There's nothing new about speculating that early in Mars' history the Northern plains were filled by an extensive ocean. What would be very unusual and interesting would be for that ocean to be composed of Liquid CO2, during the brief episodes of thick CO2 atmospheres after a major impact. There is just about enough CO2 in Mars' original inventory to fill the basin! As global temperatures cooled the northern CO2 ocean would freeze (from the bottom up, because solid CO2 sinks), and the northern basin would become a thick pole cap.

Again, I don't think this is likely, due to the carbonate problem. The water inventory of Mars would also have melted and formed a layer above the CO2 ocean. Perhaps in this way it would be insulated physically from the rocks and dust on the seafloor, so it couldn't react to form extensive carbonate deposits?

It's all a bit too speculative, I think, so let's leave this one be for now.
 

      Created: May 2002
      Last modified: May 2002
      Authorised by:  Head, Earth Sciences

      Maintained by: Nick Hoffman
      Email: nhoffman@unimelb.edu.au