Invited review Plate tectonics, flood basalts and the evolution of Earth’s oceans

The thermal history of Earth, after the initial period of global magma ocean, is governed by the balance of surface heat loss and internal heat generation. An initially hot Earth has been gradually cooled down with time because, for most of Earth’s history, surface heat loss has been greater than internal heat supply by radiogenic isotopes. This simple energy balance places firstorder constraints on various aspects of physical and chemical processes operating on the surface of Earth and within its deep interior. There have been a number of theoretical studies on Earth’s thermal history (e.g. McKenzie and Weiss, 1975; Davies, 1980; Schubert et al., 1980; Christensen, 1985; Richter, 1985; Solomatov, 2001; Korenaga, 2003; Grigne et al., 2005; Labrosse and Jaupart, 2007), and a review on so far published models on Earth’s thermal evolution has recently been published (Korenaga, 2008b). Estimating a thermal history involves both geophysics (the physics of convective heat loss) and geochemistry (the abundance of heatproducing elements), and many published models do not account for both aspects simultaneously. Available geochemical and geological data place a strict constraint on the permissible range of thermal history, and the most likely scenario is briefly reviewed in the next section. The purpose of this review article is to discuss some of major geological processes that are directly related to the thermal evolution of Earth, on the basis of this latest understanding. Topics covered include the onset of plate tectonics, the history of mantle plumes, continental growth, and the origin and evolution of Earth’s oceans. They are difficult problems, and little can be said with certainty at present. Because they are intimately coupled with thermal evolution, however, we can still derive a few important constraints. These constraints may be counter-intuitive or not obvious at first sight. Mantle plumes, for example, are often thought to be more active in the past, but such temporal trend is in direct conflict with what thermal evolution indicates. Also, the volume of oceans is unlikely to be constant, and it is probably decreasing with time. Whereas these topics tend to be considered independently, each of them represents a different aspect on the evolution of the integrated Earth system, so a proper understanding of Earth’s thermal history is essential to make self-consistent predictions about them.