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Grotzinger • Jordan • Press • Siever
Understanding Earth
Fifth Edition
Chapter 2:
Plate Tetonics:
The Unifying Theory
Copyright © 2007 by W. H. Freeman and Company
Divergent Boundaries
Oceanic Plate Separation
MidAtlantic
Ridge
Divergent Boundaries
Oceanic Plate Separation
Volcanoes and earthquakes concentrate.
MidAtlantic
Ridge
Divergent Boundaries
Continental Plate Separation
East African
Rift Valley
Divergent Boundaries
Continental Plate Separation
Parallel valleys; volcanoes and earthquakes.
East African
Rift Valley
Convergent Boundaries
Ocean-Ocean Convergence
Mariana Islands
Marianas Trench
Convergent Boundaries
Ocean-Ocean Convergence
Deep-sea trench; volcanic island arc.
Mariana Islands
Marianas Trench
Convergent Boundaries
Ocean-Continent Convergence
Andes
Mountains
Peru-Chile Trench
South
American
Plate
Convergent Boundaries
Ocean-Continent Convergence
A volcanic belt of
mountains forms.
Andes
Mountains
Peru-Chile Trench
South
American
Plate
Convergent Boundaries
Continent-Continent Convergence
Himalaya
Tibetan
Plateau
Main
thrust
fault
Eurasian
Plate
Convergent Boundaries
Continent-Continent Convergence
Crust crumbles, creating high
mountains and a wide plateau.
Himalaya
Tibetan
Plateau
Main
thrust
fault
Eurasian
Plate
Transform-Fault Boundaries
Mid-Ocean Ridge Transform Fault
Transform-Fault Boundaries
Mid-Ocean Ridge Transform Fault
Spreading centers offset.
Transform-Fault Boundaries
Continental Transform Fault
Transform-Fault Boundaries
Continental Transform Fault
Offset continental crust.
As plates
move past
each other...
As plates
move past
each other...
…creek beds
are offset
As plates
move past
each other...
…creek beds
are offset
San
Francisco
Los Angeles
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic
Ridge southwest of Iceland, showed an oscillating pattern of
magnetic field strength. This figure illustrates how scientists worked
out the explanation of this pattern.
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic
Ridge southwest of Iceland, showed an oscillating pattern of
magnetic field strength. This figure illustrates how scientists worked
out the explanation of this pattern.
A sensitive magnetometer
records magnetic anomalies,…
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic
Ridge southwest of Iceland, showed an oscillating pattern of
magnetic field strength. This figure illustrates how scientists worked
out the explanation of this pattern.
A sensitive magnetometer
records magnetic anomalies,…
Iceland
MidAtlantic
Ridge
Magnetic mapping can measure the rate of seafloor spreading
An oceanic survey over the Reykjanes Ridge, part of the Mid-Atlantic
Ridge southwest of Iceland, showed an oscillating pattern of
magnetic field strength. This figure illustrates how scientists worked
out the explanation of this pattern.
A sensitive magnetometer
records magnetic anomalies,…
…alternating bands of high
and low magnetism.
Iceland
MidAtlantic
Ridge
Symmetrical bands on both sides.
Why?
Magnetic anomalies also in volcanic lava.
Magnetic anomalies also in volcanic lava.
Normal
Reversed
Magnetic anomalies also in volcanic lava.
Earth’s magnetic field
reverses direction.
Normal
Reversed
Layers “remember”.
Older layers preserve
their direction.
Scientists constructed
a magnetic time scale.
Subchrons
5.0 Ma
4.0
Gilbert
reversed chron
3.0
Gauss
normal chron
2.0
1.0
Matuyama
reversed chron
Present
Brunhes
normal chron
Mid-ocean ridge
Million years ago (Ma)
4.0
3.0
2.0
Ocean
crust today
ASSEMBLY OF PANGAEA
RODINIA Late Proterozoic, 750 Ma
ASSEMBLY OF PANGAEA
RODINIA Late Proterozoic, 750 Ma
Formed about 1.1 billion
years ago; began to break
up about 750 million
years ago.
ASSEMBLY OF PANGAEA
Late Proterozoic, 650 Ma
ASSEMBLY OF PANGAEA
Late Proterozoic, 650 Ma
The pre-Pangean pattern
of continental drift.
ASSEMBLY OF PANGAEA
Middle Ordovician, 458 Ma
The pre-Pangean pattern
of continental drift.
ASSEMBLY OF PANGAEA
Early Devonian, 390 Ma
The pre-Pangean pattern
of continental drift.
ASSEMBLY OF PANGAEA
PANGAEA (a) Early Triassic, 237 Ma
ASSEMBLY OF PANGAEA
PANGAEA (a) Early Triassic, 237 Ma
Assembled by 237 Ma.
BREAKUP OF PANGAEA
(b) Early Jurassic, 195 Ma
BREAKUP OF PANGAEA
(b) Early Jurassic, 195 Ma
Signaled by the opening
of rifts from which lava
poured; relics can be
found today in volcanic
rocks from Nova Scotia
to North Carolina.
BREAKUP OF PANGAEA
(c) Late Jurassic, 152 Ma
BREAKUP OF PANGAEA
(d) Late Cretaceous, Early Tertiary, 66 Ma
THE PRESENT-DAY AND FUTURE WORLD
(e) PRESENT-DAY WORLD
THE PRESENT-DAY AND FUTURE WORLD
(e) PRESENT-DAY WORLD
The modern world has
been produced over the
past 65 million years.
THE PRESENT-DAY AND FUTURE WORLD
(f) 50 million years in the future
Whole-mantle convection
Mantle
Outer core
Inner core
Upper
mantle
700 km
Lower
mantle
2900 km
Outer core
Whole-mantle convection
Upper
mantle
700 km
Lower
mantle
2900 km
Outer core
Stratified convection
Boundary near
700 km separates
the two convection
systems.