4 ms·
> AFAIK our oxygen was not made recently. It accumulated over billions of years. According to wikipedia [1], the atmosphere has 34e18 mol of oxygen, and photos
by twic 6y ago
> AFAIK our oxygen was not made recently. It accumulated over billions of years.
According to wikipedia [1], the atmosphere has 34e18 mol of oxygen, and photosynthesis produces 8800e12 mol/yr of oxygen, meaning the atmosphere turns over in a little under four thousand years. There's a separate estimate of atmospheric oxygen's "residence time" in the text, of 4500 years.
So although oxygen levels have been high for billions of years, there is a sense in which the oxygen in the atmosphere right now has only been there for thousands.
[1] https://en.wikipedia.org/wiki/Oxygen_cycle https://en.wikipedia.org/wiki/Oxygen_cycle
- the8472 6y agoThat calculation is simplistic as it is based on the current steady-state. The oxygen catastrophe was a massive change away from the previous equilibrium state which first had to deplete all the buffers. That's how we got iron ore veins, by oxidizing most of the iron out of the oceans. And there are other sinks besides iron.
- samatman 6y agoAll true, this all depends on what question you're trying to answer. If it's "how long is it likely that the oldest free oxygen molecule I'm inhaling right now has been in the atmosphere", that's about 4k years. If it's "how long has the atmosphere had a double-digit partial pressure of O2", very different question with a different answer.
- mncharity 6y ago> oldest [...] [is] about [residence time] Only if the reservoir is a fifo queue. :) Otherwise there's a distribution, with a tail. But oldest in atmosphere still looks (envelope scribbling...) order Myr? Rather than Gyr. Similar for breath?