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Sea-Floor Spreading

Sea-Floor Spreading. Was Wegener Right?. Recently, new technology has given us new clues into drifting continents. Wegener’s theory of drifting continents is supported by this new evidence. Mapping the Mid-Ocean Ridge.

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Sea-Floor Spreading

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  1. Sea-Floor Spreading

  2. Was Wegener Right? • Recently, new technology has given us new clues into drifting continents. • Wegener’s theory of drifting continents is supported by this new evidence.

  3. Mapping the Mid-Ocean Ridge • In the mid-1900s, scientists found the mid-ocean ridge underwater, which is the longest chain of mountains in the world. • Scientists used sonar to map the ridge.

  4. Evidence for Sea-Floor Spreading • Finding the mid-ocean ridge supported Wegener’s theory of continental drift. • Harry Hess was a scientist who suggested that the ocean floors move like conveyor belts.

  5. Evidence for Sea-Floor Spreading • Remember, there are two types of crust. • Continental Crust ( “land”) • Oceanic Crust (the land under the oceans • There is a big crack in the oceanic crust, and this is where the mid-ocean ridge forms.

  6. Evidence for Sea-Floor Spreading • Hess suggested that along the mid-ocean ridge, magma rises from the mantle and erupts. • The magma spreads out and pushes older rocks to both sides of the ridge.

  7. Evidence for Sea-Floor Spreading • This process is called sea-floor spreading.

  8. Evidence for Sea-Floor Spreading • There are three key areas of evidence that support the theory of sea-floor spreading. • Evidence from molten material (magma) • Evidence from magnetic stripes • Evidence from drilling samples

  9. Evidence from Molten Material • Using a submarine, scientists found rocks that can only be formed when magma hits water. • This proved that molten material has erupted from the mid-ocean ridge.

  10. Evidence from Magnetic Stripes • Remember how Earth is a big magnet? • Scientists found out that Earth’s magnet has reversed itself in recent history.

  11. Evidence from Magnetic Stripes • When Earth’s magnetic field pointed north, the iron in the magma that erupted into the ocean faced one direction as it hardened. • When Earth’s magnetic field reversed, the iron faced the opposite direction. This formed stripes.

  12. Evidence form Drilling Samples • Scientists sent a ship to drill deep into the ocean floor and collect many rock samples. • They then tested the age of the rocks using carbon dating.

  13. Evidence from Drilling Samples • Scientists found out that the farther away from the mid-ocean ridge the samples were taken, the older the oceanic crust. • The oceanic crust near the mid-ocean is youngest.

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