[Loser]

Originally posted by dogscoff:
I know Mars has a thin CO2 atmosphere. If we were to build a domed ecosystem on Mars, I imagine we could use photosynthesis or some chemical process to extract all the oxygen we needed from this CO2.

I'm not so sure there's quite that much. And the thinness of the atmosphere is going to slow down the conVersion.

Originally posted by dogscoff:
However, as has already been stated in this thread, our own atmosphere is mostly nitrogen, and that is also important to us. (Nitrates in the soil for plants etc)

Does anyone know if there is any useful amount of nitrogen present in the martian atmosphere, or is it all CO2? If there is none, would we be able to extract the required nitrogen from other nearby resources (rocks, asteroids etc)?

A good source for terraforming Mars is one particular sci-fi series: Red Mars, Green Mars, Blue Mars. I would recommend these, if you don't mind the excessive sex sci-fi authors feel they need to include to get their work of the juvi-fic rack.

Originally posted by dogscoff:
Finally, would an artificial atmosphere made up in this way (say ~75% nitrogen, ~15% oxygen, ~10% CO2) be viable for a human ecosystem, or would we need to import/ locally source all the other trace elements in our own atmosphere?

On Earth it's about 70% N2, 22%O2, 4% Argon, and the remaining 4% everything else (very small amount of CO2). But it's not the percentage of Oxygen that's important, it's the amount of O2 molecules per Liter of 'air'. So at lower pressures it's important to have a greater percentage of O2 and at higher pressures it's not only important to have a lower percentage of O2, but also to have less N2 or no N2. A high enough pressures N2 will act as an intoxicant, so an inert gas, such as He (elemental Helium), is used.