Plate TectonicsPlate Tectonics

The History of Tectonic TheoryThe History of Tectonic Theory

Plate TectonicsPlate Tectonics

Presented by Presented by

Doug Winans Doug Winans

Grade Levels 5-8Grade Levels 5-8

Continental Drift HypothesisContinental Drift HypothesisScientists noted geographic fit of continentsScientists noted geographic fit of continents

1885 Austrian geologist Edward Seuss notes similarities 1885 Austrian geologist Edward Seuss notes similarities between plant fossils, and calls the continent between plant fossils, and calls the continent "Gondwanaland"."Gondwanaland".

1910 American physicist Taylor proposes concept of 1910 American physicist Taylor proposes concept of continental drift to explain formation of mountain belts.continental drift to explain formation of mountain belts.

1912, Wegener names the ancient super-continents 1912, Wegener names the ancient super-continents "Pangea," based on evidence from geology, climatology and "Pangea," based on evidence from geology, climatology and paleontology. paleontology.

Supporting evidence for Continental Drift HypothesisSupporting evidence for Continental Drift Hypothesis

Geographic fitGeographic fitFossilsFossilsMountain BeltsMountain BeltsGlaciationGlaciation

Geographic FitGeographic Fit

Continents appear to fit together like pieces of a puzzleContinents appear to fit together like pieces of a puzzle

FossilsFossils

Distribution of fossils Distribution of fossils found on both sides of found on both sides of the Atlantic Ocean, the Atlantic Ocean, such as such as Mesosaurus, Mesosaurus, and a prehistoric plant and a prehistoric plant calledcalled Glossopteris. Glossopteris.

Mountain BeltsMountain Belts

Mountain belts, like the Mountain belts, like the Appalachians, match across oceansAppalachians, match across oceans

GlaciationGlaciation

Glacial scoring indicates original location of glaciers Glacial scoring indicates original location of glaciers and direction of movementand direction of movement

Striations are grooves carved Striations are grooves carved in rock by glaciersin rock by glaciers

Blue arrows show direction of Blue arrows show direction of glacial flow away from South glacial flow away from South Pole Pole

Continental Drift HypothesisContinental Drift Hypothesis

• Alfred WegenerAlfred Wegener• MeteorologistMeteorologist• Presented his hypothesis Presented his hypothesis

to other professionals, but to other professionals, but could not explain how could not explain how continents driftedcontinents drifted

Try to put together Wegner’sTry to put together Wegner’s PangeaPangea

Seafloor SpreadingSeafloor Spreading

Seafloor SpreadingSeafloor Spreading Development of a New Theory Development of a New Theory

• Continental drift hypothesis was reexamined in 1960’s Continental drift hypothesis was reexamined in 1960’s with new information.with new information.

• Seafloor SpreadingSeafloor Spreading• Evidence supporting seafloor spreading…Evidence supporting seafloor spreading…

– PaleomagnetismPaleomagnetism

– Age of SeafloorAge of Seafloor

Seafloor SpreadingSeafloor Spreading

Harry Hess suggests new seafloor is created at Harry Hess suggests new seafloor is created at mid-ocean ridges and is destroyed in deep mid-ocean ridges and is destroyed in deep

ocean trenchesocean trenches

PaleomagnetismPaleomagnetism• Earth’s magnetic field Earth’s magnetic field

reverses approx. every reverses approx. every 600,000 years600,000 years

• As new crust is formed, As new crust is formed, normal and reverse normal and reverse polarities are polarities are preserved in the rock preserved in the rock recordrecord

• 1963, Vine & Matthews 1963, Vine & Matthews observe magnetic observe magnetic anomalies in oceanic anomalies in oceanic crustcrust

• Younger rocks (red) are found near mid-ocean ridgesYounger rocks (red) are found near mid-ocean ridges• Further away, the age of seafloor gets progressively older (blue)Further away, the age of seafloor gets progressively older (blue)

Mechanism for Mechanism for Seafloor SpreadingSeafloor Spreading

• Convection CurrentsConvection Currents– As heated magma rises, it moves away at spreading centers pulling As heated magma rises, it moves away at spreading centers pulling

plates apartplates apart– Plates slide over the asthenospherePlates slide over the asthenosphere– The upper mantle then cools and becomes more dense – sinking at The upper mantle then cools and becomes more dense – sinking at

ocean trenchesocean trenches

Plate Tectonics TheoryPlate Tectonics Theory

John Tuzo Wilson combined the ideas of Continental John Tuzo Wilson combined the ideas of Continental Drift and Seafloor Spreading into a new theory… Drift and Seafloor Spreading into a new theory…

““Plate Tectonics”Plate Tectonics”

Tectonic QuizTectonic Quiz

• What evidence was given for the What evidence was given for the Continental Drift Hypothesis?Continental Drift Hypothesis?

GlaciationGlaciation

FossilsFossils

Geographic FitGeographic Fit

All of the AboveAll of the Above

Tectonic QuizTectonic Quiz

• Who proposed the Continental Drift Who proposed the Continental Drift Hypothesis?Hypothesis?

TaylorTaylor

HessHess

WegnerWegner

SeussSeuss

Tectonic QuizTectonic Quiz

• New evidence of “Seafloor spreading” was used New evidence of “Seafloor spreading” was used to develop Tectonic Theory. What evidence did to develop Tectonic Theory. What evidence did scientists find?scientists find?

Ancient magnetic reversals in the rocksAncient magnetic reversals in the rocks

Ocean floor dating Ocean floor dating

GPS measurementsGPS measurements

Both A and B aboveBoth A and B above

Tectonic QuizTectonic Quiz

• Who combined Continental Drift and Seafloor Who combined Continental Drift and Seafloor Spreading to produce Tectonic Theory?Spreading to produce Tectonic Theory?

TaylorTaylor

HessHess

““Tuzo” WilsonTuzo” Wilson

SeussSeuss

Plate TectonicsPlate Tectonics HistoryHistory

ReferencesReferencesWeb Sites:Web Sites:Pangaea: The ContinentPangaea: The Continent

http://www.pangaea.org/wegener.htm

What on Earth is Plate Tectonics?What on Earth is Plate Tectonics?

http://wrgis.wr.usgs.gov/docs/parks/pltec/index.html

Geology Labs: Virtual EarthquakeGeology Labs: Virtual Earthquake http://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.htmlhttp://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.html

Understanding QuakesUnderstanding Quakeshttp://whyfiles.org/094quake/index.php?g=6.txthttp://whyfiles.org/094quake/index.php?g=6.txt

ALFRED WEGENER vs JUST ABOUT EVERYBODY ELSE: ALFRED WEGENER vs JUST ABOUT EVERYBODY ELSE: HOW THE CONTINENTS FORMED HOW THE CONTINENTS FORMED

http://courses.science.fau.edu/~rjordan/phy1931/WEGENER/wegener.htm

This Dynamic Earth: The Story of Plate TectonicsThis Dynamic Earth: The Story of Plate Tectonics

http://pubs.usgs.gov/gip/dynamic/dynamic.htmlhttp://pubs.usgs.gov/gip/dynamic/dynamic.html

Testing the Sea-Floor Spreading HypothesisTesting the Sea-Floor Spreading Hypothesis

http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/part9.html