Hello, Due to all the buzz by Mars One, my friend and I have been discussing hypothetical possibilities for long term colonization of Mars. He suggests the only long term solution is to extract O2 from the Ice on Mars and give the planet a breathable atmosphere. he did the math and calculated that in order to give the planet a 20kPa atmosphere of pure O2 you would need 670 Million metric tons. I am curious as to how stable a pure O2 atmosphere would be. I know it is a very reactive element so what would happen if you had an atmosphere of pure O2? Thanks for any insights.