Transcript Earth Science - Unit 2

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
• Before (avant la separation)
• After (apats la 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
• 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)
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 to go out an look for
evidence of continental separation
•Use of the Scientific method
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.
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
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?
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.
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
Continental drift hypothesis
Evidence used by Wegener
•Paleoclimatic evidence
•Glacial deposits 220-300 mya
•Ice sheets covered large areas of the Southern
Hemisphere.
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.
Summary