1. Seafloor Spreading Notes
(#20)

2. Where we’ve been w/ EQ#2…
EQ#2: What is convection and what evidence is there of convection on the surface of the Earth?
Alfred Wegener
Theory of Continental Drift
Evidence for Continental Drift (Fossils, landforms, climate)
Theory rejected in early 1900’s
In 1950’s, scientists discovered mid-ocean ridge (ocean bottom was once thought flat)

3. Where we’re going w/ EQ#2…
Magma erupting at mid-ocean ridge creates new ocean floor & subduction at plate boundaries destroys old ocean floor
Seafloor spreading!
Caused by convection currents in mantle
We now know HOW the continents can move
Theory of Continental Drift revisited! Wegener was a brilliant, brilliant man after all!

4. Video Introduction to Sea Floor Spreading

5. #20- Seafloor Spreading
WHO: Discovered by Harry Hess- U.S. Geologist at Princeton, Navy Reservist
WHEN: 1950’s
WHERE: Pacific Ocean
WHAT:
The process by which new ocean crust is formed by the upwelling of magma at mid-ocean ridges.
Cause: Convection currents in the mantle.
Result: Existing/older ocean crust is pushed to the side to make room for the new crust.

6. EQUAL DISTANCE FROM RIDGE =
Seafloor spreading
OLDER
OLDEST
OLDER
NEW
OLDEST
EQUAL DISTANCE FROM RIDGE =
SAME AGE
CONVEYOR BELT ANIMATION

7. Red=youngest rock Blue=oldest rock

8. What happens to the OLD crust?
Subduction: When the edge of one crustal plate is pushed underneath another.
This happens at the edge of oceans, where denser ocean crust is pushed underneath less dense continental crust. The rock returns to the mantle.

9. How can this move continents?
If NEW ocean floor is produced FASTER than old floor is subducted, the ocean floor GROWS, which would push continents APART.
If OLD ocean floor is subducted FASTER than new ocean floor is produced, the ocean floor SHRINKS, which would “pull” continents TOGETHER.

10. Please add the following to your EQ#2 Vocabulary List (#19)
7. Seafloor Spreading: The process by which new ocean crust is formed by the upwelling of magma at mid-ocean ridges
8. Harry Hess: an American Geologist who used SONAR to map the ocean floor in the 1950’s and discovered seafloor spreading
9. mid-ocean ridge-
10. Subduction: process by which ocean crust sinks beneath a deep ocean trench and back into the mantle at a convergent plate boundary

11. Magnetization of the Ocean Floor Animation