Why is oxygen an element?

Why can't another element substitute for Oxygen in the process of fire?

• What makes Oxygen so unique that it is the only element that can produce fire (when added with fuel and heat). Is it the only element? Is there a similar process to fire for other elements under similar conditions?

• Answer:

  Here's a video of various substances burning in a jet of fluorine gas. Fluorine is more reactive than oxygen, so that all these substances, which are stable to the oxygen in the air at ambient temperature, combust instantly when exposed to fluorine (without heating). The reason why we tend to think of oxygen as the only gas that supports combustion is that it is the only reactive gas in the atmosphere! The earth's crust and atmosphere sit relatively close to a free-energy minimum. The crust consists primarily of silica and metal oxides, whereas the atmosphere contains unreactive gases like nitrogen gas, carbon dioxide, water vapour, and noble gases. You could say that all the reactions that could have occurred already have occurred. Oxygen gas is special because it's being constantly produced by photosynthesis. If life on earth were to disappear, the atmosphere would become depleted of oxygen. Oh, and by the way, ozone also supports combustion, which is not surprising, in light of the fact that it, too, is more reactive than oxygen.