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 ContinentsAcross the AtlanticMountain ranges inSouth America line up exactly with those in Africa!
http://evolution.berkeley.edu/evolibrary/images/history/fossils3.gifNotice how fossils lined up across continents!
Amazing Facts: Did you know......that India was once in the Southern Hemisphereconnected to Antarctica?...that North America was once surrounded by warm,tropical seas?...that Africa was once covered by glaciers, which werekilometers in thickness?...that the Sahara desert was once a tropical rain forest?
An example of the proof for changing climate: At one time, the area that is New Mexico (and the rest of the USA was below the equator!As North America has drifted to different latitudes,changing climates were experienced. This shows thechanges in the state of New Mexico.
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’schanged all that!
Discovery of Sea-Floor Spreading Sea floor spreading video clip
Sea-FloorSpreading m.y. means million years ago Notice this compass. It is important for the next slide
http://platetectonics.pwnet.org/img/blocks.gifAs the sea floor spreads, the lava cools according to themagnetic poles at the time. The rocks on the oceanfloor have proved that the earth’s magnetic fieldsometimes reverses. The inner core flips and so thenorth pole moves to the southern hemisphere! Theearth itself does not flip.
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 spreadingCan you explain this diagram!?
The place where two plates moveapart or diverge is called a divergentboundary.
This is a model of sea floor spreading at a divergentboundary called a mid ocean ridge.
: www.ocean.udel.eduDid you know that the Earth’s longest mountain range isunderwater and is called the mid-ocean ridge? 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!
en ta l on tin oc ru st t t al c Continen ta l c ru s t to n en o c e a n ic ntiCo Oceanic crust to oceanic
Continental crust to continental crustcollision Before collision India-Asia (Himalayas) After collision from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270
Because one plate gets pushed under another, it is called subduction. This is where volcanoes form! Oceanic crustOceanic crust colliding colliding withwith continental crust oceanic crust all from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270
The process bywhich the oceanfloor sinksbeneath a deep-ocean trenchand back intothe mantle iscalled
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!Plate tectonics video clip
Worldwide Earthquake patterns help usknow where the edges of plates are located