If all plant life stopped how long would it take for oxygen in air to drop to zero?

[repoman]

Plants and algae most just pull oxygen off of carbon dioxide which through a chain of events and chemical equilibria came from carbonate rocks, right?

Would the oceans still have lots of dissolved iron ions if life never happened?

Or if the same early life never developed oxygen waste production.

This is a good wiki

https://en.wikipedia.org/wiki/Great_Oxidation_Event