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Sea-FloorSea-Floor
CH 4 Prentice Hallp.123-129
CH 4 Prentice Hallp.123-129
SpreadingSpreading
• 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.
Sea-Floor Spreading
CD RiftEvidence
• 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.
Sea-Floor Spreading
CD RiftEvidence
• 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.
ClimateMapping the Ocean Floor
ClimateMapping 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
• 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
Molten Material
Life Around the Mid-Ocean Ridge
Parts of the Ocean Floor
CD RiftEvidence
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 RiftEvidence
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 RiftEvidence
• 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.
Drilling the Ocean Floor
CD RiftEvidence
The Ocean Floor
Convection and Sea
The Ocean Floor