Re: Why is oxygen so important?

Your question is really a very complicated one! I compliment you on coming up with such a hard question that looks so simple! While I don't think I can completely answer your question, I think that I understand what you are asking:

1. Why is oxygen so important for life?

When you run your car on gasoline, or burn wood in your fireplace, or heat your house or cook your food with natural gas, you burn something. In every case, a fuel (gasoline or wood or natural gas) is combined with oxygen, and releases energy.

In the same way, living things combine oxygen with the food they eat and thus obtain energy. Even plants, which we normally don't think of as using oxygen, combine oxygen with the food they make to obtain energy. The reason that plants (in the daytime) give off more oxygen than they use is that, when they make food using the energy in sunlight, they change carbon dioxide and water into food and oxygen. But at night, plants absorb oxygen just like most other living things. In fact, I believe plants are sometimes removed from the rooms of hospital patients at night so that they don't use the patient's oxygen.

Of course, you can get energy from food, or wood, without combining them with oxygen. If you have a compost pile, you may notice that it is sometimes warm to the touch. And there are bacteria (called anaerobic) which do not use oxygen in their life processes; they are, in fact, poisoned by oxygen.

But combining food with oxygen gives much more energy than any other process for using food, so that aerobic organisms are able to use food much more efficiently than anaerobic organisms. This seems to be the main reason that large animals and plants (larger than a single cell) are even possible!

2. Why is oxygen so common on earth?

The oxygen in the earth's atmosphere is entirely the product of green plants! If all the plants were to die, or the earth be cut off from sunlight, the oxygen in the atmosphere would soon be gone. Even if all life were removed from the earth in a moment, the oxygen in the atmosphere would combine with rocks and soil and other inorganic materials in a fairly short time.

Interestingly, the very oxygen produced by green plants is what allows life to live out of the water. Until there was oxygen in the atmosphere, there could be no ozone layer, since ozone (O₃) is another form of oxygen (O₂). And the ozone layer is what protects life on the surface of the earth from powerful, damaging ultraviolet radiation from the sun.

3. Why is oxygen so common in the universe?

Oxygen and carbon are the two most abundant elements in the universe, other than hydrogen and helium. Both oxygen and carbon are produced in the cores of red giant stars, by a delicately-balanced series of nuclear reactions. If the reactions were just a tiny bit different, there would be no carbon, only oxygen; or there would be only carbon and no oxygen. In both cases, life "as we know it" would be impossible, and many chemists believe that life "as we know it" is the only type possible using chemical processes!

Dan Berger
Bluffton College