That's great, but one problem: molecules don't stay molecules over two thousand years. Certainly not oxygen, which is extremely chemically active. N2 somewhat less so (but http://en.wikipedia.org/wiki/Nitrogen_cycle), but the chances of any particular nitrogen molecule retaining its identity over two thousand years is incredibly low.
Redo this calculation with atoms, and I might believe you. But it'll need to be a bit more complicated, since I don't think the amount of oxygen and nitrogen getting sequestered in the ocean or the soil is actually "trivial" as stated.
Redo this calculation with atoms, and I might believe you. But it'll need to be a bit more complicated, since I don't think the amount of oxygen and nitrogen getting sequestered in the ocean or the soil is actually "trivial" as stated.