1. Alfred Wegener and Harry Hess
This Photo by Unknown Author is licensed under CC BY-SA-NC
This Photo by Unknown Author is licensed under CC BY-SA

2. Wegener A meteorologist, PhD in astronomy
Passionate about polar air circulation, polar exploration, and air balloons
Noticed east coast of South America fit exactly against the west coast of Africa
Claimed the continents once formed a single mass and labeled that “Pangea” which means “whole Earth”
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3. Wegener and “continental Drift”
To prove his theory he used
Fossil evidence (tropical plants)
Geographical features (mountains)
Layers of rock (strata)
Claimed mountains formed when edges of drifting continents crumpled

4. Wegener’s ideas were NOT accepted
He was not a geologist-why would anyone believe his theories?
Could not prove what immense force was used to split continents
Wegener died in before his ideas were explored and accepted

5. Harry Hess Geologist in 1930s
During WWII, sounding gear showed what seafloor looked like
Bounced sound waves off seafloor to determine depth and features
Discovered the following:
Bottom of sea not smooth
Full of canyons, trenches, volcanic sea mountains
Earth’s crust had been moving away on each side of oceanic ridges and were volcanically active which became known as “seafloor spreading”

6. Seafloor spreading
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7. Plate Tectonics
Not just continents move, but WHOLE plates of Earth’s crust moves
MAY include:
A continent
Parts of a continent
Undersea portions of the crust
Earth has 8-12 large plates and 20 smaller ones
Move in different directions and speeds

8. Earth’s tectonic plates
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9. So what’s the force that causes continents to move (that Wegener couldn’t prove)?
Convection currents in the mantle under the crust!!!!!
Although it is solid layer, over geological time, it slowly flows