Continental Drift, Sea Floor Spreading and Plate Tectonics PDF

Continental Drift, Continental Drift, Sea Floor Spreading Sea Floor Spreading and Plate Tectonicsand Plate Tectonics

1/28/20081/28/2008

Noticing the ContinentsNoticing the Continents

�� About 400 years ago explorers were sailing the About 400 years ago explorers were sailing the oceans and examining the coastlines. These oceans and examining the coastlines. These explorers brought back enough information for explorers brought back enough information for mapmakers to create reliable maps. mapmakers to create reliable maps.

�� In 1620, Francis Bacon noticed that the shapes In 1620, Francis Bacon noticed that the shapes of some of the continents looked as if they of some of the continents looked as if they could fit together. He proposed that they could fit together. He proposed that they once fit together but he didnonce fit together but he didn’’t have a wayt have a wayto explain it. to explain it.

�� Everyone rejected his idea!Everyone rejected his idea!

�� What continents look like they fit together What continents look like they fit together best?best?

Continental DriftContinental Drift……the beginningthe beginning

�� In 1912, a German meteorologist came up with a In 1912, a German meteorologist came up with a theory that was similar to Francis Bacontheory that was similar to Francis Bacon’’s.s.

�� His name was Alfred Wegener. He called his His name was Alfred Wegener. He called his theory, the theory, the ““Theory of Continental Drift.Theory of Continental Drift.””

�� In this theory, he said that not just Africa and In this theory, he said that not just Africa and South America were once connected but, South America were once connected but, all the all the continents were once connected and have continents were once connected and have since moved apart. since moved apart.

�� He called this giant land mass (supercontinent) He called this giant land mass (supercontinent) PANGAEAPANGAEA. This word means . This word means ““All land.All land.””

Everything was once connected!

Evidence for Continental DriftEvidence for Continental Drift

�� The continents of South America and The continents of South America and Africa look like they fit together.Africa look like they fit together.


�� Fossils of animals and plants were found Fossils of animals and plants were found on multiple continents.on multiple continents.


�� Mountain ranges Mountain ranges ““matched upmatched up”” between between different continents.different continents.

�� The mountain ranges on the East Coast of The mountain ranges on the East Coast of North America and Northern Europe were North America and Northern Europe were made of the same rock and the rock was made of the same rock and the rock was the same age.the same age.


�� When the continents are put together to When the continents are put together to form Pangaea, the remains of glacial form Pangaea, the remains of glacial materials fit together to form a pattern like materials fit together to form a pattern like the large ice sheets that cover our poles the large ice sheets that cover our poles today.today.


�� Coal usually forms in tropical climates. Coal usually forms in tropical climates. Coal can be found in areas of North Coal can be found in areas of North America which could not support coal America which could not support coal formation. formation.

�� Coal forms in Tropical climates.Coal forms in Tropical climates.

�� Similar rock layers were found across Similar rock layers were found across multiple continents.multiple continents.

Theory of Continental DriftTheory of Continental Drift

A New Idea: Sea Floor SpreadingA New Idea: Sea Floor Spreading

�� After WegenerAfter Wegener’’s death, more clues were s death, more clues were discovered that provided the reason why discovered that provided the reason why the plates moved. the plates moved.

�� It was the invention of echo sounding It was the invention of echo sounding devices (sonar) that gave insight as to devices (sonar) that gave insight as to what the ocean floor looked like. what the ocean floor looked like.

Echo SoundingEcho Sounding

Sea Floor SpreadingSea Floor Spreading

�� Scientist found that the ocean floor contained Scientist found that the ocean floor contained mountain ranges with a steep, narrow valley mountain ranges with a steep, narrow valley running down its center. These underwater running down its center. These underwater mountain ranges were all connected and spread mountain ranges were all connected and spread through the center of most oceans. The range through the center of most oceans. The range when all connected were 65,000 km long.when all connected were 65,000 km long.

�� In 1947, scientists went to map the MidIn 1947, scientists went to map the Mid--Atlantic Atlantic ridge. While studying the ridge, the scientists ridge. While studying the ridge, the scientists collected and studied rock samples. They found collected and studied rock samples. They found something astonishing. something astonishing.

�� The ocean floor was younger than the continents.The ocean floor was younger than the continents.

The MidThe Mid--Ocean RidgeOcean Ridge


�� The scientists wanted to know two things:The scientists wanted to know two things:�� How did the midHow did the mid--ocean ridges form?ocean ridges form?

�� Why where the rocks younger in the ocean Why where the rocks younger in the ocean crust when compared to the continental crust? crust when compared to the continental crust?

�� Write a hypothesis as to why the ocean Write a hypothesis as to why the ocean crust is younger than the continental crust. crust is younger than the continental crust.


�� In 1960, Dr. Harry Hess came up with In 1960, Dr. Harry Hess came up with some answers. some answers.

�� A driving force, convection currents, A driving force, convection currents, moved the plates. The ocean floor, and moved the plates. The ocean floor, and the rock beneath it, are produced by the rock beneath it, are produced by magma that rises from deeper levels. The magma that rises from deeper levels. The hot, less dense magma rises and cools, hot, less dense magma rises and cools, pushing the older crust out from the pushing the older crust out from the center.center.

Convection CurrentsConvection Currents

SeaSea--Floor SpreadingFloor Spreading

�� At the midAt the mid--ocean ridge, ocean ridge, molten material rises from molten material rises from the mantle and erupts. the mantle and erupts. The molten material The molten material spreads out, pushing spreads out, pushing older rock to both sides of older rock to both sides of the ridge.the ridge.

�� This process that This process that continually adds to the continually adds to the ocean floor is sea floor ocean floor is sea floor spreading.spreading.

Evidence for Sea Floor SpreadingEvidence for Sea Floor Spreading

�� In the 1960s scientists found In the 1960s scientists found evidence that new material evidence that new material is erupting along the midis erupting along the mid--ocean ridge.ocean ridge.

�� The presence of pillow The presence of pillow shaped rocks has showed shaped rocks has showed that molten material has that molten material has erupted again and again.erupted again and again.

Pillow Lava rocksPillow Lava rocks

Evidence for SeaEvidence for Sea--Floor SpreadingFloor Spreading

�� Evidence in the Evidence in the rocks shows that rocks shows that EarthEarth’’s magnetic s magnetic poles have poles have reversed.reversed.

�� The iron particles The iron particles lined up in the lined up in the opposite direction.opposite direction.


�� In the 1968, scientists In the 1968, scientists aboard the Glomar aboard the Glomar Challenger gathered Challenger gathered information about the information about the Sea floor. Sea floor.

�� They found rocks no They found rocks no older than 180 million older than 180 million years. years.

Evidence of SeaEvidence of Sea--Floor Floor SpreadingSpreading

�� Evidence from Evidence from drilling into the sea drilling into the sea floor shows floor shows evidence of the evidence of the ages of rocks.ages of rocks.

�� The closer you get The closer you get to the midto the mid--ocean ocean ridge the younger ridge the younger the rock. The the rock. The farther you get, the farther you get, the older the rock.older the rock.

SubductionSubduction�� The processes of The processes of subductionsubduction and seaand sea--floor floor

spreading can change the size and shape of the spreading can change the size and shape of the oceans.oceans.

�� Because of this processes, the ocean floor is Because of this processes, the ocean floor is renewed about every 200 million years.renewed about every 200 million years.

SubductionSubduction in the Oceansin the Oceans�� The Pacific Ocean is shrinking! This is due to the The Pacific Ocean is shrinking! This is due to the

fact that a deepfact that a deep--ocean trench is swallowing more ocean trench is swallowing more crust than the midcrust than the mid--ocean ridge can produce.ocean ridge can produce.

�� The Atlantic Ocean however, is expanding!The Atlantic Ocean however, is expanding!

Continental vs. Oceanic CrustContinental vs. Oceanic Crust

Continental

Ocean

CompositionDensityThicknessType of Crust

Plate TectonicsPlate Tectonics

�� The theory of plate tectonics combines the The theory of plate tectonics combines the theories of Continental drift and Sea floor theories of Continental drift and Sea floor spreading.spreading.

�� The earthThe earth’’s crust is not all in one piece. It s crust is not all in one piece. It is divided in about a dozen major is divided in about a dozen major ““platesplates””that ride on the earththat ride on the earth’’s s asthenosphereasthenosphere..

Divergent Plate BoundaryDivergent Plate Boundary

Convergent Plate BoundaryConvergent Plate Boundary

Transform Plate BoundaryTransform Plate Boundary

OceanOcean--Continent ConvergentContinent Convergent

OceanOcean--Ocean ConvergentOcean Convergent

ContinentContinent--Continent ConvergentContinent Convergent

Continental Drift, Sea Floor Spreading and Plate Tectonics PDF

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