warm-up #43 mar. 26
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Warm-up #43 Mar. 26. Brainstorming: Will California eventually slide into the ocean? Have continents really drifted apart over the centuries?. Unit 8. Plate Tectonics. Continental Drift. Alfred Wegener – German scientist proposed the theory of continental drift. - PowerPoint PPT PresentationTRANSCRIPT
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Warm-up #43 Mar. 26
Brainstorming:Will California eventually slide into the ocean?
Have continents really drifted apart over the centuries?
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PLATE TECTONICS
Unit 8
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Continental Drift Alfred Wegener – German scientist
proposed the theory of continental drift. This hypothesis stated that the
continents had once been joined to form a single supercontinent
Pangaea – all land
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Pangaea Part of Wegener’s theory was that
Pangaea started splitting into smaller continents 200 million years before
Wegener collected lots of evidence to prove this theory
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The Continental Puzzle The shorelines of the continents nearly fit
together to make a large land mass. HOWEVER The shorelines are constantly eroding and
changing.
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Matching Fossils Fossil evidence for continental drift
includes several fossil organisms found on different landmasses.
At one point the theory was that there were land bridges, however there is no evidence of this.
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Rock Types and Structures Several mountain belts that end at one
coastline reappear on a landmass across the ocean
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Ancient Climates Wegener found glacial deposits showing
that between 220 million and 300 million years ago ice sheets covered large areas of the S. Hemisphere
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Rejecting Wegener’s Hypothesis Many scientists questioned Wegener’s
theory He could not describe a mechanism that
was capable of moving the continents There was not enough evidence
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A New Theory In 1968 a new theory was proposed –
PLATE TECTONICS
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Plates The lithosphere is broken up into
segments called plates The lithosphere is the uppermost layer
of the mantle Plates continuously move and change
shape and size
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Warm-up #44 Mar. 27 Mesosaurus provided evidence that South
America and Africa were once joined
On average, how much do you think the plates move a year?
5 centimeters
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Plate Boundaries A plate boundary is where two plates
meet. There are three main types of
boundaries:DivergentConvergentTransform fault
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Divergent Also called spreading boundaries Occurs when two plates move apart Results in upwelling of material from the
mantle to create new seafloor
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Convergent Form where two plates move together Results in lithosphere plunging beneath
an overriding plate and descending into the mantle
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Transform fault Margins where two plates grind past
each other without the production or destruction of lithosphere
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What happens at boundaries? Divergent Boundaries
Seafloor spreading occurs along the boundary
Forms fractures on the ridge crestsFractures fill with molten materialWhen the boundary occurs on a continent,
rifts or rift valleys form
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Convergent Boundaries Oceanic-continental boundary
Forms a subduction zone withinVolcanic arcs form
Oceanic-oceanic boundaryOften forms volcanoes on the ocean floorIsland arc forms as volcanoes emerge
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Convergent Boundaries Continental-continental boundaries
Neither plate will subductCan produce mountains
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Transform Fault Boundaries No new crust created No crust is destroyed Most are in oceanic crust Parallel the direction of
plate movement Aids movement of crustal
material
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Boundary Brochures Needs to include:
3 types: Divergent, Convergent, TransformWhat each one is (use your notes)A picture for eachAn example for each
○ http://geology.com/plate-tectonics.shtmlNeeds to be colored
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Warm-up #45 Mar.28Brainstorming: Do you think it is possible for Earth’s
magnetic poles to be reversed? If so, what do you think could happen to
the biosphere? Also, how might geologist use that to
support plate tectonics?
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Evidence for Plate Tectonics Paleomagnetism
Most persuasive piece of evidence.Ancient magnetism preserved rocks.Paleomagnetic records show:
○ Polar wandering○ Earth’s magnetic field reversals
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Evidence for Plate Tectonics Earthquake patterns
Associated with plate boundariesDeep-focus earthquakes along trenches
provide a method for tracking the plate’s descent
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Evidence for Plate Tectonics Ocean Drilling
Deep Sea Drilling Project – Glomar Challenger
Age of deepest sediment○ Youngest are near the ridges○ Older are at a distance from the ridge
Ocean basins are geologically young
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Evidence for Plate Tectonics Hot Spots
Rising plumes of mantle material.Volcanoes can form over
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Driving Mechanism No one model explains all plate motion Earth’s heat is the driving force Several models have been proposed
Convection currents in the mantleSlab-pull and slab-push model Hot plumes
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Dynamic Earth http://www.learner.org/
interactives/dynamicearth/index.html
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Ticket out the Door1. What are the 3 main types of plate
boundaries?2. Name 2 pieces of evidence Wegener
used to prove continental drift.3. What is type of boundary is this?