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Expanding Earth

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

The Expanding earth theory is an attempt to explain the position and movement of continents on the surface of the Earth. It has a relatively small following today, compared with the more widely accepted theory of plate tectonics.

An expanding earth model was developed in the 1960s, building upon emerging evidence for sea floor expansion and continental drift. The expanded earth theory (and plate tectonics) incorporates the appearance of new crustal material at mid-ocean ridges, but the process of subduction is largely absent in this model.

Very few geologists or geophysicists today support the expanded Earth.[1] Many of those that remain are proponents of the ideas of the late Australian geologist S. Warren Carey. While Carey's ideas were popular for a time in the 1950s and 1960s, most workers in earth science believe that evidence collected over the last several decades supports a fixed size Earth, due to subduction, over the expanded Earth.[who?]

History and explanations

In 1888[2] 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.[3] In 1889[4] and 1909[5] Roberto Mantovani published another variant of the theory which is based on thermal expansion. Alfred Wegener saw similarities to his own theory:

In 1909, Mantovani drew some maps illustrating his ideas on continental displacements. His ideas are in some aspects different but in others astonishingly coinciding with mine. For instance, this was the case of the ancient grouping of the southern continents around austral Africa.[6]

However, Wegener didn't mention earth-expansion as the cause of the drift in Mantovani's theory.

Gravitational constant

The idea of an expanding Earth entered into mainstream science around 1938, when the physicist Paul Dirac (1902–1984) suggested the Earth's gravitational constant had decreased in the billions of years of its existence. This led German physicist Pascual Jordan[7] to a modification of general relativity and to propose in 1964 that all planets slowly expand.[8] Jordan thought the Earth might have doubled its radius in the last few hundred million years. However, recent measurments of a possible variation of the gravitational constant showed an upper limit for a relative change of 5·10-12. But Jordan's theory needs a variation which is ten times higher than measured.[9]

Mass creation

German geologist Ott Christoph Hilgenberg examined phase transitions of minerals in rocks with the intention to explain the presumed expansion of the Earth. Like Yarkovsky, his system is based on absorption and transformation of aether-energy into normal matter, similar to absorption in Le Sage's theory of gravitation. Contrary to the theory of Jordan, this implies a smaller gravity of the past, which might (according to proponents like Scalera[10]) also explain the size of the dinosaurs. The most well known proponent of the theory, S. Warren Carey, also proposed some sort of mass increase in planets. However, any form of (unexplained) creation of new matter from some sort of (unexplained) aether is not consistent with modern physics.

Thermal expansion

Similar to Mantovini, Irish physicist John Joly explained the Earth's expansion by heating. Of course this would mean that heat flow from radioactive decay inside the Earth had to surpass 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, when the magma freezes and becomes solid rock again, causing the Earth to shrink. The theory is in contradiction with most modern principles from rheology and is thus considered superseded.

Status of the theory

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After the paradigm shift in geology and geophysics in the fifties and sixties the idea of continental drift became accepted by the scientific community because of the development of the plate tectonic theory. The consensus that continents are rigidly fixed to the Earth's interior (fixism) was changed for the idea that the crust is divided into tectonic plates that move over a mechanically weak asthenosphere (mobilism). Plate tectonics provided a model for mobilism. However, Australian geologist Samuel W. Carey argued that mobilism can be explained by an expanding Earth too. In 1957, Hungarian geophysicist László Egyed (1914–1970) calculated that in the Cambrian (about 500 million years ago) all continents were stuck together, after which the expansion of the Earth led to the formation of oceans by oceanic spreading.

The primary objection to Expanding Earth Theory centered around the lack of a accepted process by which the Earth's radius could increase. This issue, along with the discovery of evidence for the process of subduction, caused the scientific community to dismiss the geological evidence Carey and others presented. The evidence for continental matching even on the Pacific facing sides became irrelevant, as did the claims that a smaller sized and lower gravity Earth facilitated the growth of dinosaurs to their relatively enormous size.

Subduction

The main difference between an expanding Earth model and a model in which the volume of the Earth remains 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.

Arguments against subduction

Expanding Earth Theory challenges the existence, or at least the extent, of subduction in global tectonic theory. Exponents 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. There is no agreed mechanism for such a correlation between the two processes.

  1. The mid-ocean ridges are considerably more vast in length and area than the known subduction zones and circle the entire globe in several configurations. Proponents of an expanding Earth argue that in order for the crustal material appearing there to subduct equally into the known zones, some evidence of a bottle-neck pile-up of oceanic crust should be visible nearing these subduction zones. Yet the entire ocean floor is smoothly surfaced, free of oceanic slab irregularities, indicating harmonious spreading unencumbered by such a process. Back-arc basins associated with subduction zones are not predicted or explained by subduction plate tectonics.
  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) no such evidence is visible. However, this is explained in plate tectonics by the assumption that in some cases, the direction of subduction changes.

Arguments for subduction

Since the 1970s, a vast amount of evidence was found in structural geology, seismology, petrology and isotope geochemistry that subduction is at least to some extent taking place. A problem is that it is still very hard to calculate the global rate with which material subducts, so the existence of subduction does not absolutely rule out expansion of the planet. The existence of a mechanism by which the Earth can reduce her size does, however, make expansion less likely. 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 but cannot be explained by an expanding Earth model.
  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 nicely explained by plate tectonics (subduction followed by obduction). An expanding Earth cannot explain the observed vertical motions, rather, it would predict mostly horizontal motions in the process of mountainbuilding. 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). A mechanical force to push (less dense) crustal rocks to these depths is lacking in an expanding Earth model; 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 mountians form by the "continental collision" of tectonic plates. The expanding Earth model does not explain these deep reaching shearzones.
  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.

Endnotes

  1. ^ Scalera et al., 2003
  2. ^ Yarkovsky, 1888
  3. ^ Drude, 1897
  4. ^ Mantovani, 1889
  5. ^ Mantovani, 1909
  6. ^ Scalera et al., 2003, pp. 71-74
  7. ^ Jordan, 1971
  8. ^ Born, 1964/2003, pp. 319-320
  9. ^ Born, 1964/2003, p. 489
  10. ^ Scalera et al. pp. 220-224

References

  • Yarkovsky, Ivan Osipovich (1888), Hypothese cinetique de la Gravitation universelle et connexion avec la formation des elements chimiques, Moscow{{citation}}: CS1 maint: location missing publisher (link)
  • Mantovani, R. (1889), "Les fractures de l'écorce terrestre et la théorie de Laplace", Bull. Soc. Sc. et Arts Réunion: 41–53
  • Drude, Paul (1897), "Ueber Fernewirkungen", Beilage zu den Annalen der Physik und Chemie, Neue Folge, Heft 1, 62: I–XLIX
  • Mantovani, R. (1909), L’Antarctide. Je m’instruis. La science pour tous, n°38, 19 sept., pp. 595–597
  • Hilgenberg, O.C. (1933), Vom wachsenden Erdball (The expanding Earth), Berlin: Giessmann & Bartsch
  • Born, M. (1964/2003), Die Relativitätstheorie Einsteins (Einstein’s Theory of Relativity), Berlin-Heidelberg-New York: Springer-Verlag, ISBN 3-540-00470-x {{citation}}: Check |isbn= value: invalid character (help); Check date values in: |year= (help)
  • Jordan, Pascual (1971), The expanding earth: some consequences of Dirac's gravitation hypothesis, Pergamon Press {{citation}}: Text "place: Oxford" ignored (help)
  • Carey, Samuel Warren (1988), Theories of the earth and universe: a history of dogma in the earth sciences, Stanford University Press, ISBN 0-8047-1364-2
  • Michihei, Hoshino (1998), The Expanding Earth evidence, causes and effects, Kanagawa, JAPAN: Tokai University Press, ISBN 4-486-03139-3
  • Scalera, G. and Jacob, K.-H., ed. (2003), Why expanding Earth? – A book in honour of O.C. Hilgenberg, Rome: INGV{{citation}}: CS1 maint: multiple names: editors list (link)

Historical links:

Other links:

See also

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