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Volcanoes and Igneous Activity Earth - Chapter 4

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Earth s Layered Structure (Ch. 8.4 in the Text) – PowerPoint PPT presentation

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Title: Volcanoes and Igneous Activity Earth - Chapter 4


1
Earths Layered Structure (Ch. 8.4 in the Text)
2
Earths 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 3540 km (25 miles)
    thick

3
Earths layered structure
  • Discovering Earths major layers
  • Mohorovicic discontinuity (Moho)
  • Separates crust from underlying mantle

4
Earths internal structure
  • Layers based on composition
  • Mantle
  • Below crust to a depth of 2,890 kilometers (1,800
    miles)
  • Over 82 of Earths volume
  • Common rock type in the upper mantle is Peridotite

5
Earths internal structure
  • Layers based on composition
  • Core
  • Composed of an ironnickel alloy
  • Average density of nearly 13 g/cm3
  • Radius of 3,480 kilometers

6
Earths internal structure
  • 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

7
Earths 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
    Earths magnetic field

8
Earths internal structure
  • Layers based on physical properties
  • Inner Core
  • 1220 km thick
  • Compressed into a solid state by immense pressure

9
Plate Tectonics Ch. 9 (p. 246 - 277)
10
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

11
Pangaea approximately 200 million years ago
12
Continental drift an idea before its time
  • Wegeners 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 Wegeners Hypothesis What force was
    moving the continents?

13
Similar mountain ranges on different continents
14
Paleoclimatic evidence for continental drift
15
Plate Tectonics the new paradigm
  • The Theory of Plate Tectonics
  • We are now able to measure the movement of the
    continents due to technological advancements
  • Associated with Earths rigid outer shell
  • Called the lithosphere
  • Consists of several plates
  • Largest plate is the Pacific plate

16
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

17
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

18
Divergent boundaries are located along oceanic
ridges
19
The East African rift a divergent boundary on
land
20
Plate tectonics the new paradigm
  • Plate boundaries
  • Convergent plate boundaries (destructive margins)
  • Plates collide, an ocean trench forms, and
    lithosphere is subducted into the mantle

21
Plate tectonics the new paradigm
  • Plate boundaries
  • Types of plate boundaries
  • Convergent plate boundaries (destructive margins)
  • Oceaniccontinental 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

22
An oceaniccontinental convergent plate boundary
23
Plate tectonics the new paradigm
  • Plate boundaries
  • Types of plate boundaries
  • Convergent plate boundaries (destructive margins)
  • Oceanicoceanic 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.

24
An oceanicoceanic convergent plate boundary
25
Plate tectonics the new paradigm
  • Plate boundaries
  • Types of plate boundaries
  • Convergent plate boundaries (destructive margins)
  • Continentalcontinental convergence
  • When subducting plates contain continental
    material, two continents collide
  • Can produce new mountain ranges such as the
    Himalayas

26
A continentalcontinental convergent plate
boundary
27
The collision of India and Asia produced the
Himalayas
28
The collision of India and Asia produced the
Himalayas
29
Plate tectonics the new paradigm
  • Plate boundaries
  • Types of plate boundaries
  • Transform fault boundaries
  • Plates slide past one another
  • No new crust is created or destroyed

30
Testing 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

31
Testing the plate tectonics model
  • Hot spots and Mantle Plumes
  • Caused by rising plumes of mantle material
  • Volcanoes can form over them (Hawaiian Island
    chain)

32
The Hawaiian Islands have formed over a hot spot
33
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)

34
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)

35
Directions and rates of plate motions
36
What drives plate motion
  • Driving mechanism of plate tectonics
  • Earths heat is the driving force
  • Convective Currents

37
Mantle Convection
38
Layering at 660 km
39
Plate Motion at the Surface
40
A possible view of the world 50 million years
from now
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