October 28th, 2016: Bi-stability of Earth and what life may have to do with it

We consider a model of the evolution of the Earth including the water cycle and continental growth along with mantle convection and thermal evolution. The water cycle and continental growth and erosion are strongly non-linear feedback cycles that are coupled through the subduction of water carrying sediments and oceanic crust. Mantle viscosity is taken temperature and water concentration dependent. We plot our results in a series of phase planes spanned by mantle water concentration and continental coverage. The system starts with one fixed point in the phase plane and evolves to three fixed points (attractors) after 2Ga. Of the three fixed points two are stable and one is unstable. The unstable fixed point represents the present Earth while the other two represent planets covered either mostly with oceans or mostly with continents. To model the effect of the biosphere we reduce the erosion rate while keeping other parameters constant. We find that in the latter case the system would evolve away from the unstable fixed point towards the mostly ocean world. One may speculate about the climate and the tectonic modes of these alternative Earths.

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