How does the discovery of seafloor spreading help to explain the mechanism behind why plates move? Explain your answer.

http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/description_plate_tectonics.html

http://www.pmel.noaa.gov/vents/nemo/explorer/concepts/spreading.html

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The discovery of seafloor spreading played a crucial role in understanding the mechanism behind plate movement. Seafloor spreading refers to the process by which new oceanic crust is formed at mid-ocean ridges and spreads away from the ridge, creating new seafloor.

Here's how the discovery of seafloor spreading helped explain plate movement:

1. Mapping of mid-ocean ridges: In the 1950s, scientists used sonar to map the seafloor and discovered continuous mountain ranges known as mid-ocean ridges. These ridges are found in all major ocean basins and are characterized by volcanic activity and high heat flow.

2. Magnetic anomalies: Scientists analyzed the magnetic properties of rocks on the seafloor during the 1960s. They found that the seafloor rocks exhibited a pattern of magnetic stripes with alternating polarity. These stripes were symmetrically mirrored on either side of the mid-ocean ridges.

3. Magnetism and Earth's magnetic field: Scientists knew that Earth's magnetic field has occasionally reversed in polarity throughout history. These magnetic reversals are recorded in rocks as they solidify. Therefore, the symmetric pattern of magnetic stripes on the seafloor indicated that the rocks were formed during such reversals.

4. Confirmation of seafloor spreading: Based on these findings, scientists proposed the theory of seafloor spreading. They suggested that molten material, rising from the mantle through the mid-ocean ridges, creates new crust. This new crust then moves away from the ridge due to convection currents in the underlying mantle, similar to a conveyor belt.

5. Plate tectonics: The discovery of seafloor spreading provided strong evidence in support of the theory of plate tectonics. This theory states that Earth's lithosphere is divided into distinct, rigid plates that float and move atop the underlying semi-fluid asthenosphere. The formation and movement of new oceanic crust at mid-ocean ridges showed that plates are not static but are in constant motion.

In summary, the discovery of seafloor spreading helped explain the mechanism behind plate movement by providing evidence that new oceanic crust is formed at mid-ocean ridges and spreads away, driving the movement of tectonic plates.