Inspired by the answers to What can I add to an oxygen/nitrogen atmosphere to make it unpalatable or poisonous to humans, yet stable and breathable to local creatures?, I am building a planet that currently...
- Has an iron core, for the magnetic field to help retain the atmosphere
- Has a surface gravitational acceleration of about 12.2 m/s2, some 25% greater than that of Earth (by virtue of being slightly more massive than Earth as well as somewhat smaller)
- Is covered by 73.9% land and 26.1% oceans (basically the opposite of Earth)
- Has an atmosphere consisting of 67.2% N2, 27.4% O2, 4.8% CO2, 0.4% Ar, and 0.2% miscellaneous (which I haven't decided on a complete breakdown as of yet, but which does include 2.4 ppm As)
- Has a surface atmospheric pressure of 1930 mbar
- Is highly geologically active, with lots of active volcanoes both on land and under water, as well as active plate tectonics
The planet will have lifeforms not entirely unlike those found on present-day Earth, but obviously not humans as we know them.
Now for the, IMO very much related, questions:
- Will this atmosphere be stable? If not, then why not?
- I don't mind the occasional (or even not so occasional; that's a lot of oxygen) wildfire, but I do mind if half the world goes up in flames the first time there's a meteor strike or volcanic eruption.
- Is the mixture and pressure reasonable given the planet? If not, then why not?
- Is there anything about the atmosphere that would pose particular problems to indigneous lifeforms? Anything that you can think of which I should keep in mind while designing lifeforms adapted to this atmosphere?