Transcript Plate Tectonics - Londonderry School District
Continental Drift Theory
• Alfred Wegener • German meteorologist • 1912 Proposed single supercontinent Pangaea • Continental Drift Theory
Continental Drift Theory 5 Types of Evidence • Fit of the Continents • Distribution of Fossils • Sequence of Rocks • Glacier Scraping Patterns • Ancient Climates and Wandering Polar Regions http://library.thinkquest.org/3669/media/map2dd.GIF
Wegener’s Continental Drift Evidence: • Continents ‘fit’ together in a single land mass 250 mya • CLICK Simulations http://www.ucmp.berkel
ey.edu/geology/anim1.
html http://www.eoearth.org/upload/thumb/f/fb/Plate_tectonics_over_time.gif/400px-Plate_tectonics_over_time.gif
Wegener’s Continental Drift Evidence : Plant and animal fossils of the same species were found on several different continents.
Wegener’s Continental Drift Evidence: Similar sequence of rock or rock formations have the same age
Wegener’s Continental Drift Evidence: Glacial deposits, striations, and scraping patterns
Wegener’s Continental Drift Evidence: Climate distribution Past Present Coal exists under the ice in the rock of Antarctica – yet coal can only form from plants that grow in warm climates.
Wegener’s Theory Problems
1) Wegener had no convincing mechanism (did not explain the forces) of how the continents might move. Continents plowing through the crust would destroy the crust. 2) Continents are not moving apart at the speed Wegener proposed. Wegener = 250cm/yr Actual = 2 cm/yr
Holmes Breakthrough: Heat trapped in the Earth caused Convection Currents in the mantle. • As a substance is heated its density decreases and rises to the surface until it is cooled and sinks again.
Convection currents
• Gravity causes the heated mantle to sink • The mantle heats up near the core and then rises again • Conduction is the transfer of heat between 2 materials in direct contact with each other library.thinkquest.org/C003124/images/convect.jpg
http://www.wisc-online.com/objects/index_tj.asp?objID=SCE304 Click animation
New Evidence - Magnetic pattern of rock Volcanic rocks on the seafloor have magnetization because, as they cool, magnetic minerals within the rock align to the Earth’s magnetic field.
North Magnetic Pole in No. Hemi
North Magnetic Pole in So. Hemi
Present Day North Magnetic Pole in No. Hemi
Sea-Floor Spreading Hypothesis by Hess & Deitz CLICK Animation: http://www.uwsp.edu/geo/faculty/ritter/glossary/s_u/sea_flr_spread.html
Plate Tectonics
www.wiley.com/college/herenow/ptect/pt-map1.gif
Plates ‘float’ on the Asthenosphere Plates have oceanic and continental crust
Earth’s Layers
• Inner Core • Outer Core • Mantle • Crust • Atmosphere http://library.thinkquest.org/04oct/01724/images/Earth-crust-cutaway-english.png
• Lithosphere – crust and upper mantle, plates move independently • Asthenosphere-region below the Lithosphere
Continental Crust
http://www.amonline.net.au/geoscience/images/earth_diagrams/cont_oceanic_crust.gif
• Cooling rate - slow • Crystal size - large • Density - less dense • Thickest portion of the Earth’s outer layer • Composition – made mainly of granite rock
Oceanic Crust
• Cooling rate - fast • Crystal size - small • Density – more dense • Thinnest portion of the Earth’s outer layer • Composition – Made mainly of basalt rock http://faculty.weber.edu/bdattilo/parks/plume_ocean.jpg
Volcano opening or rupture in the Earth’s crust that allows molten rock to escape http://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/rchambers/GeoBytes%20GCSE%20Bl og%20Resources/Images/Plate%20Tectonics/Plate%20Tectonics/VolcanoStructure.jpg
Earthquake- result of sudden energy release in the Earth’s crust creating seismic waves.
• http://news.bbc.co.uk/nol/shared/spl/hi/world/04/earthquake/img/earthquake.gif
More Evidence- Location of mountain ridges, rift valleys, mid-ocean ridges, and trenches on plate boundaries. Convergent, Divergent and Transform http://www.ifa.hawaii.edu/~barnes/ast110_06/tprai/Tectonic_plate_boundaries.png
SIMULATIONS ON ALL BOUNDARY TYPES CLICK http://www.pbs.org/wgbh/aso/tryit/tectonics/shockwave.html
Andes Mountains Convergent Oceanic & Continental Plates move toward each other A trench is a steep walled valley on the sea floor.
Subduction - A convergent boundary where one plate moves below the other plate blue.utb.edu/paullgj/images/Conv_Cont_Ocean.JPG
CLICK http://www.pbs.org/wgbh/aso/tryit/tectonics/convergent.html
Convergent Boundary Oceanic & Continental CLICK http://geology.com/nsta/convergent-boundary-oceanic-continental.gif
Japan or Aleutian Islands Convergent Oceanic & Oceanic
Denser oceanic crust subducts under less dense oceanic crust ceeps.colostate-pueblo.edu/.../smM1P1Fig15.gif
Convergent Boundary Oceanic & Oceanic http://geology.com/nsta/convergent-boundary-oceanic-oceanic.gif
Himalayas Convergent Continental & Continental: Faulting and Folding http://www.pbs.org/wgbh/aso/tryit/tectonics/crush.html
Convergent Boundary Continental & Continental http://geology.com/nsta/convergent-boundary.gif
Mid Atlantic Ridge Divergent Oceanic At a divergent boundary lithosphere plates move away from each other
Divergent Boundary Oceanic • Mid-Ocean Ridges – a structure formed from seafloor spreading.
CLICK http://geology.com/nsta/divergent-boundary-oceanic.gif
East African Rift Valley Divergent Continental Rift Valley – Pulling apart of crust due to tensional forces ceeps.colostate-pueblo.edu/.../smM1P1Fig15.gif
• Rift Valley Divergent Boundary Continental http://geology.com/nsta/divergent-boundary-continental.gif
San Andreas Fault Transform Plate Boundary Plates slide past or laterally along each other www.wiley.com/college/herenow/ptect/pt-map1.gif
Transform Boundary
TRANSFORM SIMUALTIONS CLICK http://geology.com/nsta/transform-boundary.gif
CLICK http://www.pbs.org/wgbh/aso/tryit/tectonics/transform.htm
http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_plate_tectonics_world.gif
Evidence - Location of earthquakes and volcanoes
Hot Spot • Volcanoes that are found in the center of plates (not on plate boundaries)
The Hawaiian-Emperor volcanic chain is the result of the drifting of the Pacific Plate over a fixed hot spot.
http://geology.com/nsta/plate-tectonics-cover.gif
The bend in the (Hawaiian – Emperor) volcanic chain is the result of a major change in the direction of the movement of the Pacific Plate.
Location of Hot Spots Hot spots result from hot, narrow plumes of material that rise deep within the mantle .
Plate Movement in the future
• http://www.scotese.com/earth.htm
It is even possible to measure the speed of continental plates extremely accurately, using satellite technology.
External Energy For Earth
• Sun & Moon keeps air and sea in motion, shapes surface • Sun warms atmosphere & crust unevenly creating winds • Winds drive ocean currents and water cycle • Erosion from winds, rains, rivers, glaciers, and waves shape surface • Weathering from winds and rains • Sun & Moon Gravitational Energy, produces tides • Planetesimal collisions
Internal Energy for Earth
• Radioactive element decay • Core heat from layers pressure • Convection currents • Volcanoes • Hot Springs • Earthquakes
Evidence for Plate Tectonics
First evidence used for Continental Drift Theory
• Continents fit together • Fossil distribution • Glacier evidence: deposits, striations, scraping • Climate distribution • Common rock formations: same age
New evidence
• Magnetic pattern of rock • Location of earthquakes and volcanoes • Location of mountain ridges, rift valleys, mid-ocean ridges, and trenches
Review: What is …?
• Hot Spot • Rift Valley • Trench • Subduction • Convection Current • Sea Floor Spreading • Mid Ocean Ridge • Convergent, Divergent or Transform Boundary