High Rayleigh number regime of temperature‐dependent viscosity convection and the Earth's early thermal history

We have carried out steady‐state calculations of thermal convection with strongly temperature‐dependent viscosity, spanning six decades in surface Rayleigh number (Ra s ). The style of convection undergoes a transition from a stagnant‐lid regime to a constant‐viscosity‐like regime at sufficiently high Ra s . For viscosity variations of 10³ this transition would occur at around Ra s of O (10 7 ) with attendant Nusselt (Nu) numbers of around 50. This transition in the style of convection with Ra suggests that there might be a change in the style of convection and surface features in the very young Earth, when the surface Rayleigh number was much higher from greenhouse effects, which took place in the last part of the accretionary period.