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The Theory of Plate Tectonics

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When Europeans viewed the first world maps including the Americas 5 centuries ago, they noticed the African and South American coastlines would fit together like a puzzle if they were not separated by the Atlantic ocean. Scientists of the era were baffled and came to the conclusion that millions of years ago the earth was approximately 60% of its current size making it a dwarf planet. The complete surface of the globe was covered by land. Earth then extended via the sea floor, the continental shell broke apart causing the ocean to form in the rifts between the continents.

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There were several theories suggesting as to why the continents drifted apart. In 1668, François Placet a French monk proposed that America and Africa separated when the lost island of Atlantis was destroyed by the biblical flood sinking and creating the Atlantic Ocean. In 1858 another theory was formed by French geographer Antonio Snider-Pellegrini who also suggested the continents moved apart laterally as a result of a biblical flood. Finally, the first scientific theory advising that continents could drift on their own by German geophysicist Alfred Wegener came in 1912. He proposed the Earth’s lands once fit together as a single continent he called Pangea (a Greek word meaning “all lands”). He believed Pangea was surrounded by a single body of water — the Panthalassa — and the continents shifted to their current locations via floating through the ocean similar to an iceberg.

This theory was accepted at the time because there was limited technology at the time to prove otherwise. Scientist knew that new land was being formed but did not know how. However, they didn’t know that land was also being destroyed in the process. That is how they came up with the idea that earth was growing in size. Wegener located fossils of identical plants and animals on continents now separated by oceans. He used this as his scientific evidence.

However, there was information that did not fit in with this theory. For example, Newton’s Law of Universal Gravitation states that a planet’s gravitational force is equivalent to its own mass. If our Earth increased twice in size and its density endured, the Earth’s mass would increase by 8x, and the gravity on the Earth’s surface would be 2x stronger. Creating visible changes over the years and would affect our planet’s orbit around the sun as it would prove catastrophic. 5 centuries ago if Earth was only half the size, the planet’s gravitational force would be incredibly weak that it is quite unlikely Earth could have held a Moon in orbit. This theory also does not support the development of the Solar System. If all planets lived by the theory of expansion why have we not noticed? On the other hand, the theory does not explain or give evidence as for why it is only the earth that undergoes expansion and not any other planets.

After this information was found and considered a new theory was developed called Plate Tectonics. Using the theory of Continental Drift discovered by German scientist Alfred Wegener in 1912, between the years 1950 and 1970 the theory was developed. Both theories are based to explain the theory of Continental Drift but have extremely different explanations. Eventually, the theory of plate tectonics won.

We now understand how the continents moved apart. The continents move apart when hot rock heated by the earth’s core called tectonic plates rise, When the plates are near the surface, it spreads in two directions and moves sideways, the tectonic plates begin to lose heat and eventually the plate which is cooler sinks down. When the plate sinks down this process also destroys land, it is called subduction. Through this spreading process, the earth’s crust is very slowly dragged apart. This explains the movement of continents as continents each sit on a tectonic plate. The plates are named from the continents found on top of them. There are 9 major Tectonic plates: North American, Pacific, Eurasian, African, Indo-Australian, Australian, Indian, South American and Antarctic. Each plate moves at a different speed, for example, the Pacific Plate has a total area of 103,000,000km2 and move an average of 7 cms a year.

The theory of plate tectonics won as it is the most accurate and does not contain information that is not supported. Tectonic plates also prove that when new land is created, land is also destroyed through a process called subduction. Therefore, the earth cannot be expanding as land is being destroyed. As well as explaining how the continents have moved it also won as it explains how earthquake, mountains and volcanoes are formed. Earthquakes are formed when two plate push against one another causing tension. Soon the plates break apart from each other due to the tension and the earthquake is formed. Mountains are formed when two Tectonic Plates move towards each other and one plate is forced downwards, the other edge of the plate is scrunched up to form mountains. This process is called subduction. Volcanoes are formed when two plates are subducted, the plates set a foundation for a volcano. The overlapping of the tectonic plates causes magma to break through the crust which creates the volcanoes birth.

Links Used

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  • Loc.gov. (2019). Waldseemuller Map, 1507 (Geography and Map Reading Room, Library of Congress). [online] Available at: https://www.loc.gov/rr/geogmap/waldexh.html [Accessed 10 Feb. 2019].
  • Maclenan, A. (2019). Plate Tectonics at 50 – Getech. [online] Getech. Available at: https://getech.com/plate-tectonics-50/ [Accessed 14 Feb. 2019].
  • Maggie’s Science Connection. (2019). Plate Tectonics, Earthquakes & Volcanoes. [online] Available at: http://maggiesscienceconnection.weebly.com/plate-tectonics-earthquakes–volcanoes.html [Accessed 11 Feb. 2019].
  • marlenadotcom. (2019). Earthquakes & Volcanoes. [online] Available at: https://marlenadotcom.wordpress.com/earthquakes-volcanoes/ [Accessed 14 Feb. 2019].
  • Popular Mechanics. (2019). We’ve Been Wrong Before: The Expanding Earth Theory. [online] Available at: https://www.popularmechanics.com/science/environment/a22594681/weve-been-wrong-before-expanding-earth-theory/ [Accessed 14 Feb. 2019].
  • Science, L. and Earth, P. (2019). What Is Plate Tectonics?. [online] Live Science. Available at: https://www.livescience.com/37706-what-is-plate-tectonics.html [Accessed 14 Feb. 2019].
  • ScienceStruck. (2019). Theory of Plate Tectonics. [online] Available at: https://sciencestruck.com/theory-of-plate-tectonics [Accessed 12 Feb. 2019].
  • Sites.google.com. (2019). Plate Tectonics and Volcano poster – Abduljalil’s ESS portfolio. [online] Available at: https://sites.google.com/site/abduljalilsessportfolio/plan-and-carry-out-scientific-investigations/volcano-poster [Accessed 11 Feb. 2019].
  • ThoughtCo. (2019). The New Solar System: What We Know So Far. [online] Available at: https://www.thoughtco.com/the-new-solar-system-3072094 [Accessed 11 Feb. 2019].

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