Transcript Notes with questions - Department of Physics and Astronomy

Plate Tectonics
5 November 2015
Chapter 17
Great Idea:
The entire Earth is still changing, due to the slow
convection of soft, hot rocks deep within the planet.
1
Chapter Outline
• The Dynamic Earth
• Plate Tectonics: A Unifying View of
Earth
• Another Look at Volcanoes and
Earthquakes
2
The Dynamic Earth
3
The Dynamic Earth
• Small-scale changes
– Construction site
• Erosion by rain
• Large-scale changes
– Volcanoes
– Earthquakes
– Erosion
4
The Case of the
Disappearing Mountains
• Erosion
– Few hundred million years
– Mountains continually forming
• Earth’s surface is not static
5
Volcanoes and EarthquakesEvidence of Earth’s Inner Forces
• Volcano
– Magma breaks
through surface
• Earthquake
– Rocks breaks
along fault
– Energy
transmitted as
wave
– Richter scale
6
The Movement of the Continents
• F. Bacon
– Continents like a
puzzle
• Wegener
– Continental Drift
• Continents in
motion
• Current Evidence
– Ocean Floors
– Magnetic
Reversals
– Rock Ages
7
Ocean Floors
• Mapping
– Ocean floor dynamic
• Canyons, mountains
• Mid-Atlantic Ridge
– Earthquakes,
volcanoes,
lava flows
8
Magnetic Reversals
• Earth’s magnetic field
– Changes periodically
• Magnetite
– Crystals in lava align to magnetic field
• Paleomagnetism
• Seafloor Spreading
– New rock comes to surface
9
Magnetic Reversals
10
Rock Ages
• Radioactive Isotopes
– Rocks near Mid-Atlantic Ridge younger
– Rocks farther away older
11
New Support for the Theory
• Measuring motion of continents
• Radio Astronomy
– Measured arrival of radio waves
– Repeated over several years
• North America and Europe
– Separating at 5 cm per year
12
iClicker Question
•
The Great Smoky Mountains look
different from the Rocky Mountains
because:
–
A
–
B
–
C
the Smokies are older and have
been eroding away
the Rockies are older and have
grown taller
the Smokies are younger and
have not eroded the softer rocks
away like the Rockies have
13
iClicker Question
•
Most geological processes such as
mountain building and erosion are very
rapid by human standards.
–
–
A
B
True
False
14
iClicker Question
•
No earthquakes greater than 9 on the
magnitude scale have ever been
recorded.
–
–
A
B
True
False
15
iClicker Question
•
In 1912 a German meteorologist named
Alfred Wegener proposed:
–
–
A
B
–
C
Earth’s continents are in motion
weather patterns are related to
earthquakes
a magnitude 10 earthquake would
strike California in 2009
16
iClicker Question
•
For most of the twentieth century,
continental drift was regarded as a
far-fetched exercise in theory, and
few geologists paid much attention to
it.
–
–
A
B
True
False
17
iClicker Question
•
Before the ocean floors were mapped
in the years following World War II,
most scientists thought that the deep
ocean bottoms:
–
–
A
B
–
C
could not be reached
contained mountains and deep
valleys
were simply flat plains
18
iClicker Question
•
The longest mountain range on Earth
is:
–
–
–
A
B
C
the Himalayas
the Mid-Atlantic Ridge
the Rocky Mountains
19
iClicker Question
•
The Earth’s magnetic field has always
pointed in the same general direction.
–
–
A
B
True
False
20
iClicker Question
•
Rocks near the Mid-Atlantic Ridge are
very old, while rocks collected
successively farther away from the
ridge are successively older.
–
–
A
B
True
False
21
iClicker Question
•
The shape of the continents, the
magnetic stripe pattern on the ocean
floor, and the relative ages of rocks on
the ocean floor are all evidences for
–
–
–
–
A
B
C
D
man’s influence on the Earth
paleomagnetism
continental drift
tsunamis
22
Plate Tectonics: A Unifying
View of Earth
23
Plate Tectonics
• Plate Tectonics
– Large-scale surface
features
– Related phenomena
• Tectonic plates
– Rigid, moving sheet of
rock
– Crust and upper mantle
– Continental
• 100 km thick
• Lower density (granite)
– Oceanic
• 8-10 km thick
• Dense rock (basalt)
• Earth’s surface
– ¼ continent, ¾ water
24
Earth’s Plates
25
The Convecting Mantle
• Mantle convection
– Motion driven by Earth’s interior heat energy
• Sources of energy
– Gravitational potential energy
– Decay of radioactive elements
• Movement
– Heat moves to cooler regions
– Convection cells in mantle
– Very slow
• 200 million years for one cycle
26
Plate Boundaries
• Three Main Boundary Types
– Divergent
– Convergent
– Transform
27
Divergent Boundaries
• Characteristics
– Volcanoes
• Chain of mountains
– Earthquakes
• Seafloor spreading
– Plates pushed apart
– Old spreading centers
• Located in middle of ocean
– New spreading centers
• May begin anywhere
28
Convergent Plate Boundaries
• Types
– Oceanic-oceanic
• Subduction zone
– Deep oceanic trench
– Island arc
– Continental-continental
• High, jagged mountain chain
– Continental-oceanic
• Subduction zone
– Deep oceanic trench
– Coastal mountain range
29
Transform Plate Boundary
• Two plates move past each other
– NOT smooth
– Earthquakes as a result of movement
30
The Geological History of
North America
• Northeastern Canada and Greenland
– Several billion years old
• Western US
– Terranes
• Added to continent over time
• Appalachian Mountains
– Formed 450-300 million years ago
– Continental-continental convergence zone
• Rocky Mountains
– 60 million years ago
– Warping, folding and fracturing of continent
• The Colorado Plateau
– Gentle uplift
• The Sierra Nevada
– Molten rock pushed up sediments
31
Another Look at Volcanoes
and Earthquakes
• Plates and Volcanism
– Divergent Plate
Boundaries
– Convergent Plate
Boundaries
• Subduction zones
– Hotspots
• Source stationary,
plates move
• Chain of volcanoes
• Earthquakes
– At plate boundaries
or elsewhere
32
Seismology: Exploring Earth’s
Interior with Earthquakes
• Seismology
– Study of sound vibrations within earth
– Used to determine earth’s inner structure
• Seismic waves
– Compressional or longitudinal
• P-waves (pressure waves)
– Transverse or shear waves
• S-waves
33
Seismology: Exploring Earth’s
Interior with Earthquakes
34
• Plate tectonics is
involved in the
formation of the
three major
categories of
rocks
– Igneous Rock
• cooled from
molten material
– Sedimentary Rock
• Layered eroded
material formed
by the action of
wind, water, or
ice
– Metamorphic Rock
• Rock that has
been altered in
the solid state
by extreme heat
and pressure
35
iClicker Question
•
The central idea of plate tectonics
theory is that
–
A
–
–
B
C
the surface of the Earth is broken
up into about a dozen large pieces
the Earth is rigid and unchanging
the continents are moving
36
iClicker Question
•
Which type of plates are on average 810 km thick and made of dense rocks
known as basalt?
–
–
–
A
B
C
oceanic
continental
mountain
37
iClicker Question
•
Which type of plates are on average
35km thick and made of lower-density
rocks such as granite?
–
–
–
A
B
C
oceanic
continental
mountain
38
iClicker Question
•
What causes tectonic plates to move:
–
–
–
A
B
C
solar energy
oceanic wave and tidal motion
mantle convection
39
iClicker Question
•
Volcanoes are common in which
geological situations?
–
–
–
–
A
B
C
D
divergent plate boundaries
convergent plate boundaries
hot spots
all of the above
40
iClicker Question
Rocks formed when molten material cools
and solidifies are called
A
igneous rocks
B
sedimentary rocks
C
metamorphic rocks
D
fault rocks
E
scarp rocks
41
iClicker Question
•
If a scientist predicted with 80%
certainty that a major earthquake would
strike your location in the next 30 days
what would you do?
–
–
–
–
A
B
C
D
leave the area
ignore the prediction
panic
none of the above, take other action
42