Chapter 7.2Chapter 7.2Restless ContinentsRestless Continents

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IN: How did scientists come up IN: How did scientists come up with the idea that the lithosphere with the idea that the lithosphere

is broken into tectonic plates?is broken into tectonic plates?

Restless ContinentsRestless Continents

Wegener’s TheoryWegener’s Theory

Inspired by the puzzle-like fit of the continents Alfred Wegener developed the theory in the early 1900s

Continental Continental driftdrift is the theory that is the theory that continents can drift apart from one another continents can drift apart from one another and have done so in the past.and have done so in the past.

What is Wegener’s Evidence?What is Wegener’s Evidence?

1.) 1.) FossilsFossils of the same plant of the same plant (glossopteris) and animal species (glossopteris) and animal species (mesosaurus) are found on both sides of (mesosaurus) are found on both sides of the Atlantic Ocean.the Atlantic Ocean.

What is Wegener’s Evidence?What is Wegener’s Evidence?

2.) 2.) Geological Evidence: Geological Evidence: Similar types of Similar types of rock and evidence of the same ancient rock and evidence of the same ancient mountain formations were found on mountain formations were found on several continents.several continents.

What is Wegener’s Evidence?

Glacial grooves in rocks on different continents created by receding glaciers that match and are in the same direction.

3.) Evidence of Climate Change:

PangaeaPangaea

Wegener thought that 245 mya all the Wegener thought that 245 mya all the separate continents of today were joined separate continents of today were joined in a in a single landmass the he called single landmass the he called Pangaea Pangaea and a single ocean called and a single ocean called Panthalassa Panthalassa ..

PangaeaPangaea

About 180 mya it began to break into two About 180 mya it began to break into two main pieces. The northern half is known main pieces. The northern half is known as as LaurasiaLaurasia, the southern is known as , the southern is known as GondwanalandGondwanaland..

PangaeaPangaea

About 65 mya, around the time the About 65 mya, around the time the dinosaurs went extinct, they broke into dinosaurs went extinct, they broke into many pieces and looked not too different many pieces and looked not too different from what the continents look like today.from what the continents look like today.

What he didn’t knowWhat he didn’t know

Wegener could not explain what force Wegener could not explain what force could move the continents.could move the continents.

He died in 1930 in an expedition to He died in 1930 in an expedition to Greenland.Greenland.

The Theory of Continental The Theory of Continental Drift Died with Alfred Drift Died with Alfred

Wegener!!!Wegener!!!OUT: Name three pieces of OUT: Name three pieces of evidence Wegener used to evidence Wegener used to explain his theory.explain his theory.

The Theory of Plate TectonicsThe Theory of Plate TectonicsSection 7.2 (Part II)Section 7.2 (Part II)

The Theory of Plate Tectonics states that The Theory of Plate Tectonics states that the lithosphere is divided into tectonic the lithosphere is divided into tectonic plates that move around on the plates that move around on the asthenosphere.asthenosphere.

It was developed in the 1950s and 60s It was developed in the 1950s and 60s and and replacesreplaces Alfred’s theory Alfred’s theory

New EvidenceNew Evidence

New technology from World War II such New technology from World War II such as submarines, the ability to test the age as submarines, the ability to test the age of rocks and sonar helped scientists revive of rocks and sonar helped scientists revive Alfred’s ideas.Alfred’s ideas.

Mid-Ocean RidgeMid-Ocean Ridge

Underwater mountain chains that run Underwater mountain chains that run through Earth’s ocean basins.through Earth’s ocean basins.

Mid-Atlantic RidgeMid-Atlantic Ridge

Ships with sonar began to map the ocean Ships with sonar began to map the ocean floor, and a undersea mountain chain was floor, and a undersea mountain chain was discovered.discovered.

1.)Mid-Ocean Ridges are1.)Mid-Ocean Ridges are

volcanic and are wherevolcanic and are where

sea-floor spreading sea-floor spreading

occurs.occurs.

Sea-floor SpreadingSea-floor Spreading The process by which The process by which newnew oceanic oceanic

lithosphere is created as lithosphere is created as olderolder materials materials are pulled away.are pulled away.

The youngest crust is closest to the MOR, The youngest crust is closest to the MOR, and the oldest is near the continents.and the oldest is near the continents.

RiftsRifts

This also happens on land creating “Rift This also happens on land creating “Rift valleys”valleys”

Magnetic ReversalMagnetic Reversal

2.) Magnetic Reversals, or 2.) Magnetic Reversals, or paleomagnetism, is when Earth’s paleomagnetism, is when Earth’s magnetic poles change place.magnetic poles change place.

This happens 4-5 times every This happens 4-5 times every million yearsmillion years

Tracking Plate MotionTracking Plate Motion

3.) Satellites like GPS track the 3.) Satellites like GPS track the movement of the plates.movement of the plates.

The plates move centimeters per year.The plates move centimeters per year.

OUT: Name three pieces of evidence OUT: Name three pieces of evidence used to describe the Theory of Plate used to describe the Theory of Plate Tectonics.Tectonics.