Alfred Wegener
● Some people thought the Earth was shrinking and cracking
● Wegener thought whole sections of the crust moved (plate tectonics)
● Some people did not understand and thought the continents floated around in the oceans (continental drift)
● He died before people accepted his ideas
Background to Continental Drifthttp://www.sciencechannel.com/tv-shows/greatest-discoveries/videos/100-greatest-discoveries-continental-drift/
Seafloor Spreading● Harry Hess figured out the mechanism that was moving the continents. This proved
Wegener’s theory. ● Surface of the earth is a thin layer of moving plates
Seafloor Spreading● Large continents begin to
crack and split apart ● The gaps fill with water ● Small seas become
oceans ● The mid ocean ridge
continues to produce new crust
J. Tuzo Wilson (1908 - 1993)
● A Canadian ● Developed theory of Plate tectonics
in the 1960s ● Used technology to further
Wegener’s ideas ● Plates of the Earth (20 in total) move
over a weak layer of hot rock very slowly
More Evidence - Magnetic Poles
More evidence has been found for Wegener’s theory
● The Earth’s North and South pole have flipped many times
● These leaves magnetic ‘stripes’ in rock containing iron minerals
So the Earth must be growing? ● Dense heavy oceanic crust can be
subducted (one plate moves under another) below less denser continental crust. ○ The friction melts rock
○ This magma rises through the crust to form
new volcanoes
● This is happening in South America (The Andes)
Recap - Seafloor spreading explainedhttp://nationalgeographic.org/encyclopedia/seafloor-spreading/
1. Valleys form due to natural circumstances, sometimes water can collect inside it. (picture 1 and 2)
2. As the continental crust continues to erode, a larger body of water can form over time and oceanic crust takes its place.
3. As the seafloor spreads, the ocean becomes larger. The oceanic crust continues to erode, cool, contract, and sink, new oceanic crust forms.
4. Eventually, the oceanic crust will split in two. The split pieces continue to spread away. In between the splits, you will find volcanoes/ocean mountain ridges.
Continents Collide ● Eventually when plates move
together the continental crust collides
● The heat and pressure make metamorphic rock
● It also pushes and folds the rocks into high mountains
● The Himalayas rise to 8848m and are still growing today
Convection Currents ● Theory that plates are moved by an unequal distribution of heat● Convection – as fluid rises and carries heat with it, it is replaced with cooler
fluid which in turn rises again