1. Plate Tectonics: A Scientific Theory Unfolds from Continental Drift
Earth Science
Plate Tectonics: A Scientific Theory Unfolds from Continental Drift

3. Objectives
Review the historical background leading to the Theory of Plate Tectonics
Discuss the Continental Drift hypothesis
Review evidence supporting the Continental Drift hypothesis

4. Historical Background on the theory of plate tectonics
Abraham Ortelius
Dutch map maker, 1596
Suggested that the Americas were “torn away from Europe and Africa by great floods and earthquakes”
1st time suggested in written form

5. Historical Background on the theory of plate tectonics
Catastrophism
Until the 1700’s most Europeans thought that a biblical flood played a role in shaping the earth’s surface.
Geology was based on the belief that all changes were sudden and caused by a series of catastrophes

6. Historical Background on the theory of plate tectonics
James Hutton
Father of modern Geology, 1785
Doctrine of uniformitarianism
The present is the key to the past
Geologic forces and processes - both gradual and catastrophic

7. Historical Background on the theory of plate tectonics
Antonio Pellegrini
Geographer, 1858
Made two maps
Before (avant la separation)
After (apats la separation)

8. Historical Background on the theory of plate tectonics
Eduard Suess
Viennese Geologist, 1880
Recognized an Atlantic type of margin
Identified by abrupt truncation of former mountain belts
Recognized a pacific type of margin
Identified by parallel mountain ranges, lines of volcanic areas and frequent earthquakes

10. Historical Background on the theory of plate tectonics
Alfred Wegener
32 year old german meterologist, 1912
Published 2 articles
The Origin of Continents and Oceans
Theory of continental drift
First proposed hypothesis of continental drift, 1915
Supercontinent - Pangea (next slide)

11. Continental drift hypothesis
Supercontinent called Pangaea began breaking
apart about 200 million years ago
Continents "drifted" to present positions
Continents "broke" through the ocean crust
Figure 15.2

12. Continental drift hypothesis Evidence used by Wegener
1st scientist to go out an look for evidence of continental separation
Use of the Scientific method

13. Continental drift hypothesis Evidence used by Wegener
Evidence: The Continental Puzzle
Wegener -
Noticed the similarity between the coastlines on opposite sides of the South Atlantic Ocean
Thought that the continents might have been joined
He used present-day shorelines to show how the continents fit together.
However, his opponents correctly argued that erosion continually changes shorelines over time.

14. Continental drift hypothesis Evidence used by Wegener
Fossil evidence
Several fossil organisms found on different landmasses
Organisms could not have crossed the vast oceans presently separating the continents

15. Continental drift hypothesis Evidence used by Wegener
Fossil Evidence continued
Example:
Mesosaurus
Aquatic reptile
Fossils limited to eastern South America and southern Africa
If could swim the vast South Atlantic Ocean
Fossils should be more widely distributed
Land bridges?

16. Continental drift hypothesis Evidence used by Wegener
Rock types and structures match
Appalachian Mountains eastern side of North America into Newfoundland
Similar in age and structure in the British Isles and Scandinavia.
Landmasses form a nearly continuous belt.

17. Continental drift hypothesis Evidence used by Wegener
Ancient climates
The Northern Hemisphere was once tropical
Evidence:
Coal deposits that were formed from tropical plants.
Assumption:
Large change in climate could not have taken place without continental drift
Instead, N. Hempishere nearer equator

18. Continental drift hypothesis Evidence used by Wegener
Paleoclimatic evidence
Glacial deposits mya
Ice sheets covered large areas of the Southern Hemisphere.

19. Continental drift hypothesis Evidence used by Wegener
Paleoclimatic evidence
Layers of glacial till
Southern Africa
South America
India
Australia.
Below beds of glacial debris
Scratched and grooved bedrock carved by the ice.
Looked like ice moved from sea onto land.

20. Summary