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Plate Tectonics
Bellringers!! 
Bellringer 11/11-12
Define plate tectonics:
Use ONE word to describe the
– Lithosphere:
– Asthenosphere:
Which contains the plates? L or A
Which has convection currents? L or A
Which has oceanic crust? L or A
Which is HOTTER? L or A
Bellringer 11/15
How do heated currents (of molten rock, water,
etc.) tend to move in natural systems, and
WHY?
What process drives the movement of tectonic
plates?
How will lithospheric plates that are directly
above a rising current move?
– Together or Apart
How will plate above a sinking current move?
– Together or Apart
Bellringer 11/16
What theory suggests that South America
and Africa were once part of a larger
continent that broke and moved apart?
Who was the German scientist who
proposed the most famous version of this
theory?
List 3 lines of evidence he used to support
his theory.
Bellringer 11/17
What do we know about the distribution of earthquakes
and volcanoes on Earth?
a. They occur randomly across the world
b. Quakes tend to happen along plate boundaries but volcanoes
are random
c. Both quakes and volcanoes tend to occur at plate boundaries
What type of boundary is the most “active”?
a.
b.
c.
Convergent
Collision
Subduction
Magnetic minerals in undisturbed rocks will
a.
b.
c.
Indicate where “north” was at the time of formation
Align with “north” as we know it to be now, no matter what
Change in their direction of alignment slowly over time
Evidence for Plate Tectonics
Theory
Earthquakes and Volcanoes
2. Magnetism
Heat Flow and Seafloor Elevation
1.
3.
1. Earthquakes and Volcanoes
Earthquakes
– Occur in limited belts around the world
– These same belts also contain most of Earth’s
volcanoes
– These belts locate plate boundaries
Plate boundaries are
active areas
– This is where plates
are moving!
– Stress from friction
builds up  causes
fractures 
earthquakes
– Heat flow as plates
subduct  rising
magma to surface 
volcanoes above plate
boundaries
“Ring of Fire”
– World’s largest belt of volcanoes and earthquakes, nearly
surrounds the Pacific Ocean
– 90% of earthquakes occur here
– Many famous volcanoes
2. Magnetism
Magnetic minerals in
rocks record the
direction of the
Earth’s poles when
they were formed
– Found that Earth’s
crust had drifted or
shifted since the time
many rocks were
formed
There is evidence
Earth’s magnetic
poles often reversed.
– North Pole ‘became’
the South Pole, and
vice-versa
Magnetic Polarity
Reversals
– Show in bands in the
igneous rock on the
ocean floor, where
plates are moving
apart
– Age dating found that
the youngest rocks are
at plate boundaries
where plates are
spreading apart
– Rock gets older away
from these boundaries
Spreading Centers
– Found on ocean floors
– Where plates are
moving apart
– Lava wells up,
continuously forming
new oceanic crust
– Older crust moves
away in both
directions, carrying
continents with it
3. Heat Flow and Seafloor
Elevation
If convection currents within the
asthenosphere drive plate movement, then
evidence for this should be found at
spreading centers…
Heat Flow: the measure of the amount of
heat leaving the rocks of the lithosphere.
– Unusually high at spreading centers
– Decreases away from them
Elevation of the
seafloor
– Heated materials
expand…it has been
found that spreading
centers have higher
elevations than the
rest of the seafloor
– Elevations decrease
away from spreading
centers as the crust
cools and contracts
(shrinks back down)
Generalization- Evidence for P.T.
If spreading centers create new crust
constantly, does that mean the earth is
getting bigger?
Describe the age of rocks at a spreading
center?
How does heat flow support plate
tectonics theory?
Why do we see higher elevations at “midocean ridges”?
Bellringer 11/19
What type of plate boundary is it???
Where plates are pulling apart
Plates sliding past each other
Boundary where you will see mountains
Boundary that creates mid ocean ridges
San Andreas Fault
Mid-Atlantic Ridge
Where we see lots of quakes and volcanic
activity
Bellringer 11/22
What type of boundary produced the San
Andreas Fault?
What is a famous example of a divergent
boundary?
What type of boundary produced the
Himalayas? Where are they located?
Give a famous example of a subduction
boundary. List the continental and oceanic
crusts involved.
Bellringer 11/23
Label the tectonic plates
Bellringer Collection- 7 pts total
11/11 or 12
11/15
11/16
11/17
11/19
11/22
11/23