Plate Tectonics Theory

The plate tectonics theory, advanced by Alfred Wegener in 1912, is comparatively new idea – having been imagined and established in the last 100 years and it is broadly recognized as the best description of the formation of continents and oceans. Further, it is the best explanation for creating of earthquakes and volcanoes. It has now revised and repealed other previous theirs such as the continental drift.

Contraction theory

The contractionist theory was accepted by some scientists at the close of the nineteenth century as one of the explanations for the formation of the continents and oceans (Stallings, 1995, p. 114). The theory postulated that mountains, oceans and the continents were formed due to a gradual cooling of the earth. It stated that cooling caused shrinkage of the earth’s surface, which resulted in the formation of earthquakes and mountains (Stallings, 1995, p. 115). From around 1858, different scientists challenged the contraction theory. However, it was only Alfred Wegner, who created a comprehensive explanation of what he termed as the continental drift theory.

Stabilist theory

Prior to plate tectonics acceptance as a unifying theory of geology, other theories that explained the behavior and the origin of the continents were available. One of such theories included the stabilist theory, which held that continents were static, thus, the continents are presently where they were many years ago (Laporte, 2000, p. 115). Nonetheless, biogeographical evidence opposed this notion. Biogeography refers to the study of geographical distribution of animals and plants. Since the fossils of India and South Africa were very similar geologists suggested that an ancient continent existed that linked them but the continent had sunk under the ocean. Therefore, they referred to their continent as Lemuria since the lemur was one species that appeared in areas that were not linked by land, therefore the lemurs and their predecessors may not have made the journey themselves.

In spite of this hypothesis, another proof that contradicted the stabilist view existed. Glacial fossils are considered to be the “trails” that glaciers display and reveal where, when in what route they moved (Laporte, 2000, p. 196). Many glacial fossils did not show any significance when considered under the stabilist theory. However, the glacial fossils in Australia, South America, South Africa, and India appeared inconsistent and implausible. Thus, Alfred Wegener suggested that the continental drift as opposed to land bridges triggered these similarities. He theorized the existence of an antique super continent that split apart many years ago. Wegener called this continent Pangaea, which means “single earth”. Therefore, once the continents reshuffled as Wegner had hypothesized, the glacial fossils displayed consistent movement external from a single point. Similar species during the time were now seen to have been in the same region.

Shock dynamics theory

The main idea of Shock Dynamics theory is that for a long time, a big mass hit the earth at a region between Madagascar and Africa. The shocks from the impact broke the continents apart and made them move into different directions. The theory stated that after the mass collided, the generated momentum made the earth’s surface to wrinkles, creating valleys and mountains (Gioncu, & Mazzolani, 2010, p. 109). The theory gave examples of mountains in Australis, South America and North America. Near the crater, the pressure moved the magma in between the seafloor crust, creating the Seychelles islands and the Seychelles islands. Further, the rupture caused the formation of Mount Kilimanjaro and the Kenya Dome. Further, the point is believed to be the location of impact since the continents look like the radiated directly outwards from it. Further, the Impact Mountains, named the “Brake Mountains” was another method that the mountains formed. The Shock Dynamics theory states that as the continents were sliding over the earth, the front of land masses lost momentum first while the back continued to move, and thus pressing against it. Therefore, the land masses wrinkled to create mountains on the front side of the land mass, which is best evident with the brakes m0units such as the Rockies.

The Shock Dynamics theory is suspected of being inadequate because of the belief that the force created by the theory was small. It is argued that to create a force that would have caused mountains like the Himalayas, it would have required about 1500-6000 bars while the force observed with the plate tectonics was much less.

Continental drift theory

Continental drift theory came before the tectonic plate theory. It alludes that the positions of continents have changed over time. Continental drift was proposed by Alfred Wegener in 1912. According to continental drift, 200 million ago earth existed as one mega-continent referred to as Pangaea. According to Vavrek, et al. (2016), Pangaea split to from two large landmasses namely Gondwanaland and Laurasian (Meschede, 2015). Over time both Gondwanaland and Laurasia broke apart and drifted to occupy a different position. Earth rotation caused significant changes to the two land masses floating on the sea. From the friction drag along the floating continents, mountains were created. The scientific community disagreed most of the ideas in this theory. This led to the development of the tectonic theory (Vavrek, et al. 2016).

Tectonic plate theory

Alfred Wegener observed continents have the jigsaw fit. For example, South America and Africa coastlines seem to fit together, which suggests that at one time they were connected to the one super continent named Gondwanaland and another one known as Laurasia (Condie, 2013). This observation was later supported by fossil material, where dinosaur remains were found in the Gabon and Brazil Coasts. Further, additional and similar fossilized rock sediments and pollen species were also found on the outlined coastlines.

Through the Wegener’s concepts were simple, they were later proven to be right and build upon and enlarged the knowledge of the tectonic events. The discovery of the Sea floor spreading pointed to the evidence that the rock was being created and destroyed, which proves on the reality of the plates and the plate boundaries (Kelemen et al., 2016). For example, the Sea floor spreading was demonstrated at Atlantic, in which it was considered that the North American and Eurasian were moving apart, at the constructive plate boundary. In this location, magma rises in the rift and cools quickly on the surface, producing a new plate substance and volcano ridge named mid-Atlantic ridge. The above shaped Iceland that has rift valleys, pointing to evidence that the plates move apart. The 1963 Surtsey eruption produced a new Island proves that plate and land created along the same margin.

Modern technology has successfully proved the plate tectonics. Carbon dating for oceanic crust indicated that crust that is near the UK seems to be older than the crust that is beside mid-Atlantic ridge. Further, deep sea search exposed the paleomagnetism and ‘black smokers.’ The Palaeomagnetism describes a case in which metallic quantities in the crust get associated with the opposing layers (Kelemen et al., 2016). Notably, after some 100000 years, ogles flip – which implies that at this time metallic components align in the opposite direction and face pole that they drew close. Therefore, every each band of opposing aligned components for the crust shows some hundred thousand years crust produced at the time. The above evidence proves the sea floor is spreading, but also indicates that when a plate as being produced at one location, then it must have been getting destroyed at another place.

Breuer et al., (2015), argued that the core is separated into liquid outer and solid inner core. The main content of the core is nickel and iron. The mantel is split into two sections, upper and lower mantle; its main components are magnesium, oxygen, and silicon. Breuer et al., (2015), suggested that the outermost layer of the earth supports life since it is rich in silicon, oxygen, sodium, magnesium, potassium and iron. Tectonic plates are found between the mantle and the crust (Condie, 2013). Condie et al. (2013) suggested that the outermost of the earth’s surfaces dived into asthenosphere or lithosphere depending on their physical characteristics (Kelemen et al., 2016). The asthenosphere is seen as the lower category since it is composed of flowing mantle, while lithosphere is the upper category. Lithosphere includes both the crust and rigid mantle layers.

Deep sea exploration has also proven the plate tectonics theory. Many volcanoes and earthquakes happen along the Pacific Ring of Fire. Parallel and close to the boundaries are deep ocean trenches such as the Marianas Trench. Scientists proved that ocean trenches demonstrated that various plates are subducted – which is the point at which they are destroyed. In this stage, the oceanic plate is dense would subduct the continental plate, and plate could melt in the mantle and create a pool of magma that could rise amid the rocks to form a volcano. The above addition to plate tectonic theory showed why the volcanoes are usually located along plate boundaries that are constructive – because of growing magma – caused by plate melting.

However, the plate boundaries are noted to be dissimilar. Most earthquakes get dispersed along the Indo-Australian or Eurasian plate boundary in places where no volcanoes are present. Further, the region has very high mountains like the Himalayas (Condie, 2013). The plate tectonics explain the oceanic plates since they become denser and they continually subducts the continental plates. However, in this region, two continental plates meet – which made the scientists formed the theory of Fold Mountains (Kelemen et al., 2016). The continental plates converge, but none subducts, and they push sediments up to create high fold mountains. There is pressure build-up and finally the plates faulted upwards, leading to the breaking and addition to the formation of the mountain, which explains a way in which the plates could be shattered – through fracturing.

Plate tectonic theory clearly explains why earthquakes and volcanoes were created along the imaginary lines – since there existed some different plate boundaries. However, some issues exist. For example, the Yellowstone and Hawaii Volcanoes exist in the middle of plates (intra-plate) and thus did not relate to the dominant knowledge that volcanoes would occur along the plate boundaries viewed. Tuzo Wilson successfully explained the above phenomenon through the Hawaiian hot spot theory. He stated that magma plumes created the hot spots in the mantle that caused the crust melting at the point establishing the volcano. He outlined that the plume would be stationary and that crust transferred over it. After plume had created a volcano, crust moved, and thus plume would not further from a volcano there and thus start another one along. Wind and wave would erode the old volcano until it falls into the sea, forming the coral reef about it such as the Midway Islands (Condie, 2013). Finally, Seamount could get wrecked as the destructive plate boundary around Russia. Therefore, the intra-plate hot spot assists in proving the plate movement and thus the plate tectonics theory.

According to Kelemen et al., (2016), oceanic crust tends to be denser than the continental crust. Therefore, when the two plates collide the continental crust overrides the oceanic crust. Three forms of tectonic boundaries usually exist. Divergent boundary tends to be the first boundary that frequently occurs in mid-ocean ridges. Due to the override, the oceanic crust is bent leading to the formation of a subduction zone. In a subduction zone, most of the old oceanic crust is recycled and dragged down. Subduction zones result in the formation of the deep-sea trenches (Kelemen et al., 2016).

Conclusions

The plate tectonic theory best explains the formation of continents and oceans. The plates are constantly shifting, and the earthquakes and the volcanoes are located sideways the boundaries. It combines concepts in both sea floor spreading theory and the continental drift to explain the structures of earth’s surface. This approach primarily has been developed from three main stages. Continental drift initiated the discovery of the tectonic theory through concepts related to the sea floor spreading to oceanic subduction which lay a great foundation for the tectonic. The second stage involved the oceanic subductions, via continental subduction to instances of collisional orogeny. The third stage involved activities from continental collision to effective marginal orogeny which lead to intercontinental reworking.

References

Breuer, D., Rueckriemen, T., & Spohn, T. (2015). Iron snow, crystal floats, and inner-core growth: modes of core solidification and implications for dynamos in terrestrial planets and moons. Progress in Earth and Planetary Science, 2(1), 39.

Ciochon, R. L. (Ed.). (2013). Evolutionary biology of the New World monkeys and continental drift. Springer Science & Business Media.

Condie, K. C. (2013). Plate tectonics & crustal evolution. Elsevier.

Fokas, A. S., & Pelloni, B. (Eds.). (2014). Unified transform for boundary value problems: applications and advances. Society for Industrial and Applied Mathematics.

Formisano, M., Federico, C., De Angelis, S., De Sanctis, M. C., & Magni, G. (2016). The stability of the crust of the dwarf planet Ceres. Monthly Notices of the Royal Astronomical Society, 463(1), 520-528.

Geist, H., McConnell, W., Lambin, E. F., Moran, E., Alves, D., & Rudel, T. (2006). Causes and trajectories of land-use/cover change. Land-use and land-cover change, 41-70.

Gioncu, V., & Mazzolani, F. (2010). Earthquake engineering for structural design. CRC Press.

Kelemen, P. B., & Behn, M. D. (2016). Formation of lower continental crust by relamination of buoyant arc lavas and plutons. Nature Geoscience

Knighton, D. (2014). Fluvial forms and processes: a new perspective. Routledge.

Laporte, L. F. (2000). George Gaylord Simpson: paleontologist and evolutionist. Columbia University Press.

Lobkovsky, L. I. (2016). Deformable plate tectonics and regional geodynamic model of the Arctic region and Northeastern Asia. Russian Geology and Geophysics, 57(3), 371-386.

Meschede, M. (2015). Plate Tectonics: An Overview.

Stallings, R. A. (1995). Promoting risk: Constructing the earthquake threat. Transaction Publishers.

Vavrek, M. J. (2016). The fragmentation of Pangaea and Mesozoic terrestrial vertebrate biodiversity. Biology Letters, 12(9), 20160528.

 

 

 

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