Plate tectonics is the theory that Earth's outer layer is made up of plates, which have moved throughout Earth's history. The theory explains the how and why behind mountains, volcanoes, and earthquakes, as well as how, long ago, similar animals could have lived at the same time on what are now widely separated continents.
In 1912 a German meteorologist named Alfred Wegener (1880-1931) hypothesized a single proto-supercontinent that divided up into the continents we now know because of continental drift and plate tectonics. This hypothesis is called Pangaea because the Greek word "pan" means "all" and Gaea or Gaia (or Ge) was the Greek name of the divine personification of the Earth. Pangaea, therefore, means "all the Earth."