1. Sea Floor Spreading

2. Crust – Earth’s Outer Layer
There are two kinds of crust on the Earth
Continental Crust
Makes up the continents
Oceanic Crust
Is found under the oceans
Is denser than continental

4. Mid-Ocean Ridges Are openings in the Earth’s crust
Part of underwater mountain ranges on the ocean bottom (longest on Earth)
Above the surface they are islands (ex. Iceland)
Deep cracks in the center allow magma to come out, harden, and form new sea floor
As new magma comes up, it pushes the sea floor further apart

6. It is this spreading of the sea floor that drives the movements of the continents (continental drift)!!!

8. Mid-Atlantic Ridge
(and others)

9. Rift Valleys
The flat area between two ridges, formed from crust spreading apart
Lots of earthquakes and volcanoes occur here
Magma comes out of the ocean floor here

11. Ocean Trenches
Very deep area where ocean crust meets continental crust
Subduction Zone: place where old oceanic crust is forced under continental crust, back into the mantle at an ocean trench

13. Age of the Seafloor Young ocean crust = middle of ocean floor
Magma coming out of rift cools, forms new rock
Old ocean crust = far away from ridge
Rocks are older because they were pushed away from the ridge

14. Disappearing Ocean Crust
Oldest ocean floor rocks are only 160 million years old (earth is 4.6 billion years old)

15. Complete the following…
Define: Sea Floor Spreading List evidence that supports it: