plate tectonics
DESCRIPTION
Plate Tectonics. lithosphere. asthenosphere. mesosphere. Lithosphere (hard). Asthenosphere (soft). Mesosphere. Earth formed 4.6 bya. Inner Core- 4300 o C mostly iron core inner part is so compressed that it is solid Outer Core- 3700 o C iron and sulfur liquid. Crust - PowerPoint PPT PresentationTRANSCRIPT
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asthenosphere
lithosphere
mesosphere
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Lithosphere (hard)
Asthenosphere (soft)
Mesosphere
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Mantle- 1000oCmesosphere
•Solid•~ 2300 km thick
asthenosphere• Soft•~3000 km thick
lithosphere•hard •~100 km thick
Inner Core- 4300oC
• mostly iron core
• inner part is so compressed that it is solid
Outer Core- 3700oC
• iron and sulfur
• liquid Crust
• floats on top of lithospherecontinental crust (granite)
•20 to 70 km thick oceanic crust (basalt)
• ~ 8 km thick
Earth formed 4.6 bya
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Principles of plate tectonics
• The Earth is composed of a mosaic of thin rigid plates (pieces of lithosphere) that move horizontally with respect to one another
• Plates interact with each other along their plate boundaries
• Plate boundaries associated with tectonic activity (mountain building, earthquakes, active volcanoes)
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Alfred Wegener
• Proposed Theory of Continental Drift (1915)• Failed to provide a mechanism
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Evidence for Continental Drift
• continental shape• similar geology • fossil evidence (animal and plant)• volcano and earthquake zone• paleomagnetism
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Objections to the continental drift model
• Wegener envisioned continents plowing through ocean basins
• Wegener did not provide a plausible mechanism to explain how the continents could have drifted apart
• Most Earth scientists rejected continental drift because it was– Too far-fetched– Contrary to the laws of physics
Lacked technologyLacked technology
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Evidence for continental drift
• Matching coastlines on different continents
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Evidence for continental drift
• Matching mountain ranges across oceans
300 million years agoToday
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Evidence for continental drift• Glacial ages and climate evidence
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Mesosaurus
Distribution of fossils such as Mesosaurus
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Present Day
Jurassic 135 mya Cretaceous 65 mya
Triassic 200 myaPermian 225 mya
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Marie Tharp
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Marie Tharp's "World Ocean Floor Map”
1977
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Evidence for plate tectonics• Pattern of worldwide earthquakes (left)
matches plate boundaries (right)
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Hess- Convection Cell TheoryHess- Convection Cell Theory
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The 3 types of plate boundaries
1. Divergent
2. Convergent
3. Transform
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Divergent plate boundaries
• The Mid-Atlantic Ridge is a divergent plate boundary where sea floor spreading occurs
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Divergent plate boundaries
• Iceland sits atop a divergent plate boundary where continental rifting occurs
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Divergent plate boundaries
• Formation of an ocean basin by rifting and sea floor spreading
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Convergent plate boundaries
• Convergent plate boundaries vary depending on the type of crust
a. Ocean-continent
b. Ocean-ocean
c. Continent-continent
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Convergent plate boundaries
• An ocean-continent convergent plate boundary produces the Cascadia subduction zone and Cascade Mountains
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Convergent plate boundaries
• A continent-continent convergent plate boundary produces the Himalaya Mountains
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Transform plate boundaries
• Transform plate boundaries occur between segments of the mid-ocean ridge
• Can also occur on land (ex: San Andreas Fault)
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The world as it may look 50 million years in the future
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Glomar Challenger (1960’s)Deep sea ocean drilling
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S
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Mid-Ocean Ridge (Atlantic Ocean)
There have been 170 reversal in the last 76 million years. The earth’s present orientation has existed for the past 60,000 years.
+ +++ + +--- - - -
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Age of the Atlantic
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Inquiry
1. What layer of the mantle do the plates move on?
2. What is the convection cell theory?
3. Wegeners evidence for continental drift includes: ______.
4. Why was his theory disregarded?
5. What did Marie Tharp discover?
6. How are trenches formed?