Sea Floor Spreading Chapter 4 Section 2 Pages 105-107

Sea Floor Spreading-Harry Hess

1. SONAR and other forms of technology helped prove his ideas.

2. Discovered the Mid-Ocean Ridge – a very large under water mountain chain.

3. Hess determined that this is where sea-floor spreading takes place.

4. Sea Floor Spreading is when tectonic plates move away from each other and magma moves up and fills in the gap.

5. As new crust is made, older crust gets pushed further away from the MOR

Evidence

Molten Material

– “Alvin” – small submersible found rocks that can only be formed when molten material erupts and hardens quickly under water.

Magnetic Stripes Magnetic North and South Poles have

reversed over time. Molten material contains magnetic

material such as iron. The magnetic material aligns with the

direction of the magnetic field at the time.

A pattern is preserved in the ocean floor, and the pattern is a mirror image on each side of the MOR.

Drilling Samples

– Glomar Challenger -Determined age of rocks

– Younger rocks closest to the MOR