Download What is Plate Tectonics Theory?

What is Plate
Tectonics Theory?
Use this part
of the PPT for
p. 7 of your
INB!!!
The Discovery of Plate
Tectonics
A. Continental Drift (Alfred
Wegener)
Proposed largescale movement
of the continents
Evidence:
1. “Puzzle fit” of
continents to form
“Supercontinents”
a. Suess (1900)Gondwana
b. Wegner (1915)Pangea
More Evidence…
2. Similar rock ages
3. Similar geologic
structures such as
mountain ranges
4. Fossil Evidence
from the
Mesosaurus
5. Climate Evidence
such as glacial
deposits
**Wegener’s theory did
not gain much support
because he could not
explain how the
tectonic plates move
B. Seafloor Spreading- Henry
Hess)
1.
2.
3.
4.
Convection currents
move plates around
Mantle source of
heat and convection
proposed new and
recycled seafloor
Evidence from
submarines during
WWII around the
Mid-Atlantic Ridge
showed the seafloor
is a mirror image on
each side of the
ridge
**There was no
evidence for this
theory, until…
Magnetic Pole Reversals or
“Tape Recording”
1. Magnetic Reversals
a. Switching strength to the
south from the north
b. Preserved in lava
because iron points
towards stronger pole
c. Age of these iron bands
can be calculated and if
the seafloor is spreading
from a center, they
should be mirror images
on each side of ridge
(continued)
2. Seafloor ages
a. Speed = distance /
time
Mid-ocean ridge
Million years ago (Ma)
4.0
3.0
2.0
Ocean
crust today
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?
Looking at pole reversals
preserved in the ocean floor
provides the evidence needed
to support seafloor spreading.
Seafloor spreading provides
the mechanism for “how” the
continents move! (Wegener)
A Mosaic of Plates
A. Entire Earth’s surface
is made up of
tectonic plates
A.
Made up of a special
layer of the Earth
called the lithosphere
and “ride” on top of
the mantle
B. Plates have both
oceanic crust &
continental crust
A.
Continental crust is
less dense than
oceanic crust
A Mosaic of Plates
(cont.)
C. Specific Geologic activities that occur
along plate boundaries or because of
plate movement:
1. Volcanoes
2. Mountain building
3. Earthquakes
4. Hot spots
5. Faults/cracks in crust