|MadSci Network: Chemistry|
Dear Eager Student, The atmosphere is composed, by volume, of 21% molecular oxygen, 78%, molecular nitrogen, and 1% other compounds most of which is carbon dioxide and water vapor. The last 1% varies a lot depending on the regional climate and altitude, but the other 99% is pretty much constant throughout the atmosphere until you reach ultra high altitudes. These molar percentages are a result of an equilibrium established on Earth through four and a half billion years of volcanism, comet impacts, and chemical-biological processes. If the Earth were at a different distance from the sun, if the life had never formed on Earth, or if any number of other factors were different, the equilibrium would be different. The only thing nature knows as “good” are those that are in a state of equilibrium. Anything out of equilibrium is quickly changed until an equilibrium is set. The process of photosynthesis and respiration is a cycle which results in an equilibrium between atmospheric carbon dioxide and oxygen. If you suddenly had, say 23% instead of 21% oxygen in the atmosphere, the Earth's atmosphere would be out of its equilibrium and things would proceed very rapidly to re-establish an equilibrium. If you took chemistry, you may be familiar with Le Chatlier's principle. It basically states that a chemical reaction will proceed so that an excess of a compound in a reversible reaction will drive a reaction in the direction to decrease the excess compound. The reaction here is : O2 + carbon compound <-> CO2 + H2O A reaction to the right is respiration. The opposite direction is photosynthesis (assuming you have light). So according to LeChatlier's principle, an increase in oxygen will result in a shift in the equilibrium so that respiration will proceed more readily. Fire, is an instance of chemical respiration and that is the respiration pathway most likely affected by the increased oxygen. We would see a marked increase in the number and spread of wildfires. You may even get a fire that would be impossible to put out until there was nothing left to burn. And eventually, a new equilibrium would be established. This new equilibrium, would necessarily include much more carbon dioxide in the atmosphere. This, of course, would lead to increased global warming, which would lead to increased desertification, which would lead to less food... and so on and so forth. There are of course, many other equilibriums that would be affected. A change in any one equilibrium has a way of affecting numerous other equilibriums since the various chemical and biological components of the Earth's surface are interdependent. As per your question regarding, nitrogen, there are a slew of reactions involving nitrogen, including ones that produce tropospheric smog and destroy stratospheric ozone. So you see, I'm not sure if it would be a “good” thing to have more oxygen in the atmosphere. But my instincts as a scientist and human being is that it's best to let a good thing be. In Koo Kim
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