Piecing together the Pangea puzzle

Two hundred and fifty million years ago, all the major continents were joined together, forming a continent called Pangea (which means "all land" in Greek). The plate thickness of continents can now be measured using seismology, and it is surprisingly variable, from about 90 km beneath places like California or Western Europe, to more than 200 km beneath the older interiors of the U.S., Eastern Europe, and Russia.