What has Earth's geography been like during past geological eras? Movements of the continents since the breakup of the supercontinent Pangea about 180 million years ago are very well known from studies of the world's ocean basins. However, Pangea existed for a relatively short interval of geologic time, having assembled from precursor continents late in the Paleozoic era about 250 million years ago. Paleozoic ocean crust has been destroyed by its descent into the Earth's mantle as the Paleozoic continents converged to form Pangea. Thus, there is no ocean floor record to constrain Paleozoic continental movements. The configuration of the continents during the Paleozoic must be inferred from land-based observations. This work is fraught with difficulties and our knowledge has, therefore, increased slowly.