We developed a time-integrated thermogeographic model to demonstrate conditions under which benthic marine algal assemblages evolve biogeographic patterns in their distribution and abundance. The graphical model applies to rocky marine sublittoral zones in which seasonal temperatures, coastline area, isolation, and evolutionary time are primary factors. Time is treated by using the temperature/area/distributions for the present (interglacial period) integrated with that of 18,000 years before present (glacial period). These two alternate states characterize the global marine realm since the late Pliocene to Pleistocene time during which many extant species have evolved. The resulting abiotic “thermogeographic” model defines 20 regions that correspond with the cores of 24 recognized biogeographic regions and/or provinces determined by published distributions of organisms. Modern biogeographic regions conform closely with thermogeographic regions where temperature, area, and time are integrated. We also propose that biogeographic patterns should be determined by the abundance of species assemblages rather than presence and absence or percent endemism as is commonly done. We test the efficacy of thermogeographic regions with abundance-weighted patterns in the biogeography of crustose coralline red algae (Rhodophyta/Corallinales) in the colder part of the northern hemisphere. Based on abundance, rather than presence/absence, coralline red algal biogeographic regions correspond closely with the model's thermogeographic regions.