mollwollfumble said:
CrazyNeutrino said:
Signatures of Alien Life Hidden in Gas
Huddled in a coffee shop one drizzly Seattle morning six years ago, the astrobiologist Shawn Domagal-Goldman stared blankly at his laptop screen, paralyzed. He had been running a simulation of an evolving planet, when suddenly oxygen started accumulating in the virtual planet’s atmosphere. Up the concentration ticked, from 0 to 5 to 10 percent.
more…
The planet in the solar system with the highest percentage of oxygen in its atmosphere is Mercury, with nearly 40% oxygen. Therefore oxygen is not a reliable marker for the presence of life. Life can only develop on a planet in a region with a very low concentration of diatomic oxygen. Life as we know it can survive quite well in an atmosphere with no free oxygen.
OK, I admit it, I cheated.
The 42% oxygen in Mercury’s atmosphere
http://www.space.com/18644-mercury-atmosphere.html is actually monatomic oxygen.
The 69% oxygen in Venus’s atmosphere is in the form of carbon dioxide.
So diatomic oxygen may still be a marker for photosynthetic life.