During our brief human life span and, indeed, throughout the entire course of human history, the appearance of our globe has changed very little. While ice cover has waxed and waned with the climate, the basic shape of our oceans and continents has been relatively stable. Only the intermittent earthquakes and volcanic eruptions hint of the ongoing evolution of Earth's surface.
In fact, the crust of our planet, 30 miles thick, is composed of seven large and many smaller tectonic plates, all of which are continually in motion, colliding, subducting or scraping along one another. During this process, which is powered by heat within the Earth, they drift, change shape, split apart or merge with other plates; these latter events are mediated by the opening and closing of oceans. This rifting and suturing continues today, at a rate that is too slow for us to perceive.
The East African Rift, which began to form 40 million years ago, will eventually open a seaway through the Continent; 100 million years from now, the African Ocean may separate the two segments. Perhaps the Pacific Ocean will stop forming along its southern and eastern edges and, over 200 million years, be consumed in the Aleutian and East Asian trenches; in concert, the Atlantic may continue to spread and the American Continents may approach the eastern coasts of Asia and Australia. We, of course, will never know.
