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Continental Drift & PaleomagnetismContinental Drift & Paleomagnetism

Which of the following best describes tectonics on Earth?Which of the following best describes tectonics on Earth?

A.A. Continents float in the oceans andContinents float in the oceans andmove as independent bodies likemove as independent bodies likeboards floating in a pool.boards floating in a pool.

B.B. Continents float on the mantle andContinents float on the mantle andmove as independent bodies likemove as independent bodies likeboards floating in a pool.boards floating in a pool.

C.C. Continents and ocean floor areContinents and ocean floor areconnected and constitute largerconnected and constitute larger‘‘boardsboards’’ that form a rigid that form a rigidframework (like a roof). Motionframework (like a roof). Motionresults when the results when the ‘‘roofroof’’ collapses collapsesunder its weight.under its weight.

D.D. Continents and ocean floor areContinents and ocean floor areconnected and constitute largerconnected and constitute larger‘‘boardsboards’’ that float on the that float on theasthenosphere. Motion results whenasthenosphere. Motion results whenthe board sinks or is pushed beneaththe board sinks or is pushed beneathanother.another.

EarthEarth’’s magnetic field provides evidence of a dynamic Earth surfaces magnetic field provides evidence of a dynamic Earth surface

•• Convection of earthConvection of earth’’s outers outercore creates a magneticcore creates a magneticfield!field!

•• Magnets follow the fieldMagnets follow the fieldflux lines (point N)flux lines (point N)–– From this we can determineFrom this we can determine

location on Earthlocation on Earth

•• InclinationInclination indicates indicateslatitude!latitude!

Cell phone and Brunton

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Rocks as MagnetsRocks as Magnets

•• Some volcanic rocks haveSome volcanic rocks havemagnetic minerals inmagnetic minerals inthem.them.–– Example: wehrliteExample: wehrlite

•• Draw how this works:Draw how this works:•• So, rocks can be used as aSo, rocks can be used as a

sort of magnet that recordssort of magnet that recordsits location at the time itits location at the time itcooled! (Paleomagnetism)cooled! (Paleomagnetism)

Combining paleomagnetism and age datingCombining paleomagnetism and age dating

•• Consider volcanic rocksConsider volcanic rocksfrom some continentfrom some continent

•• Paleomagnetism ofPaleomagnetism ofdifferent age rocks givedifferent age rocks givedifferent locations ofdifferent locations ofapparent Northapparent North–– Interpreted in 1950s asInterpreted in 1950s as

evidence of Polar Wanderevidence of Polar Wander

•• HoweverHowever……

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Comparing Continents:Comparing Continents:

•• Wander paths of continents donWander paths of continents don’’t agree.t agree.•• Unless the continents were once joined! (Pangaea)Unless the continents were once joined! (Pangaea)•• Alfred Wegener first to propose PangaeaAlfred Wegener first to propose Pangaea

Alfred WegenerAlfred Wegener•• German meteorologistGerman meteorologist•• Wounded in WWIWounded in WWI

–– Researched duringResearched duringrecoveryrecovery

–– 1915 Published1915 PublishedOrigins of ContinentsOrigins of Continentsand Oceansand Oceans

•• Died 1930 GreenlandDied 1930 Greenlandexpedition.expedition.

WegenerWegener’’s Hypothesis (1912):s Hypothesis (1912):

•• Continents drift over geologic time through theContinents drift over geologic time through theocean basins.ocean basins.–– Mountains form at leading edge of continents byMountains form at leading edge of continents by

plowing through ocean rocks.plowing through ocean rocks.•• Prior to this hypothesis, EarthPrior to this hypothesis, Earth’’s surface wass surface was

considered Static despite observations of considered Static despite observations of ‘‘fit offit ofcontinental marginscontinental margins’…’…

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Fit of the continental margins:Fit of the continental margins:

Previously noted by: Bacon 1500s, Buffon 1700s, Humboldt 1800s, Suess 1885Previously noted by: Bacon 1500s, Buffon 1700s, Humboldt 1800s, Suess 1885

Read section 2.2 in your text and understand the lines of evidence supportingRead section 2.2 in your text and understand the lines of evidence supportingcontinental drift hypothesis: fit of continents, past glaciations, climate belts, fossilcontinental drift hypothesis: fit of continents, past glaciations, climate belts, fossildistribution, geologic units.distribution, geologic units.

Wegener proposed PangaeaWegener proposed Pangaea

He was ahead of his time. Incorrect Hypothesis, but correct observation;He was ahead of his time. Incorrect Hypothesis, but correct observation;EarthEarth’’s surface is dynamic and not static!s surface is dynamic and not static!

Wegener was wrong, but not completely.Wegener was wrong, but not completely.•• All his evidence points to the continents once being joined inAll his evidence points to the continents once being joined in

the supercontinent Pangaeathe supercontinent Pangaea–– He was correct in this regard, and this is no longer disputed.He was correct in this regard, and this is no longer disputed.–– He was incorrect in explaining how continents move and theHe was incorrect in explaining how continents move and the

relationship between continents and oceansrelationship between continents and oceans……

•• Science waited 30 years before we could understand thisScience waited 30 years before we could understand thisproblem (Tectonics).problem (Tectonics).

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Comparing Continents:Comparing Continents:

•• Wander paths of continents donWander paths of continents don’’t agree.t agree.•• Unless the continents were once joined! (Pangaea)Unless the continents were once joined! (Pangaea)•• So, Wegener was rightSo, Wegener was right……or was he?or was he?

–– His problems still exist, so we canHis problems still exist, so we can’’t accept his Hypothesis. We need at accept his Hypothesis. We need anew onenew one……

Review QuestionsReview Questions

•• What are the flaws/problems with the Continental DriftWhat are the flaws/problems with the Continental DriftHypothesis?Hypothesis?

•• What important contributions did Wegener make with hisWhat important contributions did Wegener make with hisproposed Continental Drift hypothesis?proposed Continental Drift hypothesis?

•• How does magnetism of rocks prove continents move?How does magnetism of rocks prove continents move?•• What produces EarthWhat produces Earth’’s Magnetic s Magnetic fieldfield