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