1. Inside Earth Section 1.4 Pages 33-39
Sea-Floor Spreading
Inside Earth Section 1.4
Pages 33-39

2. 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.

3. Mid-Ocean Ridge
Computer generated image of MOR

4. 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.

5. Subduction
Subduction is the sinking of old, dense crust back into the mantle
Subduction occurs at deep-ocean trenches

6. 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