The Earth’s Dynamic
Processes
Prince George’s Community College
PSC 1210
Barbara A. Gage
 Earthquakes and volcanoes are occurring
in distinct areas.
 Continents look like they fit together as
puzzle pieces.
 The Atlantic Ocean seafloor is
spreading.
 Mountains in the Himalaya Range are
getting taller.
What’s happening?
Prince George’s Community College
PSC 1210
Barbara A. Gage
Some Historical Perspective…
Continental Drift
 Land masses were once joined into a
supercontinent known as Pangaea which
split into the present day continents
 Major evidence is the fit of the coasts
(with continental shelves) of Africa
and South America
 Theory most fully developed by Alfred
Wegener in 1915
http://www.wwnorton.com/college/geo/e
geo/flash/2_2.swf
Prince George’s Community College
PSC 1210
Barbara A. Gage
Modern Evidence for Continent
Movement
 Paleomagnetism - Molten rock material will align
its iron atoms with current north and south poles
as it solidifies. Over time, the poles have
reversed positions at irregular intervals of 10
thousand to a million years. This record of
reversals, captured in igneous rocks, is referred
to as paleomagnetism.
 http://www.wwnorton.com/college/geo/egeo/flash
/2_3.swf
Prince George’s Community College
PSC 1210
Barbara A. Gage
Modern Evidence for Continent
Movement
 Sea-floor spreading - The ocean floors of the
Atlantic and southern Pacific (and others) are
spreading from a central region called a mid-ocean
ridge. Paleomagnetic data supports this. (Recall
your model with colored strips emerging from a
central slit).
http://openlearn.open.ac.uk/file.php/2717/S279_b1
_c3_f37.swf?d=590x405
http://www.wwnorton.com/college/geo/egeo/flash/
2_5.swf
Prince George’s Community College
PSC 1210
Barbara A. Gage
Modern Evidence for Continent
Movement
 Similarity of fossils and rock formations on
continents that are now separate
Prince George’s Community College
PSC 1210
Barbara A. Gage
Modern Evidence for Continent
Movement
 Patterns of global volcanic activity
Prince George’s Community College
PSC 1210
Barbara A. Gage
Modern Evidence for Continent
Movement
 Patterns of global seismic activity
Prince George’s Community College
PSC 1210
Barbara A. Gage
Modern Evidence for Continent
Movement
 Actual measurements of continental separation and
movement together – Scientists can bounce laser
beams from one station to a satellite and back to a
second station. The delay in transfer indicates the
change in distance between the stations. This was
first measured in 1984.
Prince George’s Community College
PSC 1210
Barbara A. Gage
Theory of Plate Tectonics
The upper section of the Earth is
divided into sections called plates.
These plates move and change size
over time.
Plate boundaries are defined by seismic
and volcanic activity.
Prince George’s Community College
PSC 1210
Barbara A. Gage
Earth’s Plates
Prince George’s Community College
PSC 1210
Barbara A. Gage
Prince George’s Community College
PSC 1210
Barbara A. Gage
How do we know what the
layers are? P and S Waves!
Prince George’s Community College
PSC 1210
Barbara A. Gage
Layers of the Earth
http://scign.jpl.nasa.gov/learn/plate1.htm
Prince George’s Community College
PSC 1210
Barbara A. Gage
For Some Perspective…
Prince George’s Community College
PSC 1210
Barbara A. Gage
Earth’s Layers (based on seismology)
CRUST
 Two forms - continental and oceanic
 Continental crust is composed of less dense
rock rich in silicates; thicker than oceanic
 Oceanic crust is basaltic and denser than the
continental crust; rich in silicates
Prince George’s Community College
PSC 1210
Barbara A. Gage
Earth’s Layers (based on seismology)
MANTLE
 Composed of iron-rich silicates
 Has an upper layer that is “plastic” or semifluid
 Has a higher temperature than the crust
Prince George’s Community College
PSC 1210
Barbara A. Gage
Earth’s Layers (based on seismology)
CORE
 At the center of Earth
 Has two sections, outer and inner cores
composed mainly of iron and nickel
 Outer core is molten while inner core is solid
 Fluidity of outer core may account for Earth’s
magnetic field
Prince George’s Community College
PSC 1210
Barbara A. Gage
Another Way to View Earth
Layers
 Lithosphere - composed of crust and uppermost
section of the mantle; rigid layer that composes
the plates
 Asthenosphere - “plastic” region in the upper part
of the mantle under the lithosphere; the plates
“ride” on the asthenosphere
Prince George’s Community College
PSC 1210
Barbara A. Gage
Lithosphere and Asthenosphere
Prince George’s Community College
PSC 1210
Barbara A. Gage
Prince George’s Community College
PSC 1210
Barbara A. Gage
Plate Motion
 Plates can move away from each other at
divergent plate boundaries or spreading centers.
 Plates can move together in convergent plate
boundaries.
 Plates can slide past each other in transform fault
boundaries.
 http://www.classzone.com/books/earth_science/t
erc/content/visualizations/es0804/es0804page01
.cfm?chapter_no=visualization
 http://www.pbs.org/wgbh/aso/tryit/tectonics/#
Prince George’s Community College
PSC 1210
Barbara A. Gage
Divergent Plate Motion
 Tensional forces stretch the lithosphere
 New Earth materials are formed between
plates where hot mantle material rises into
stretched area
Prince George’s Community College
PSC 1210
Barbara A. Gage
Divergent Plate Motion
 Mid-Ocean
Ridge in Atlantic
Ocean has been
active for about
160 MY
 Rift valleys may
result from
divergent motion
as seen in East
African Great
Rift Valley
Prince George’s Community College
PSC 1210
Barbara A. Gage
Convergent Plate Motion
 Causes collision of plates with compressional
forces. Convergence leads to subduction of one
plate under another
 Oceanic crust may go under continental crust
generating a trench and causing mountain building
Prince George’s Community College
PSC 1210
Barbara A. Gage
Convergent Plate Motion
 Continental crust may go under other continental
crust with mountain building
Prince George’s Community College
PSC 1210
Barbara A. Gage
Convergent Plate Motion
 The Indian plate collided
with the Eurasian Plate 4050 million years ago to form
the Himalayas. These
mountains are still growing
about 1 cm/year because of
the “push” from the Indian
Plate.
Prince George’s Community College
PSC 1210
Barbara A. Gage
Convergent Plate Motion
 Ocean crust may go under ocean crust in a trench
causing oceanic volcanoes and a deep ocean trench.
Prince George’s Community College
PSC 1210
Barbara A. Gage
Transform Fault Boundary
 Plates may slide past
each other laterally
with no subduction
 Seismic activity is
high along these slip
boundaries
Prince George’s Community College
PSC 1210
Barbara A. Gage
Transform Fault Boundary
 The San Andreas
Fault in California
is an example of
this boundary
Prince George’s Community College
PSC 1210
Barbara A. Gage
Hot Spots
 Sometime a plate will pass over an active spot
beneath that “punches through” the lithosphere
as a volcanic eruption. The Hawaiian Islands
formed (and are still forming) this way.
 http://www.classzone.com/books/earth_science/t
erc/content/visualizations/es0904/es0904page01
.cfm?chapter_no=visualization
Prince George’s Community College
Can you identify the types
of plate boundaries and
geologic features?
Prince George’s Community College
PSC 1210
Barbara A. Gage
Boundaries and Features
Prince George’s Community College
PSC 1210
Barbara A. Gage
Plate Motion Over Time
http://www.ucmp.berkeley.edu/geology/tectonics.html
http://www.uky.edu/AS/Geology/howell/goodies/elearning/modul
e04swf.swf
Prince George’s Community College
PSC 1210
Barbara A. Gage