The Theory Of Continental Drift

At one point in geologic time, the world was made up of a single continent called Pangaea. Over time, this supercontinent separated and drifted apart, forming the different continents that exist today. The process is always in motion; the plates always moving, as they will continue to do far into the geologic future. In fact, the configuration of the Earth's landmasses may change drastically from the way they are today.

620 million years ago

420 million years ago

620 million years ago

420 million years ago

Permian 225 million years ago
Jurassic 135 million years ago

Cretaceous 65 million years ago

O Infobase Publishing

Cretaceous 65 million years ago

Present day

O Infobase Publishing

The Earth's plates have shifted over geologic time.

In 1912, Alfred Wegener, a German scientist, geologist, and meteorologist, was the first to propose the theory that the Earth's landmasses were not stable, but instead drifted slowly across the Earth's surface. He used the theory of Pangaea's existence along with field data collected from rocks. He believed that the continents are made of lighter rocks that rest on heavier crustal material—similar to the way an iceberg floats in water. Wegener proposed that the positions of the continents are not rigidly fixed, but instead move at a slow rate—about one yard per century. It was not until the 1960s that geologists gained the technology to understand the processes at work that move the Earth's plates. The concepts of seafloor spreading and plate tectonics emerged as powerful new hypotheses to explain the movements of the Earth's surface. Scientists concluded that the Earth's surface was not composed of one large sheet, but rather of more than 12 major pieces of crust called plates that fit together like pieces of a jigsaw puzzle.

Each rigid plate, or slab, of lithosphere averages at least 50 miles (80 km) thick. They move relative to one another at speeds of a few inches per year—about the same rate as a human fingernail grows. Although these rates are slow by human standards, they are very rapid by geologic ones, where processes can take millions or billions of years. Plates can move 30 miles (50 km) in 1 million years, and they have already been in motion for 100 million years. Scientists recognize three common boundaries between the moving plates: divergent, convergent, and transform.

0 -1

Post a comment