Download Continental Drift and Plate Tectonics

Where did the idea come
from that the continents
were once connected?
• As long ago as 1620, the English thinker
Francis Bacon noticed similarities between
the coasts of South America and Africa.
What is continental drift?
• Continents were once connected
into one supercontinent and have
since drifted to their current
positions
• Alfred Wegner developed the idea in
1912
– He called the supercontinent Pangaea
all gaea = ________)
land
PANGAEA (greek: pan = _____,
• Stretched from pole to pole
• Centered where Africa is today
Wegner’s Evidence Supporting
Continental Drift
• Coastlines
• Landforms
• Fossils
• Climate
Continental Drift Evidence
Coastlines
• Coasts of some continents look like they
fit together.
Example: east coast of
South America and west
coast of Africa
Continental Drift Evidence
Landforms
• Mountain ranges on different continents line up
• Similar coal and rock formations found on
different continents line up; are same age
Example:
Appalachians
line up with the
mountain ranges
in Europe. They
are the same
type of rock and
age.
Continental Drift Evidence
Fossils
• Fossils of the same organisms are found
on different continents
Continental Drift Evidence
Climate
1. Evidence of past tropical climates in the
Antarctic
Example: fossils of Glossopteris (tropical
plant) found in areas that are now colder
Continental Drift Evidence
Climate
1. Evidence of past tropical climates in
what is now the Antarctic
2. Evidence of glacier marks in what is
now the tropics
Continental Drift
Why was the idea of
continental drift rejected
for more than 40 years?
Wegner could not provide the
force that caused the continents
to move.
How could huge solid chunks of
land have plowed through the
ocean floor???
What Is the Theory of Plate
Tectonics?
• Pieces of Earth’s
lithosphere are in
constant slow motion;
driven by convection
currents in the
asthenosphere
• Explains creation,
movement, destruction
of Earth’s plates
What Are Plates and Plate
Boundaries?
• Plates: broken pieces of
the lithosphere
• Plate boundaries: the
edges of the plates
What Happens at Plate
Boundaries?
• Plates can pull away from each
other
–Divergent boundaries
• Plates can grind past each other
–Transform boundaries
• Plates can crash into each other
–Convergent boundaries
Divergent Plate Boundary
• A place where two plates move apart or divide
• Crust is created from cooled magma
What geologic features form at
divergent plate boundaries?
1. Mid-ocean ridges
– divergent plate boundaries beneath the
ocean
– world’s longest mountain range!
– circle Earth like a seam on a baseball
– Example: Mid-Atlantic Ridge
Volcanoes
http://www.smithsonianmag.com/specialsections/lifelists/Icelands-Volcanoes.html#
Eldfell in Heimaey
What geologic features form at
divergent plate boundaries?
2. Rift valleys
– divergent plate boundaries on land
– Examples: Rio Grande Rift (North
America), Great Rift Valley (East Africa)
http://worldwildlife.org/photos/great-rift-valley-kenya
http://www.getintravel.com/great-rift-valley-kenya/lanscape-of-the-great-rift-valley-in-kenya-africa/
Transform Plate Boundary
• A place where two plates grind past each
other, moving in horizontal opposite directions
• Crust is neither created nor destroyed
http://geology1403.blogspot.com/2011_09_01_archive.html
What geologic features form at
transform plate boundaries?
• Responsible for creating strike-slip
faults, which lead to strong earthquakes
– Example: San Andreas Fault (Calif.)
San Andreas Fault
Convergent Plate Boundary
• A place where two plates come together
• Crust is destroyed due to subduction
(edge of plate sinks under another plate
into the mantle)
• Collisions happen between:
1. Oceanic/Continental
2. Oceanic/Oceanic
3. Continental/Continental
What geologic features form at
convergent plate boundaries?
1. Collision between oceanic crust and
continental crust
– basalt (oceanic crust) more dense than
granite (continental crust)
– forms deep ocean trenches where ocean
crust is subducted into mantle
– forms volcanoes on continent due to
melting crust
– Examples: Andes, Cascades, Sierra Nevada
DEEP-OCEAN TRENCH
Link to
Simulation
Subduction
&
Volcanic eruption
What geologic features form at
convergent plate boundaries?
2. Collision between oceanic crust and
oceanic crust
– forms deep ocean trenches where one ocean
crust is subducted under the other
– forms volcanic arc islands
– Examples: Aleutian, Tonga, Mariana
Islands
Link to
Simulation
What geologic features form at
convergent plate boundaries?
3. Collision between continental crust and
continental crust
– forms high mountain ranges
– Examples: Himalayas
Link to
Simulation
Collision of India and Asia