1. Seafloor Spreading

2. Technology Lends A Hand  In the 1940’s and 1950’s, two significant inventions were used to help support Wegener’s Theory of Continental Drift. SONAR SONAR The Magnetometer The Magnetometer

3. SONAR  SONAR is an acronym (Sound Navigating and Ranging).  It is a device that can measure the depth of water, find submarines, and… map the ocean floor  A fish finder is a simple example of sonar.

4. What SONAR Showed Us  When we used this new-found technology, we learned that the ocean floor was not flat, but rather… had mountain ranges, canyons, volcanoes, plains and deep sea trenches.

5. Mid-Ocean Ridge

6. The Magnetometer  A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. magnetic fieldmagnetic field  The Earth has its own magnetic field.  When magma cools, the metallic elements (iron and magnesium) align with the Earths magnetic field  Scientists used this to measure the magnetic strength and direction in the rocks that made up the ocean floor

7. What We Learned From The Magnetometer  We learned that the rocks that make up the ocean floor flip-flop their magnetic polarity every million years or so (scientists still do not know why).  We also learned that these patterns mirror one another on either side of the mid-ocean ridges.  This was a good piece of evidence to support the idea that the ocean floors are spreading… evenly… in opposite directions… from the mid-ocean ridges  As they spread, new floor is created at the ridge, pushing older floor out in opposite directions, leaving older floor further and further out.  Along these cracks, earthquakes and volcanoes are common.

8. Harry Hess - Putting It All Together  During WWII, US Navy Captain Harry Hess spent a lot of time using SONAR and mapping the floor of the Pacific Ocean.  He learned that the ocean floor had mountains, ridges, trenches, volcanoes, etc…  He also learned that the rocks near the ridges were younger, and the rocks near the trenches were older.  He published a report to the Office of Naval Research on his findings.  The Navy officially published Hess’s research as the “History of Ocean Basins”

9. The Mid-Atlantic Ridge

10. So What Does It All Mean?  Hess’s research showed that new seafloor was being created at the mid- ocean ridges, and destroyed at the deep sea trenches.  This was the missing link (the mechanism) needed to establish Wegener’s theory of Continental Drift.  THIS IS A BIG DEAL!  This is often regarded as one of the most significant discoveries of the 20 th Century

11. Gas Escaping at a Mid-Ocean Ridge

12. A Black Smoker Vent