What evidence was used to Support Sea Floor Spreading

1. Earthquakes

2. Volcanic Activity

3. Hydrothermal Vents

4. Magnetic Rock Alignment

5. Rock Dating Techniques

Rock Dating Techniques• Rock samples were taken at different locations near the mid-ocean ridge.

• Scientists found the youngest rock near the ridge.

• The oldest rock was found far away from the ridge.

• This provided evidence that sea floor spreading and that newcrust was being created at the ridge.

• How do we know some rock was new and some rock was old?

More Proof: Magnetic Clues• Magnetite is magnetic.

• Magnetite minerals are attracted to Earth’s magnetic field.

• When magma containing these minerals cool, it freezes the magnetic mineral grains to point in the direction of the Earth’s magnetic North Pole.

More Proof: Magnetic Clues• Over time, Earth’s magnetic field changes (reverses direction).

• As a result, the direction the minerals point change with the pole reversal.

More Proof: Magnetic Clues• These changes result in magnetic striping along the ocean floor.

• Each red and yellow stripe indicates a change in the Earth’s Magnetic field and thus a changein direction in which the magnetic minerals point.

• Thus, Earth’s magnetic field has recorded the formation of new ocean crust as the sea floor has spread apart at the mid-ocean ridge.

Mid-Ocean Ridge and Hydrothermal Vents

• At the center of the ridge where the plates are pulled apart lies the Mid-Ocean Ridge.

• Water seeps down through cracks, gets heated by the mantle, then emerges as steam through hydrothermal vents.

Mid-Ocean Ridge and Hydrothermal Vents

• Dissolved minerals from the mantle (sulfides) are brought up.

• Black smokers form when minerals solidify around a vent.

• Marine life have been found around these hydrothermal vents (chemosynthesizers).

• Chimney-like structures that build up around vents as the minerals solidify.

• This could only be possible if magma chambers were close to the surface to heat the water.

Studying SFS – Earthquakes and Volcanoes• As scientists began to investigate

SFS…

• They saw something interesting when they began to look at Volcanoes and Earthquakes locations.

• They plotted the locations of volcanoes and earthquakes on a big map.

• They noticed that all the earthquakes and volcano plot points seem to be located in certain areas across the globe…

• …at the boundary lines between plates!