BY DR. JOEY PALU-AY DACUDAO
A RHETORICAL question which every student of the life sciences (and every learned person) knows the answer to: What is the most effective way by which living organisms take out Carbon dioxide from the atmosphere?
Answer: Photosynthesis.
6 CO2 + 6 H2O → C6H12O6 + 6 O2
C6H12O6 is a six carbon carbohydrate. The often cited substance with this formula is glucose. But aside from this, photosynthetic organisms also convert carbon dioxide and water (CO2 and H2O) into three and four carbon carbohydrates.
The most common substances into which carbon dioxide (and water) is chemically reduced to by photosynthetic organisms are cellulose, hemicellulose, and lignin.
In the usual course of events, much of the above (except perhaps lignin which is quite hard to biodegrade) are oxidized back into carbon dioxide and water by decomposition by microbes, or by naturally occurring fires. However, a considerably amount are also buried in the earth and sea bottom under anoxic conditions. When this happens, heat and pressure underground further chemically reduce these organic compounds, eventually transforming them into fossil fuels (such as methane, petroleum, and coal). The most carbon-rich of these is coal. Further chemical reduction under the earth’s heat and pressure drives away hydrogen and oxygen (which if combined is just water H2O), thus transforming coal into graphite, the most stable form of elemental carbon. For simplicity’s sake, let the following formula represent this process:
C6H12O6 → 6 H2O + 6 C
The above process is called carbonization. Charring and pyrolysis taken to the extreme is carbonization. It is an exergonic process, which means it gives off heat energy, and thus once started tends to proceed by itself. We can easily watch this process happen when we char wood and other plant material. Once started, charring proceeds by itself until most of the wood had been turned into charcoal, which is mostly elemental carbon.
Notice that if we sum up the above processes of photosynthesis and carbonization, 6 CO2 + 6 H2O → C6H12O6 + 6 O2 (photosynthesis) C6H12O6 → 6 H2O + 6 C (carbonization) we end up with 6 CO2 → 6 O2 + 6 C
This is what essentially happened massively during the formation of coal in the Carboniferous (specifically its latter half the Pennsylvanian around 320 to 300 million years ago) and the succeeding early Permian geological periods. Carbon dioxide was fixed as elemental carbon, namely coal. The process of coalification also produced enormous amounts of free oxygen (as can be seen in the equation above).
It is hypothesized that CO2 levels may have dropped to below 200 parts per million. (To be continued)/PN
