Just as species are constantly evolving—changing and adapting from generation to generation—so, too, is our planet constantly evolving. Plate tectonics is the theory that is used to explain the structure of the Earth’s crust and how it moves about. Specifically, it deals with large scale movements, like the the continents.

True, it is called a “theory;” however, don;’t take this to mean that the Earth might not be moving. We know that it is. It’s just that a scientific theory is a bit different from what most people typically think when they hear the word “theory.” But that’s a bit of a digression. if you want to know more about scientific theories and how they are defined, just head here.

To return to the topic at hand: The rocky, outer shell of our planet (called the lithosphere) is split into 15 major plates. These slowly that slowly move on top of (and underneath) one another. Plate tectonics studies this faulting and folding. The idea for plate tectonics goes back to German geophysicist Alfred Wegener. In 1915, his first ideas came about because he noticed that the continents fit together very closely along the continental shelves, almost like a puzzle that has been pulled apart.

Wegener guessed that the coastlines didn’t fit together perfectly, but only “almost” fit together, because they would have faced erosion and weathering. And it turns out, he was right. During several expeditions on either side of the Atlantic, he analyzed the rock type and fossil distribution and found a significant match between the geological records on the East and West. Ultimately, the 2 billion year old rock types on either side of the ocean appeared to line up perfectly when you put the continents together. In terms of fossils, the water reptile Mesosaurus was found in a band across South Africa and southern South Africa, and the land reptile Lystrosaurus was uncovered right from India, across Africa and into Antarctica.

And so he pieced the puzzle that is planet Earth back together. But if you want more evidence that our planet is moving, just look at the video below. In March 2011, an earthquake struck Japan. Over 18,000 people were killed by the magnitude 9.0 earthquake and subsequent tsunami. In this video, the ground can literally be seen opening and closing like a great maw.

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