Dix Planetary Science Seminar
The Earth is the only body in the Solar System for which significant observational constraints are accessible to such a degree that they can be used to discriminate between competing models of Earth's tectonic evolution. It is a natural tendency to use observations of the Earth to inform more general models of planetary evolution. However, our understanding of Earth's evolution is far from complete. In recent years, there has been growing geodynamic and geochemical evidence that suggests that plate tectonics may not have operated on the early Earth, with both the timing of its onset and the length of its activity far from certain. Over the last five years, the potential of tectonic bi-stability (multiple stable, energetically allowed states) has been shown to be dynamically viable, both from analytical analysis and through numeric experiments in two and three dimensions. This indicates that multiple tectonic modes may operate on a single planetary body at different times within its evolution. It also allows for the potential that a feedback between internal dynamics and surface processes (e.g., surface temperature changes driven by long-term climate evolution) can cause terrestrial worlds to alternate between multiple tectonic states over giga-year timescales. Here, I will present a framework of planetary evolution that incorporates the potential of tectonic regime transitions and multiple tectonic states being viable at equivalent physical and chemical conditions. Implications for the terrestrial planets will be discussed.