http://plainedgeschools.org/sw
ells/power_point_links.htm
Who believes in plate
tectonics?
Evidence: Fossils
Matching Mountain Ranges
Glacier Evidence
What is the
Mid-Atlantic ridge?
A new hope:
Sea-Floor Spreading
MID-ATLANTIC
RIDGE
50,000 km. Long
mountain range on
the ocean floor
Spreading Center
New Ocean
forming –
linear Red
Sea
When it grows
up, it will be
like the
Atlantic
Ocean
In Afar, Ethiopia, a 40-mile magmatic
rift that opened up 1 year ago
Which graph best represents the geologic age of the surface bedrock on the ocean bottom?
• Mid-ocean ridges (rifts) normally form
where tectonic plates are
• (1) converging
(3) stationary
• (2) diverging
(4) sliding
past each other
• If new crust is created at divergent
boundaries, is earth getting larger?
CONVERGENT BOUNDARIES – DESTROYS CRUST
Oceanic Crust converging with Continental Crust
Oceanic crust converging with Oceanic Crust
Continental Crust converging with Continental
Crust
OCEAN CRUST - CONTINENTAL CRUST
SUBDUCTION – TRENCH FORMS
Oceanic-Continental
Convergent Boundary - SUBDUCTION
DENSER OCEANIC CRUST
GOES DOWN INTO MANTLE
OCEAN CRUST –OCEAN CRUST
CONVERGENCE - SUBDUCTION
Oceanic Crust – Oceanic Crust
Older, denser oceanic crust is SUBDUCTED (sinks below)
VOLCANIC ISLAND ARC FORMED – ALEUTIAN ISLANDS
TRENCH FORMS
Continental Crust – Continental Crust
Convergent Boundary
NO SUBDUCTION - COLLISION ZONE
Collision of India and Asia
Convergent
IndianAustralian
Plate and the
Pacific Plate
(oceanic crust
to oceanic
crust) are
converging
forming the
Tonga Trench.
Deep
EQ’s
f07_58_pg196
3 types of plate boundaries caused by convection currents
CASCADES
MIDATLANTIC
RIDGE
TRENCH
Can magnetic poles
really switch?
Evidence for Plate Tectonics
During WWII, the U.S. in an
effort to find any advantage
that would help out submarines
in the war effort, scientists
found that the iron in the rock at
the mid-ocean ridge sometimes
pointed North and sometimes
pointed South
How could this be?
Basalt is iron rich and contains magnetite.
Magnetite acts like a little magnet and aligns
itself with the orientation of earth’s magnetic
field.
When magma solidifies, the alignment is
“locked in” recording Earth’s magnetic
orientation at the time of cooling.
MAGNETIC STRIPE EVIDENCE
North Oriented Rocks are said to have NORMAL POLARITY
South Oriented Rocks are said to have REVERSED
POLARITY
The earth’s
magnetic field
has reversed
hundreds of
times
More Evidence for Plate
Tectonics
 Hot
Spots
• A hot spot is a concentration of heat in the
mantle capable of producing magma, which
rises to Earth’s surface; The Pacific plate
moves over a hot spot, producing the
Hawaiian Islands.
• Hot spot evidence supports that the plates
move over the Earth’s surface.
HOT SPOTS
• Major regions of volcanic activity in the interior of
plates away from plate boundaries.
• The cause of these hot spots is thought to be
plumes of magma rising up from mantle
producing sites of active volcanism.
• As the plate moves over a hot spot, a chain of
volcanic mountains forms, like Hawaiian Islands
Hot spots:
• http://plainedgeschools.org/swells/plate%2
0tectonics%20%20revised.ppt#367,59,Slide 59
This diagram provides evidence that the Pacific Tectonic
Plate is moving toward the
(1) south
(3) southwest
(2) east
(4) northwest