Harry Hammond Hess: Father Of The Unifying Theory Of Plate Tectonics

Harry Hammond Hess, Chair of Geology at Princeton. Photo: Princeton University Archives

While we now know that the continents were once whole and drifted apart from each other, due to the activity of volcanic ocean ridges, it wasn’t always this way. The man typically credited with revealing this now generally accepted scientific theory was Harry Hammond Hess, a geologist, and officer in the United States Navy during World War II.

Continental Drift

The theory of continental drift had been proposed before Hess’ time, perhaps as early as 1907 by various scientists and researchers. However, the individual who formally postulated the theory of continental drift was Alfred Wegener, who published a paper on the topic in 1912. Wegener proposed in his paper the idea that the continents had once been a single massive landmass, which he dubbed Pangea, before drifting apart.

Wegener’s theory that the continents had once been whole and had drifted apart over millions of years was dismissed by many academics of his time, and it would not be until around 1953 when the theory of plate tectonics was introduced, thanks in large part to Hess, that continental drift would be taken seriously.

Hess received his doctorate from Princeton University in 1932, and he then went on to teach at Rutgers University for a short time before heading back to Princeton in 1934. Hess stayed at Princeton for the majority of his life and would serve as the Chair of Geology at Princeton from 1950 to 1966.

Hess was deeply interested in how volcanic activity could impact the formation of island arcs and mountain ranges and was researching how crystallized magma could lead to the creation of island arcs when the second World War broke out. Hess was a reserve officer in the US Navy at the time, so he reported for duty and was eventually assigned to command an attack transport ship.

Guyots and the Great Global Rift

Luckily for Hess, the vessel he commanded was full of equipment for monitoring the ocean floor using sounding. Hess used the equipment to conduct research and gathered a large amount of data on the floor of the Pacific Ocean. One of his discoveries was the existence of flat seamounts which he called “guyots” (named for the first professor geology at Princeton, A.H. Guyot).

Guyots are flat-topped formations found under the ocean. Hess found out they resulted from the movement of eroded volcanoes thanks to plate tectonics. Photo: e-education.psu.edu

When the war ended, Hess would continue to study guyots as well as the mid-ocean ridges of both the Pacific and Atlantic. The data Hess collected at sea was shelved for a number of years, until 1953. In 1953, two scientists, Maurice Ewing and Bruce Heezen announced the discovery of “Great Global Rift”. The Great Global Rift, now dubbed the Mid-Ocean Ridge, was a mountainous ridge that ran all the way through the Atlantic ocean to the south of Africa. It was also discovered that there was a deep canyon in the middle of this underwater mountain range. Ewing and Heezen’s findings inspired Hess to re-examine the data he collected during the war.

A map of the Mid-Ocean Ridges. Photo: U.S. Geological Survey

After years of extensive research and evaluation, Hess published the paper History of Ocean Basins in 1962. Hess’ paper explained how Wegener’s theory of continental drift could be possible. It showed that there was a mechanism that could actually shift the continents around over millions of years. In his paper, Hess showed how magma could fill in areas tectonic plates pushed apart. Hot magma would bubble up from under the Earth’s crust and when the magma eventually cooled it created more land that filled in the gaps as the tectonic plates came apart. Hess referred to this process as “seafloor spreading”.

Hess’ theory solved a few unanswered geological questions, such as how it was possible that fossils older than 180 million years could be found on land but not under the ocean. Hess also provided an explanation for the apparent contradiction that the ocean floor was 4 million years old but there was almost no sediment deposited on it. According to Hess, new crust is created at the mid-ocean rift, and then it is pushed under the continental crust after 300 million years, where it is eventually melted and turned into magma. This process happens at “subduction zones”.

Seafloor moves under the crust of a plate and becomes magma at subduction zones. Photo: columbia.edu

Hess even found an explanation for the guyots he had discovered earlier in his career, they were at one time volcanic mountains that were eroded and were dragged along by the moving oceanic plate.

Evidence for Seafloor Spreading

Much like Wegener before him, Hess ran into considerable resistance to his hypothesis by other geologists. There was little data from the ocean floor that could support his current hypothesis. Knowing that he still needed more data to convince the scientific community, Hess continued to work on his research. However, some key discoveries around the same time supported his idea.

Dating of ocean-core samples done in the early 1960’s offered more support for Hess’ theory, as they found that the floor of the ocean was the youngest right at the Mid-Atlantic Ridge and that it got progressively older as it moved away. Yet more evidence would come thanks to the efforts of Frederick Vine and Drummond Matthews, who discovered that the Earth’s magnetic field had been reversing every 200,000 years or so. This meant that rock formations with the same age would have the same magnetic polarity that the part of the crust it was on had when it was formed. Samples collected of rocks in the Mid-Atlantic ridge found a symmetrical arrangement of polarity stripes, alternating with changes in the Earth’s magnetic field, further confirming Hess’ hypothesis.

Seismic data was also collected on the ocean floor, and it found that the oceanic crust was sinking into the trenches in the Mid-Atlantic Ridge, just as Hess had hypothesized.

The combination of discoveries vindicated Hess, and by extension Wegener. Though Wegener had died before seeing the field of geology side with him, Hess lived to be recognized for his achievements. Hess was the recipient of a Penrose Medal, the top prize awarded by the Geological Society of America. Hess would go on to play a large role in the creation of NASA and the space program, thanks to recognition from President John F. Kennedy. Kennedy made Hess the Chairman of the Space Science Board of the National Academy of Sciences, and Hess oversaw the planning stages for the Apollo moon landings.

Hess died relatively early, at only 63. Hess had a heart attack at a meeting of the Space Science Board in August of 1969. Hess was honored posthumously, given NASA’s Distinguished Public Service Award.

Hess’ contributions to science created a concrete theory to backup continental drift, and our understanding of the world would not be the same without him.

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