Wegener1880-1930

earthobservatory.nasa.gov

Alfred Wegener first proposed the theory of continental drift.

Continental drift was Wegener’s theory that all continents had once been joined together in a single landmass and have drifted apart since.

Wegener named this supercontinent Pangaea.

Wegener’s theory was rejected by scientists because he could not explain what force pushes or pulls continents.

Continental drift video clip

Fit of Continents Across the Atlantic

Mountain ranges in South America line

up exactly with those in Africa!

Notice how fossils lined up across continents!

http://evolution.berkeley.edu/evolibrary/images/history/fossils3.gif

Amazing Facts: Did you know...

...that India was once in the Southern Hemisphere connected to Antarctica? ...that North America was once surrounded by warm, tropical seas? ...that Africa was once covered by glaciers, which were kilometers in thickness? ...that the Sahara desert was once a tropical rain forest?

As North America has drifted to different latitudes, changing climates were experienced. This shows the changes in the state of New Mexico.

An example of the proof for changing climate:

At one time, the area that is New Mexico was below the equator!

He could not find the force that was causing the continents to drift.Because of this, he could not convince anyone that continents could move.He died in Greenland on an expedition. At the time of his death, no one believed his hypothesis!

Technology developed during the 1940’s changed all that!

Discovery of Sea-Floor Spreading

Sea floor spreading video clip

Sea-Floor Spreading

m.y. means million years ago

Notice this compass. It is important for the next slide

As the sea floor spreads, the lava cools according to the magnetic poles at the time. The rocks on the ocean floor have proved that the earth’s magnetic field sometimes reverses. The inner core flips and so the north pole moves to the southern hemisphere! The earthh itself does not flip.

http://platetectonics.pwnet.org/img/blocks.gif

What causes sea floor spreading? Convection currents!

Click here for a hyperlink to an animation of convection

Be sure to click the play button!

Animation of sea floor spreading

Can you explain this diagram!?

The place where two plates move apart or diverge is called a divergent boundary.

This is a model of sea floor spreading at a divergent boundary called a mid ocean ridge.

Did you know that the Earth’s longest mountain range is underwater and is called the mid-ocean ridge?

: www.ocean.udel.edu

The Mid-Ocean Ridge system, shown above snaking its way between the continents, is more than 56,000 kilometers (35,000 mi) long. It circles the earth like the stitching on a baseball!

A convergent boundary is where two plates come together, or converge. The result of the plates hitting together is called a collision.

A transform boundary is a place where two plates slip past each other, moving in opposite directions.

Continental crust to continental

Continental crust to oceanic

Oceanic crust to oceanic

from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270

Continental crust to continental crust collision

India-Asia (Himalayas)

Before collision

After collision

Also the way the Appalachian Mountains formed!

Because one plate gets pushed under another, it is called subduction. This is where volcanoes form!

Oceanic crust colliding with oceanic crust

Oceanic crust colliding with continental crust

all from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270

The process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle is called

Plate tectonics video clip

Here is an great link for seeing where each type of boundary is located.Click here for a great hyperlink! Make sure you click on each type of boundary in the key!

Worldwide Earthquake patterns help us know where the edges of plates are located

The Earth’s Plates

Here you see the two slides together. What do you see?

http://www.livescience.com/images/pangea_animation_03.gif