Milankovitch cycles
Hays is probably best known as a co-author of the 1976 paper in "Science", "Variations in the Earth's orbit: Pacemaker of the ice ages." Using ocean sediment cores, the "Science" paper verified the theories of Milutin Milanković that oscillations in climate can be correlated with Earth's orbital variations of eccentricity, axial tilt, and precession around the Sun (see Milankovitch cycles).