Evidence that p‐d or d‐d fusion could be occurring in the earth stimulated the original laboratory search for cold fusion. That evidence is reviewed here. It is found that the geologic ratio of heat to3He is too high to be explained by the usually accepted fusion processes. Laboratory evidence indicates that fusion can be made to occur in processes of fracture and high strain rate similar to earth processes. An extension of the Oppenheimer‐Phillips theory of neutron tunneling advanced to illustrate alternate fusion paths which could explain the high heat/3He ratio. The search for fusion as a source for additional heat and non‐primordial3He is further stimulated by recent data and analysis indicating that radioactivity can supply less than five percent of the earth’s heat budget. Evidence of deep convection suggests that primordial3He should have been lost in early earth formation and in ongoing outgassing. In this paper, only surface‐related (seawater) deuterium is considered.