Download Sea Floor Spreading (SFS)

Sea Floor Spreading (SFS) Notes
What is sea-floor spreading?
 Sea-floor spreading is the moving apart of the ocean at the mid-ocean ridge.
What is the mid-ocean ridge?

The mid-ocean ridge is the long continuous mountain range that runs along the ocean
floor. It begins at the North Pole and continues down into the Atlantic Ocean. Off the
coast of Antarctica it travels into the Pacific Ocean where it splits into two as well as into
the Indian Ocean around Africa and splits again around Australia.
How does sea -floor spreading work?
1. Magma or molten rock from inside the Earth moves up to the ocean floor and comes out of
the mid-ocean ridge.
2. When the hot magma comes into contact with the cold ocean water it cools and hardens and
forms new oceanic crust (igneous rock).
3. Over millions of years the oceanic crust moves away from the mid-ocean ridge and towards
the plate boundary with the continental crust.
4. When the oceanic crust and the continental crust collide, the oceanic crust sinks because the
oceanic crust is denser than continental crust.
5. As the oceanic crust sinks deeper into the earth it melts back into molten rock or magma.
6. Over millions of years the molten rock or magma moves inside the Earth and will eventually
make its way back out of the mid-ocean ridge.
SFS is a continuous cycle.
Evidence to support sea-floor spreading.
1. Age of Rocks
 Rocks located closer to the mid-ocean ridge are younger that rocks located farther away
from the mid-ocean ridge.
 Think of the mid-ocean ridge as the “birthplace” of rocks and the place where ocean crust
and continental crust meet is where rocks “die”. So as they travel along the ocean floor
life goes on.
2. Magnetic Reversals
 The earth has a magnetic field that extends from pole to pole. The North Pole is called
magnetic north and the South Pole is called magnetic south. Think of the earth as having
a large bar magnet running through the center.
 Inside the earth molten rock or magma contains magnetic minerals. When the molten
rock cools and hardens into rock the magnetic minerals are hardened (frozen) in the rock.
These magnetic minerals can no longer move. When the rock hardens the magnetic
minerals are aligned (point to) magnetic north. The magnetic minerals are like minicompasses. The rocks on the ocean floor show that the magnetic minerals have reversed
(flip-flopped) over time.