Walter Maurice Elsasser was a German-born American physicist considered a "father" of the presently accepted dynamo theory as an explanation of the Earth's magnetism. He was born on March 20, 1904 in Mannheim, Germany. He proposed that this magnetic field resulted from electric currents induced in the fluid outer core of the Earth. He revealed the history of the Earth's magnetic field through pioneering the study of the magnetic orientation of minerals in rocks. Elsasser received the Ph.D. from the University of Göttingen in 1927, then accepted teaching appointments at Frankfurt, Paris, and the California Institute of Technology. While Elsasser was a graduate student he correctly predicted that a beam of electrons would be diffracted by a crystalline material; after the neutron was discovered, he predicted the same behaviour for neutrons. Independently of Nobel Prize winner Hans Bethe, Elsasser carried out important work on the likelihood of certain interactions between neutrons and atomic nuclei. In 1987, he was awarded the National Medal of Science "for his fundamental and lasting contributions to physics, meteorology, and geophysics in establishing quantum mechanics, atmospheric radiation transfer, planetary magnetism and plate tectonics.".