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.

• 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 super-continent called Pangea.– Believes all continents are presently

moving on the Earth’s surface.

Continental Drift

• Wegner believed the continents were joined together 225 million years ago to form the super-continent called Pangea.– Pangea means "ALL LAND”

• About 200 million years ago, Pangea began to break apart forming the current position of the continents.

Pangea

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.

Evidence of Pangea and Continental Drift

•How can the same striations be on different sides of the world?

•The continents must have been joined together in the past!

Striations

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.

Evidence of Pangea and Continental Drift

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.

How did it get there??

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. Americab) 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 compositionc) The way that continents move through solid ocean floors d) The locations of tropical plants on Antartica.

4. For the last 200 million years, continents on opposite sides of the Atlantic Ocean have generally:

a) Been drifting closer togetherb) Been drifting farther apartc) Remained the same distance apart

5. Which statement best supports the theory that all the continents were once a single landmass?

a) Rocks of the ocean ridges are older than those of the adjacent floor.

b) Rock and fossil correlation can be made where the continents appear to fit together

c) Marine fossils can be found at high elevations above sea level on all continents.

d) Great thicknesses of shallow-water sediments are found at interior locations on some continents.

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

Do Now

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

Evidence of Crustal Movement

Mid ocean Ridge

Old rock Old rockNew rock

Convection Cell Animation

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!!

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.

Evidence of Crustal Movement

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.

Do Now

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”.

Evidence of Crustal Movement

• By studying and interpreting earthquake data and seismic waves, scientists believe they can map the different layers of the Earth.

Earth’s Interior

• Crust - Thin outer most layer of the Earth, including the ocean floor– relatively light 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

Layers of the Earth

•Acts like a liquid

•The lithosphere floats on top

• 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.

Layers of the Earth

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?

Warm Up…11/6/14

Earth’s crust is broken up into 2 types of plates:1. Continental “Land” Plates – Thicker than oceanic

plates. Density = 2.7g/cm³2. Oceanic “ocean” Plates – Thinner and more

dense than continental plates. Density = 3.0g/cm³

Plate Tectonics

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 – The place where 2 plates meet.

3 types of boundaries1. Divergent boundary2. Convergent boundary3. Transform boundary

Plate Boundaries

NazcaS. Amer

• Where 2 plates move apart from each other.– Tensional forces pull apart

Divergent “Divide” Boundaries

Features1. Rift valley2. Mid ocean ridge

Divergent “Divide” Boundaries

Mid Ocean Ridge

• 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– Continental2. Oceanic – Oceanic3. Continental– Continental

Convergent “come together” Boundaries

• 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

1. Oceanic – Continental

2. Oceanic – Oceanic

•2 ocean plates collide.• The cooler, more dense plate gets subducted.

Features:•Trench•Island arc volcanoes

• Alaska – The Aleutian Islands are an Island arc created by 2 ocean plates colliding.

2. Oceanic – Oceanic

3. Continental– Continental

•2 continental plates collide.•NO SUBDUCTION. Both plate 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.