plate tectonics
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Plate Tectonics. BIG Idea:. Most geologic activity occurs at the boundaries between plates. I. Drifting Continents. - PowerPoint PPT PresentationTRANSCRIPT
Plate TectonicsPlate Tectonics
BIGBIG Idea: Idea: Most geologic activity
occurs at the boundaries between plates.
I. Drifting ContinentsI. Drifting Continents
• MAIN IDEA: The shape and geology of the continents suggests that they were once joined together.
Continental DriftContinental Drift
theory proposed by Alfred Wegener (VAY guh nur) in 1912
stated that the continents were once a single landmass
the continents have moved...
--Pangaea (“all the earth”): Pangaea (“all the earth”): supercontinent; single landmass single landmass --Panthalassa (“all seas”):Panthalassa (“all seas”): huge ancient huge ancient oceanocean
A. Evidence of Continental A. Evidence of Continental DriftDrift
1. Puzzle-Piece Fit
2. Rock Formations2. Rock Formations
Ages, types and layers of coastal rocks of widely separated regions matched…
Western Africa and Eastern Brazil
Appalachians (along eastern U.S.) fit Greenland and Europe
3. Fossils3. Fossils
Mesosaurus: freshwater reptile that lived 270 million years ago
• remains (fossils) found in South America and Africa
• impossible for these reptiles to have crossed the Atlantic
4. Climate4. Climate
(a) Glossopteris: fern that grew in temperate climates
places where fossils had been found were once closer to the Equator
rocks containing these fern fossils had once been joined
(b) Coal Deposits: Coal forms from ancient
swamp plants Coal beds found in
Antarctica indicated that this frozen land once had a tropical climate
Antarctica must have been closer to the Equator
(c) Glacier Deposits: found in Africa and South
America climates are much warmer
there today
A Rejected Notion…A Rejected Notion…
• Wegener’s Continental Drift Hypothesis was never accepted by the scientific community
• He could not explain what forces could cause such massive movement
• Wegener died in 1930, on expedition in Greenland, while collecting evidence to further support his theory
II. Seafloor SpreadingII. Seafloor Spreading
• MAIN IDEA: Oceanic crust forms at ocean ridges and becomes part of the seafloor.
1.Mid-Atlantic Ridge: undersea mountain range with a steep narrow valley down the center
• the middle of the ocean floor is very young
2. Renewal of the Ocean Floor:seafloor spreading - floor moving
away from the centerHarry Hess and Robert Dietz
3. Paleomagnetism: as magma solidifies the iron-rich minerals align with magnetic north like a compass
reverse polarityreverse polarity: magnetic : magnetic orientation pointing southorientation pointing south
III. Plate BoundariesIII. Plate Boundaries • MAIN IDEA: Volcanoes,
mountains, and deep-sea trenches form at the boundaries between the plates
Theory of Plate TectonicsTheory of Plate Tectonics• Plate Tectonics:
theory that the lithosphere is made of rigid plates that ‘float’ on the asthenosphere
• Tectonics: the study of the formation of Earth’s features
What are the What are the inferredinferred properties of Earth’s properties of Earth’s
interior?interior?
Zones of EarthZones of Earth1. Crust: thin,
solid outermost layer; surrounds Earth like a shell surrounds an egg.
Two Types of Crust:Two Types of Crust:
Continental Crust: makes up the continents (land); thicker, less dense; granitic rock
Oceanic Crust: under the oceans; thinner, MORE dense; basaltic rock
2. Moho: boundary between the crust and mantle.
3. Mantle: thickest layer sits below the crust makes up 2/3 of the Earth’s
mass
•Lithosphere (‘rocky sphere’): upper part of mantle, cool and rigid
•Asthenosphere (‘weak sphere’): lower (‘plastic’) mantle; flows like hot tar
•Plasticity: the ability of a solid to flow
4. Core: center of the Earth; two parts:
• InnerInner Core: ball of hot, solidsolid metals (iron and nickel)
OuterOuter Core: only true liquidliquid zone
If we’ve never been If we’ve never been there, how have we there, how have we learned about the learned about the interior of Earth?interior of Earth?
By studying seismic By studying seismic waves…waves…
Seismic Wave:Seismic Wave: vibration that travels through the Earth; results from earthquakes or huge explosions
Types of Plate Types of Plate BoundariesBoundaries
1. 1. Divergent BoundariesDivergent Boundaries: • two plates that are moving
AWAY from each other• as plates move apart, the
asthenosphere flows up to fill the empty space
What forms when plates What forms when plates DIVERGEDIVERGE??
a. Mid-Ocean Ridges Mid-Ocean RidgesMid-Atlantic RidgeMid-Atlantic Ridge
b. Rift Valleys:b. Rift Valleys:(1) narrow valleys in the (1) narrow valleys in the middle middle of ocean ridgesof ocean ridges
(2) where continents (2) where continents separateseparate
East African Rift East African Rift ValleyValley
2. 2. Convergent Convergent BoundariesBoundaries
• direct collision of one plate with another
Three types of converging Three types of converging boundaries:boundaries:
• Types of Convergent Boundaries
OceanicOceanic vs. vs. ContinentalContinental
Subduction Zone:Subduction Zone: – oceanic crust moves (dives) under continental crust
forms an oceanic trench and volcanic mountain range
oceanic crust is more dense than continental, thus it dives down or subducts
Andes Mountain RangeAndes Mountain Range
Mount Saint Helens - Mount Saint Helens - Cascade Cascade
Mountain RangeMountain Range
OceanicOceanic vs. vs. OceanicOceanic
older, more dense oceanic crust subducts
forms trenches and arcs of volcanic islands
Aleutian IslandsAleutian Islands
Mariana TrenchMariana Trench
ContinentalContinental vs. vs. ContinentalContinental
no subduction two continental plates collide
pushing up and creating folded mountains
3. 3. Transform BoundariesTransform Boundaries • Plates slide horizontally
past each other
IV. Causes of Plate IV. Causes of Plate MotionsMotions•MAIN IDEA: MAIN IDEA: Convection Convection
currents in the mantle currents in the mantle cause plate cause plate motions.motions.
coolcool material sinkssinks as hothot material risesrises, due to
DENSITY DIFFERENCESDENSITY DIFFERENCES.