Sea-Floor Spreading

Why Was Continental Drift Not Accepted? Wegener couldn’t explain what force was strong enough to move the plates.

The Great Global Rift In 1953, American physicists Ewing and Heezen discovered that through an underwater mountain range ran a deep canyon. In some places the canyon, called the Great Global Rift, came very close to land. The rift appeared to be breaks in the earth's crust, but perfectly fitted breaks, like joints made by a carpenter.

The Hypothesis of Sea-Floor Spreading Who proposed this hypothesis? In 1960, Harry Hess proposed that the movement of the continents was a result of sea-floor spreading. He hypothesized that the sea-floor was spreading from vents in the Great Global Rift, where hot magma oozed up. As the magma cooled it forced the existing sea-floor away from the Rift on either side.

What Goes On At Mid-Ocean Ridges? 1. Sea-floor spreading

What Goes On At Mid-Ocean Ridges? 2. The youngest rocks of the sea floor are forming in the middle at the rift between the ridges.

What Goes On At Mid-Ocean Ridges? 3. Magnetic striping has been observed. The Earth’s magnetic field reverses itself Every few thousand years.

What Goes On At Mid-Ocean Ridges? Magnetic reversals have been recorded on the ocean floor.

What Was The Proof Of Sea-Floor Spreading? 1. Ancient magnetism records flip-flops of earth’s magnetic field.

What Was The Proof Of Sea-Floor Spreading? 2. The Age of the Sea Floor Oceans are youngest at the Mid-Ocean ridges and oldest near the continents. This diagram shows the Americas being separated from the Europe and Africa as the seafloor spreads. Continents are grey in color. Youngest seafloor is red and as seafloor gets older it becomes yellow, green and then blue.

What Was The Proof Of Sea-Floor Spreading? 3. New ocean floor is created at mid-ocean ridges. And ocean floor is destroyed in subduction zones.

What happened? Hess' ideas neatly explained why the Earth does not get bigger with sea floor spreading and why oceanic rocks are much younger than continental rocks. Hess died in 1969. Unlike Wegener, he was able to see his seafloor-spreading hypothesis largely supported as knowledge of the ocean floor increased dramatically during his lifetime.

The End BONUS: What does this picture show?