• Plate Tectonic Theory states the outermost layer of Earth is
composed of 9 to 15 large plates and numerous small ones
• Most plates are located on the ocean floor
• Cracked egg used as a Model for Earth’s
tectonic plates
• Lithosphere composed of the crust and upper mantle forms
the Earth’s tectonic plates
• Asthenosphere composed of very hot, melted plastic-like
material lies below the lithosphere
• Giant plates drift around on the asthenosphere at a rate of 1
to 2 centimeters per year
• Area of interaction between adjacent plates referred to
as the plate boundary
• Three types of plate boundaries as determined by the type
of interaction occurring are: divergent, convergent and
transform
DIVERGENT BOUNDARY
• Formed when two adjacent plates move apart
• Causes molten rock to erupt to the surface and create new crust; seafloor
spreading is a result of this process
• Creates mid-ocean ridges such as the mid-Atlantic ridge (bottom of Atlantic
Ocean)
• Continues to form new rocks that move away from ridges, explaining how crust
can move and supporting the theory of Continental Drift
• Causes underwater volcanos, earthquakes and forms rifts such as the Great
Rift Valley in Eastern Africa
CONVERGENT BOUNDARY
CONTINENTAL-CONTINENTAL
• Formed when two plates move together
• Plates’ crust type determines geologic
activity at interaction point
• Equally dense continental crust plates buckle and
are pushed upward, forming mountain ranges
• Examples: Himalayas (still forming), Alps and Appalachians
CONVERGENT BOUNDARY
CONTINENTAL - OCEANIC
SUBDUCTION
• Oceanic crust is denser but less thick than
continental crust
• Oceanic crust collides with continental crust
• Oceanic crust bends, slides under the
continental crust, goes down into the mantle:
this interaction is called subduction
• Results in earthquakes, volcanos and
rock deformation
• Examples: Cascade Range in the
Pacific Northwest and the Andes
in South America
TRANSFORM BOUNDARY OR TRANSFORM FAULT MARGIN
• Formed when two plates slide past each other
• Usually move in opposite directions but may move in the
same direction at different speeds
• Fault: a deep crack in the Earth’s surface
• Transform boundary : where plates catch and grind but
crust is not produced or destroyed
San Andreas Fault
•
Plates build tension along boundary and release it
with a burst of energy and motion, resulting in earthquakes
•
Most transform boundaries located on the ocean floor
•
Notable exception is San Andreas Fault Zone in California
which passes through two thirds of the state: it has
produced many earthquakes, including those in
San Francisco and Los Angeles
REVIEW OF THE THREE TYPES OF PLATE BOUNDARIES
WHAT’S ON YOUR PLATE???
COMPARE THE THREE LAYERS OF AN EGG
TO THE THREE MAIN LAYERS OF THE EARTH
A
B
EARTH
C
A
B
C
STRUCTURE OF THE EARTH
•
Three main layers of the Earth: Core (inner and
outer), mantle (upper and lower) and crust
•
Inner core under extremely high pressure,
solid state, very dense, composed mostly of
iron
•
Outer core liquid state, composed mostly of
iron
•
Mantle largest layer, composed of silicon,
oxygen, magnesium and iron, divided into
upper and lower divisions as determined by
different seismic wave speeds
•
Crust outermost layer, varies in thickness from
more than 60 km to less than 5 km
•
Contains higher percentage of silicon and aluminum and
lower percentage of magnesium and iron than the mantle
•
Generally less dense than the mantle