Sea Floor Spreading
MID OCEAN RIDGE
Where ocean floor moves away from itself and
Magma rises up to form new oceanic crust
YOUNGEST
Evidence for Sea Floor Spreading
1. Rock Types (pillow basalt)
2. Age of Rocks (new in middle)
3. Rock Patterns (match on either
side of M.O.R., magnetic reversals,
represented by colors)
OLDEST
SUBDUCTION = Sea Floor Goes Under
SUBDUCTION = Sea Floor Goes Under
OLDEST
Process of sea floor spreading occurs when oceanic
crust moves away and allows magma to rise up and
COOLS
cool to form new ocean floor. Old ocean floor is
pushed away from center, until it is finally driven back
in to the mantle where it is melted and recycled.
HOT MAGMA RISES
Sea Floor Spreading
Who developed this ‘idea’?
When/Why?
SEA-FLOOR SPREADING is….

Harry Hess developed this
idea around 1960.

A process that continually
adds new material to the
ocean floor.

Magma rises up to the
surface in the middle of the
sea floor

Ocean floor was not flat,
but very mountainous.

Makes the floor of select
oceans bigger and in some
cases, smaller.

They found PILLOW
BASALT – which can only
be formed when magma is
quickly cooled.

Proves that this magma has
erupted again and again.

Maps of the mid-ocean
ridge and findings from
continental drift led to his
hypothesis.
SUPPORT
Evidence from Drilling Samples:
 From these samples, the
age of the rock was
determined.


Rock near the center (midocean ridge) was the
youngest.

As you move away from the
M.O.R. the rock gets older

As rock gets older, it moves
away from the M.O.R.
What is SUBDUCTION?
Where does this occur?

SUPPORT
Evidence from Magnetic Stripes:
 Iron bits in rock line up
with magnetic north pole
SUBDUCTION is when
oceanic crust GOES UNDER
another piece of crust.

Occurs at DEEP OCEAN
TRENCHES
The changes in the rock
create patterns on either
side of the mid-ocean ridge
that match up.
In Continental Drift, there was no
explanation for the movement of the
continents/landmasses. According the
Sea-Floor Spreading, how do the
CONTINENTS MOVE?


When magnetic poles
switch, it changes the rock
According to Sea-Floor
Spreading, the continents are
carried around by the
spreading ocean floor.
SUPPORT
Evidence from Molten Material:
The Mid-OCEAN RIDGE is a place...

Where Sea Floor Spreading
Occurs (where sea floor
spreads from)

Middle of most major
bodies of water.

Molten material from inside
the Earth (magma) rises up
and cools to form new
oceanic crust.
Sea Floor Spreading