[daveguy]

habitable*

*survivable in terms of temperature. It still has a 96% carbon dioxide, oxygen free atmosphere, so not directly habitable. The temperature is about room temperature at an altitude of 55km with atmospheric pressure (and T=75C) at about 50km. Earth atmosphere would float in the more dense carbon dioxide atmosphere of venus. You could conceivably have an airship full of earth atmosphere where the cabin is within the balloon.

[Drdrdrq]

Could plants survive at 55km altitude?

[daveguy]

Good question. Seems like they could -- although co2 might be toxic at given levels like o2 would be at 3-4x concentration for us. I don't know about what else they would need -- surely some other nutrients that aren't just floating around. Wouldn't it be awesome if we could just throw some single celled lighter-than-co2 algae in there that could float and produce oxygen and nitrogen. Wait 10,000/100,000/1,000,000? years and just fly around the newly atmosformed atmosphere.