Alfred Wegener was a German meteorologist who had a keen interest in how the continents of the Earth came to be in their present locations. He developed a theory known as the theory of continental drift, which basically stated at one time, all the major land masses of the Earth were together in one super-continent, which he called Pangaea. Surrounding this one super-continent was one super-ocean, called Panthalassa. For whatever reason, the super-continent broke into pieces and the pieces drifted to their present-day locations. His inspiration was the visual appeal of the continents, they looked like pieces of a giant jigsaw puzzle. His evidence was the discovery of similar rock formations, coal deposits, and fossil discoveries on continents separated by major bodies of water. His theory failed to gain much acceptance due to the fact he could not explain how the continents drifted. The modern theory of plate tectonics was developed and furthered by a United States naval officer, Harry Hess, who discovered underwater mountain ranges while taking sound readings of the ocean floor. The cracks in the middle of the mountain ranges fueled the theory of ocean-floor spreading, which provided an explanation of how the continents moved.