OT: Carbon Dioxide races -> known vs unknown -> terraforming mars -> is or is not

[Erax]

Getting back to the CO2 atmosphere : it could mean any one of a number of things, but these are the more interesting possibilities :

- CO2 with some oxygen; depending on the oxygen level, CO2 'breathers' (who might actually breathe oxygen) and oxygen breathers would have few compatibility problems.
- CO2, nitrogen and other inert gases; both species would need breathers / gas tanks to survive in the other environment. The CO2 species might need an environmental suit (an insectoid species might not need a suit, if it had a resistant, airtight exoskeleton).