“Continental Drift”

• I. Early Evidence of Continental Movement:

A. Continental Drift:

1. Continental Drift - A hypothesis, which states that continents have moved around the globe, over time, to reach their current positions.

2. Alfred Wegener came up with this theory in 1912.

3. He believed that all continents were connected as one large landmass about 200 million years ago. 4. Then they broke and drifted to their current positions.

5. He called this super land mass Pangaea.

B. Wegener’s Proof:

1. Some continents look like they fit together.

2. Geological Clues:

A.) Mountain Belts lined up. (ex. North America & Europe) B.) Rock layers matched. (Ex. South America & Africa)

3. Fossil Clues:A.) Fossils of living things were found on different continents that are separated by large bodies of water. B.) Ex. Mesosaurus found in S.America & Africa. Glossopteris found in S. America, India, Africa, & Antarctica.

As the plate moves, themountains grow

4.Climate Clues:

A.) He found coal deposits in N. America that matched coal deposits in Europe.

B.) He found salt deposits in the desert part of Africa.

C.) Glacial deposits in tropical regions like India and Australia.

C. Modern Day Proof:

1. Seafloor Spreading:

A.) The theory states that magma travels to the earth’s surface.

B.) The magma forms cracks in the ocean floor.

C.) These cracks are called Mid-Ocean Ridges.

D.) The magma pushes out of the mid-ocean ridge.

E.) As the magma hardens it pushes the layers of the ocean floor away from the mid-ocean ridge.

F.) The process then repeats it self.

D. Seafloor Spreading Proof:

A.) The oldest layers of the Atlantic Ocean floor are on the coastline of the continents. (180 million years old.) B.) The youngest layers of the Atlantic Ocean floor are in the center of the ocean. (50 million years old)

C.) The Atlantic Ocean is getting larger.

http://scign.jpl.nasa.gov/learn/plate4.htm

• II. Plate Tectonics:II. Plate Tectonics:

A. Layers of the Earth:

1. Crust - Thin, outermost

layer of the earth.

2. Mantle - Layer of the earth

between the crust

and outer core. * Thickest layer of the Earth.

3. Outer Core - Liquid layer

of the Earth.

4. Inner Core - Solid, inner most

layer of the earth.

Structure of the Earth

B. The Theory of Plate Tectonics:

1. Plate Tectonics - Is the theory that earth’s crust and upper mantle are broken into sections that slowly move around on the lower mantle.

2. Plates - Sections of the earth’s crust and upper mantle that move around on the bottom part of the mantle.

3. The crust and upper mantle together are called the lithosphere. 4. The lower mantle is called the asthenosphere. 5. The lithosphere is less dense than the asthenosphere, so the lithospheric plates “float” on top of the asthenosphere.

C. Plate Boundaries:

1. There are three types of plate boundaries.

A.) Divergent Boundaries - When plates separate or move apart. (Divide)

B.) Convergent Boundaries - When plates collide into each other.

C.) Strike-slip Boundaries - When plates grind together and slide by each other.

D. Why do plates move?

1. Plates move because of convection currents.

A.) Convection Current - Is the movement of a fluid caused by differences in temperature.

2. Material close to the core is hot and has a low density.

3. Material close to the crust is cool and has a high density. 4. More dense material sinks and less dense material rises causing a convection current.

5. When the material reaches the plates it pushes them away or toward the plate boundary.

E. Effects of Plate Tectonics:

1. The lithosphere is divided into seven major plates and about ten smaller plates.

2. The interaction of the different plates causes different land features.

3. There are two different types of plates:

A.) Continental Plates - Made from relatively light continental crust.

B.) Ocean Plates - Made from dense ocean crust.

4. Plate interaction land features:

A.) Volcanoes - Form when two ocean plates collide, or when an ocean plate collides with a continental plate causing the more dense plate to sink and melt.

B.) Mountains - Form when two continental plates collide. Since continental plates are to light to sink the crust thickens and is forced upward.

C.) Rift Valley /Ridges- Form when any two plates separate. The ground between them sinks and forms a valley. D. Earthquakes - Caused from any sudden movement of plates that

causes the plates to break.

E. Trench - A deep V-shaped valley formed at the base of a convergent plate boundary. (Ocean ocean collision, or ocean continental collision.)

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