Continental Drift

Alfred Wegener

the gradual movement of the continents across the earth's surface through geological time

Drifting Continents Geologists believed that the

continents remained fixed in their position

In 1910 Alfred Wegener hypothesized that all the continents had once been joined together in a single landmass and have since drifted apart

He named the single landmass – Pangaea (“all lands”)

His theory became known as continental drift

Present Day

Jurassic 135 mya Cretaceous 65 mya

Triassic 200 myaPermian 225 mya

The continents are still slowly moving, at about the speed your fingernails grow. Satellite measurements have confirmed that every year the Atlantic Ocean gets a few inches wider!

Quick Check

Turn and tell your neighbor who came up with the continental drift theory.

Drifting ContinentsWegener supported his theory with evidence from:

LandformsFossilsClimate

Landform EvidenceWegener suggested that by looking at the shapes of the continents on a map, it seemed reasonable to suspect that they had all once been joinedToday, we have a much better idea of the true outer boundary of each continent by examining its continental shelf

The seaward edge of a continental shelf lies submerged below the ocean. When the edges of the continental shelves at a depth of 900 meters are placed together, the fit is remarkable

• Matching coastlines on different continents

Landform Evidence Mountain ranges and other features on the continents provided further evidence

For example, the Appalachian mountains of eastern North America matched with the Scottish Highlands

When these landmasses are reassembled on a map of Pangaea the mountain chains form a nearly continuous belt

• Matching mountain ranges across oceans

300 million years agoToday

Fossil EvidenceWegener found identical fossils on the matching coastlines of both South America and Africa

Wegener argued that South America and Africa must have at one time been joined

Distribution of fossils such as Mesosaurus

Fossil Evidence

Climatic EvidenceHe found evidence for dramatic global climatic changes

Deep scratches on bedrock in Africa indicated that at one time it was covered in glaciers, which means it must have been much closer to the South Pole

He also found that the fossils found in a certain place often indicated a climate utterly different from the climate of today

i.e. tropical fossils in climates that currently have a harsh polar climate

Evidence for Continental Drift

• Glacial ages and climate evidence

Quick Check

Turn and tell your neighbor the three pieces of evidence Wegener used to support his continental drift theory

Scientists Reject Wegener’s HypothesisAs compelling as this evidence was, Wegener’s theory was not accepted by the scientific community

It would take another 50 years for this to occurHe could not provide a satisfactory explanation for the force that pushes or pulls the continents

Wegener Video