The Phactor has a penchant for starting at the beginning, and the botany textbook for this new course is strangely written in places. For example, the textbook correctly notes that only 6 elements constitute >99% of all living matter, and then it's sounds as if this was somehow amazing that out of 92 naturally occurring elements, only these 6 constitute life. And there the discussion is dropped! If you can't offer a better explanation than that, don't bother! OK, have you decided what 6 elements constitute living matter? CHNOPS - carbon, hydrogen, nitrogen, oxygen, phosporus, and sulfur. How did you do? Don't feel bad my class only got 4.
First if you step back from things a bit, the universe is even simpler: hydrogen is 71% of everything, helium is 28% of everything (a direct "fossil" of the Big Bang), which leaves just 1% for everything else to be composed of the other elements. Stellar fusion accounts for all the other elements, and they are dispersed when a dying star goes super nova, and the Sol system is composed of such star death debris.
Now if you look at CHNOPS in living organisms, you get the following proportions: H - 62%, O - 27%, C - 8.5%, N - 1.9%, S -0.1%, P - 0.1% (99.6% in total). If you compare that to the volatile fraction of comets, thoserocky ice balls left over from the formation of the solar system you get the following proportions: H - 56%, O - 31%, C - 10%, N - 2.7%, S - 0.3%, P - 0.08%. Well, there you have it. Living matter is made up of the 6 most common elements in the universe, except for helium that seems to exist just for filling balloons, and in the approximate same proportions. So life is common star stuff in the unusal proportions, and that doesn't seem so amazing now does it?
1 Comments:
I agree. The "6 elements of life" statistic is meaningless. I'd have a little more respect for helium, however. While we humans got along fine without it for hundreds of millenia (and discovered it on the sun before we found it here on earth) it has important uses beyond making balloons buoyant. Organic chemistry would be much more difficult without nuclear magnetic resonance (NMR) spectroscopy and NMR would be very difficult without superconductors. So until we find materials that superconduct at relatively high temperature, liquid helium is a necessity for much scientific progress. MRI scanners also require liquid helium for the same reason. There is actually an impending worldwide helium shortage which threatens to make MRI scans and NMR prohibitively expensive for routine analyses. And yet we still fill our balloons with it!?
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