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Someone claimed that the dinosaurs could only live because back then athmospheric density was around 650 kg/m³, providing some buyoncy, this claim is checked on Skeptics SE. The claim itself is beside the point now. A simple calculation shows us that an atmsphere with this density would be supercritical in underwise normal conditions, the pressure would be increased by a factor of roughly 520. See my answer to the skeptics question for a bit more explanation. I would say that a supercritical air atmosphere rules out life for several reasons:

  • The high effusity of the fluid may mean that cell membranes don't work
  • Proteins fold differently under high pressure, requiring specific adaptions
  • If the partial pressure of oxygen is increased proportionally, the atmosphere is highly toxic
  • If the partial pressure of oxygen remains at current levels, it is a trace gas and reactions relying on oxygen may run into kinetic problems (There may be a sweet spot between the last two issues)

Anyway, those are just my hunches, I never heard of experiments about life in supercritical fluids and I'm no biologist so my hunches may be totally wrong. My question is: Can we rule out life in supercritical fluids; if not can we rule out air breathing, multi cellular animal life?
Or has any life been shown to thrive in a supercritical fluid?

To stress again, the part with buoyant dinosaurs was given for background (and amusement), I'm only asking here to check my hunch that suprecriticality rules out life.

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