Seafloor SpreadingSeafloor Spreading

Technology Lends A HandTechnology Lends A Hand

In the 1940’s and 1950’s, two significant In the 1940’s and 1950’s, two significant inventions were used to help support inventions were used to help support Wegener’s Theory of Continental Drift.Wegener’s Theory of Continental Drift.

SONAR SONAR The MagnetometerThe Magnetometer

SONARSONAR

SONAR is an SONAR is an acronym (Sound acronym (Sound Navigating and Navigating and Ranging). Ranging).

It is a device that It is a device that can measure the can measure the depth of water, find depth of water, find submarines, and… submarines, and… map the ocean map the ocean floorfloor

A fish finder is a A fish finder is a simple example of simple example of sonar.sonar.

What SONAR Showed UsWhat SONAR Showed Us When we used this new-found technology, we learned When we used this new-found technology, we learned

that the ocean floor was not flat, but rather… had that the ocean floor was not flat, but rather… had mountain ranges, canyons, volcanoes, plains and deep mountain ranges, canyons, volcanoes, plains and deep

sea trenches.sea trenches.

Mid-Ocean RidgeMid-Ocean Ridge

The MagnetometerThe Magnetometer A A magnetometermagnetometer is a scientific is a scientific

instrument used to measure the instrument used to measure the strength and/or direction of the strength and/or direction of the magnetic fieldmagnetic field in the vicinity of in the vicinity of the instrument. the instrument.

The Earth has its own magnetic The Earth has its own magnetic field.field.

When magma cools, the When magma cools, the metallic elements (iron and metallic elements (iron and magnesium) align with the magnesium) align with the Earths magnetic fieldEarths magnetic field

Scientists used this to measure Scientists used this to measure the magnetic strength and the magnetic strength and direction in the rocks that made direction in the rocks that made up the ocean floorup the ocean floor

What We Learned From The MagnetometerWhat We Learned From The Magnetometer

We learned that the rocks that make up the ocean floor flip-flop their 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).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 We also learned that these patterns mirror one another on either side of the mid-ocean ridges.mid-ocean ridges.

This was a good piece of evidence to support the idea that the ocean floors 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 are spreading… evenly… in opposite directions… from the mid-ocean ridgesridges

As they spread, new floor is created at the ridge, pushing older floor out in As they spread, new floor is created at the ridge, pushing older floor out in opposite directions, leaving older floor further and further out. opposite directions, leaving older floor further and further out.

Along these cracks, earthquakes and volcanoes are common.Along these cracks, earthquakes and volcanoes are common.

Harry Hess - Putting It All Together Harry Hess - Putting It All Together During WWII, US Navy During WWII, US Navy

Captain Harry Hess spent a Captain Harry Hess spent a lot of time using SONAR lot of time using SONAR and mapping the floor of the and mapping the floor of the Pacific Ocean.Pacific Ocean.

He learned that the ocean He learned that the ocean floor had mountains, ridges, floor had mountains, ridges, trenches, volcanoes, etc…trenches, volcanoes, etc…

He also learned that the He also learned that the rocks near the ridges were rocks near the ridges were younger, and the rocks near younger, and the rocks near the trenches were older.the trenches were older.

He published a report to the He published a report to the Office of Naval Research on Office of Naval Research on his findings. his findings.

The Navy officially published The Navy officially published Hess’s research as the Hess’s research as the “History of Ocean Basins” “History of Ocean Basins”

The Mid-Atlantic RidgeThe Mid-Atlantic Ridge

So What Does It All Mean?So What Does It All Mean? Hess’s research showed Hess’s research showed

that new seafloor was that new seafloor was being created at the mid-being created at the mid-ocean ridges, and ocean ridges, and destroyed at the deep sea destroyed at the deep sea trenches. trenches.

This was the missing link This was the missing link (the mechanism) needed (the mechanism) needed to establish Wegener’s to establish Wegener’s theory of Continental Drift.theory of Continental Drift.

THIS IS A BIG DEAL!THIS IS A BIG DEAL! This is often regarded as This is often regarded as

one of the most significant one of the most significant discoveries of the 20discoveries of the 20thth CenturyCentury

Gas Escaping at a Gas Escaping at a Mid-Ocean RidgeMid-Ocean Ridge

A Black Smoker VentA Black Smoker Vent