Continental Drift Theory

• Alfred Wegener• German meteorologist

• Found papers describing similar fossils on opposite sides of the Atlantic

• Researched more cases of similar organisms separated by oceans

• 1912 Proposed single supercontinent Pangaea

Continental Drift Theory5 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.berkeley.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=SCE304Click animation

Volcanic rocks on the seafloor have magnetization because, as they cool,

magnetic minerals within the rock align to the Earth’s magnetic field.

New Evidence: Magnetic pattern of rock

North Magnetic Pole in No. Hemi

North Magnetic Pole in So. Hemi

Present DayNorth 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 Theory

Plates ‘float’ on the AsthenospherePlates have oceanic and continental crust

www.wiley.com/college/herenow/ptect/pt-map1.gif

Earth’s Layers

• Inner Core• Outer Core• Mantle• Crust• Atmosphere

• Lithosphere – crust and upper mantle, plates move independently

• Asthenosphere-region below the Lithosphere

http://library.thinkquest.org/04oct/01724/images/Earth-crust-cutaway-english.png

Continental Crust

• Cooling rate - slow• Crystal size - large• Density – less dense• Thickest portion of the Earth’s outer layer• Composition – made mainly of granite rock

http://www.amonline.net.au/geoscience/images/earth_diagrams/cont_oceanic_crust.gif

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%20Blog%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 TYPESCLICK http://www.pbs.org/wgbh/aso/tryit/tectonics/shockwave.html

Andes MountainsConvergent Oceanic & Continental

Plates move toward each other

blue.utb.edu/paullgj/images/Conv_Cont_Ocean.JPG

CLICK http://www.pbs.org/wgbh/aso/tryit/tectonics/convergent.html

A trench, a steep walled valley on the sea floor, forms here.

Denser oceanic crust subducts under less dense continental crust

Convergent BoundaryOceanic & Continental

CLICK http://geology.com/nsta/convergent-boundary-oceanic-continental.gif

Japan or Aleutian IslandsConvergent Oceanic & Oceanic

ceeps.colostate-pueblo.edu/.../smM1P1Fig15.gif

Denser oceanic crust subducts under less dense oceanic crust

Convergent BoundaryOceanic & Oceanic

http://geology.com/nsta/convergent-boundary-oceanic-oceanic.gif

HimalayasConvergent Continental & Continental:

http://www.pbs.org/wgbh/aso/tryit/tectonics/crush.html

Faulting and Folding

Convergent BoundaryContinental & Continental

http://geology.com/nsta/convergent-boundary.gif

Mid Atlantic RidgeDivergent Oceanic

At a divergent boundary lithosphere plates move away from each other

Divergent BoundaryOceanic

• Mid-Ocean Ridges – a structure formed from seafloor spreading.

CLICK http://geology.com/nsta/divergent-boundary-oceanic.gif

East African Rift ValleyDivergent Continental

Rift Valley – Pulling apart of crust due to tensional forces

ceeps.colostate-pueblo.edu/.../smM1P1Fig15.gif

Divergent BoundaryContinental

• Rift Valley

http://geology.com/nsta/divergent-boundary-continental.gif

San Andreas FaultTransform Plate Boundary

Plates slide past each other

www.wiley.com/college/herenow/ptect/pt-map1.gif

Transform Boundary

TRANSFORM SIMUALTIONSCLICK http://geology.com/nsta/transform-boundary.gifCLICK 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 Spots

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 continentalplates 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

• Continents fit together• Fossil distribution• Common rock formations: same age• Glacier evidence: deposits, striations, scraping• Climate distribution

New evidence • Magnetic pattern of rock• Location of earthquakes and volcanoes • Location of mountain ridges, rift valleys,

mid-ocean ridges, and trenches

First evidence used for Continental Drift Theory