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Plate Tectonics
• Ever notice how all the continents appear to
fit together like a jigsaw puzzle?
• Scientists often wondered why opposing
coastlines had similar geographic features.
Plate Tectonics
• The study of how the Earth’s crust moves.
– The surface of the Earth is made up of a number
of plates that have moved over millions of years.
Continental Drift
• In 1915, the “puzzle pieces” led German
scientist, Alfred Wegner, to purpose the
theory of continental drift.
• His theory explains that the continents were
once pieced together forming the supercontinent called Pangea.
– Believes all continents are presently
moving on the Earth’s surface.
Pangea
• Wegner believed the
continents were joined
together 225 million years
ago to form the supercontinent called Pangea.
– Pangea means "ALL LAND”
• About 200 million years
ago, Pangea began to break
apart forming the current
position of the continents.
Evidence of Pangea and
Continental Drift
1. Matching Mountain
Ranges
– Mountain ranges on
the east coast of North
America and west
coast of Europe and
Africa are similar in
size and composition.
•
They are made of the
same rocks and
minerals!
Evidence of Pangea and
Continental Drift
2. Fossil Clues
– Plants and animal fossils were found at similar
locations where continents were thought to have been
connected. (Ex. Lystrosaurus, Mesosaurus)
Evidence of Pangea and
Continental Drift
• Mesosaurus Fossils – A freshwater reptile, found
in South America and Africa.
– The same fossils, separated by an ocean.
How can this happen?
The Plates must have been joined together in the past.
Evidence of Pangea and
Continental Drift
•
•
Fossil Clues:
Glossopteris Fossil – Tropical plant found in
Antarctica!!
How did it get there?
The plates must have been joined together in the past .
Evidence of Pangea and
Continental Drift
3. Climate clues:
– Glaciers: By viewing rock samples in southern Africa,
India, South America, and Antarctica, observations
indicate striations in the bedrock.
•
Striations are grooves in the rock that indicate glacial
movement.
•How can the same striations be
on different sides of the world?
•The continents must have been
joined together in the past!
Striations
Evidence of Pangea and
Continental Drift
Climate clues:
Glaciers
• Glaciers once
covered southern
areas of Africa,
India, and South
America.
– As glaciers move,
they carve grooves
in the bedrock.
Evidence of Pangea and
Continental Drift
• Present day of the continents. Notice the
locations of where the glaciers once were.
How did it get there??
Even though Wegner had some compelling
evidence about continental drift, the scientific
community never did accept his theory!
Why not????
Wegner could never prove how
the continents moved.
Do Now
1. According to Wegener's hypothesis that continents are moving today, what
supercontinent apparently broke up about 200 million years ago?
a) Eurasia
b) Mesopotamia
c) Pangea
d) Caucasia
2. Besides the fitting together of the continents, Wegener’s idea of continental drift was
based upon which of the following?
a) Mid-ocean-ridge system
c) Color of the sand in N. America
b) Fossils found in S. America and Africa d) Gravitational pull of the moon
3. Although Wegener presented an interesting theory of continental drift. What was
the one part of his continental drift theory that he could not convince others was
possible??
a)“Land bridges” were proven to have connected S. America and Africa that aided
migration of species found as fossils.
b) The mountain ranges on both sides of the Atlantic ocean are similar in
composition
c) The way that continents move through solid ocean floors
d) The locations of tropical plants on Antarctica.
Do
Now
Do Now
• Explain why Wegner’s Hypothesis of
continental drift was not accepted by the
scientific community.
• Come up with your own hypothesis of why the
continent drifted apart
Evidence of Crustal Movement
1. Seafloor spreading
– Mid Atlantic Ridge
– Convection currents
– Magnetic Reversal
2. Hawaiian Hotspots
Evidence of Crustal Movement
1. Seafloor spreading
• Henry Hess, a U.S. geologist supported
Wegner’s theory of continental drift.
– Stated that ridges in the middle of the oceans are
pulling apart causing magma to rise to the surface
creating new ocean floor at mid ocean ridges.
Evidence of Crustal Movement
1. Seafloor spreading:
• As magma rises, old rock gets pushed to the sides
as new rock forms in the middle of the ridge.
– Oldest rocks in the ocean are only 180 million years old
Mid ocean Ridge
New rock
Old rock
Old rock
Convection Currents cause movement
1. Seafloor Spreading:
•Convection – Process by which materials with
high heat rise, then cool and sink, and re-circulate.
•What causes hot material to rise and cool
material to sink?
DENSITY!!
Convection Cell Animation
Evidence of Crustal Movement
1. Seafloor Spreading:
Magnetic Reversal:
• Some rocks contain magnetite:
– mineral that has a magnetic field.
• As magma rises, cools, and hardens, the
magnetic material will point in the direction of
Earth’s magnetic field.
Evidence of Crustal Movement
Magnetic Reversal:
• Rock records show that Earth’s magnetic field
has reversed repeatedly throughout history.
– Alternating bands of rock pointing North and South
along mid ocean ridges.
Do Now
Hawaii is a chain of islands that rests in the
middle of the Pacific plate, not near any plate
boundary.
Attempt to explain Hawaii’s volcanic activity
in 3-4 sentences.
Evidence of Crustal Movement
2. Hawaiian Hotspots:
• Hotspots are areas in the ocean where magma
breaks through the surface creating an island. As
the plate continues to move over the hotspot,
new islands begin to “pop up”.
Do Now
• Describe the process of seafloor spreading.
• What is the driving force behind seafloor
spreading?
• How does the record of earth’s magnetic field
support the theory of seafloor spreading?
• What is a Hot Spot?
Earth’s Interior
• By studying and interpreting earthquake data
and seismic waves, scientists believe they can
map the different layers of the Earth.
Layers of the Earth
• Crust - Thin outer most layer of the Earth, including
the ocean floor
– relatively low density and brittle.
• Most earthquakes occur within the crust.
Layers of the Earth
• Lithosphere: Made up of the crust and upper
part of the mantle (approx. 100km thick).
– Tectonic plates make up the lithosphere.
Layers of the Earth
• Mantle: Approx. 2,000 miles thick, directly
below the crust.
• Upper part of the mantle is called the
Asthenosphere
•Acts like a liquid
•The lithosphere
floats on top
Layers of the Earth
• Outer “ Liquid” Core – Believed to behave as a
thick liquid composed of liquid iron.
Layers of the Earth
• Inner “ Solid” Core: consists of iron and
nickel.
– Scientists believe that samples of meteorites
containing iron and nickel can infer the
composition of the Earths core.
Do Now
1. List in order (outside – in) the layers of the
Earth. *include Asthenosphere and
Lithosphere.
2. Which layer is believed to be composed of
liquid Iron?
3. Which layers contains the tectonic plates?
Plate Tectonics
Earth’s crust is broken up into 2 types of plates:
1. Continental “Land” Plates – Thicker than oceanic
plates. Density = 2.7g/cm³
2. Oceanic “ocean” Plates – Thinner and more
dense than continental plates. Density =
3.0g/cm³
Type of Crust
Average Thickness
Average Age
Major Component
Continental Crust
20-80 kilometers
3 billion years
Granite
Oceanic Crust
10 kilometers
Generally 70 to 100
million years old
Basalt
Plate Boundaries
Plate boundaries – The place where 2 plates
meet.
S. Amer
Nazca
3 types of boundaries
1. Divergent boundary
2. Convergent boundary
3. Transform boundary
Divergent “Divide” Boundaries
• Where 2 plates move apart from each other.
– Tensional forces pull apart
Features
1. Rift valley
2. Mid ocean ridge
Divergent “Divide” Boundaries
Mid Ocean Ridge
Do now
1. What types of convergent boundaries will
create volcanic activity?
2. Which type of boundary is know as the
“mountain builder”?
3. What occurs at a subduction zone?
Convergent “come together” Boundaries
• Where 2 plates collide into each
other.
– When 2 plates collide, the denser
plate gets pushed under the less dense
plate.
3 plate combinations are possible:
1. Oceanic– Continental
2. Oceanic – Oceanic
3. Continental– Continental
1. Oceanic – Continental
• More dense ocean plate is pushed under the
less dense continental plate.
– Area where ocean plate is pushed into the mantle is
called the SUBDUCTION ZONE.
Features
• Trenches
• Volcanic ranges
1. Oceanic – Continental
• Andes Mountains –
South America
• Deep sea trench
• Volcanic Mountain
Range
2. Oceanic – Oceanic
•2 ocean plates collide.
•The cooler, more dense plate gets subducted.
Features:
•Trench
•Island arc volcanoes
2. Oceanic – Oceanic
• Alaska – The Aleutian Islands are an Island arc
created by 2 ocean plates colliding.
3. Continental– Continental
•2 continental plates collide.
•NO SUBDUCTION. Both plates are less dense
than ocean plates.
Features:
•“Mountain Builders”
3. Continental– Continental
•Himalayas – Mountain range that
borders North India and Southern Tibet.
•Highest peaks in the world!
•Everest = 29,035 ft
•K2 = 28,250 ft
•Hunter Mtn. N.Y. = 4,000ft
Transform Boundary
•2 plates slide past each other in opposite
directions, or the same direction but different rates.
Features:
•Hotspot for earthquakes
•San Andreas Fault
Transform Boundary
•San Andreas fault in California.
Do Now
• Using you plate tectonics map, place an X on
the following coordinates
• 10 N, 80 E
• 50 S, 120 W
• 45 N, 80 W
• 65 S, 60 W
• 40 N, 140 E