The Expanding Earth theory
is an attempt to explain the position and movement of continents
) on the surface of the Earth. 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. In this model the continents drifted away from each other because of further expansion at the rip-zones, where oceans currently lie. The result is an increasing radius of the earth.
The theory 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. 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.
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.
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.
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.
On the other hand, Lindemann (1927),
László Egyed (1956),
and Owen (1983)
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.
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
. 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.
The most well known proponent of expanding earth 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.
Decrease of the gravitational constant
suggested in 1938 that the universal gravitational constant
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.
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.
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."
Expanding Earth concepts
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.
Formation of the continents and oceans
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. An exception is Owen, who combines Earth expansion with subduction.
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.
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.
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. 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. 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. The oldest oceanic crusts are 200 million years old, but the continental crusts are nearly 20 times older. To explain this fact, expanding Earth theory proposes 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. 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. 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.
Arguments against subduction
The expanding Earth theory questions 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 superficially appears unlikely, but would be required by conservation of mass
under the assumption that the Earth is not lessening in density.
- 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.
- 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.
Rate of expansion
As explained above, there are many different proposals for expansion rates - from very slow to very fast. However, 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, McElhinney et al. (1978) used paleomagnetic
data to calculate that the radius of the Earth 400 million years ago was 102 ± 2.8% of today's radius. Furthermore, 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.
Arguments for subduction
Since the 1970s, a vast amount of evidence was found in structural geology
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:
- 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.
- 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.
- 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.
- 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.
- 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
). Plate tectonics provided a model for mobilism.
The primary objections to Expanding Earth Theory 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. Although there are still some supporters of the theory like Weijermars (1986), Michihei (1998), Scalera et al. (2003), Edwards (2006), 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.
Growing Earth hypothesis
One prominent present day advocate of an expanding Earth is comics artist Neal Adams , who calls his ideas "Growing Earth Theory". He picks up the old expanding Earth theme that an Earth with half its present radius would allow the continents to fit together like a jigsaw puzzle, completely closing both the Atlantic and Pacific oceans. Using his skills in digital 3-D imaging technology, Adams has made video animations that graphically illustrate the expansion from a smaller Earth covered with continental crust to the Earth as we know it today. His addition to the old theory is the proposal of a mechanism of expansion, in which new mass is created by some sort of electron/positron pair production within the core of the Earth.
Some additional current advocates of similar hypotheses are Vedat Shehu, James Maxlow, and Stavros Tassos.