cambridge University Press
  13. ^ a b c d Owen, H.G. (1983), "The Earth is expanding and we don't know why", New Scientist, 22: 27–29
  14. ^ Stewart, A.D. (1978), "Limits to palaeogravity since the late Precambrian", Nature, 271: 153–158
  15. ^ Stewart, A.D. (1983), "Quantitative limits to the palaeoradius of the Earth", in Carey, S.W. (ed.), Expanding Earth Symposium, University of Tasmania, pp. 305–319
  16. ^ Yarkovsky, Ivan Osipovich (1888), Hypothese cinetique de la Gravitation universelle et connexion avec la formation des elements chimiques, Moskau{{citation}}: CS1 maint: location missing publisher (link)
  17. ^ Hilgenberg, O.C. (1933), Vom wachsenden Erdball, Berlin: Giessmann & Bartsch
  18. ^ Hilgenberg, O.C. (1974), "Geotektonik, neuartig gesehen", Geotektonische Forschungen, 45: 1–194
  19. ^ Carey, S. W. (1956), "The tectonic approach to continental drift", Continental Drift – A Symposium, Hobart: 177–363
  20. ^ Carey, S. W. (1988), Theories of the earth and universe: a history of dogma in the earth sciences, Stanford University Press, ISBN 0-8047-1364-2
  21. ^ a b c d e Carey, S. W. (1997), Earth, Universe, Cosmos, Hobart: University of Tasmania {{citation}}: External link in |title= (help)
  22. ^ Jordan, P. (1971), The expanding earth: some consequences of Dirac's gravitation hypothesis, Oxford: Pergamon Press
  23. ^ Born, M. (1964/2003), Die Relativitätstheorie Einsteins (Einstein's theory of relativity), Berlin-Heidelberg-New York: Springer-publisher, ISBN 3-540-00470-X {{citation}}: Check date values in: |year= (help)
  24. ^ Tesla, N. (1935), Expanding Sun Will Explode Someday Tesla Predicts, New York: New York Herald Tribune
  25. ^ Vogel, K. (1983), Carey, S.W. (ed.), "Global models and Earth expansion", Expanding Earth Symposium=38, University of Tasmania: 17–27
  26. ^ Bailey, P.K & Stewart, A.D. (1983), "Problems of ocean water accumulation on a rapidly expanding Earth", in Carey, S.W. (ed.), Expanding Earth Symposium, University of Tasmania{{citation}}: CS1 maint: multiple names: authors list (link)
  27. ^ Neal Adams' New Model of the Universe
  28. ^ "New Model of the Universe". Neal Adams. Retrieved 2008-06-02.
  29. ^ "Video clip of continental matching". Continuity Studios. Retrieved 2008-06-02. {{cite web}}: External link in |publisher= (help)
  30. ^ O'Brien, Jeffrey (2001). "Master of the Universe". Wired (9.03). Retrieved 2008-06-02. {{cite journal}}: Unknown parameter |month= ignored (help)
  31. ^ Growing Earth Consortium
  32. ^ Malte C. Ebacha nd Raymond S. Tangney, eds. Biogeography in a Changing World.; CRC, 2006. p. 191. ISBN-10: 0849380383, ISBN: 978-0849380389.
  33. ^ James Maxlow; Terra Non Firma Earth; One Off Publishing; ISBN 0952260328.
  34. ^ James Maxlow's Global Expansion Tectonics. Primary source.
  35. ^ Excess Mass Stress Tectonics (EMST}: An outline of the hypothesis.; Stavros T. Tassos, Institute of Geodynamics, National Observatory of Athens.
  36. ^ Weijermars, R. (1986), "Slow but not fast global expansion may explain the surface dichotomy of Earth", Physics of the Earth and Planetary Interiors, 43: 67–89
  37. ^ Michihei, Hoshino (1998), The Expanding Earth evidence, causes and effects, Kanagawa/Japan: Tokai University Press, ISBN 4-486-03139-3
  38. ^ Scalera, G. and Jacob, K.-H., ed. (2003), Why expanding Earth? – A book in honour of O.C. Hilgenberg, Rom: INGV{{citation}}: CS1 maint: multiple names: editors list (link)
  39. ^ Edwards, M. (2006), "Graviton decay without decreasing G: a possible cause of planetary heating, expansion and evolution", Annals of geophysics, 49: 501–509 See online Chapter 12

Historical:

Contemporary:

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