A supervisor of mine made an off-hand comment about the fact that Mars used to have plate tectonics, and there is evidence that Mars used to have plate tectonics, however now it does not. The theory that she mentioned was that Mars is either heterogenoeous or homogeneous, however I have forgotten which one she said! Now I can't find anything online which says which one it is! Can anyone help me out here?
Also, the follow on from this was that this led to the ceasing of mantle convection which ended the possibilities of plate tectonics? Could somebody more knowledgable than I perhaps outline a theory of why this is?
In addition if mantle convection has ceased, than when do we think it stopped being active?