The Taste of Carbon Dioxide

by James R. Barrante, Ph.D.

A few years back, the Environmental Protection Agency deemed that the gas carbon dioxide is a pollutant.  The dictionary defines a pollutant as a substance that contaminates or poisons.  It would be useful to look at how carbon dioxide stands up to this definition.

The composition of Earth’s early atmosphere was approximately 95% carbon dioxide and water vapor, very similar to the atmosphere of Venus today.  It contained no oxygen.  Any oxygen that might have formed, reacted chemically with metals in the hot crust (e.g., iron, copper, calcium, magnesium, aluminum) and metalloids (silicon) to form oxides.  As the planet cooled to below 100˚C, something that Venus was never able to do because of its nearness to the sun, the water vapor began to condense forming lakes and rivers, and because of its high solubility in liquid water, the atmospheric carbon dioxide began to dissolve in the Earth’s waters.  When carbon dioxide dissolves in water, it forms a weak acid, known as carbonic acid, that will react with any alkaline (basic) substances to form bicarbonates and carbonates.  Earth’s waters began to attack the alkaline oxide minerals, like calcium oxide, to form carbonates, and since most carbonates are not soluble in water, they settled out of lakes and oceans to form rock such as limestone and marble.  This left more room for more carbon dioxide to dissolve.  The level of atmospheric CO2 began to drop.  Moreover, certain chemical reactions in the atmosphere began to produce nitrogen gas, a relatively inert gas that reacts slowly with other elements.  The composition of the atmosphere began to drastically change.

The appearance of living organisms on the planet further changed the chemistry of the planet.  While the chemical reaction

CO2     +     H2O       →     sugars     +       O2   

is not energetically possible, certain plants learned to make a photosensitizer, known as chlorophyll, that allowed them to use the sun’s energy to force this reaction to occur.  Because chlorophyll absorbs in the red region of the spectrum, plants appeared to be green.  The formation of large quantities of green algae further reduced the level of atmospheric carbon dioxide, producing an atmospheric waste poison, oxygen gas.  Luckily, the level of oxygen gas in the atmosphere would remain low.  This is because any newly formed oxygen gas would quickly react with metals in the Earth’s crust to form the metal ores that are present today.  Likewise, the reaction of vast amounts of silicon, the second most abundant element with oxygen, formed silicates and large regions of sand.

Animals began to evolve in the waters, feeding on the green plants (and on each other), but were confined to the waters, because of the deadly ultraviolet radiation reaching the surface of the Earth from the sun.  One good effect, however, did result from the oxygen in the air.  Lightening storms supplied large amounts of energy that allowed another type of oxygen, O3, and known as ozone, to form and this gas began to build up in the upper atmosphere.  Ozone has the ability to filter the ultraviolet radiation from sunlight, and this eventually allowed animals to move from the oceans onto the land.  We must keep in mind, however, that the food chain remained in tact.  Carbon based plants obtain their carbon atoms solely from atmospheric carbon dioxide.  Animals get their carbon atoms by eating the plants or eating the animals that eat the plants.  At levels of atmospheric CO2 in the thousands of parts per million range, lush plant life covered the Earth’s surface, allowing animals that fed on these plants or fed on the animals that ate these plants to grow very large. This could never happen today.  At levels of 100 ppm (parts per million) CO2 plants begin to die.  At levels of 200 ppm plants struggle to survive.  At levels of 300 ppm (pre-industrial CO2 levels) there was barely enough food for pre-industrial populations to survive, at todays levels of 400 ppm, it is not likely that there will be enough food on the planet to feed the expected large increases in population in the 21st century.

We know that atmospheric CO2 levels are controlled by the temperature of the oceans. If we are lucky, oceans will not cool and cause carbon dioxide levels to plummet. It appears that declaring our source of all the food on this planet a pollutant was not a stroke of genius. It was a stroke of ignorant stupidity.


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Filed under Basic Science, Carbon Dioxide Properties

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