Ch. 1 Sec. 4

Sea-Floor Spreading

mid-ocean ridgemid-ocean ridge• winds beneath Earth’s oceans

• mapped using sonar= device that bounces sound waves off underwater objects & records echoes

The mid-ocean ridge (shown in red) winds its way between

the continents much like the seam on a baseball.

Harry Hess’ idea-

Ocean floors move like conveyor belts- carrying continents with them

Movement begins at mid-ocean ridge

Molten material rises from mantle & erupts

Molten material spreads out- pushing older rock to both sides of the ridge

sea-floor spreadingsea-floor spreading

• new material continually being added to ocean floor

evidence for

sea-floor spreading

1.molten

material

2.magnetic

stripes

3.drilling samples

1. Evidence from molten material

The submersible Alvin photographed pillow lava along the mid-ocean ridge.

2. Evidence from magnetic

stripes

• The Glomar Challenger was the first research vessel specifically designed in the late 1960s for the purpose of drilling into and taking core samples from the deep ocean floor.

3. Evidence from drilling samples3. Evidence from drilling samples

deep-ocean trenchdeep-ocean trench

• deep, underwater canyon

• forms where oceanic crust bends

• subduction takes place here

subductionsubduction• process where oceanic crust sinks down

beneath trench into mantle

Because of sea-floor spreading, the

distance between Europe and North

America is increasing by a few

centimeters per year.

Growing an Ocean

Ocean crust is returned to the mantle

through subduction

1. oceanic lithosphere is created @ mid ocean ridge

2. moves across ocean basin for 175 mill. yrs.

3. returns to mantle in Earth's subduction zones

mid-ocean ridgemid-ocean ridge

• winds beneath Earth’s oceans

• mapped using sonar= device that bounces sound waves off underwater objects & records echoes

sea-floor spreadingsea-floor spreading

• theory proposed by Harry Hess

• new material is continually being added to ocean floor

deep-ocean trenchdeep-ocean trench

• deep, underwater canyon

• forms where oceanic crust bends

• subduction takes place here

Evidence for sea-floor spreading

1. molten material2. magnetic

stripes3. drilling samples

subductionsubduction• process by which oceanic crust sinks down beneath trench mantle

Harry Hess

What scientist helped to discover the process of sea-

floor spreading?

mid-ocean ridges

Along what feature of the ocean floor does sea-floor

spreading begin?

Evidence from

The submersible Alvin photographed pillow lava along the mid-ocean ridge.

molten material

• The Glomar Challenger was the first research vessel specifically designed in the late 1960s for the purpose of drilling into and taking core samples from the deep ocean floor.

Evidence fromEvidence from drilling samplesdrilling samples

Evidence from

magnetic stripes