Expansion theory

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Graphic representation of the earth's expansion: the increase in the size of the planet over the course of earth's history (from bottom to top) and the emergence of the current configuration of the continents. Left: Western hemisphere with the opening of the Atlantic . Right: Eastern hemisphere with opening of the Pacific .

The expansion theory of the earth (also known as the expansion hypothesis) is a geotectonic theory developed towards the end of the 19th century and discussed especially in the 1950s and 1960s and is now obsolete . In its more modern version, it tries to explain the continental drift postulated by Alfred Wegener , above all the breakup of the supercontinent Pangea , by a constant increase in the earth's radius . The most important representatives are the German geoscientist Ott Christoph Hilgenberg , the Hungarian geophysicist László Egyed and the Australian geologist Samuel Warren Carey .

The theory is no longer represented in the scientific and academic environment since plate tectonics can explain continental drift on the basis of convection currents in the earth's mantle . Measurements of the earth's body show that no expansion is currently taking place.

History and attempts at justification

As the coming to opposite conclusions contraction theory is the expanding earth an early attempt of Paleogeography trace the history of the earth. Findings about geological basins, uplifts and subsidence gave reason to want to understand geodynamic processes . The need for explanation arose when similar rock complexes were found on both sides of the Atlantic Ocean and similar living and extinct animals and plants were found. These findings, as well as the fact that the coastlines on both sides of the Atlantic fit together, prompted Alfred Wegener to develop the theory of continental drift . Fossils of marine animals have also been found in mountains at high altitudes. The latter indicates vertical movements of parts of the earth's crust .

Expansion at constant mass

Roberto Mantovani published a theory of earth expansion in 1889 and 1909. He assumed that a closed continent covered the entire surface of what was then a much smaller earth. This was said to have broken apart due to volcanic activity due to thermal expansion , whereby the fragments from which today's continents emerged moved further and further apart, as the erosion zones expanded further and further and now form the area of ​​the oceans.

The newly discovered radioactivity was proposed as the mechanism of this expansion shortly after the turn of the 20th century : The "theory of thermal cycles" by John Joly and Arthur Holmes also represents a compromise between earth expansion and earth contraction. By an excess of internal heat production , that is, if more heat is produced through radioactive decay than is lost through natural cooling , a kind of heat build-up occurs. It was believed that the rise in temperature caused the earth's body to expand, creating crevices in the earth's crust. Magma pushes in these fissures and partially reaches the surface of the earth as lava . As a result of the associated increased heat dissipation, a phase of cooling and shrinking would occur after the phase of warming up and expansion. These phases formed a continuous sequence in the history of the earth.

In contrast, Bernhard Lindemann (1927), Jacob Karl Ernst Halm (1935), László Egyed (1956), and Hugh Gwyn Owen (1983) assumed expansion through phase transitions in the Earth's core. The core consisted of a super dense material that changes into a less dense form and expands in the process. Egyed combined his theory with a possible decrease in the gravitational constant.

The theory based on thermal expansion contradicts most modern principles of rheology . There was also no recognized explanation for the required phase transitions. As A. D. Stewart noted, a smaller earth radius with the same mass would mean that, due to the law of gravitation in the past, the force of gravity on the earth's surface would have to have been 4 times as large as it is today. That could only be reconciled with the size of the dinosaurs living at the time if it were assumed that they all lived in water. However, since there undoubtedly also existed terrestrial dinosaurs and pterosaurs , not only the volume but also the mass of the earth should have been lower earlier.

Expansion through increase in mass

Hilgenberg's globes for earth expansion

Ivan Ossipowitsch Jarkowski proposed in 1888 in connection with his mechanical explanation of gravitation a kind of absorption of the ether , which would be transformed into new chemical elements in the celestial bodies and thus cause an expansion of the celestial bodies. However, he does not mention the connection with the formation of the continents. A comprehensive work on the expansion of the earth, which was based on the increase in mass and volume due to the absorption of ether, is entitled "From the growing earth", comes from Ott Christoph Hilgenberg and appeared in 1933. Hilgenberg also tried to show that the continents can be accommodated without gaps on a globe of smaller diameter ("shelf sphere") and the ocean basins would only have formed through the expansion of the earth's body. Bruce C. Heezen interpreted the discovery of the Rift Valley in the Atlantic in 1960 as an indication of an expanding earth. Some supporters of the theory suspect an etheric effect as the cause. The emergence of new earth matter through the absorption of “ether” cannot be reconciled with modern physics, if only because there is demonstrably no “ether” in space , at least not in the original sense of the ether hypothesis. The only “matter” accepted by modern physics that comes at least halfway close to the “ether” are neutrinos , which, however, do not actually interact with the earth's matter, but simply penetrate it and which are also virtually massless.

Samuel Warren Carey

The best-known exponent of the Earth expansion model, Samuel Warren Carey , also proposed a mass increase in 1996, but restricted that a real solution to the problem could only be achieved on a cosmological level in connection with the expansion of the universe . As Carey notes, this model is at least not affected by Stewart's criticism: if, in addition to the radius, the earth's mass was also smaller in the past, these effects compensate each other and the gravity on the surface would remain at least approximately constant and would not decrease. If the increase in mass were greater than the increase in radius, the force of gravity would even have increased to this day, and the enormous size of some dinosaurs, according to Carey, could easily be explained by a lower gravity at the time.

According to calculations by NASA, about 100 tons of meteorites enter the earth's atmosphere every day. Most of it burns up in the atmosphere and partly goes down as dust. Such accretion , however, is considered a very small fraction of the mass increase required by the expanding earth hypothesis.

Decrease in the gravitational constant

This hypothesis was based on the assumption of Paul Dirac (around 1938) that the value of the gravitational constant has decreased continuously since the creation of the universe and therefore also since the creation of the solar system and the earth. This led Pascual Jordan to postulate an expansion of all planets in the solar system in 1964 . In contrast to the other explanatory models, this hypothesis was classified as entirely possible, at least in the context of physics . Max Born describes Jordan's modification of the gravitational hypothesis as a “systematic generalization” of Einstein's general theory of relativity .

This hypothesis, like constant mass theories, causes problems of explanation for the existence of dinosaurs. The force of gravity on the surface would be much greater than it is today not only because of the smaller radius, but also because of the higher gravitational constant, and here, too, some species of dinosaur would have collapsed under their own body weight. The main objection to this theory is that recent measurements of a possible variation in the gravitational constant have given an upper limit for a relative change of only 5 · 10 −12 . That is a value 10 times less than what Jordan needs for his theory.

More modern versions of the expansion theory

A younger generation of expansionists, including the British geophysicist Hugh G. Owen and the Italian geophysicist Giancarlo Scalera, are recognizing the evidence for the existence of plate movements and, in particular, the concept of subduction, which has been gathered over the decades since the theory of plate tectonics was formulated oceanic lithosphere (see below ). Instead, they argue, based on alleged weaknesses of the plate tectonics theory, that despite subduction an expansion of the earth took place. In a 1984 New Scientist article, Owen focuses primarily on the fit of the passive continental margins. South America and Africa, and even more so the edges of the Indian Ocean, can only be perfectly joined on a globe that is smaller than today's earth. In doing so, he ignores the widely accepted view at the time that the Indian Ocean is the successor to the Tethys Basin, which was completely subducted during India's northern drift. Giancarlo Scalera argues, among other things, with the help of inconsistencies in the concept of subduction, which would result from seismic investigations of the sublithospheric mantle on and in the vicinity of subduction zones. He states that subduction does take place, but to the extent that it would be necessary on an earth of constant size, due to the physical conditions in the earth's mantle, it is not possible. Like their predecessors, neither Owen nor Scalera can name convincing causes or mechanisms for an earth expansion.

Earth expansion and large tectonics

Urcontinent

After the earth was formed, a supercontinent is said to have existed that practically completely covered the surface of the earth, although the earlier existence of the Palaeotethys is ignored. Due to the increase in the earth's volume, the earth's crust was torn open at its weakest points, where the oceans now lie, and so led to the formation of continents . As in the established theory of plate tectonics, new ocean floors are created by spreading the ocean floor at the mid-ocean ridges . In the original version of the expansion theory, as advocated by Hilgenberg or Carey, there is no compensation through the process of subduction , through which old crust sinks, thus compensating for the formation of new crust and making a constant radius possible. More modern expansionists accept the concept of subduction and associate it with expansion theory.

Shape of the continents

The main argument for the earth's expansion is that if one mentally reduced the earth's radius so that today's ocean basins closed, the continents supposedly matched each other better, taking into account their greater curvature, than in the reconstructions of the Wegener's primary continent Pangea with a constant radius is the case. Most representatives assume an ideal radius of approx. 50–60% of today's value in the Mesozoic era 250 million years ago. There is agreement that the formation of the mid-ocean ridges began towards the end of the Permian or in the Mesozoic Era, including in the Pacific Ocean. Therefore, in contrast to the theory of plate tectonics, a correspondence of the contours of the opposite Pacific coasts is postulated, for which various models have been proposed. The more modern expansionists, who do not postulate the same period for the emergence of the Atlantic and Pacific, are an exception here.

Mountain formations

Following some models by German and Italian geologists of the 19th century, Carey explains the mountain formation as a result of the ascent of lighter rock areas ( diapir ) due to the interplay of gravity , thermal expansion and phase transitions . In contrast, the theory of plate tectonics explains the formation of fold mountains with the accumulation of material in the collision zone of two continental blocks during the final phase of plate convergence (see →  subduction ). Among other things, the existence of tectonic nappes and entire nappe complexes speaks in favor of plate tectonics , especially in the geologically young fold mountains. Such ceilings are created when, as a result of the accumulation of material, the upper areas of the earth's crust are stacked on top of one another along approximately horizontal shear surfaces. Such structures are not compatible with simple diapirism.

Formation of the ocean basins or floors

Stewart stated that if the earth's radius were reduced by half, the entire surface of the earth would be covered by an ocean with a depth of at least 8 km, provided that the amount of water corresponded to the current value. During the expansion, the continents emerged from this primordial ocean, with the water collecting in the rupture or expansion zones that form today's ocean basins. Carey, on the other hand, denied the existence of a world-wide primeval ocean and instead suggested that the water outgassed from the corresponding lava when the ocean floors formed and that it was added to the water of the primeval ocean. The oceanic crust is much younger compared to the continental crust . The oldest oceanic crust in today's sea basins is around 280 million years old (Permian), whereas the oldest known continental crust is around 4 billion years old. While the classical expansion theory explains the age differences with the fact that only the continental crust corresponds to the crust of the primordial earth and the ocean basins are the result of the earth's expansion, the theory of plate tectonics explains the low age of the oceanic crust as the result of a cycle between new formation and subduction, which it has probably been around for at least 3.8 billion years. Compared to the classical expansion theory, a plate tectonic interpretation of these facts does not give rise to an additional need to explain that, despite an Earth's age of around 4 billion years, the formation of today's ocean floors only began around 300 million years ago, nor for that in contrast to the Atlantic The continental margins of the Pacific basin that do not really fit together well, the asymmetry of the Pacific basin (cf. →  East Pacific Ridge ) and the existence of the Pacific ring of fire . According to plate tectonic reconstructions, the Pacific Basin is roughly twice as old as the Atlantic Basin and its edges have changed significantly over the course of the Earth's history (see also →  Panthalassa ). The more modern supporters of the expansion theory also recognize this.

Speed ​​of expansion

Some like Jordan or Egyed assumed a steady, slow expansion. Egyed stated the annual increase in the earth's radius by about 0.5 to 1 mm, with the expansion already beginning when the earth was formed. A consistently low rate of expansion, however, contradicts the relatively rapid drift of the continents, which has been proven to have taken place since the turn of the Triassic Jurassic approx. 200 million years ago when Pangea began to break up. That is why less orthodox proponents of expansion also include subduction in their models, which is supposed to guarantee a steady, slow expansion with relatively rapid continental drift. Carey, on the other hand, completely rejects subduction and therefore assumes a rapid expansion. The question arises, however, why the Pangea only broke up in the Mesozoic Era and what happened in the billions of years before. He therefore supplemented his hypothesis with the assumption that the expansion was relatively slow at the beginning, but that the rate of expansion increased exponentially over time . However, he was unable to give a reason for this acceleration.

Main arguments against earth expansion

Since 1970, a large body of evidence has been found in structural geology , seismology , petrology, and isotope geochemistry that the process of subduction is actually taking place. Although this does not exclude an expansion in principle, it makes a constancy of the earth's radius much more likely. Observations that are considered convincing evidence for the subduction are as follows:

  • The existence of the Wadati-Benioff zones , which are formed by the plunging plates during subduction.
  • 3D models of the earth's mantle created by seismic tomography show cold zones of sinking material precisely in the regions in which plate tectonics predicts the sinking of the earth's crust into the earth's mantle .
  • Petrological research into rocks from mountain ranges shows that these often come from very deep places, whereby this vertical movement can be explained by the interplay of subduction and autopsy . The existence of eclogite in mountains shows that rock was pushed deep into the earth's mantle, which can be explained by the so-called "slab-pull" force in the mid-ocean ridges in the context of plate tectonics.
  • The existence of large shear zones ( suture ) in most of the mountain ranges. Paleomagnetic and mineralogical studies show that rocks lie next to each other that were originally thousands of kilometers apart. In other words, part of the crust is missing. The structural geology shows that these missing parts of the crust are not directly below the shear zones. Instead, they appear to have moved into the mantle along the suture. This is a sure sign of the existence of continental collisions and subduction.
  • Rare earth metals from volcanic rock, which are formed over subduction zones, correspond to the sediments at the top of a plate subjected to subduction.

Status of the theory

Although still represented by some researchers outside of the scientific mainstream, the current state of science believes that the concept of earth expansion is wrong. A current earth expansion could not be verified experimentally, nor could an acceptable mechanism to explain the expansion be established. The theory, neither the numerous processes of geodynamics nor through the different disciplines of geology (eg. As tectonics , paleomagnetism , historical geology ) collated evidence on the paleogeography of the earth and the by seismic explain determined image of the Earth's crust and upper mantle. These facts, together with the advancement of the theory of subduction , led to the disappearance of the theory from the current scientific discussion.

See also

Individual evidence

  1. ↑ a b X. Wu, X. Collilieux, Z. Altamimi, BLA Vermeersen, RS Gross, I. Fukumori: Accuracy of the International Terrestrial Reference Frame origin and Earth expansion . In: Geophysical Research Letters . tape 38 , no. 13 , July 1, 2011, ISSN  1944-8007 , p. L13304 , doi : 10.1029 / 2011GL047450 ( repository.tudelft.nl [PDF; 875 kB ]).
  2. ↑ a b NASA Research Confirms it's a Small World, After All . NASA. November 16, 2011. Retrieved June 4, 2012.
  3. ^ R. Mantovani: Les fractures de l'écorce terrestre et la théorie de Laplace . In: Bull. Soc. Sc. et Arts Réunion . 1889, p. 41-53 .
  4. ^ R. Mantovani: L'Antarctide. Je m'instruis. La science pour tous . No. 38 , September 19, 1909, pp. 595-597 .
  5. ↑ Rudolf Hohl: Geotectonic Hypotheses . In: The evolution of the earth. Brockhaus reference work geology with an ABC of geology . 4th edition. tape 1 , 1970, p. 279-321 .
  6. ^ B. Lindemann: Chain Mountains, continental splitting and earth expansion . Jena 1927.
  7. ↑ JKE Halm: An astronomical aspect of the evolution of the earth . In: Astron. Soc. S. Afr. tape 4 , no. 1 , 1935, p. 1-28 .
  8. ↑ L. Egyed: The change of the Earth's dimensions determined from palaeo-geographical data . In: Geofisica Pura e Applicata . tape 33 , 1956, pp. 42-48 .
  9. ↑ a b L. Egyed: Physics of the solid earth . Akadémiai Kiadó, Budapest 1969.
  10. ↑ HG Owen: Atlas of continental displacement . Cambridge University Press, Cambridge 1983.
  11. ^ HG Owen: Continental displacement and expansion of the earth during the Mesozoic and Cenozoic 1975
  12. ↑ a b c d e H.G. Owen: The Earth is expanding and we don't know why . In: New Scientist . tape 22 , 1983, pp. 27-29 .
  13. ↑ a b A.D. Stewart: Limits to palaeogravity since the late Precambrian . In: Nature . tape 271 , 1978, pp. 153-158 .
  14. ↑ Ivan Osipovich Yarkovsky: Hypothesis cinetique de la Gravitation universelle et connexion avec la formation des elements chimiques . Moscow 1888.
  15. ^ OC Hilgenberg: From the growing globe . Giessmann & Bartsch, Berlin 1933 ( nuclearplanet.com ).
  16. ^ OC Hilgenberg: Geotectonics, seen in a new way . In: Geotectonic Research . tape 45 , 1974, p. 1-194 .
  17. ^ Geoscience: Depth charge Nature, 2012
  18. ^ SW Carey: The tectonic approach to continental drift . In: Continental Drift - A Symposium . Hobart 1956, p. 177-363 .
  19. ^ SW Carey: Theories of the earth and universe: a history of dogma in the earth sciences . Stanford University Press, 1988, ISBN 0-8047-1364-2 .
  20. ↑ a b c d S. W. Carey: Earth, Universe, Cosmos . University of Tasmania, Hobart 1997.
  21. ^ NASA Science: What's hitting the earth?
  22. ↑ Michael Zolensky et al .: Flux of Extraterrestrial Materials
  23. ^ Alain Buis, Whitney Clavin: NASA Research Confirms it's a Small World, After All
  24. ↑ Pascual Jordan: The expansion of the earth: Conclusions from Dirac's gravitational hypothesis . Vieweg & Son, Braunschweig 1966.
  25. ^ Pascual Jordan: The expanding earth: some consequences of Dirac's gravitation hypothesis . Pergamon Press, Oxford 1971.
  26. ↑ Max Born: Einstein's theory of relativity . Ed .: Jürgen Ehlers, Markus Pössel. 7th edition. Springer, Berlin / Heidelberg / New York / Hong Kong / London / Milan / Paris / Tokyo 2003, ISBN 3-540-00470-X , doi : 10.1007 / 978-3-662-41810-9 (first edition: 1920).
  27. ^ BF Windley: Metamorphism and tectonics of the Himalaya. In: Journal of the Geological Society. 140, 1983, pp. 849-865, doi: 10.1144 / gsjgs.140.6.0849 and literature cited therein
  28. ^ A b G. Scalera .: The expanding Earth: a sound idea for the new millennium. In: G. Scalera, K.-H. Jacob (Ed.): Why expanding Earth? - A book in honor of OC Hilgenberg. Istituto Nazionale di Geofisica e Vulcanologia, Rome 2003, pp. 181-232 ( earth-prints.org ).
  29. ^ G. Scalera: TPW and Polar Motion as due to an asymmetrical Earth expansion
  30. ↑ K. Vogel: Global models and Earth expansion . In: SW Carey (Ed.): Expanding Earth Symposium . University of Tasmania, 1983, pp. 17-27 .
  31. ^ GE Williams: Geological constraints on the Precambrian history of the Earth's rotation and the moon's orbit . In: Reviews of Geophysics . tape 38 , no. 1 , 2000, pp. 37–59 ( eos.ubc.ca [PDF; 4.9 MB ]).
  32. ↑ G. Scalera, K.-H. Jacob (Ed.): Why expanding Earth? - A book in honor of OC Hilgenberg . INGV, Rome 2003.
  33. ↑ Hoshino Michihei: The Expanding Earth evidence, causes and effects . Tokai University Press, Kanagawa / Japan 1998, ISBN 4-486-03139-3 .
  34. ^ J. Marvin Herndon: Origin of mountains and primary initiation of submarine canyons: The consequences of Earth's early formation as a Jupiter-like gas giant. In: Current Science. 102, No. 10, 2012, pp. 1370–1372, ( nuclearplanet.com ; PDF; 520 kB).

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