I’ve noticed that most of, if not all living things rely on oxygen in one way or another to breath, live. We humans need oxygen so then is carried to our bloodstream to oxygenate our internals, same with a fish for example where the oxygen is obtained from the water. But why oxygen? Why live couldn’t have happen with other elements like hydrogen for example? Why oxygen is any life’s fuel in our universe?
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Oxygen has two properties (well, it has a lot, but we’ll focus on two) that make it incredibly useful for life.
a ) It’s incredibly reactive, making it very useful in things like the controlled burning of sugars that give your cells the energy they need to do stuff, facilitating many of the chemical reactions in your body. What we call “burning” is just code for “stuff rapidly reacting with oxygen”. Most of the things that burn burn because of an oxygen reaction, from a log fire to sugars converting in your cell to rust forming on iron. All of it is cut from the same cloth at different speeds and intensities.
b ) it’s abundant in nature, meaning that the lifeforms that depend on it don’t have to struggle with obtaining oxygen: it’s already a large portion of the atmosphere. You could use other molecules for similar purpose, but then you’d have to find a near-never-ending supply of that molecule.
Now, oxygen in itself isn’t strictly “needed” for life if you limit your life to fairly simple lifeforms : many of the first lifeforms that developed on earth were anarobic, meaning they could survive in environments with very limited or no oxygen. In the dawn of life the earth was much more hostile to life and nearly all oxygen was locked up in other molecules, like water or Co2. The life that lived then didn’t need molecular oxygen, but instead used other molecules that could perform similar jobs (albeit not always as effectively). Things like nitrate or sulfate (Which, technically, do have an oxygen atom in them but we’ll sidestep that technicality). Anarobic cells may even *dislike* free oxygen. The first massive extinction event was caused by single-celled organisms that started producing oxygen, accidentally poisoning the earth for the other cells that couldn’t use it.
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