After World War II, Hapgood taught history at Springfield College in New Hampshire. A student question one day about the Lost Continent of Mu led to a class project to investigate Atlantis. This led to an investigation of possible ways that massive earth changes could occur, including the sensationalistic theories of Hugh Auchincloss Brown.
In 1958 Hapgood published his first book, The Earth's Shifting Crust. The Foreword to this was written by Albert Einstein, shortly before his death in 1955. In this book, and two successive books, Maps of the Ancient Sea Kings (1966) and The Path of the Pole (1970), Hapgood proposed the radical theory that the Earth's axis has shifted numerous times during geological history. This theory is not widely accepted by orthodox geologists.
Hapgood's Maps of the Ancient Sea Kings used numerous archival maps, including the Piri Reis map, which show a vast southern continent roughly similar to Antarctica in shape, to propose that a 15 degree pole shift occurred 9,500 years ago, and that a part of the Antarctic was ice-free at that time. By implication an ice-age civlization could have mapped the coast at that point in time. This theory, although used by recent Atlantis theorists as a jumping-off point for speculation is not supported by current knowledge of the history of the Antarctic ice-cap.
Hapgood's theory was given novelistic treatment in the Hab Theory by Allan Eckert.