GEO 101 Lecture Notes - Lecture 8: Jigsaw Puzzle, Continental Drift, Supercontinent Cycle
21 Feb 2018
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Plate Tectonic Theory-
• Earth’s surface shell consists of about 20 plates
• The tectonic pates move relative to one another
• Plate movement causes continents to drift
• Interactions at plate boundaries cause earthquakes,
volcanoes, and mountain building
(The smaller the plate, the more it will move)
Earth’s Compositional Layers-
• Inner Core- solid
• Outer core- liquid
• Mantle- plastic consistency (neither liquid or solid)
• Crust- oceanic and continental
Earth’s Mechanical Layers-
• Lithosphere
o Crust and uppermost mantle
o Rigid and brittle
• Asthenosphere
o Mantle down to 660 km
o Plastic, flows very slowly
o Not molten!!!
Oceanic vs. Continental Lithosphere-
• Continental
o Thicker than oceanic
o Composed primarily of granite (less dense)
• Oceanic
o Thinner than continental
o Composed of basalt and gabbro (more dense)
• Pieces of the lithosphere= plates
Wegner’s Hypothesis of continental drift-
• Suggested- once there was a supercontinent (Pangaea) that
broke apart to form modern continents
The Wilson Cycle- the rise and fall of supercontinents through deep
time
Wegner’s Lines of Evidence-
• “Jigsaw puzzle” fit of all the continents
• Evidence of past glaciations
o Locations of glacial deposits not in polar locations
o Striations- scratches on rock produced by ice moving
over it
o Striations pointed outward from a common point
• Tropical/sub-tropical climates across southern North America
and northwest Africa
o Coal deposits (formed by swamps and jungle)
o Tropical reef environments
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