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Continental Drift. Continental Drift Theory. 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.
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Continental Drift Theory 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
Permian 225 mya Triassic 200 mya Jurassic 135 mya Cretaceous 65 mya Present Day
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 Continents • Wegener supported his theory with evidence from: • Landforms • Fossils • Climate
Landform Evidence • Wegener suggested that by looking at the shapes of the continents on a map, it seemed reasonable to suspect that they had all once been joined • Today, 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
Jigsaw Puzzle • 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
Similar Geology • Matching mountain ranges across oceans Today 300 million years ago
Fossil Evidence • Wegener 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
Fossil Evidence Distribution of fossils such as Mesosaurus
Climatic Evidence • He 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 Hypothesis • As compelling as this evidence was, Wegener’s theory was not accepted by the scientific community • It would take another 50 years for this to occur • He could not provide a satisfactory explanation for the force that pushes or pulls the continents • Wegener Video
