Historical Hilgenberg globesPotential reconstruction of continents bordering the Atlantic (left column) and Pacific (right column) oceans as they might have appeared at different points, going back in history, using the expanding Earth hypothesis, based on reconstructions by expanding Earth proponent Neal Adams
The expanding Earth or growing Earthhypothesis was a hypothesis arguing that the position and relative movement of continents is due at least partially to the volume of Earth increasing. Conversely, geophysical global cooling was the hypothesis that various features could be explained by Earth contracting.
Although the hypothesis was suggested historically, since the recognition of plate tectonics during the mid 20th century, scientific consensus has rejected the idea of any significant expansion or contraction of Earth.[2][3][4][5][6]
Different forms of the hypothesis
Expansion with constant mass
In 1834, during the second voyage of HMS Beagle, Charles Darwin investigated stepped plains featuring raised beaches in Patagonia which indicated to him that a huge area of South America had been "uplifted to its present height by a succession of elevations which acted over the whole of this space with nearly an equal force". While his mentor Charles Lyell had suggested forces acting near the crust on smaller areas, Darwin hypothesized that uplift at this continental scale required "the gradual expansion of some central mass" [of the Earth] "acting by intervals on the outer crust" with the "elevations being concentric with form of globe (or certainly nearly so)". In 1835 he extended this concept to include the Andes Mountains as part of a curved enlargement of the Earth's crust due to "the action of one connected force". Not long afterwards, he abandoned this idea and proposed that as the mountains rose, the ocean floor subsided, explaining the formation of coral reefs.[7]
In 1889 and 1909 Roberto Mantovani published a hypothesis of Earth expansion and continental drift. He assumed that a closed continent covered the entire surface of a smaller Earth. Thermal expansion caused 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.[8][9] Although Alfred Wegener noticed some similarities to his own hypothesis of continental drift, he did not mention Earth expansion as the cause of drift in Mantovani's hypothesis.[10]
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 Earth surpasses the cooling of Earth's exterior. Together with British geologist Arthur Holmes, Joly proposed a hypothesis in which Earth loses its heat by cyclic periods of expansion. By their hypothesis, expansion caused cracks and joints in Earth's interior that could fill with magma. This was succeeded by a cooling phase, where the magma would freeze and become solid rock again, causing Earth to shrink.[11]
After initially endorsing the idea of continental drift, Australian geologist Samuel Warren Carey advocated expansion from the 1950s (before the idea of plate tectonics was generally accepted) to his death,[17] alleging that subduction and other events could not balance the sea-floor spreading at oceanic ridges, and describing yet unresolved paradoxes that continue to plague plate tectonics.[18] Starting in 1956, he proposed some sort of mass increase in the planets and said that a final solution to the problem is only possible by cosmological processes associated with the expansion of the universe.[19]
Bruce Heezen initially interpreted his work on the mid-Atlantic ridge as confirming S. Warren Carey's Expanding Earth Theory, but later ended his endorsement, finally convinced by the data and analysis of his assistant, Marie Tharp.[20][21] The remaining proponents after the 1970s, like the Australian geologist James Maxlow, are mainly inspired by Carey's ideas.[17][22]
To date no scientific mechanism of action has been proposed for this addition of new mass. Although the earth is constantly acquiring mass through accumulation of rocks and dust from space[23] such accretion, however, is only a minuscule fraction of the mass increase required by the growing earth hypothesis.
Decrease of the gravitational constant
Paul Dirac suggested in 1938 that the universal gravitational constant had decreased during the billions of years of its existence. This caused German physicist Pascual Jordan to propose in 1964, a modification of the theory of general relativity, that all planets slowly expand. This explanation is considered a viable hypothesis within the context of physics.[24]
Measurements of a possible variation of the gravitational constant showed an upper limit for a relative change of 5×10−12 per year, excluding Jordan's idea.[25]
Formation from a gas giant
According to the hypothesis of J. Marvin Herndon (2005, 2013) the Earth originated in its protoplanetary stage from a Jupiter-like gas giant. During the development phases of the young Sun, which resembled those of a T Tauri star, the dense atmosphere of the gas giant was stripped off by infrared eruptions from the sun. The remnant was a rocky planet. Due to the loss of pressure from its atmosphere it would have begun a progressive decompression. Herndon regards the energy released due to the lack of compression as a primary energy source for geotectonic activity, to which some energy from radioactive decomposition processes was added. He terms the resulting changes in the course of Earth's history by the name of his theory Whole-Earth Decompression Dynamics. He considered seafloor spreading at divergent plate boundaries as an effect of it.[26] In his opinion mantle convection as used as a concept in the theory of plate tectonics is physically impossible. His theory includes the effect of solar wind (geomagnetic storms) as cause for the reversals of the Earth magnetic field. The question of mass increase is not addressed.[26][27]
Main arguments against Earth expansion
The hypothesis had never developed a plausible and verifiable mechanism of action.[17] During the 1960s, the theory of plate tectonics— based initially on the assumption that Earth's size remains constant, and relating the subduction zones to burying of lithosphere at a scale comparable to seafloor spreading[17]—became the accepted explanation in the Earth Sciences.
The scientific community finds that significant evidence contradicts the Expanding Earth theory, and that the evidence used for it is explained better by plate tectonics:
Measurements with modern high-precision geodetic techniques and modeling of the measurements by the horizontal motions of independent rigid plates at the surface of a globe of free radius, were proposed as evidence that Earth is not currently increasing in size to within a measurement accuracy of 0.2mm per year.[2] The main author of the study stated "Our study provides an independent confirmation that the solid Earth is not getting larger at present, within current measurement uncertainties".[28]
The motions of tectonic plates and subduction zones measured by a large range of geological, geodetic and geophysical techniques helps verify plate tectonics.[29][4][30]
Imaging of lithosphere fragments within the mantle is evidence for lithosphere consumption by subduction.[4][30]
Paleomagnetic data has been used to calculate that the radius of Earth 400 million years ago was 102 ± 2.8 percent of the present radius.[31][6]
Examinations of data from the Paleozoic and Earth's moment of inertia suggest that there has not been any significant change of Earth's radius during the last 620 million years.[3]
1 2 3 Bucher, K. (2005), "Blueschists, eclogites, and decompression assemblages of the Zermatt-Saas ophiolite: High-pressure metamorphism of subducted Tethys lithosphere", American Mineralogist, 90 (5–6): 821–835, Bibcode:2005AmMin..90..821B, doi:10.2138/am.2005.1718, S2CID129874595
↑ Mantovani, R. (1889), "Les fractures de l'écorce terrestre et la théorie de Laplace", Bulletin de la Société des Sciences et Arts de l'Île de la Réunion: 41–53
↑ Mantovani, R. (1909), "L'Antarctide", Je M'instruis. La Science Pour Tous, 38: 595–597
↑ Hohl, R. (1970), "Geotektonische Hypothesen", Die Entwicklungsgeschichte der Erde. Brockhaus Nachschlagewerk Geologie mit Einem ABC der Geologie, Bd. 1 (4.ed.): 279–321
↑ Yarkovsky, Ivan Osipovich (1888), Hypothèse cinétique de la Gravitation universelle et la connexion avec la formation des éléments chimiques, Moscow{{citation}}: CS1 maint: location missing publisher (link)
↑ Oreskes, Naomi, 2003, Plate Tectonics: An Insider's History of the Modern Theory of the Earth, Westview Press, p. 23, ISBN0813341329
↑ Frankel, Henry, The Continental Drift Debate, Ch. 7 in Scientific controversies, p. 226, 1987, Cambridge University Press, ISBN978-0-521-27560-6
↑ Wills, Matthew (8 October 2016). "The Mother of Ocean Floor Cartography". JSTOR. Retrieved 14 October 2016. 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.
↑ Jordan, P. (1971), The expanding earth: some consequences of Dirac's gravitation hypothesis, Oxford: Pergamon Press, Bibcode:1971eesc.book.....J
↑ Born, M. (2003) [1964], Die Relativitätstheorie Einsteins (Einstein's theory of relativity), Berlin-Heidelberg-New York: Springer-publisher, ISBN978-3-540-00470-7
↑ Herndon, J. Marvin (4 July 2013). "A New Basis of Geoscience: Whole-Earth Decompression Dynamics". NCGT Journal. Cornell University Physics. arXiv:1307.1692.
↑ McElhinney, M. W.; Taylor, S. R. & Stevenson, D. J. (1978), "Limits to the expansion of Earth, Moon, Mars, and Mercury and to changes in the gravitational constant", Nature, 271 (5643): 316–321, Bibcode:1978Natur.271..316M, doi:10.1038/271316a0, S2CID4258162
Bibliography
Carey, S.W.; 1976: "The Expanding Earth", Developments in Geotectonics (10), Elsevier, ISBN0-444-41485-1; digital edition 2013: ASIN B01E3II6VY.
Carey, S.W.;1988: "Theories of the Earth and Universe: A History of Dogma in the Earth Sciences", Stanford University Press, ISBN0-804-71364-2.
Continental drift is the hypothesis, originating in the early 20th century, that Earth's continents move or drift relative to each other over geologic time. The hypothesis of continental drift has since been validated and incorporated into the science of plate tectonics, which studies the movement of the continents as they ride on plates of the Earth's lithosphere.
Plate tectonics is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since about 3.4billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid-to-late 1960s.
Orogeny is a mountain-building process that takes place at a convergent plate margin when plate motion compresses the margin. An orogenic belt or orogen develops as the compressed plate crumples and is uplifted to form one or more mountain ranges. This involves a series of geological processes collectively called orogenesis. These include both structural deformation of existing continental crust and the creation of new continental crust through volcanism. Magma rising in the orogen carries less dense material upwards while leaving more dense material behind, resulting in compositional differentiation of Earth's lithosphere. A synorogenic process or event is one that occurs during an orogeny.
Seafloor spreading, or seafloor spread, is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
A lithosphere is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time scales of up to thousands of years or more. The crust and upper mantle are distinguished on the basis of chemistry and mineralogy.
Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year.
A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subduction zone. A transform fault is a special case of a strike-slip fault that also forms a plate boundary.
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts, which eventually become rift valleys. Most active divergent plate boundaries occur between oceanic plates and exist as mid-oceanic ridges.
Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone. They are the principal way by which continental growth is achieved.
Tectonophysics, a branch of geophysics, is the study of the physical processes that underlie tectonic deformation. This includes measurement or calculation of the stress- and strain fields on Earth’s surface and the rheologies of the crust, mantle, lithosphere and asthenosphere.
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.
Samuel Warren Carey AO was an Australian geologist and a professor at the University of Tasmania. He was an early advocate of the theory of continental drift. His work on plate tectonics reconstructions led him to develop the Expanding Earth hypothesis.
Antonio Snider-Pellegrini (1802–1885) was a French geographer and scientist who theorized about the possibility of continental drift, anticipating Wegener's theories concerning Pangaea by several decades.
Roberto Mantovani, was an Italian geologist and violinist. He proposed an early model of continental drift in which an original single continent was split apart and the continents resulting displaced by thermal expansion and volcanism.
László Egyed was a Hungarian geophysicist who published over 100 scientific articles. In 1956 he wrote the book Physics of the solid earth, which was reworked and republished in 1969.
The evolution of tectonophysics is closely linked to the history of the continental drift and plate tectonics hypotheses. The continental drift/ Airy-Heiskanen isostasy hypothesis had many flaws and scarce data. The fixist/ Pratt-Hayford isostasy, the contracting Earth and the expanding Earth concepts had many flaws as well.
The evolution of tectonophysics is closely linked to the history of the continental drift and plate tectonics hypotheses. The continental drift/ Airy-Heiskanen isostasy hypothesis had many flaws and scarce data. The fixist/ Pratt-Hayford isostasy, the contracting Earth and the expanding Earth concepts had many flaws as well.
Ridge push is a proposed driving force for plate motion in plate tectonics that occurs at mid-ocean ridges as the result of the rigid lithosphere sliding down the hot, raised asthenosphere below mid-ocean ridges. Although it is called ridge push, the term is somewhat misleading; it is actually a body force that acts throughout an ocean plate, not just at the ridge, as a result of gravitational pull. The name comes from earlier models of plate tectonics in which ridge push was primarily ascribed to upwelling magma at mid-ocean ridges pushing or wedging the plates apart.
The plate theory is a model of volcanism that attributes all volcanic activity on Earth, even that which appears superficially to be anomalous, to the operation of plate tectonics. According to the plate theory, the principal cause of volcanism is extension of the lithosphere. Extension of the lithosphere is a function of the lithospheric stress field. The global distribution of volcanic activity at a given time reflects the contemporaneous lithospheric stress field, and changes in the spatial and temporal distribution of volcanoes reflect changes in the stress field. The main factors governing the evolution of the stress field are:
Changes in the configuration of plate boundaries.
Vertical motions.
Thermal contraction.
Intraplate volcanism is volcanism that takes place away from the margins of tectonic plates. Most volcanic activity takes place on plate margins, and there is broad consensus among geologists that this activity is explained well by the theory of plate tectonics. However, the origins of volcanic activity within plates remains controversial.
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