Air Date: Week of April 25, 1997

Facts about... plate tectonics.

Transcript

CURWOOD: In 1620 English philosopher Sir Francis Bacon looked at a map of the world and pointed out that the coastlines of South America and Africa fit together like puzzle pieces. Since then, scientists have been trying to explain why. One answer came 30 years ago this month, when geophysicist Jason Morgan offered the idea of plate tectonics. He drew on theories of continental drift and sea floor spreading, and included observations about similarities among plant and animal species on both continents. Dr. Morgan concluded that the lithosphere, the upper part of the Earth's crust, was not solid but made of several enormous plates, as much as 200 kilometers thick and moving at a rate of nearly 2 inches per year. Today, his theory is one of the tenets of geology, and it's widely accepted that the movement of the plates is responsible for earthquakes, volcanoes, mountains, and ocean basins. And if you're inclined to smirk at warnings about California falling into the sea, in theory it already has. The state's coast sits on the eastern edge of the Pacific plate, so geologically speaking, it is not part of North America. And for this week, that's the Living on Earth Almanac.