He received his Ph.D. in geology and geophysics from Yale in 1983, and is best known for his argument that the Great Sphinx of Giza is much older than conventionally thought and that possibly some kind of catastrophe has wiped out other evidence of a significantly older civilization. In 1991, Schoch redated the famous monument to 7000–5000 BC, based on his assertion that its erosion was due mainly to the effects of water, rather than wind and sand, and also based on seismic studies around the base of the Sphinx and elsewhere on the plateau.[7000-5000BC being the latest possible date of erosion, the structure must predate that-DD]