Continental Drift

Mobile Continents

Alfred Wegener: Continental Drift in 1915

• German geophysicist and meteorologist.

• He suggested that a single super-continent Pangaea began to fragment in the Mezoic era, about 200mya.

• 1st to publish, but not to mention Continental Drift

Earth ~200 million years ago

•The continents appear to fit together as if they were different pieces of the same puzzle.

1 Jigsaw Puzzle

2 Glacial Evidence

Glacial deposits found in tropical regions near the equator should not be there.

Glacial Evidence

Large tropical swamps in the Northern Hemisphere at the same time

3 Rock Evidence

Mountains and crust of comparable age and structure are found in North America, Greenland, The British Isles, across the ocean in Africa and in Northern Europe.

4 Fossil Evidence

Fossil Evidence

• Glossopteris, a fossil fern from a plant with large seeds not easily distributed was found dispersed in Africa, Australia, India and South America during the Paleozoic era.

• Also found in Antarctica as well. These plants do not grow in Polar Climates!

Mesosaurus

5 Desert Evidence

6 Paleomagnetic Evidence

• Highly complex

• Some sea floor rocks behave like compasses

• Magnetic Rocks indicate latitude.

• Put Continental Drift on the scientific map.

Alternatives

• Growing Earth

• Island Stepping Stones

• Land Bridges

Scientific Controversy: • Wegener’s idea of mobile continents was met with harsh criticism and it

took until the late 60s for continental drift to be generally accepted by the scientific community.

• Chief complaint vs. Wegener was a lack of an agent for motion. How did the plates move? Wegener provided two incorrect possibilities:

• 1) Tidal Forces of the Sun moon (which cause the tides) could account for

continental movement. Harrold Jeffreys showed that tidal forces of this magnitude would halt the rotation of the earth in a few years.

• • 2) Continental crust cut through softer oceanic crust as ice breakers cut

through ice but there was no evidence to suggest the oceanic crust was soft enough to allow this without significant continental deformation.