Continental Drift and Seafloor Spreading Notes Part 3

Earth’s Magnetism and Seafloor Spreading Age of Sea Floor

Evidence of Sea-Floor Spreading 3. Evidence from drilling samples: In 1968, the Glomar Challenger drilled 6km deep. They took samples of rock from the ocean floor. They concluded that the further away from the ridge a sample was taken, the older the rock was.

Deep-Ocean Trenches What are deep-ocean trenches? They are locations where the oceanic crust dips under the continental crust. This action sends oceanic crust material back into the mantle.

Subduction at Deep-Ocean Trenches

Mariana Trench Video http://www.youtube.com/watch?v=m8gppBCneNA

What Happens at a Deep-Ocean Trench? Subduction and the Earth’s Crust: The Process of Subduction The ocean floor is renewed about every 200 million years. Pacific ocean is shrinking, while the Atlantic is expanding. The Pacific Ocean’s trenches “swallow” more of the Earth’s crust than can be produced. This is when the Earth’s deep-oceanic crust sinks beneath the trench and back into the mantle. As crust moves away from the mid-ocean ridge, the new crust cools and becomes more dense.

http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_ subduction.html Subduction Animation http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_ subduction.html