The Earth is split up into tectonic plates. The tectonic plates are like the skin of our planet. When two of these plates rub together there form volcanos or a violent earthquake occur.
Some scientists believe that back in the day there was only one tectonic plate: Pangea. These scientists say that there is "scientific proof" of this giant continent. They believe that the reason that South America looks like it can fit together with Africa (as shown below) proves their theory.
Scientists believe that Pangea can be proven by the discovery of two similar fossils. One of them was in Africa and the other in South America. They were two of the same species of dinosaur. This lead scientists to believe that the two continents were once connected.
The tectonic plates make up the top layer of the earth, the lithosphere. Under the tectonic plates, there is another layer which is molten rock. This layer is called the asthenosphere. The tectonic plates are always floating on this layer.