Techtonic plates Essay

Volcanic and seismic events are major pieces of evidence towards proving that the plate tectonics theory is valid.

The theory of tectonic plates was first posed by Alfred Wenger in 1912. Is the theory of how the earth lithosphere is made up of many separate pieces of the earth’s crust known as tectonic plates. He put forward the idea that all the earth’s continents were once conjoined in one supercontinent called Pangaea, and that these continents were moved by convection currents over a period of many millions of years in to their current positions. These convection currents are made by radioactive energy in the earth’s core causing the semi molten mantle to rise and fall moving the tectonic plates above them. These tectonic plates cause both volcanic and seismic activity which is why these events are crucial to proving the theory of tectonic plates. Throughout this essay the theory of plate tectonics will be discussed extensively with key references to the volcanic and seismic events and how they are a direct result of the movement of tectonic plates. There will also be discussions on some of the visual evidence there is for the tectonic plate theory, such as the mid-Atlantic ridge, with particular reference to its formation, as well as a detailed explanation of the development of the tectonic plate theory and why it is so widely accepted as fact.

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There will also be large numbers of annotated diagrams to help explain and clarify some of the ideas put forward in the text as well as making the topic easier to understand as the text will be directly related and aided by the diagrams. It was Francis Bacon in 1620 who first noted that parts of the world fit together like a ‘jig-saw puzzle’ like the east coast of South America and the west coast of Africa, but no one had any explanation for it until 1912 when German meteorologist Alfred Wenger stated that all the continents had once all been joined together in one supercontinent he named ‘Pangaea’. He used many different pieces of evidence to support his theory, the most important piece of evidence was his use of fossil records of many different species, he showed how there was fossils of the same species found across different continents (as shown in figure 1). As he showed the type of species he selected would have been unable to cross oceans to have moved between continents, so he stated that the population spread is so because the animals walked across the continents as they were all connected.

Although he believed in his theory and found evidence for it no reason for why the continents would move could be found so his theory was not accepted. This remained the case until the discovery of the mid-Atlantic ridge in 1948 by Maurice Ewing which supported the tectonic plate theory and posed the idea of different plate margins which will be explained later in the essay. Volcanoes are very strong supporting evidence for the theory of tectonic plates. This is due mainly to how and where a volcano is formed. Volcanoes are formed at both constructive and destructive plate margins. A constructive plate margin (as shown in figure 2) is where two similar plates are forced apart from each other from the pressure and force of the convection currents in the mantle below. This shows how if it is possible for two adjacent plates to be forced apart creating a gap between the two, that the earth’s crust cannot be one solid and intact piece of rock. This is then explained by the tectonic plate theory which is the first of many pieces of evidence for this theory. A real world example of this is the mid-Atlantic ridge. This was then discovered to still be releasing magma which then cools down creating new parts of the earth’s crust. This process is known as sea floor spreading as it causes the sea floor to widen with the continuous addition of new crust. This theory was first put forward by Harry Hess who in 1962 studied the age of rocks from the middle of the Atlantic ridge outwards.

He found that the new addition of rock meant that the at Atlantic was widening by up to 5cm a year, which is obviously impossible without some other part of the crust being destroyed at the same rate. However when this was discovered his theory was accepted by the scientific community and became and still is the preferred theory for the mid-Atlantic ridge. This theory is crucial evidence for the idea of tectonic plates as it relies on that theory to make the mid-Atlantic ridge possible. The area that was found to destroy parts of the earth’s crust as predicted by Hess is known as a destructive plate margin. Figure 3 shows how a denser oceanic crust is sub ducted under a lighter continental crust.

A volcano forms through this process as the sub ducted crust melts in the high temperatures of the mantle there for expanding due to the transition from solid to liquid/molten as this medium is far less dense. Causing a build up of pressure which then causes a weak point in the continental crust to fail and split releasing magma. This is how this form of volcano in created showing how they are created as a direct result of a collision between two tectonic plates, as if there was just one piece of crust around the world the pressure build up in the mantel would be impossible as there would not be enough material. This paragraph shows how two of the ways a volcano can form are only possible with the tectonic plate theory, therefore as these forms of volcanoes exist so to must the tectonic plates that the volcanoes need to form.

The tectonic plate theory is also reinforced by seismic activity along a variety of plate boundaries. The first form of plate boundary is known as a conservative plate boundary. This is where two similar types of plate rub against each other as they travel in opposite directions to each other (or in the same direction at different speeds). This contact between these two plates creates very large amounts of friction and pressure. Occasionally as the edges of these plates are very rough the two plates will get stuck on each other. However while these two plates are not moving the convection currents beneath them are still attempting to move the two plates. This causes a build up of pressure until eventually this pressure releases as the two plates suddenly shift. This creates very large scale earthquakes such as the 1906 earth quake in San Francisco, which is on the San Andreas Fault. This type of seismic event shows how two tectonic plates can rub against each other causing potentially devastating pressure build ups.

These earth quakes are evidence of the tectonic plate theory as they are due to the friction between two plates. The very existence of the San Andreas Fault caused by this plate margin is also evidence of the tectonic plate theory. This is because as shown in figure 5 you can literally see the meeting point between the North American and pacific plates as they move past each other. This fault line is roughly 810 miles long cutting through California in the USA. And is the most monitored plate boundary because of its location and tendency for large scale earthquakes. This means that since the tectonic plate theory was put forward a hundred years ago a great amount of research has gone in to and evidence gained from the San Andreas Fault about tectonic plates.

The final piece of evidence that volcanic and seismic activity is an area known as the ring of fire. This is a line of all of the most active and some of the largest volcanoes in the world, along with a large percentage of the world’s earthquakes on it. As show in figure 6 this makes an almost perfect line around much of the pacific plate and some of the Nazca plat. This line shows how there is an obvious and strong connection between plate boundaries and volcanic and seismic activity. This proves that volcanic and seismic activity are powerful pieces of evidence for the tectonic plate theory as all of the theories describing volcanic and seismic activity are proven to be related to plate movement as the positioning of this activity is to perfectly positioned around the edge of plates for it to be a coincidence.

The direction of the plate seems to effect the severity and frequency of volcanic or seismic activity as when to plates are moving towards each other there is a noticeable increase in the number of these events. Take the pacific and Eurasian plates as an example. As figure 7 shows these to plate are moving towards each other and contact each other around the Philippines. This area of the globe is where the highest frequency of volcanoes is found. Some of which have erupted more than 50 times in there recorded history, like volcano Mayon.

In conclusion I feel that Volcanic and seismic events are major pieces of evidence towards proving that the plate tectonics theory is valid. I feel this because I think that the only possible theory of how these events exist and have the variety they do is the theory of plate tectonics, as well as this theory being unanimously accepted by the scientific community who reject any theory that is not perfectly explained and supported by physical evidence, which this theory is supported by. I believe in this essay I have supplied sufficient evidence to support this statement and adequately explained the processed that produce volcanoes and earthquakes.