Continental Drift

Alfred Wegener (1915)

• German scientist

• noticed continental coastline similarities

• proposed Continental Drift Hypothesis

Continental Drift: Wegener's Hypothesis

According to Wegener’s Continental Drift Hypothesis, continents had once been joined to form a single supercontinent (Pangaea).

• also proposed that ~200 mya, Pangaea began breaking into smaller continents that then drifted slowly to their present positions

Evidence for Continental Drift:

Wegener’s evidence to support Continental Drift included similar fossils, types of rock, and ancient climates on widely separated landmasses.

Matching Fossils

Fossil evidence for Continental Drift includes several fossil organisms found on different landmasses.

Wegener reasoned that these organisms could not have crossed the vast oceans presently
separating the continents.

Continental Drift

• Cynognathus - land reptile

  • fossil remains in South America and Africa

• Lystrosaurus - land reptile

  • fossil remains in Africa, India, and Antarctica

• Mesosaurus - freshwater reptile

  • fossil remains in eastern South America and southern Africa

• Glossopteris - small plant (fern)

  • fossil remains in South America, southern Africa, India, Antarctica, Australia

Plate Tectonics:

Continental Drifts:

Rock Types

Matching types of rock in several mountain belts that today are separated by oceans provide evidence for Continental Drift.

• if the continents were once part of Pangaea, the rocks formed in a particular region on one continent should closely match the age and type of those in adjacent position on the adjoining continents

Continental Drift:

• Appalachian Mountains in eastern North America end off the coast of Newfoundland

• mountains of similar age with similar rocks and structures found in the British Isles and Scandinavia

Continental Drift:

Ancient Climates

Wegener found glacial deposits showing that between 220-300 mya, ice sheets covered large areas of the Southern Hemisphere.  Deposits of glacial till occurred at latitudes that today have temperate or even tropical climates: southern Africa, South America, India, and Australia.

Continental Drift:

• bedrock scratched and grooved by ice found below glacial debris in areas now located near the equator

• large tropical swamps that are now major coal fields found in eastern United States, Europe, and Siberia

Rejection of Wegener's Hypothesis

The main objection to Wegener’s hypothesis was that he could not describe a mechanism capable of moving the continents.

• most scientists of his day (1915) rejected Wegener’s hypothesis

• As technology developed, mapping the ocean floor, data about earthquake activity, and data about Earth’s magnetic field led to the development of the Theory of Plate Tectonics by 1967, which proved Wegener’s hypothesis correct.