CONTINENTAL DRIFT AND PLATE TECTONICS. HISTORY OF CONTINENTAL DRIFT In German "die Verschiebung der...
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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
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?
Slide 5
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 clues Wegener 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 - Wegeners
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 didnt 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 1950s/1960s. Why? Wegener was
appreciated posthumously
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1960s: Harry Hess given credit for providing some of the proof
necessary to support Wegeners theory Hesss theory of seafloor
spreading Believed that material moved up at mid- ocean ridges and
pushed material outward
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Mid-Ocean Ridges Discovered in 1950s
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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 Hesss theory and further
supported Wegeners 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 1960s Wilson and other scientists gave mechanism to explain
HOW the plates are moved. Scientists proposed that the Earths
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.
Slide 24
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 BOUNDARIES TWO 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 FAULT DOES 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 1960s Post 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 Earths
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.
Slide 47
How far would you have to drill through the lithosphere to get
to the asthenosphere? 7 70 km (4 45 miles)