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

2. 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
Catastrophism
Ortelius
Hutton
Pellegrini
Suess
Wegener

5. 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. 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

7. 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

8. Antonio Snider-Pellegrini
Geographer, 1858
Made two maps
Before (avant la separation)
After (apats la separation)

9. 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
Frequent earthquakes

11. Alfred Wegener Young German meteorologist
First proposed continental drift in1915
Published 2 articles:
The Origin of Continents and Oceans
Theory of Continental Drift

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

13. Continental Drift Wegener stated that:
Continents move apart and together over time
All continents moved together about 300 mya
They formed a supercontinent - Pangaea
They began breaking apart about 200 mya
Continents "drifted" to present positions
Continents "broke" through the ocean crust
Figure 15.2

14. Continental Drift Hypothesis
Wegener used four lines of evidence to support his hypothesis:
Continental Puzzle
Matching fossils on continents
Matching mountain ranges across the Atlantic Ocean
Ancient climate
N. Continents located over the equator
S. Continents covered in giant ice sheet

15. 1) The Continental Puzzle
Wegener
Saw a similarity between the coastlines on opposite sides of the South Atlantic Ocean.
Thought that the continents likely had been joined.
Used present-day shorelines to show how the continents fit together.
Where did he get this idea from?
Ortelius and Pellegrini

16. 2) Fossil Evidence
Several fossil organisms found on different landmasses
Organisms could not have crossed the vast oceans presently separating the continents
Organisms evolving on separate continents does not fit with Natural Selection

17. 3) Matching Mountain Ranges
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.

18. 4) Ancient Climates Northern Continents Southern Continents
Likely located over the equator
Evidence:
Found coal deposits formed from tropical plants.
Southern Continents
Ice sheets likely covered large areas of S.Africa, S.America, India and Australia.
Layers of glacial till
Scratched and grooved bedrock carved by the ice

19. 4) Ancient Climate Continued.
Assumption:
Tropical forests would not exist in the Northern hemisphere at the same time as a glacial ice sheet covering most of the southern hemisphere
Instead: present day northern continents were nearer the equator and all continents were connected

20. Summary