Transcript Continental Drift Lecture

Earth Science
Plate Tectonics: A Scientific Theory
Unfolds from Continental Drift
Objectives
Review the historical background leading
to the Theory of Plate Tectonics
Discuss the Continental Drift hypothesis
Review evidence supporting the
Continental Drift hypothesis
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
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.
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
Historical Background on the
theory of plate tectonics
Antonio Pellegrini
• Geographer, 1858
• Made two maps of the world
• Before separation
After separation)
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
Historical Background on the
theory of plate tectonics
Alfred Wegener
• German meterologist
• 1912 Published 2 articles
• The Origin of Continents and Oceans
• Theory of continental drift
• 1915 proposed hypothesis of continental drift,
Supercontinent - Pangea (next slide)
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
Continental drift hypothesis
Evidence used by Wegener
• Wegener
•1st scientist look for
evidence of continental
separation using the
Scientific method!
Continental drift hypothesis
Evidence used by Wegener
Wegener -
Observation 1:
He 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.
- His opponents argued that erosion continually changes
shorelines over time.
Continental drift hypothesis
Evidence used by Wegener
Observation 2: Fossil evidence
•Several fossil organisms are found on different
landmasses in matching locations.
•Organisms could not have crossed the vast
oceans presently separating the continents
•Example: Mesosaurus
•Aquatic reptile
•Fossils limited to eastern South America
and southern Africa
• If the mesosaurs could swim the vast South Atlantic
Ocean, the fossils should be more widely distributed
•
Continental drift hypothesis
Evidence used by Wegener
Observation 3: Rock types and
structures match
•
•
•
Appalachian Mountains eastern side of North
America continues into Newfoundland
Rocks are similar in age and structure in the
British Isles and Scandinavia.
Landmasses form a nearly continuous belt of
matching rock types.
Continental drift hypothesis
Evidence used by Wegener
Observation 4: 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
Continental drift hypothesis
Evidence used by Wegener
•More Paleoclimatic evidence
•Glacial deposits 220-300 mya
•Shows ice sheets covered large
areas of the Southern Hemisphere
•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.
Satellite photo of parallel
lakes and mountain ridges
Greenland Glacier