Too Big to Walk by Brian J. Ford

Author:Brian J. Ford
Language: eng
Format: epub
Publisher: HarperCollins Publishers
Published: 2018-04-13T16:00:00+00:00

CO2 + H2O ↔ H2CO3

The reaction is reversible and in the oceans we find a chemical equilibrium between CO2 and H2CO3. Ions of hydrogen and bicarbonate can be released:

HCO−3 ↔ H+ + HCO23−

It is this reaction that serves to buffer seawater against random fluctuations in acidity. Many microbes and other minute marine organisms can fix bicarbonate biologically with calcium (Ca+2) to create calcium carbonate, CaCO3, which is produced in several different forms, including aragonite and calcite, and this process gives rise to their exoskeletons and microscopic shells that fall to the seabed, accumulate in strata, and eventually become sedimentary rocks. This form of limestone comprises 10 per cent of all sedimentary rocks, and our civilization is founded upon it. Almost everywhere you look there is limestone.

You may think that fossils are a specialized subject, but our society is founded on fossils. We burn fossil fuels (once it was only coal, now it is oil and gas) and have built our cities, hospitals, airports, schools … of fossils. Microscopic fossils gave us the limestone of which our buildings are made – our lofty cathedrals and churches are carved from limestone, and held together with lime mortar, itself made from limestone; it is limestone that is furnace-burned to produce cement and concrete; it underpins everything in our lives. Aggregate, used to create roads and massive embankments, is made from limestone; acidic farmland is neutralized and made productive by the application of billions of tons of pulverized limestone, and the fumes from power stations are treated with limestone dust to make it safe. You find powdered limestone in paper and paint, plastic and toothpaste; it is added to flour and medicines, cereals and cosmetics, it boosts animal feed and is a crucial component in the manufacture of iron and steel. Chances are the room in which you may be reading these words is made with concrete (or stands on a bed of it), and the source of all these present-day products was all laid down, atom by atom, by microscopic creatures nobody ever sees. The microbes that made limestone created our environment as well as giving us the air to breathe.

It was microbial metabolic processes that locked away atmospheric CO2 in a form we are now exploiting. About 90 per cent of the CO2 in the oceans is in the form of bicarbonate HCO3– and the other roughly 10 per cent is as the carbonate ion CO3−. Only about 1 per cent is dissolved CO2 gas. When the temperature of the sea increases, it encourages the replacement of the carbonate by the bicarbonate ion, and this makes the calcium carbonate dissolve more readily. Marine organisms find it harder to secrete their shells, and existing carbonate deposits become increasingly soluble. Since the solubility of gases is inversely proportional to temperature, less CO2 is absorbed by the oceans as they warm, which further increases the problem. Today’s world is getting warmer, and that includes the sea. The oceans are also becoming more acidic, and it is microbes that notice it first.

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