Continental Drift

Continental drift describes how the Earth’s continents move in relation to each other. Early scientists found it curious that, for example, Africa and South America seem to fit together. As early as 1900, the similarities in fossil fauna and geological formations lead geologists to speculate that all the continents had once been a supercontinent known as Pangaea. While the continental drift theory seemed logical, it was imperative to find evidence of continental drift if the theory were to be widely accepted.

The main difficulty to overcome was explaining exactly how the continents drift apart. An early explanation by Alfred Wegener suggested that these centrifugal force of the Earth’s rotation caused continental drift, a theory not appreciated by the scientific community.

Evidence of continental drift has come from a wide range of disciplines. Plant and animal fossils occur near different continent shores, suggesting the shores may have been once joined. For example, fossils of the aquatic reptile Lystrosaurus, all of the same age, have been found as far apart as Antarctica, Africa, and South America. Living creatures also testify to continental drift, like the earthworm common to both South Africa and South America.

Geophysical evidence began to accumulate after World War II. Before that time, the theory of continental drift led to bitter disagreements among geologists. It seemed unbelievable that huge landmasses would plow through the rocky ocean floor.

With the discovery of plate tectonics, continental drift got a new lease on life. It is now understood that the continents move because of convection currents, which are in turn driven by the heat at the core of the earth. Essentially the continents are on a giant conveyor belt, constantly moving. This contrasts with early theories where the continents floated aimlessly around, banging and bumping into each other randomly.

The theory of continental drift is widely accepted now. However, as recently as 30 years ago it remained controversial. New evidence continues to come to light, expanding our knowledge and understanding of the movement of continents.

So, how quickly are the continents moving? Africa and South America are moving away from each other at a rate of about 2 inches per year. The seafloor along the mid Atlantic ridge is spreading, causing the continents to move apart. But that’s not the fastest moving piece of ground – the East Pacific Rise seafloor is spreading at close to 7 inches per year! That’s faster than your fingernails grow.

Fossil patterns across continents. Courtesy Wikipedia.
Map of Pangaea. Courtesy Wikipedia.