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Drifting ContinentsDrifting ContinentsKey TerminologyKey TerminologyHypothesisHypothesis- a proposal intended to explain certain - a proposal intended to explain certain facts or observations, but that is not yet verified.facts or observations, but that is not yet verified.TheoryTheory- a hypothesis that survives experimental - a hypothesis that survives experimental testing becomes a scientific theory" testing becomes a scientific theory" Plate- a large, rigid slab of solid rock. Plate- a large, rigid slab of solid rock. TectonicsTectonics "to "to build." build." The The theory of plate tectonicstheory of plate tectonics states that the Earth's states that the Earth's outermost layer is fragmented into a dozen or more outermost layer is fragmented into a dozen or more large and small plates that are moving relative to one large and small plates that are moving relative to one another as they ride atop hotter, more mobile material.another as they ride atop hotter, more mobile material.Continental drift Continental drift was the forerunner of plate was the forerunner of plate tectonics.tectonics.

Concepts and TermsConcepts and Terms Focus QuestionsFocus Questions What was Alfred What was Alfred

Wegener’s hypothesis Wegener’s hypothesis about continental drift?about continental drift?

What evidence What evidence supported Wegener’s supported Wegener’s hypothesis?hypothesis?

Why was Wegener’s Why was Wegener’s hypothesis rejected by hypothesis rejected by most scientists of his most scientists of his day?day?

TermsTerms Continental DriftContinental Drift PangaeaPangaea FossilFossil

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1912- Alfred Wegener 1912- Alfred Wegener proposed the hypothesis of proposed the hypothesis of

continental drift.continental drift. Hypothesis:Hypothesis: All the continents were once All the continents were once

joined together in a single joined together in a single landmass and have since drifted landmass and have since drifted apart.apart.

SupercontinentSupercontinent PangaeaPangaea Wegener thought that over tens Wegener thought that over tens

of millions of years, Pangaea of millions of years, Pangaea began to break apart. The pieces began to break apart. The pieces of Pangaea slowly moved toward of Pangaea slowly moved toward their present day locations their present day locations becoming the continents they are becoming the continents they are today.today.

This idea became known asThis idea became known as Continental DriftContinental Drift

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Supercontinent Supercontinent

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200 million years ago Pangaea 200 million years ago Pangaea began to break apart.began to break apart.

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Continental DriftContinental Drift

Wegener gathered evidence from Wegener gathered evidence from different scientific fields to support different scientific fields to support his ideas about continental drift. He his ideas about continental drift. He studied studied land featuresland features, , fossilsfossils, and , and evidence of evidence of climate changeclimate change. .

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Evidence from land featuresEvidence from land features

If maps of Africa and South America If maps of Africa and South America are pieced together, mountain are pieced together, mountain ranges on both continents line up.ranges on both continents line up.

European coal fields match up with European coal fields match up with similar coal fields in North America.similar coal fields in North America.

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Evidence from FossilsEvidence from Fossils

Similar fossils on different continentsSimilar fossils on different continents What is a fossil?What is a fossil? Any trace of an ancient organism Any trace of an ancient organism

preserved in rock.preserved in rock. How did Wegener explain similar fossils How did Wegener explain similar fossils

on different continents?on different continents? The organisms lived on a single The organisms lived on a single

landmass that has since split apart.landmass that has since split apart.

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Plant and animal fossilsPlant and animal fossils

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Evidence from ClimateEvidence from Climate Climate doesn’t match Climate doesn’t match

fossil records.fossil records. What would explain What would explain

tropical foliage fossils tropical foliage fossils found in Alaska? found in Alaska?

Either the climate of the Either the climate of the Earth was different when Earth was different when the palms grew 60 the palms grew 60 million years ago or else million years ago or else the rocks in which the the rocks in which the fossils occur moved in fossils occur moved in from someplace else. from someplace else.

Wegener believed that Wegener believed that continental drift continental drift explained fossils of explained fossils of tropical plants are found tropical plants are found in places that today have in places that today have polar climates.polar climates.

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Glacier movement matchGlacier movement match

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Wegener’s Hypothesis Wegener’s Hypothesis RejectedRejected

Unfortunately, Wegener could not provide a Unfortunately, Wegener could not provide a satisfactory explanation for the force that satisfactory explanation for the force that pushes or pulls the continents.pushes or pulls the continents.

Because he could not identify the cause of Because he could not identify the cause of continental drift, most geologists rejected continental drift, most geologists rejected his idea.his idea.

Hypothesis RejectedHypothesis Rejected How did he think mountains formed?How did he think mountains formed? He proposed that when continents He proposed that when continents

collide their edges crumble and fold. collide their edges crumble and fold. The folding continents push up huge The folding continents push up huge

mountains.mountains. How did the locations of mountains How did the locations of mountains

support his idea of how mountains support his idea of how mountains formed?formed?

Mountains sometime occur on narrow Mountains sometime occur on narrow bands along the edges of continents bands along the edges of continents where continents collide.where continents collide. 1616

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What evidence was he missing What evidence was he missing for it to be accepted as a for it to be accepted as a

theory?theory? Wegener failed to prove how the Wegener failed to prove how the

plates moved.plates moved. He proposed that the continents move He proposed that the continents move

by plowing through the rock.by plowing through the rock. Use of sonic instruments to map the Use of sonic instruments to map the

ocean floor lead to the discovery of ocean floor lead to the discovery of Sea-floor Spreading. Sea-floor Spreading.