earth’s layered structure (ch. 8.4 in the text). earth’s internal structure layers based on...

Earth’s Layered Structure (Ch. 8.4 in the Text)

Earth’s internal structure Earth’s internal structure

Layers based on composition • Crust

•Thin, rocky outer layer •Varies in thickness

•Oceanic crust: Roughly 7 km (5 miles) thick

•Continental crust: Averages 35–40 km (25 miles) thick

Layers based on composition • Crust

•Thin, rocky outer layer •Varies in thickness

•Oceanic crust: Roughly 7 km (5 miles) thick

•Continental crust: Averages 35–40 km (25 miles) thick

Earth’s layered structure Earth’s layered structure Discovering Earth’s major layers • Mohorovicic discontinuity (Moho)•Separates crust from underlying mantle

Discovering Earth’s major layers • Mohorovicic discontinuity (Moho)•Separates crust from underlying mantle


Layers based on composition• Mantle

•Below crust to a depth of 2,890 kilometers (1,800 miles)

•Over 82% of Earth’s volume•Common rock type in the upper mantle is Peridotite

Layers based on composition• Mantle

•Below crust to a depth of 2,890 kilometers (1,800 miles)

•Over 82% of Earth’s volume•Common rock type in the upper mantle is Peridotite

Earth’s internal structure Earth’s internal structure Layers based on composition

• Core•Composed of an iron–nickel alloy •Average density of nearly 13 g/cm3

•Radius of 3,480 kilometers

Layers based on composition• Core

•Composed of an iron–nickel alloy •Average density of nearly 13 g/cm3

•Radius of 3,480 kilometers


Layers based on physical properties• Lithosphere

•Crust and uppermost mantle •5 - 100 km thick•Cool, rigid, solid

• Asthenosphere•Beneath the lithosphere •Part of the Upper mantle•To a depth of about 660 km•Soft, weak layer that is easily deformed

Layers based on physical properties• Lithosphere

•Crust and uppermost mantle •5 - 100 km thick•Cool, rigid, solid

• Asthenosphere•Beneath the lithosphere •Part of the Upper mantle•To a depth of about 660 km•Soft, weak layer that is easily deformed

Earth’s internal structure Earth’s internal structure Layers based on physical properties• Lower Mantle

•2230 km thick•More rigid layer than the Asthenosphere•Rocks are very hot and capable of gradual flow

• Outer Core •Liquid layer •2,260 km (1,410 miles) thick•Convective flow of metallic iron within generates Earth’s magnetic field

Layers based on physical properties• Lower Mantle

•2230 km thick•More rigid layer than the Asthenosphere•Rocks are very hot and capable of gradual flow

• Outer Core •Liquid layer •2,260 km (1,410 miles) thick•Convective flow of metallic iron within generates Earth’s magnetic field

Earth’s internal structureEarth’s internal structure

Layers based on physical properties Inner Core

1220 km thickCompressed into a solid state by immense pressure

Layers based on physical properties Inner Core

1220 km thickCompressed into a solid state by immense pressure

Plate TectonicsCh. 9 (p. 246 - 277)

Plate TectonicsCh. 9 (p. 246 - 277)

Continental drift: an idea before its time Continental drift: an idea before its time

Alfred Wegener • First proposed hypothesis of Continental Drift in 1915

Continental drift hypothesis• Supercontinent called Pangaea began breaking apart about 200 million years ago

• Continents “drifted” to present positions

Alfred Wegener • First proposed hypothesis of Continental Drift in 1915

Continental drift hypothesis• Supercontinent called Pangaea began breaking apart about 200 million years ago

• Continents “drifted” to present positions

Pangaea approximately 200 million years ago

Pangaea approximately 200 million years ago

Continental drift: an idea before its time Continental drift: an idea before its time

Wegener’s continental drift hypothesis• Evidence used by Wegener

•Fit of South America and Africa •Fossils match across the seas•Rock types and structures match •Ancient climates

• Problem with Wegener’s Hypothesis: What force was moving the continents?

Wegener’s continental drift hypothesis• Evidence used by Wegener

•Fit of South America and Africa •Fossils match across the seas•Rock types and structures match •Ancient climates

• Problem with Wegener’s Hypothesis: What force was moving the continents?

Similar mountain ranges

on different continents

Similar mountain ranges

on different continents

Paleoclimatic evidence

for continental drift

Paleoclimatic evidence

for continental drift

Plate Tectonics: the new paradigm Plate Tectonics: the new paradigm

The Theory of Plate TectonicsWe are now able to measure the movement of the continents due to technological advancements

Associated with Earth’s rigid outer shell • Called the lithosphere • Consists of several plates

•Largest plate is the Pacific plate

The Theory of Plate TectonicsWe are now able to measure the movement of the continents due to technological advancements

Associated with Earth’s rigid outer shell • Called the lithosphere • Consists of several plates

•Largest plate is the Pacific plate

Plate tectonics: the new paradigm Plate tectonics: the new paradigm Asthenosphere

• Exists beneath the lithosphere • Hotter and weaker (fluid like) than lithosphere

• Allows for motion of lithosphere Plate boundaries

• All major interactions among plates occur along their boundaries

Asthenosphere • Exists beneath the lithosphere • Hotter and weaker (fluid like) than lithosphere

• Allows for motion of lithosphere Plate boundaries

• All major interactions among plates occur along their boundaries

Plate tectonics: the new paradigm Plate tectonics: the new paradigm

Plate boundaries • Types of plate boundaries

•Divergent plate boundaries (Constructive margins)•Two plates move apart•Mid Ocean ridges and seafloor spreading

•Oceanic ridges develop along well-developed boundaries

•Along ridges, seafloor spreading creates new seafloor


•Divergent plate boundaries (Constructive margins)•Two plates move apart•Mid Ocean ridges and seafloor spreading

•Oceanic ridges develop along well-developed boundaries

•Along ridges, seafloor spreading creates new seafloor

Divergent boundaries are located along oceanic ridges

Divergent boundaries are located along oceanic ridges

The East African rift – a divergent boundary on land

The East African rift – a divergent boundary on land


Plate boundaries •Convergent plate boundaries (destructive margins)•Plates collide, an ocean trench forms, and lithosphere is subducted into the mantle

Plate boundaries •Convergent plate boundaries (destructive margins)•Plates collide, an ocean trench forms, and lithosphere is subducted into the mantle



•Convergent plate boundaries (destructive margins)•Oceanic–continental convergence

•Denser oceanic slab sinks into the asthenosphere

•Pockets of magma develop and rise •Continental volcanic arc forms•Examples include the Andes, Cascades, and the Sierra Nevadan system


•Convergent plate boundaries (destructive margins)•Oceanic–continental convergence

•Denser oceanic slab sinks into the asthenosphere

•Pockets of magma develop and rise •Continental volcanic arc forms•Examples include the Andes, Cascades, and the Sierra Nevadan system

An oceanic–continental convergent plate boundary

An oceanic–continental convergent plate boundary



•Convergent plate boundaries (destructive margins)•Oceanic–oceanic convergence

•Two oceanic slabs converge and one descends beneath the other

•Often forms volcanoes on the ocean floor

•Volcanic island arc forms as volcanoes emerge from the sea

•Examples include the Aleutian, and Mariana.


•Convergent plate boundaries (destructive margins)•Oceanic–oceanic convergence

•Two oceanic slabs converge and one descends beneath the other

•Often forms volcanoes on the ocean floor

•Volcanic island arc forms as volcanoes emerge from the sea

•Examples include the Aleutian, and Mariana.

An oceanic–oceanic convergent plate boundary

An oceanic–oceanic convergent plate boundary



•Convergent plate boundaries (destructive margins)•Continental–continental convergence

•When subducting plates contain continental material, two continents collide

•Can produce new mountain ranges such as the Himalayas


•Convergent plate boundaries (destructive margins)•Continental–continental convergence

•When subducting plates contain continental material, two continents collide

•Can produce new mountain ranges such as the Himalayas

A continental–continental convergent plate boundary

A continental–continental convergent plate boundary

The collision of India and Asia produced the Himalayas

The collision of India and Asia produced the Himalayas



•Transform fault boundaries •Plates slide past one another

•No new crust is created or destroyed


•Transform fault boundaries •Plates slide past one another

•No new crust is created or destroyed

Testing the plate tectonics modelTesting the plate tectonics model

Evidence from ocean drilling• Some of the most convincing evidence confirming seafloor spreading has come from drilling directly into ocean-floor sediment•Age of sediments•Thickness of ocean-floor sediments verifies seafloor spreading

Evidence from ocean drilling• Some of the most convincing evidence confirming seafloor spreading has come from drilling directly into ocean-floor sediment•Age of sediments•Thickness of ocean-floor sediments verifies seafloor spreading

Testing the plate tectonics modelTesting the plate tectonics model

Hot spots and Mantle Plumes•Caused by rising plumes of mantle material

•Volcanoes can form over them (Hawaiian Island chain)

Hot spots and Mantle Plumes•Caused by rising plumes of mantle material

•Volcanoes can form over them (Hawaiian Island chain)

The Hawaiian Islands have formed over a hot spot

The Hawaiian Islands have formed over a hot spot

Testing the plate tectonics model Testing the plate tectonics model

Evidence for the plate tectonics model • Paleomagnetism

•Probably the most persuasive evidence •Ancient magnetism preserved in rocks •Paleomagnetic records show

•Polar wandering (evidence that continents moved)

Evidence for the plate tectonics model • Paleomagnetism

•Probably the most persuasive evidence •Ancient magnetism preserved in rocks •Paleomagnetic records show

•Polar wandering (evidence that continents moved)

Measuring plate motion Measuring plate motion

Measuring plate motion• By using hot spot “tracks” like those of the Hawaiian Island chain

• Using space-age technology to directly measure the relative motion of plates •Global Positioning System (GPS)

Measuring plate motion• By using hot spot “tracks” like those of the Hawaiian Island chain

• Using space-age technology to directly measure the relative motion of plates •Global Positioning System (GPS)

Directions and rates of plate motionsDirections and rates of plate motions

What drives plate motion What drives plate motion Driving mechanism of plate tectonics • Earth’s heat is the driving force

•Convective Currents

Driving mechanism of plate tectonics • Earth’s heat is the driving force

•Convective Currents

Mantle Convection Mantle Convection

Layering at 660 kmLayering at 660 km

Plate Motion at the SurfacePlate Motion at the Surface

A possible view of the world 50 million years from now

A possible view of the world 50 million years from now

earth’s layered structure (ch. 8.4 in the text). earth’s internal structure layers based on...

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