Tuesday, December 16, 2008

A Clever Experiment

The chemistry of life is the chemistry of the carbon atom. Of the 92 naturally occurring chemical elements--from hydrogen, the smallest, to uranium, the heftiest--only carbon has the complex and delicate balance of atomic forces necessary to form the vast array of chemical compounds on which life depends.

Some elements--such as the noble gases like helium, neon, and krypton--are loners; they stand aloof from making many compounds with other elements. On the other hand, some elements--such as nitrogen, oxygen, and sulfur--are far more social; each makes hundreds or thousands of different compounds with other elements. But carbon, by contrast, makes millions. In fact, carbon makes more different chemical compounds than all the other 91 elements added together.

Next, a word about the isotopes of carbon. Most carbon has an atomic weight of 12--its nucleus has six protons and six neutrons; each proton and each neutron has an atomic weight of one. But there is a heavy form of carbon with two extra neutrons in its nucleus; it still has six protons so it has exactly the same chemical properties as c-12, but it is two units heavier, hence c-14.

An important difference between c-12 and c-14 is that c-14 is radioactive; the nucleus is unstable and decays over a period of time (a long period of time--the half-life of c-14 is just over 5,000 years). As an atom of c-14 decays, a beta particle is emitted; these can be readily detected. Although the concentration of c-14 is typically very low--in the atmosphere, about one trillionth the concentration of c-12--by counting the frequency of beta radiation, the amount of c-14 present in a sample of carbon (or one of its many compounds) can be measured very precisely.

There is always new c-14 being made. High in the atmosphere, nitrogen is bombarded by cosmic rays, and when a nucleus of nitrogen is hit just right, it turns into a c-14 nucleus. In the atmosphere, this c-14 combines with oxygen to form radioactive (that is, c-14-containing) carbon dioxide which mixes with regular c-12 carbon dioxide throughout the atmosphere all over the world.

To return now to the story of the chemistry of life: green plants take up the carbon dioxide from the air (both the c-12 variety of carbon dioxide and the rare c-14 form) and, through photosynthesis, make simple sugars that enter into the metabolic processes of living cells to make the vast array of carbon compounds that living organisms need.

As carbon proceeds on its metabolic journey, perhaps being passed from one to another of a thousand different organisms, perhaps being transformed from one to another of a thousand different carbon compounds, the c-14 gradually decays. Carbon sources that are hundreds of thousands of years old (like coal or oil) have practically no c-14 left; all of their carbon is the c-12 variety.

It is important, in studying atmospheric pollution and greenhouse gasses, to be able to trace carbon dioxide in the atmosphere--it is the main greenhouse gas responsible for global warming--and to determine whether it is formed from new-grown plants or derived from fossil fuels such as coal and oil. One group of researchers hit on a clever way of getting plant samples from precisely known locations and times in the past. For fine wines, a careful record is kept of the precise location of the vineyard and date of harvesting. The researchers were able to acquire 175 fine wines representing vineyards around the world and dating back several decades. By determining the precise concentration of c-14 in the wines, they were able to plot the pollution caused by fossil fuels.

How wonderful that the superficial drivel of the world of oenology should inadvertently make a contribution to the elegant, high-cultural endeavor of scientific inquiry. Never mind that the particular scientific research involved produced (like almost all scientific research) no information of value. In science it is the careful, disciplined mental exercise that really matters, not the result; just as in the "science" of fine wines, it is the debauchery that defines the ultimate success.

It is also noteworthy--when considering the cleverness of this experiment--that only a few ounces of wine was needed from each bottle for the chemical analysis, so at the end of the experiment the researchers had more than three-fourths of a bottle of each of 175 fine wines "left over."

So some data from the absurd and trivial world of wines provided clever scientists with useful information in pursuing their scholarly inquiry; and these same clever scientists, being also regular folks just like the rest of us, were able to use stuffy academic and federal grant money to juice up a few good parties.