17% O2 is like being at 2000m altitude. Humans can survive permanently up to about 5000 or 6000 meters, which is a pressure of about 55-50% of sea level, or 11% O2 concentration at sea level pressure. You would feel effects if subjected to that immediately (even fatal), but you can acclimate to it.

Maximum CO2 of a few percent is good. 5% is where it is considered toxic, but even at 1% you feel effects -- basically increased breathing rate and some tiredness. Maximum O2 is harder, there's actually no hard established limit to my knowledge. We can breathe 100% O2 for a little while, but it does have toxicity in the long term. For permanence, probably 30-40% is safe I would guess.

The maximum of 35% was reached towards the end of the Carboniferous period (about 300 million years ago), a peak which may have contributed to the large size of insects and amphibians at that time.

It could also just be something wrong with their experiment or analysis; they must be replicated elsewhere.

If this is so, the occurrence of these particles might indicate the presence of 'dark matter'

How young can a terra-type planet be to have marine unicellular life begin in it's oceans? In Space Engine, I find terras with life that are less than 1 or 2 billion years old.