IHSL Joanne

2015年4月20日星期一

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2015年4月16日星期四

Plate Tectonic

Alfred Wegener propounded the theory of Plate Tecton in 1912, he claimed that all continents were once together in a supercontinent called Pangaea in 220 years ago, and plates move over time. His idea were dismissed as prattling until today it once again proved to be true. From the precise research and refined analyses in both text and illustrations, we find 3 main pieces of evidences to support this theory, they are puzzel, rock and fossil.

First, let’s talk about puzzle. By looking at the map of east coast of South America and the west coast of Africa, you will notice that the shapes of continents seem to fit. If you move them together, it’ll fits like separate pieces of a single land.

In addition, geologists also suggest that other patterns such as the location of mountain, volcanoes, earthquake and the distribution of rocks assist the idea of plates move. There are mountain ranges being formed where plates are pushing against, moving apart and occurrence of earthquake in where plates shift slide passes each other. For example, Himalaya, one of the highest fold mountains in the world, is located in convergent boundary, where two continental crusts move toward, fold layers and form a mountain. Where oceanic and continental plates being pushed together and denser oceanic crust goes under the continental, is called subduction zone.

A boundary where plates shift away from each other is called divergent boundary, we can see valley and mid-ocean ridge being created by the divert movement of land. Also, we all know the general knowledge about earthquake that it is cause by the activity of crust. More specifically, this kind of activity is crusts passing away from each other in transform boundary. What forces plates to move at those is known as convection currents. It mainly circulates hot and cold materials inside the mantle and cause the crust on the top to move. Those things I’ve been discuss all help the theory of continents slowly move apart over time.

Moreover, geologists has kept discovering plants, animals fossils of same species in separate continents, it is hard to explain unless continents had once been joined. For instance, fossils of Cynognathus have been found in both Africa and South America, providing evidence that these two plates were a puzzle many years ago.

However, some stubborn people might still argue that the continents were separate in this way and will last forever, they never once together because plates can’t move. Then, how could you explain why the continents all seem to fit each other, and why fossils of one organism appear in different plates? Also, there’s basically no earthquake without movement of lands.

In conclusion, the evidences such as continents fit together, mountain boundaries, earthquake and similarity between fossil in different continents, have proved that plates had once in conjunction and slowly keep moving by force.