Continental Drift

For years men studying maps of the Earth have noticed that the continents can be put together like parts of a giant puzzle. Most scientists in the past refused to accept the idea that the Earth's land masses had broken up and drifted apart—a theory known as "continental drift". After all, no known force could have moved large continents across the Earth's surface.

In 1912, Alfred Wegener formally proposed the theory that in areas where the coasts of South America and West Africa might have been joined, the composition, age, and layering of rock matched. Remains of plants and animals on one continent were the same as those on other continents, even though they were separated by many miles of ocean.

More evidence came out of the ocean itself. By 1959, geologists had discovered and made maps of an undersea mountain chain, running through the middle of the major oceans. The water temperatures near these mountains are slightly higher than those in the rest of the ocean. Also, the geologists discovered unusual cracks in the ocean floor that seem to have been caused by movement of the floor itself. Then they measured the depth of the layer of sediment on the ocean floor and the amount of sediment collected tells scientists the approximate age of the ocean bottom. The more sediment that has collected, the older the ocean floor is. The geologists' sediment measurements showed that the ocean floor is only a few hundred million years old, compared to the oceans which are billions of years old.