Seafloor Spreading

Who proposed the Seafloor Spreading theory and when did he propose it?

In 1960, Harry Hess proposed the theory of Seafloor Spreading.

Mid-Ocean Ridge

An undersea mountain chain where new ocean floor is produced

What is the evidence for Seafloor Spreading?

1. Evidence from Molten Material- Rocks from when molten material hardens quickly erupting underwater. 2. Evidence from Magnetic Stripes- Scientists discovered that the rock that makes up the ocean floor lies in a pattern of magnetized "stripes". 3. Evidence from Drilling Samples- They found that the further away from the ridge the samples were taken, the older the are.

What are the steps in the process of Seafloor Spreading?

1. The seafloor spreads apart along both sides of the mid-ocean ridge. 2. New crust is added

Describe a Mid-Ocean Ridge.

A Mid-Ocean Ridge is a contiguous range of mountains.

Deep Ocean Trench

A deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle.

Sonar

A device that determines the distance of an object underwater by recording echoes of sound waves.

What happens to old oceanic crust as new molten material rises from the mantle.

As new molten material rises the oceanic crust is being subducted into the mantle.

What happens at deep ocean trenches?

At deep ocean trenches part of the ocean floor sinks back to the mantle. (subduction)

When were the ocean floors mapped and what was the tool used to map the ocean floor?

In the 1960's the ocean floor was mapped by using the device Sonar.

Why does subduction occur?

Subduction occurs because as new rocks form older rocks sink back into the mantle.

Seafloor Spreading

The process by which molten materials add new oceanic crust to the ocean floor.

Subduction

The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent boundary.

Describe the process of Seafloor Spreading.

The process of Seafloor Spreading, squeezes magma up through cracks between the plates and hardens to form a new rock. Then newer eruptions push older rocks away from the ridge.

What are three types of evidence found to support the idea of the ocean floor spreading away from the ridge?

Three kinds of evidence scientist have to support this idea include evidence from molten material, magnetic stripes, and drilling samples