Expanding earth theory

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 almost universally accepted theory of plate tectonics, and is considered to be discredited by mainstream geologists.

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. 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.

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History and explanations

Expansion with constant mass

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. ^{[1] [2]} 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. ^[3] 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. ^[4]

On the other hand, Lindemann (1927), ^[5] Halm (1935), ^[6] László Egyed (1956), ^{[7] [8]} and Owen (1983) ^{[9] [10]} 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 as Stewart remarked,

Expansion from half the present radius implies surface gravity g would have been four times its present value, which is at odds with the great size of the dinosaurs living at that time. ^[11]

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. ^[12] Also the system of Ott Christoph Hilgenberg (1933, 1974) is based on absorption and transformation of aether-energy into normal matter. ^{[13] [14]} The most well known proponent of the theory, 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. ^{[15] [16] [17]}

However, modern physics does not support the idea of an aether which is absorbed by matter or is transformed into new matter.

Decrease of the gravitational constant

Paul Dirac suggested in 1938 that the Earth's 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 the other explanations this one was at least within the framework of physics considered as a viable hypothesis. ^[18]

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. ^[19]

Expanding earth and subduction

Formation of the continents and oceans

  Expansion contra subduction: The main difference between the 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. Most proponents of expanding earth like Carey are denying the existence of subduction, so seafloor spreading is uncompensated which leads to earth expansion. ^[17] An exception is Owen, who combines earth-expansion with subduction. ^[10]

Shape of the continents: A Supercontinent is supposed to have existed that covered the surface of the earth practically completely. Proponents see the main argument for this model in the assumption, that if the oceans were removed and earth's radius is decreased, the continents allegedly are fitting better together than it is the case in the reconstructions of Pangaea at a constant radius. Most proponents argued that in the mesozoic 250 million years ago the earth radius was only 50-60% of the current radius. Therefore in many of these model a continental matching of the pacific facing sides is assumed. ^[20] 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. ^[10]

Mountainbuilding : Following some models of German and Italian geologists in the 19^th century, Carey explained orogeny as a consequence from the uplift of light material (Diapir) because of phase transitions, thermal expansion and gravitation. ^[17] However, in plate tectonics orogeny is explained by collisions of continental plates. An illustrative example for plate tectonics is the Indian subcontinent, which broke away from Africa, drifting for a long time in the indian ocean, and than collided with Asia causing the Himalaya to pile up.

Formation of the oceans: Stewart argues that with elimination of all oceans all continents would be drowned under 8 km of water, presupposing the same amount of water as it exists today. ^[11] 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. However, Carey denied this mechanism and proposed that the present atmosphere and hydrosphere have been outgassed from the interior during a long period. ^[17] The oldest oceanic crusts are 200 Million years old but the continental crusts are nearly 20 times older. In expanding earth theory this is explained by the assumption, that the formation of the oceans was beginning in the mesozoic. And in plate tectonics this is explained by seafloor spreading and subduction.

Rate of expansion: Some proponents like Jordan or Egyed assume constant and slow expansion. Egyed set an annual increase of earth's radius by 0,5 mm, whereby the expansion begins at the origin of earth. ^[8] However, it was criticised that such an expansion rate is much too small to explain the continental drift since the mesozoic 250 Million years ago. Therefore Owen included subduction in his model, which allows a small expansion rate but at the same time might guarantee a sufficient velocity of continental drift. ^[10] However, most of the proponents of earth expansion like Carey reject any form of subduction and therefore assume fast expansion. This leads to the question what was happening in the billions of years before the mesozoic, when Pangaea was broken. Carey modified his hypothesis by introducing the assumption that at the beginning the expansion rate was very slow, but than it increased at an exponential rate. But Carey gave no explanation for this accelerated expansion. ^[17] However, Williams (2000) alluded to examinations of earth's moment of inertia, saying that no significant change of earth's radius in the last 620 Million years could have taken place and therefore earth-expansion is untenable. ^[21]

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 greater 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.
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. It is still very hard to calculate the global rate with which material subducts. Proponents of the expanding Earth theory claim the existence of subduction does not necessarily rule out expansion of the planet, but the existence of a mechanism by which the Earth can keep its crust size constant is a significant problem for the expanding earth theory and is one of the major reasons why it was abandoned. 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.

Status of the theory

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.

The primary objection to Expanding Earth Theory centered around the lack of an accepted process by which the Earth's radius could increase. Although there are still some supporters of the theory^[22][23], this issue, along with the discovery of evidence for the process of subduction, caused the scientific community to dismiss the theory of an expanding Earth. The evidence for continental matching even on the Pacific facing sides became irrelevant, as did the claims that a smaller Earth with lower gravity facilitated the growth of dinosaurs to large sizes.

References

Other links:

• Scalera: The expanding Earth: a sound idea for the new millennium
• Neal Adams Animation collection of Expanding Earth Theory
• The Expanded Earth
• Expanding Earth / The Evidence
• Keith Wilson's Expanding Earth Knowledge Co.
• Plate Tectonics and Expanding Earth
• David Noel, Fixed-Earth and Expanding-Earth Theories -- Time for a Paradigm Shift?
• Lawrence Myers' Expanding Earth
• Growing Earth Consortium
• Video Explaining the Expanding Earth theory

See also

• Growing Earth Theory