What is Continental Drift?

continental drift map, gondwana
The theory of continental drift reconciled similar fossil plants and animals now found on widely separated continents. Gondwana is shown here.
Credit: USGS

Continental drift was the first attempt to explain why similar animal and plant fossils are found on different continents. The theory was set forth in 1912 by Alfred Wegener and published in a 1915 book. He wasn't the first person to suggest Earth's continents were once connected in a giant land mass called a supercontinent, but he was the most reviled.

Wegener's theory of continental drift was soundly denounced by geologists. Part of the opposition was because Wegener didn't have a good model to explain how the continents moved back and forth.

Though most of Wegener's observations were correct, he was wrong on a couple key points. Wegener thought the continents drifted around the planet by plowing through the crust underlying the seafloor, like icebreakers smashing through ice. He also suggested they sailed at a speedy 10 inches (250 millimeters) per year. At the time, geologists thought Earth's mountains and other topography were created as it cooled and shrunk since the planet formed. Scientists now know Earth's outer shell moves about ten times more slowly than Wegener thought, in giant tectonic plates that include the ocean and continents. [Have There Always Been Continents?]

A map of the continents inspired Wegener's quest to explain Earth's geologic history. Trained as a meteorologist, he was intrigued by the interlocking fit of Africa's and South America's shorelines. Wegener then assembled an impressive amount of evidence to show that Earth's continents were once connected in a single supercontinent, which he named Pangaea.

Plate tectonics
Tectonic plates of the Earth.
Credit: USGS

Evidence for continental drift

Wegener knew that fossil plants and animals such as mesosaurs, a freshwater reptile found only South America and Africa during the Permian period, could be found on many continents. Previously, scientists had explained the widely separated fossils by suggesting a land bridge connected the continents.

He also matched up rocks on either side of the Atlantic Ocean like puzzle pieces. For example, the Appalachian Mountains (United States) and Caledonian Mountains (Scotland) fit together, as do the Karroo strata in South Africa and Santa Catarina rocks in Brazil.

Despite his incredible evidence for continental drift, Wegener never lived to see his theory gain wider acceptance. He died in 1930 at age 50 of a probable heart attack while on a scientific expedition in Greenland.

In the 1950s, the discovery of new oceanic crust forming at seafloor-spreading ridges led researchers to revive the idea of continental drift and develop the theory of plate tectonics.

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Becky Oskin, OurAmazingPlanet Staff Writer

Becky Oskin

Becky Oskin is a senior writer for Live Science. She covers earth science, climate change and space, as well as general science topics. Becky was a science reporter at The Pasadena Star-News and has freelanced for New Scientist and the American Institute of Physics. She earned a master's degree in geology from Caltech, a bachelor's degree from Washington State University, and a graduate certificate in science writing from the University of California, Santa Cruz.
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