# Evidence of Plate Tectonics

Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

After reading this lesson, you'll learn what things scientists observe in the natural world that lead them to believe that plate tectonics is the way our continents were formed.

## What Is Plate Tectonics?

Take a moment and look at a world map. Doesn't it look as if the continents are puzzle pieces that fit together? For instance, doesn't it look as if South America, Brazil, in particular, fits into the eastern border of Africa?

According to the theory of plate tectonics, the continents are moving because the plates the continents sit on are moving slowly over the molten mantle of the Earth. And yes, this same theory of plate tectonics also explains why earthquakes typically happen along plate boundaries. As the plates move across the molten mantle, the plates rub against each other and cause earthquakes.

Scientists didn't just come up with this theory out of the blue. They came up with the scientific theory of plate tectonics after considering the pieces of evidence we'll explore in this lesson.

## Crustal Rock Age

The first piece of evidence is the age of the Earth's crust. Scientists have found that the deeper the crust, the younger the rock is. How is this an evidence of plate tectonics? Well, if the plates are rubbing against each other, then old rock will be pushed upwards, while the youngest rock is at the bottom. Scientists have found that the youngest rock follows a path along the plate boundaries.

## Fossils and Rocks

Second, when looking at the fossils found on the edges of the continents, scientists find that similar fossils are found on separate continents which points to the idea that these continents were once connected to each other as one giant continent called Pangea. The continents are now separated because the plates have moved over the years.

For example, fossils of Cynognathus are found in South America as well as in Africa. The location where this fossil is found follows a path from the one continent to the other. The same is true of the fossils for Lystrosaurus. This fossil can be found in Africa, India, and Antarctica.

Scientists have also found that similar rocks are found in different continents and if you move the continents around so that the puzzle pieces seem to fit, then the rocks also match up. For example, the rock types found on the western coast of South America match up with the rock types found on the matching eastern cost of Africa.

## Continental Shapes

Third, as mentioned before, the continents look like as if they are puzzle pieces that fit together. South America matches up with Africa. India bends down to match up with Africa, and Antarctica fits in nicely under India and next to Africa. The western side of Antarctica tucks in nicely to the eastern side of Australia.

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