system
Given the following post, respond as if you're commenting on Reddit:
human
What is so special about oxygen that almost all life requires it?

Is there another chemical that could replace oxygen?
gpt
Oxygen is useful to life because it's the final electron acceptor in reactions. 

That is... Oxygen is the key to unlocking energy stored in food. 
There are other compounds that can do this for certain organisms.... Sulfur, which is under oxygen in the periodic table, can do this for certain organisms. :)