continental drift and plate tectonics

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Continental Drift and Plate Tectonics

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Continental Drift and Plate Tectonics. History of Continental Drift. In German "die Verschiebung der Kontinente" As long as 400 years ago, map makers noted that the continents ’ shapes looked to fit together like a puzzle. LOOK! - PowerPoint PPT Presentation

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Page 1: Continental  Drift and Plate Tectonics

Continental Drift and Plate Tectonics

Page 2: Continental  Drift and Plate Tectonics

History of Continental Drift• In German "die Verschiebung der Kontinente"

• As long as 400 years ago, map makers noted that the continents’ shapes looked to fit together like a puzzle.

• LOOK!

• Cartographer Abraham Ortelius in his work Thesaurus Geographicus ... suggested that the Americas were "torn away from Europe and Africa ... by earthquakes and floods"

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The Completed Puzzle

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Theory of Continental Drift

• 1912: Alfred Wegener proposed that continents move!

• Reaction by the scientific community-• HAHAHAHAHAHA. ROFL - ARE YOU KIDDING?

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Why did Wegener theorize continental drift?

#1 Shape of the continents

#2 Fossil clues: •Wegener found similar fossils on different continents•The fossils that he found could probably not have spread between continents

• Freshwater reptile fossil• Plant fossil • Similarly evolved species

•Why are these two significant? Would finding a bird on two continents support continental drift as well?

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•#3 Climate clues•Wegener found warm climate fossils in the Arctic and cold climate fossils near the equator.

• Warm weather fossils

• Evidence of glaciers

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•#4 Rock cluesWegener found similar strata (layers) of rocks on

different continents.

• Could this be a coincidence?

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Matching Rock Layers

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• Pangaea – (“all land”) existed about 250 million years ago and began separating around 200 million years ago.

• Problem - Wegener’s theory proposed only that the continents were once one supercontinent and they had “moved” apart but could not explain HOW.

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• Things Wegener didn’t know:

• What the inside of the Earth looked like• That the Earth was broken into plates• That the location of earthquakes and

volcanoes shows plate boundaries• Convection Currents

• Was his theory accepted by other scientists?• His theory did not become accepted

until the 1950’s/1960’s. Why?• Wegener was appreciated

posthumously

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• 1960’s: Harry Hess given credit for providing some of the proof necessary to support Wegener’s theory

• Hess’s theory of seafloor spreading

• Believed that material moved up at mid-ocean ridges and pushed material outward

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Mid-Ocean RidgesDiscovered in 1950’s

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•Why Did Hess believe that the seafloor was spreading?

• The discovery of the mid-ocean ridges

• Core samples of ocean floor showed that the age of rocks INCREASED the farther they were from mid-ocean ridges

• Core samples also showed corresponding magnetic reversals on each side of the mid-ocean ridge

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Rock Ages

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Magnetic Reversals

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So where are we at this point?

• We believe the continents have moved.

• These findings provided proof for Hess’s theory and further supported Wegener’s theory

• Theory of Plate Tectonics has still not been developed.

• But no one still understands why or how the plates move. We are still lacking the MECHANISM.

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3

• 1960’s Wilson and other scientists gave mechanism to explain HOW the plates are moved.

• Scientists proposed that the Earth’s lithosphere is broken into plates, and that CONVECTION CURRENTS in the plastic asthenosphere moved the lithospheric plates above.

• All of this information, plus LOTS more, developed into our current theory of Plate Tectonics.

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Mapping Volcanoes

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Mapping Earthquakes

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Plate boundaries:

• This is where two or more lithospheric plates meet

• Called faults or boundaries

• Lots of tectonic activity (i.e. volcanoes and earthquakes) occurs at these places

• Three types:

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Convergent Boundaries

• Two plates colliding (moving together)

• If the plates are ocean-continental: Subduction zones, mountains, volcanoes and ocean trenches will form

• Oceanic crust is destroyed here• More dense (basalt vs. granite)• Examples are Ring of Fire and Andes Mts

• If the plates are both continental

• No subduction, only mountain building• Himalayas are example• Crust is neither created nor destroyed

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“Ring of Fire”

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Andes Mountains

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Himalayan Mountains

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Divergent BoundariesTwo plates moving apart

• If the plate is an ocean plate:• Forms mid-ocean ridge• Mid-Atlantic Ridge is example

• If the plate is continental:• Forms rift valleys• Great Rift Valley is example

• New rock is created here

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Mid-Atlantic Ridge

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Great Rift Valley

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Transform Boundaries

a.k.a. Strike-Slip boundaries

• Two plates sliding/scraping past each other• Earthquakes are common• Crust is neither created nor destroyed • San Andreas Fault and Haiti our examples

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San Andreas Faultdoes NOT involve the Juan de Fuca plate

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Haiti 2010

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• Where would each form?• Volcano• Seafloor Spreading• Mountains• Subduction Zone• Rift Valley

• Name two places where each type of boundary would form using your text.

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Plate Tectonics – late 1960’sPost Harry Hess’ Seafloor Spreading

• Plate tectonics (from the Latin tectonicus, from "pertaining to building”) is a scientific theory that describes the large-scale motion of Earth's lithosphere on a molten asthenosphere, due to convection currents caused by the transfer of heat from the Earth’s core.

• Plate motions range up to a typical 10–40 mm/year (Mid-Atlantic Ridge; about as fast as fingernails grow), to about 160 mm/year (Nazca Plate; about as fast as hair grows).

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Why do the plates move?

• Solid lithospheric plates move because the plastic asthenosphere is moving.

• Radioactive reactions in the core heat magma deep in the Earth which becomes less dense and rises.

• As magma cools it becomes more dense, sinks, then reheats, forming CONVECTION CURRENTS (50 million years, though deeper convection can be closer to 200 million years).

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Measuring plate movement

• Scientists NOW use lasers, GPS and satellites to measure plate movement over time.

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How far would you have to drill through the lithosphere to get to

the asthenosphere?7 – 70 km (4 – 45 miles)

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