Date post: | 20-Dec-2015 |
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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
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)
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 plate tectonics• Pattern of worldwide earthquakes (left)
matches plate boundaries (right)
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
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)
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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