1. Deformation of Earth’s Crust
Chapter 4
Layers of the Earth
Continental Drift
Plate Tectonics
Deformation of Earth’s Crust

2. Layers of the Earth Crust Mantle Core Thin, outermost layer of Earth
uppermost part of lithosphere
Mantle
Layer of Earth between crust and core
Core
Central, spherical part of Earth below the mantle

6. Crust 5 to 100 km thick thinnest layer of Earth continental crust
similar to granite
oceanic crust
similar to basalt

8. Mantle between crust and core contains most of Earth’s mass
similar to olivine
large amounts of iron and magnesium

9. Layers of the Mantle Lithosphere Asthenosphere Mesosphere
Outermost, rigid layer of Earth
consists of crust and rigid upper part of mantle
Asthenosphere
Soft layer of mantle on which pieces of the lithosphere move
Mesosphere
“middle sphere”
strong, lower part of mantle between asthenosphere and outer core

11. Core extends from bottom of mantle to center of Earth
slightly larger than Mars
mostly iron
small amounts of nickel
possibly some sulfur and oxygen

12. Outer Core Inner Core liquid layer of Earth’s core lies beneath mantle
surrounds inner core
solid, dense center of Earth

14. Tectonic Plate a piece of lithosphere moves around on top of the
asthenosphere

16. How do Scientists know about the structure of the inside of the Earth?
Earthquakes
When an earthquake occurs, seismographs measure the difference in arrival times of seismic waves and record them
Seismologists use these measurements to calculate the density and thickness of each layer

17. Continental Drift
The theory that continents can drift apart from one another and have done so in the past

19. Pangea
“all earth”
land mass that existed 245 million years ago made up of all of the continents put together
Laurasia
northern half of Pangea; formed 180 million years ago when Pangea broke in half
Gondwana
southern half of Pangea; formed 180 million years ago when Pangea broke in half

20. Pangea

21. On the Sea Floor… Mid-Ocean Ridge Sea Floor Spreading
The process by which new oceanic lithosphere is created at mid-ocean ridges
older materials are pulled away from the ridge
Mid-Ocean Ridge
a long mountain chain that forms on the ocean floor where tectonic plates pull apart
usually extends along the center of ocean basins

23. Magnetic Reversals
the process by which the Earth’s north and south magnetic poles periodically change places

25. Wegener’s Theory What was Wegener’s theory of continental drift?
The theory that continents can drift apart from one another and have done so in the past
Why was Wegener’s theory not accepted at first?
Scientists at that time did not understand what force of nature could move continents

26. Sea Floor Spreading Mid-Ocean Ridges
How does sea floor spreading provide a way for continents to move?
It forms new crust in between the places where the spreading takes place
How does new oceanic crust form at mid-ocean ridges?
As tectonic plates move away from each other, the sea floor spreads apart and magma rises to fill in the gap
This magma cools to form new crust

27. How do magnetic reversals provide evidence for sea-floor spreading?
The molten rock contains tiny grains of magnetic materials which align themselves with Earth’s current magnetic field
They are “set in stone” as the molten rock cools and solidifies
As the sea-floor continues to spread, these rocks are carried away from the spreading center
The magnetic fields are found in bands along the oceanic crust

28. Plate Tectonics
The theory that states that Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere

29. Convergent Boundaries
Convergent Boundary
The boundary between two colliding tectonic plates
Subduction Zone
The region where an oceanic plate sinks down into the asthenosphere at a convergent boundary
usually between continental and oceanic plates

30. Three Types of Convergent Boundaries
Continental/Continental Collisions
Continental/Oceanic Collisions
Oceanic/Oceanic Collisions

31. Divergent Boundaries
The boundary between two tectonic plates that are moving away from each other

32. Transform Boundaries
The boundary between two tectonic plates that are sliding past each other horizontally

33. What are the 3 forces thought to move tectonic plates?
Convection
Slab Pull
Ridge Push

34. Convection
Hot material from deep with in Earth rises while cooler material near the surface sinks
As warmer material cools, it becomes more dense and sinks
The motion drags tectonic plates sideways

35. Convection

36. Slab Pull oceanic lithosphere is denser than the asthenosphere
the edge of the oceanic plate sinks
pulls the rest of the tectonic plate with it

38. Ridge Push
An oceanic plate sides down the lithosphere-asthenosphere boundary
occurs where oceanic lithosphere is higher than continental lithosphere

40. Measuring Plate Movement
using a network of satellites called the Global Positioning System
allows scientists to record the time it takes for radio signals from a position on Earth to reach the satellite
by monitoring changes in this, scientists can tell how much the plates have moved

41. Stress
The amount of force per unit area that is put on a given material
Deformation
the change in the shape of rock in response to stress applied

42. Compression Tension
The type of stress that occurs when an object is squeezed
The type of stress that occurs when forces act to stretch an object

43. Fault
A break in the Earth’s crust along which blocks of the crust slide relative to one another due to tectonic forces

44. Types of Faults Normal Fault Reverse Fault Strike-slip Fault
a fault in which the hanging wall moves down relative to the footwall
Reverse Fault
a fault in which the hanging wall moves up relative to the footwall
Strike-slip Fault
a fault in which the two fault blocks move past each other horizontally
Fault Block
The blocks of crust on each side of the fault

46. Folding
The bending of rock layers due to stress in the Earth’s crust

47. Types of Mountains
Folded
Fault-Block
Volcanic Mountains

48. Folded Mountains
form when rock layers are squeezed together and pushed upward
example:
Appalachian Mountains

51. Fault Block Mountains
where tectonic forces put enough tension on the Earth’s crust, a large number of normal faults can result
this faulting causes large blocks of Earth’s crust to drop down relative to other block
example:
The Tetons (in western Wyoming)

54. Volcanic Mountains when molten rock erupts onto the Earth’s surface
examples:
Ring of Fire
Mount St. Helen’s