Inside Earth Section 1.4 Pages 33-39 Sea-Floor Spreading Inside Earth Section 1.4 Pages 33-39
What is Sea-Floor Spreading? Using SONAR, geologist Harry Hess mapped out the Mid-Ocean Ridge (MOR) The MOR is a massive underwater mountain chain where molten material is rising from the mantle, into the ocean The molten material cools, forming new crust and pushing old crust – spreading out the sea floor.
Mid-Ocean Ridge Computer generated image of MOR
Evidence for Sea-Floor Spreading Pillow Basalts – rocks that cooled quickly, indicating that magma is entering the ocean Magnetic Stripes – layers of rock with alternating magnetic directions, indicating different ages in the rock Drilling Samples – testing the age of rock samples from the sea floor shows young rocks near the MOR and old rocks near trenches.
Subduction Subduction is the sinking of old, dense crust back into the mantle Subduction occurs at deep-ocean trenches
What Should I Know? What the Mid-Ocean Ridge is What Sea-Floor Spreading is One piece of evidence for Sea-Floor Spreading What Subduction is