2Animation of Continental Drift pangea movingPangea w/ labelsPANGAEA:Name of a supercontinent.All continents were once combined.Broke apart to form our current continents.
3Sect 1: Continental Drift Alfred Wegener came up w/ Continental Drift HypothesisContinents are constantly moving (on the surface of Earth).So slowly we don’t feel it.No one believed him … WHY?Couldn’t explain HOW the continents moved.
4Evidence FOR Cont. Drift (4 Ways) 1) Fossil Clues: Fossils found on the edge of continents that were once joined MATCH.Ex. Glossopteris (plant) – found on different continents.Other fossils of similar organisms found on several continents – separated by oceans. (Organisms that cannot swim!)2) Rock Clues: Same rocks on the edge of continents that were once joined MATCH.Ex. West Africa rocks match East South AmericaLook at Chemistry and age of rocks.Mountain ranges in N. Europe match eastern N. America (Caledonian Mts to Appalachian Mts.)
5Evidence Cont.3) Climate Changes: Certain areas have evidence that the continents once had different climates … AGAIN: Continents match!Ex.) Sediments left from glaciers …-Same in S. America & Africa-Same in India & Australia*Beneath sediments – grooves (marks left by glaciers)4) Continents look like puzzles pieces that fit together.
6Sect. 2: Seafloor Spreading Process by which:New oceanic crust forms along mid-ocean ridgesOlder oceanic crust moves away from the ridge.Began to explore ocean floor after WWII –led to new discoveries – led to this process.Started using Sound Waves to map ocean floor.Created detailed maps.Discovered:Mountain Ranges, Valleys, etc. like those found on Continents.Mid-Ocean Ridges = mountain ranges in the middle of the oceans. (Much longer than on land.)
7Theory states: (Helped explain how continents move): Seafloor spreads = plates are moving apart.Mantle (crust) melts and forms magma (like lava only inside Earth).Magma is less dense than mantle (crust) so it… rises through cracks along the mid-ocean ridges.Seeps through = lava … cools quickly forms a rock type called basalt. (Forms shape like a pillow so called pillow lava.)**Means: young rocks are by ridges and rocks get older as you move away from ridges.
8Why this discovery was important: Wegener was RIGHT!This explains HOW the continents are moving.Continents do NOT move through the solid mantle or seafloor.Continents move as the seafloor moves.
9iv) Evidence supporting Seafloor Spreading … Ages of Rocks: younger at ridges and increasingly older as you move away from center of ridges.Magnetic Pole Reversal: found in rocks – showed a pattern parallel to ridges. (Basalt contains iron-rich minerals –magnetic)Normal Polarity: magnetized objects point North.Magnetic Reversal: changes direction.Reversed Polarity: magnetized objects point SOUTH instead of North.
10How ? Studied magnetic minerals in rocks on seafloor. Found parallel magnetic strips on either side of M-O ridges. (Same composition, age and magnetic character.)Patterns = line up a certain way during periods of normal or reversed polarity.Sediment from seafloor can be dated – next to m-o. ridges younger than farther away. (Sediment thickness increases too.)
11What does this image show? Seafloor spreading, stripes of basaltic rockWhich stripes are the oldest? Newest?Further outside, further insideHow can you tell? New magma rises from mid-ocean ridge
12Sect. 3: Plate Tectonics PLATE TECTONICS THEORY: PLATES: Rigid SECTIONS OF THE EARTH’S CRUST THAT MOVE. (picture P. 234)PLATE TECTONICS THEORY:- Theory that combines Cont. Drift and Seafloor Spreading.- Crust is broken into sections that move.-Layer below is thick liquid like material that moves.Video
13Force Behind Plate Techtonics CONVECTION CURRENT!!!OCCURS THROUGHOUT MANTLECYCLE OF HEATING, RISING, COOLING, SINKING.
14Closer look at Crustasthenosphere and lithosphere
15Top Layer Vocab:LITHOSPHERE: Includes the CRUST and part of the Upper Mantle.RIGID!! (HARD)ASTHENOSPHERE: movable layer below the Lithosphere. Where convection current IS!!MOVABLE !!! (Thick liquid like material.)
163 WAYS PLATES MOVE 1)Convergent: move TOWARDS each other. 2.) Divergent: move AWAY from each other or pull apart.3.) Transform:Slide by each other.Different directions ORSame direction but one plate is moving slower.
17Divergent BoundaryAlmost all the Earth's new crust forms at divergent boundaries.Most are not well known because they lie deep beneath the oceans.These are zones where two plates move away from each other, allowing magma from the mantle to rise up and solidify as new crust.
24Plate MotionConvection Current – circulation of material caused by diff. in temp. and density.Forces:Basal Drag = conveyor belt movement (lithosphere moves)Ridge Push = force causes plates to move away from m-o ridges in opposite directions.Slab Pull = force pulls slab (harder, older crust) down into mantle
25Features on Earth made by Plate Tectonics … 1) AT Divergent Plate Boundaries:Normal FAULTS (Tension forces pull crust apart and cause rocks to break and move = fault line.)Rift Valleys: continent & continent pulling apart (ex. Africa)Mid Ocean Ridges
262) AT Convergent Boundaries Continent to Continent = Mountain Ranges: forces cause massive folding and faulting.(Ex. Himalaya Mountains are still forming.)Ocean to Ocean = Volcanoes …Island Arcs: Curved chain of volcanic islands – form above the sinking plate.Trenches
27Convergent Cont.Ocean to Continent = Volcanic Mountain ranges: continent is again folding and faulting.Volcanoes form w/in the mountains.(Along coasts)Of course, Trenches
283) Transform Boundaries Strike - Slip FAULTS:the plates try to move past each other they stick and then slide.When they stick and then suddenly move , this motion causes vibrations = earthquakes.Ex. San Andreas Fault
29Rate of Plate Movement Varies … 1 cm to 12 cm / yr. Use lasers and satellites to figure out how much.Hawaii is moving TOWARD Japan = 8.3 cm / yr.Maryland is moving AWAY from England= 1.7 cm/yr
30Flow Chart for Features Landforms Compression Tension Shear Stress (Converge) (Diverge) (Transform) Mts. Vol. M-O Cont. Trans Fracture Fault Arcs Ridges Rift Fault Zones Zones (Rift Trenches Valleys)
31Ch 8 Vocab Transform Fault: Fault Zone: Plates slide past each other Break in Earth’s crustFault Zone:Area of MANY fractured pieces BY a large fault.
32Mountains 1) Fault Block Mountains 2) Uplifted Mountains Tension forces WITHIN a continent.Some blocks rise or fallParallel Ridges.2) Uplifted MountainsRise VERTICALLYLittle DeformationDon’t totally understand … think sections break off = mantle sinks and the other side rises.
33Mountains Cont. 3) Folded Mts. Happens deeper in crust. Therefore: sections are warmer & under pressure**that is why they FOLD instead of break.HOW do Mts. change over time?Collisions & RiftingWeatheringEx) Appalachians – old, not growing so not as high or rugged as Rockies.UpliftBALANCE (Erodes – wears down – new crust rises to replace it.)