Plate Tectonics
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Transcript of Plate Tectonics
asthenosphere
lithosphere
mesosphere
Lithosphere (hard)
Asthenosphere (soft)
Mesosphere
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
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)
Alfred Wegener
• Proposed Theory of Continental Drift (1915)• Failed to provide a mechanism
Evidence for Continental Drift
• continental shape• similar geology • fossil evidence (animal and plant)• volcano and earthquake zone• paleomagnetism
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
Evidence for continental drift
• Matching coastlines on different continents
Evidence for continental drift
• Matching mountain ranges across oceans
300 million years agoToday
Evidence for continental drift• Glacial ages and climate evidence
Mesosaurus
Distribution of fossils such as Mesosaurus
Present Day
Jurassic 135 mya Cretaceous 65 mya
Triassic 200 myaPermian 225 mya
Marie Tharp
Marie Tharp's "World Ocean Floor Map”
1977
Evidence for plate tectonics• Pattern of worldwide earthquakes (left)
matches plate boundaries (right)
Hess- Convection Cell TheoryHess- Convection Cell Theory
The 3 types of plate boundaries
1. Divergent
2. Convergent
3. Transform
Divergent plate boundaries
• The Mid-Atlantic Ridge is a divergent plate boundary where sea floor spreading occurs
Divergent plate boundaries
• Iceland sits atop a divergent plate boundary where continental rifting occurs
Divergent plate boundaries
• Formation of an ocean basin by rifting and sea floor spreading
Convergent plate boundaries
• Convergent plate boundaries vary depending on the type of crust
a. Ocean-continent
b. Ocean-ocean
c. Continent-continent
Convergent plate boundaries
• An ocean-continent convergent plate boundary produces the Cascadia subduction zone and Cascade Mountains
Convergent plate boundaries
• A continent-continent convergent plate boundary produces the Himalaya Mountains
Transform plate boundaries
• Transform plate boundaries occur between segments of the mid-ocean ridge
• Can also occur on land (ex: San Andreas Fault)
The world as it may look 50 million years in the future
Glomar Challenger (1960’s)Deep sea ocean drilling
S
N
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.
+ +++ + +--- - - -
Age of the Atlantic
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?