CO-EVOLUTIONARY IMPLICATIONS OF ALTERNATIVE MODELS OF PLATE TECTONICS IN EARTH HISTORY

Conceptual and numerical models of the co-evolution of life and environment have a fundamental underpinning that is now being called into question. Models to date are based on the assumption that heat loss from Earth’s interior, expressed as rates of tectonic activity (especially volcanic degassing) at Earth’s surface, have declined smoothly (exponentially) over billions of years, although some models allow for quasi-periodic fluctuations associated with the Wilson supercontinent cycle. Two new twists on this scenario have been introduced in the last couple years: sluggish Archean plate tectonics (Korenaga, 2008, Terra Nova 20, 419) and intermittent tectonics (shutdowns of plate tectonic activity for extended intervals: Silver and Behn, 2008, Science 319, 85; Condie et al., 2009, Earth and Planetary Science Letters 282, 294). Here we explore the implications of these new hypotheses for the evolution of the biosphere, including: solutions to the Faint Young Sun Problem and whether the environment for the origin and early evolution of life was hot or cold; the cause of the rise of oxygen at the Archean/Proterozoic boundary and the ensuing Paleoproterozoic glaciation; and the redox state of the Proterozoic ocean.