Sea-Floor
Spreading
CH 4 Prentice Hall
p.123-129
Sea-Floor Spreading
• Harry Hess- American Geologist
• 1960- Proposed Sea-Floor
Spreading
– The process that continually adds
new material to the ocean floor.
– Occurs at the mid-ocean ridge,
• new material rises from the mantle
and erupts.
• The molten material spreads out
pushing older rock to the side.
CD Rift
Evidence
Sea-Floor Spreading
• Occurs at the mid-ocean ridge, new material
rises from the mantle and erupts.
• The molten material spreads out pushing
older rock to the side.
CD Rift
Evidence
Mapping Climate
the Ocean Floor
• 1900’s Scientists Mapped the Ocean Floor
• Used Sonar- a device that bounces sound
waves off of underwater objects and records
echoes of the sound waves.
Mapping Climate
the Ocean Floor
• Mapped the Mid-Ocean Ridge
– East Pacific Rise
– Mid-Atlantic Ridge
• Rift Valley, a central valley twice as deep as Grand
Canyon
The Ocean Floor
Molten Material
• Alvin- a submersible unit traveled to the
central valley of the mid-ocean ridge.
– Found Pillow Lava
• Indicates that new molten material has formed.
• It cooled quickly underwater
Magnetic Reversals
• Earth has a Magnetic North
and a South Pole
• The poles have reversed in
the past.
• The reversals are recorded
in the igneous rock.
– Serve as a record of the
magnetic field.
CD Rift
Evidence
Magnetic Reversals
• Basalt contains iron
• The bits of iron line up in the direction of the
poles.
• When the rock hardens completely, the
direction of the poles is recorded in the rock.
– Permanent “magnetic memory”
CD Rift
Evidence
Drilling the Ocean Floor
• Glomar Challenger- A
drilling Ship
– Drilled through 6km of
water.
– Determined that the age
of the rock was younger
at the ridge and older
away from the ridge.
– Shows that sea floor
spreading is taking
place.
CD Rift
Evidence
Parts of the Ocean Floor
CD Rift
Evidence
Convection and Sea