Scientist Harry Hess: Biography & Theory

Instructor: Josh Corbat

Josh has taught Earth Science and Physical Science at the High School level and holds a Master of Education degree from UNC-Chapel Hill.

It is a common misconception that all important scientific contributions about our planet were made centuries ago. However, in 1960, Harry Hess made a contribution that changed the way we understand the Earth. This lesson details Hess' career and scientific contribution.

Harry Hess: A Short Biography

Within the last century, the way we think about the composition of our planet was forever changed by one scientist's work. It's a bit strange to think that it was made on board a military ship instead of in a lab!

Harry Hess is best known for his theory of seafloor spreading. His work was incredibly important in building our modern understanding of how the Earth changes beneath our feet. You've heard of Pangaea, right? The super-continent back when all the land was together? Harry Hess gave us the tools to finally understand just how Pangaea drifted apart all those (billions) of years ago.

Though his major discoveries happened while he was enlisted in the military, Hess was not strictly a military man. Born May 24, 1906, his early career was in the university setting as a professor at Princeton University, where he eventually served as the Chair of the Geology department. He is known for many scholarly publications, and published his most important book in the field of geology in 1960. Hess died August 25, 1969.

Harry Hess aboard the naval ship he captained.
Harry Hess

Hess' Science on the Side

Harry Hess joined the United States Navy during World War II, and was granted the post of commander of an attack transport ship. All of this sounds very unscientific, right? Well, the ship was equipped with a brand new type of equipment: Sonar. Sonar (which stands for SOund NAvigation and Ranging) uses sound waves to measure the distance of objects by timing how long it takes for the sound to bounce off the object and return. In the war, sonar was intended to be used to find enemy submarines. But Harry Hess had another idea.

Hess used the sonar to make detailed maps of the ocean floor. By aiming the sonar at the floor of the ocean, he was able to quite accurately map the depths of the northern Pacific Ocean. Since the surface of the water is level, he was essentially discovering underwater mountains, volcanoes, and valleys. When analyzing his data, he discovered underwater flat-topped mountains that he called guyots. His data and later work also contributed to the understanding of a giant mountain chain in the middle of the Atlantic that has a massive rift valley in the middle. This went on to be known as the Mid-Atlantic Ridge. It wasn't his data discoveries alone that made Hess famous, though; it was hypothesis on how ridges in the sea formed.

The Seafloor Spreading Hypothesis

Ever notice how the continent on our planet look a little like puzzle pieces that could fit together? Several scientists before Hess' time had noticed this too, and many had attempted to explain the movement of the continents around the Earth. However, no scientist before Hess could find any hard data to prove these ideas.

Calling upon the work of other scientists, as well as his own research and data, Harry Hess hypothesized that the continents were moving away from each other at spreading zones. His idea of the spreading of the seafloor became known as (drumroll, please) the Seafloor Spreading Hypothesis. Hess took it one step further when we hypothesized on the mechanism for this movement.

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