If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle…..the shapes of the coastlines of Africa and South America are a good example. As you discovered through your modeling activity, they once fit together. The Earth as we see it was not always like it is today. Land masses have been pulled apart and joined together by the process we call Plate Tectonics….

Continental Drift Alfred Wegener proposed in 1910 that million years ago all continents were joined together in a single land mass that drifted apart. Fossils of the same plants and animals were found on different continents. Wegener called this supercontinent Pangaea, Greek for “all Earth or all Lands.”

Fit of Continents Across the Atlantic Evidence of Continental Drift

Similar rock layers along the edges and relationship among mountain ranges on different continents Red line marks area where start of separation between Africa and South America probably started

Sea Floor Spreading 1963 Harry Hess developed the theory of Sea Floor spreading by applying the discovery of mid-ocean ridges and trenches Mid Ocean Ridges – underwater mountain chains that run through the Earth’s Basins Magma rises to the surface and solidifies and new crust forms Older Crust is pushed farther away from the ridge Continuing research led to the development of the theory of Plate Tectonics

Sea Floor Spreading