Sea-Floor Spreading http://www.phschool.com/atschool /phsciexp/internet_activity/cfd- 1014_midocean.html

Introduction Tube Worms - live in the Pacific Ocean about one mile deep near the hydrothermal vents. http://www.learningde mo.com/noaa/

Mapping the mid-ocean ridge Mid-Ocean Ridge: underwater mountain chain. The Mid-ocean Ridge is wrapped around the earth like the curves around like the seam on a baseball. hidden under hundreds of meters of water.

Sonar A device that bounces sound waves off underwater objects and then records the echoes of these sound waves. Sonar mapped mid- ocean ridges.

Harry Hess An American geologist who studied mid-ocean ridges. He suggested that the ocean floors move like conveyor belts, carrying the continents along with them.

Sea-floor spreading The process that continually adds new material to the ocean floor. The ocean floors move like conveyor belts, carrying the continents along with them.

The process of Sea Floor spreading At the mid-ocean ridge: 1: Magma erupts along the mid-ocean ridge. 2. It then cools to form new ocean floor. 3. The ocean floor spreads away from the ridge pushing older rock to both sides of the ridge.

3 Types of Evidence for Sea Floor Spreading molten material magnetic stripes and drilling samples.

Evidence #1 - Molten Material The submersible, Alvin, found strange rocks shaped like pillows or like toothpaste squeezed from a tube. Such volcanic rocks can form only when molten material hardens quickly after erupting under water.

Evidence #2 - Magnetic Stripes Scientists discovered that the rock that makes up the ocean floor lies in a pattern of magnetized “stripes”. They have a “magnetic memory” of the earth.

Evidence #3 - Drilling Samples The Glomar Challenger did a drilling sample. They found that the father away the crust was from the ridge, the older it was. The youngest ocean crust is at the ridge center.

Subduction at Deep-Ocean Trenches Deep Ocean Trenches: Ocean floor plunges into deep underwater canyons Subduction: the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

Subduction At deep-ocean trenches, subduction allows part of the ocean floor to sink back into mantle, over tens of millions of years. http://www.learningdemo.com/noaa/ Earth’s ocean floor is renewed about every 200 million years.

Subduction in the Pacific & Atlantic Deep ocean trenches are swallowing more oceanic crust than the mid-ocean ridge can produce. Thus, the width of the Pacific will shrink. The Atlantic is expanding. It has short trenches. In some places, the oceanic crust is attached to the continental crust which moves the continents.