Abstract
Various models for the oceanic heat flow can be grouped into three classes by the difference of thermal condition at the lower boundary of the plate. We summarize characteristics of each model paying attention to physical meaning implicitly contained in the thermal boundary conditions. On the basis of the considerations we propose a new model for the cooling of the oceanic plate which fits well to the observed data of heat flow. The essence of the model is that it takes time for the heat flow in the deep mantle to reach the surface by conduction through the solid plate. Cooling of the oceanic plate has relevance to the cooling of the deep mantle. We discuss briefly the significance of plate tectonics on the cooling of the earth.
