His children confirmed the death but did not provide a specific cause.

At an April 1967 meeting of the American Geophysical Union in Washington, Dr. Morgan had initially been scheduled to speak about the Puerto Rico trench, the deepest point in the Atlantic Ocean.

He decided instead to share what he considered much newer and more exciting work, based on his months of research poring over data from the seafloor, much of it gathered by oceanographic institutions. The talk would almost immediately transform the field of earth sciences, although Dr. Morgan wryly noted years later that “most of the people left the room because I was the last talk before lunch break.”

At the meeting, he distributed to scientists an extended outline that he had prepared for the new presentation, which he had titled, “Rises, Trenches, Great Faults and Crustal Blocks.” The crustal blocks would later become known as plates.

“As soon as I read it, I realized the importance of what he developed in [the paper] and dropped everything else to work on the implications,” French geophysicist Xavier Le Pichon wrote in an essay for a celebration of Dr. Morgan’s work in 2003.

At the time, many paleontologists believed the continents had once been connected. The evidence lay in the similar fossils and geology observed across several continents. On maps, it was easy to look at South America and Africa and see two enormous puzzle pieces that appeared to have fit together. What the scientists lacked was a definitive theory to explain how these enormous land masses had separated.

“All science was moving in one direction, and suddenly there’s a whole new way of looking at it that solved a lot of puzzles,” said Lincoln S. Hollister, an emeritus professor of geosciences at Princeton University, recalling the impact of Dr. Morgan’s talk. “If you were working on some obscure mountain range, you realized this was how this mountain range came to be. This was how this rock came to be.”

Dr. Morgan’s training in a branch of math called spherical trigonometry enabled him to look at the maps in a different way, as three-dimensional sections on a spherical Earth rather than as flat shapes on a map.

The techniques “that give plate tectonics its power wouldn’t work on a plane,” Richard Hey, who became Dr. Morgan’s first plate tectonics graduate student and is now a marine geophysicist at the Hawaii Institute of Geophysics and Planetology at the University of Hawaii at Manoa, wrote in an email. “Jason’s the one who showed that spherical thinking was necessary.”

However, questions soon arose concerning credit for the theory. Dr. Morgan did not publish his paper on the theory in the Journal of Geophysical Research until March 1968. In the 11 months between his talk and the peer-reviewed paper, two other scientists — Dan McKenzie and Bob Parker — independently arrived at the idea of plate tectonics and co-wrote a paper in Nature.

“After I’d done quite a bit of the stuff, I then discovered that Jason was doing things,” McKenzie told an interviewer in 2017, adding that he was advised to publish right away and did so.

The ensuing controversy “definitely affected him, but he was a Southern gentleman,” said his son, Jason P. Morgan, who became a geophysicist and co-authored papers with his father. “He was so in love with what was going on in the science that he did not push at all in terms of recognition.”

His daughter, Michèle Morgan, now a curator at Harvard University’s Peabody Museum of Archaeology and Ethnology, added, “My mother seethed.”

Rather than dwell on the question of credit, Dr. Morgan plunged deeper into research, studying a global map of earthquakes. He “‘connected the dots’ of these earthquakes to produce the first accurate map of plate boundaries,” Hey noted in his email.

In the ensuing years, plate tectonics became embedded in the earth science textbooks handed out to millions of high school and university students. And advances in technology only strengthened support for the theory.

“Jason himself would say that the most compelling evidence for plate tectonics today is GPS,” the satellite-based navigation system known formally as the Global Positioning System, Judith Hubbard, author of the 2016 book “Plate Tectonics: The Engine Inside the Earth,” wrote in an email. “We can watch plates move incrementally, year by year, by measuring the movement of GPS stations using satellites.”

In 1971, Dr. Morgan laid out a second major theory addressing a geological feature that did not easily fit the theory of plate tectonics. He examined volcanic “hot spots” that typically appeared in the middle of plates, rather than at the turbulent boundaries between them.

Building on earlier work by Canadian geophysicist John Tuzo Wilson, Dr. Morgan proposed that these “hot spots” developed when tall pillars of scorching material rose from the border between the Earth’s mantle layer and its super-heated core. The hot material would melt to produce magma beneath a tectonic plate.

Like plate tectonics, mantle plumes won a place in science textbooks. But in the early 2000s, a new wave of scientists challenged the idea, insisting they could not find evidence for the phenomenon. Dr. Morgan remained unwavering in his belief, continuing to assemble evidence for the theory.

“He just felt the truth would win out,” his son said, adding, “He did have a quality of assuming other people could see what he saw.”

William Jason Morgan was born in Savannah, Ga., on Oct. 10, 1935. His parents ran a family business that sold hardware and machine parts.

Dr. Morgan was 9 when his father died. Although it had been assumed that he would one day join the family business, he became intrigued by trigonometry in high school, and his interests steered him toward a career in science.

He graduated in 1957 from the Georgia Institute of Technology, then served for two years in the Navy. In the military, he learned about navigation and map projections, skills that prepared him for the discovery of plate tectonics.

Dr. Morgan received a doctorate from Princeton in 1964 and became an assistant professor in the geoscience department two years later. He was guided toward plate tectonics by a love of puzzles and a desire to ask the most sweeping questions: How was the earth formed? Why are there volcanoes and ocean trenches?

He was married to Cary Goldschmidt from 1959 until her death in 1991. Survivors include his children, Jason, of Prato, Italy, and Michèle of Natick; and six grandchildren.

During his 40 years teaching at Princeton, Dr. Morgan received many of the highest honors in his profession, including the National Medal of Science, which was awarded to him in 2002 for having “revolutionized the geophysical study of the Earth and its history,” and the Japan Prize in 1990.

According to a story recounted by the journalist John McPhee in his Pulitzer Prize-winning 1998 book on geology, “Annals of the Former World,” Dr. Morgan, was once asked by Princeton colleague Kenneth Deffeyes how he could possibly follow up his achievement in formulating plate tectonics.

“I don’t know,” Dr. Morgan said with shrug. “Prove it wrong, I guess.”