How did Pangea change over time?
Land masses shifted due to convection currents in the mantle
A very, very long time ago the continents were one large land mass. The land masses (the crust) sit upon the mantle. The mantle is like a very thick liquid and the heat from the core sets up convection currents in the mantle. These convection currents cause the movement of the land masses.
Evidence for the existence of Pangea, is based upon the fossil record (similar fossils are found on different continents that are now geographically far apart) and the shapes of the continents fitting together like puzzle pieces.