The continents and ocean basins are in constant motion due to plate tectonics. This animation shows the plate tectonic evolution of the Earth during the last 540 million years. Modern countries are shown in shads of brown and tan. The age of the ocean floor is show in colors that range from blue (oldest) to red (youngest). The age in millions of years is shown in the upper left-hand corner of the screen. The geologic period is shown in the lower left-hand corner of the screen. Text and animation