As these convection currents go to work in the mantle, say for a few hundred million years or so,continents shift considerably from their "original" position (if there was such a thing). Alfred Wegener proposed the idea that all continents on Earth were once connected like a super-continent.He had evidence that they were once together, but could not explain how they moved together or apart. Wegener proposed the idea of a super-continent called Pangaea, meaning all of Earth, and backed it with the following evidence:
It wasn't until 1960 that Harry Hess, found evidence that the sea floor was spreading, that Wegener's theory of continental drift was accepted. If the sea floor was spreading, convection currents could be driving it to move apart. This meant that convection currents have driven continents together and apart several times throughout Earth's history. And just to let you in on a little secret, plates are still moving...the continents will come together again at some point in Earth's future! |
Earthquakes:
Earthquakes occur under the surface of Earth and release seismic waves in all directions. P- waves travel faster so they arrive first. The particle motion moves parallel to the wave motion.and can go through solid, liquid and gas. S-waves stand for secondary or shear waves. They travel slower so they arrive second and can only move through solid material. In an S-wave, the particle motion moves perpendicular to the wave motion. |
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Sea Floor Spreading:
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Magnetic Reversals:
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