Essay code: B10/C4≠≠
Carbon Dioxide, a Simple but Miracle Molecule
Carbon dioxide is an essential constituent of the Earth atmosphere. If oxygen is
considered to be the most important element required for the sustainability of life, then its
carbonic form (carbon dioxide) is considered as a miracle molecule to the biosphere at the
planetary level, despite its tiny percent composition to the whole atmosphere (0.04 percent)
(1). When talking about carbon dioxide, most of people are usually concerned about its current
level in the atmosphere that relates to global warming. However, without carbon dioxide, the
Earth will not have the right temperature to develop and support live. Throughout the history,
carbon dioxide plays different roles in regulation of the Earth climate though different methods.
Plus, photosynthesis also requires carbon dioxide as a main ingredient. Therefore, it is very
important to learn about the roles of carbon dioxide in the atmosphere to have better
understandings about the Earth climate and how to protect it.
Carbon dioxide was discovered 260 years ago by a Scottish chemist named Joseph Black
(6). On June 11, 1754 while experimenting with limestone, he discovered a gas that he called
“fixed air”, which turned out to be carbon dioxide. His wonderful discovery of this molecule
enhanced scientists’ knowledge about the Earth’s atmosphere at that time. Carbon dioxide is a
naturally occurring molecule with one carbon bonded linearly with two oxygen atoms through
sharing of electrons (as shown in the picture below (2)). This molecule has polar property with
zero dipole moment.
The structure of carbon dioxide maybe simple, but it played many important roles in the
Earth circulation. Firstly, this gas molecule can dissolve minerals on Earth. Through acid/base
reaction, the carbon dioxide gas dissolves in water and produce carbonic acid.
H2O + CO2  H2CO3
This weak carbonic acid can lead to two different outcomes. In the first path, it usually
dissociates itself to create H+ ions and thus reduce the pH of the environment. With the
decreasing in pH, many subsequent reactions can occur.
H2CO3  H+ + HCO3More interestingly, the carbonic acid has the ability to dissolve minerals on the Earth’s crust.
For instance, it can react with limestone and can dissolve it by turning into soluble Ca2+ cations.
This reaction helps reduce the amount of carbon dioxide in the early Earth’s climate.
CaCO3 + H2CO3 -> Ca2+ + 2 HCO3Secondly, through the redox reaction of carbon dioxide and water, a new molecule was
introduced to Earth’s early atmosphere. This process is known as photosynthesis and it led to
the appearances of many possible lives on the planet. About two billion years ago,
Cyanobacteria appeared on Earth and started photosynthesis.
This organism took the
abundant carbon dioxide in the atmosphere and reacted it with water in the presence of light
to produce oxygen.
2nH2O + 2nCO2 + light -> 2(CH2O)n + 2nO2
Another example is methanogenesis, a process of redox reaction that gives rise to methane and
produce energy by reducing carbon dioxide using hydrogen gas (7). Methane is one the most
significant greenhouse gases because it provides an ultraviolet shield for the earth from the sun
and regulates the earth climate (7).
CO2 + 4H2 -> CH4 + 2H2O
Carbon dioxide, together with methane, is a very important greenhouse gas for the
Earth’s atmosphere. These greenhouse gases act as a bubble shield to protect the Earth from
the incoming solar radiation (5).
The greenhouse gases like carbon dioxide, methane, and water vapor absorb the
ultraviolet radiation in the sun’s rays; however, some of solar radiations are still able to pass
through the greenhouse gases shield and warm up the Earth surface (5). The Earth surface then
continually emits infrared radiation to the atmosphere and produce cooling effect. Some of this
infrared radiation are trapped by the greenhouse gases and then are reflected or re-emitted
back to Earth thus resulted in warming effect. This keeps the surface of the Earth warm at
nighttime when there is no incoming solar radiation (5).
The interaction of carbon dioxide in the atmosphere with the ocean is also a critical
factor to understand the carbon cycle. The phytoplankton in the ocean uses photosynthesis to
react carbon dioxide on the surface of the ocean with the water molecules in the presence of
sunlight. This process is taking out carbon dioxide in the atmosphere by converting it into
organic carbons and stores them in the deep ocean. In addition, the maximum density is about
4 degree Celsius; hence, this colder water will sink underneath the warmer water and take
carbon dioxide with it. Due to these processes, the carbon dioxide is stored in the deep ocean
until upwelling occurs, which will then reintroduce carbon dioxide back to the ocean surface.
The carbon dioxide in the atmosphere also interacts with the lithosphere. The silicate
weathering occurs when carbon dioxide in the atmosphere is dissolved in rain water, producing
carbonic acid with the same mechanism showed above. Carbonic acid will once again interact
with limestone on rocks to produce calcium and bicarbonate ions that run off into river and
then back to the ocean. In the ocean, the calcium and bicarbonate ions will be further
precipitated by sea organisms to create shells and skeletons. Therefore, carbon dioxide will
always be maintained and circulated within the atmosphere by the process of this carbon cycle.
To understand the roles of carbon dioxide in the earth atmosphere, let’s discuss the
Earth neighbor planets: Venus and Mars. Venus and Mars have starting off with the having of
water like Earth, but these three planets evolved differently and ended up with three different
outcomes. Venus is about the size of the Earth, but it is closer to the Sun (4). Therefore, the
temperature on Venus is extremely higher than Earth (462 °C; 863 °F). Consequently, the water
on Venus always evaporates into water vapor and therefore, sooner or later, the atmosphere of
Venus is covered with water vapor (4). The temperature on Venus continued increasing
because the heat on Venus cannot escape. As a result, all of the water on Venus disappeared.
Venus’s atmosphere does not have water for carbon dioxide to dissolve into so the amount of
carbon dioxide in Venus atmosphere rocketed (4). Venus has too much carbon dioxide, no
water, and the temperature is too hot to be able to support live.
Mars is about 1/3 of the Earth and further away from the Sun than the Earth, therefore,
Mars has lower temperature than Earth (3). Also, the activity of volcano is decreasing, which
leads to less carbon dioxide introducing into the atmosphere. The temperature on Mars
continues to decrease until the core of Mars loses its ability to create magnetic field (3).
Without the magnetic field, Mars loses most of its atmosphere to the solar wind and this
consequently leads to thinner atmosphere on Mars. The atmosphere on Mars extends further
than Earth because of the low gravitation force of Mars since Mars has a thinner atmosphere
than Earth (3). The carbon dioxide is frozen as dry ice and the temperature of Mars is too cold
to be able to support lives.
Unlike Venus and Mars, the Earth has just the right amount of carbon dioxide and the
temperature is not too hot or too cold. In the early history of Earth, the dense iron sank to the
core of the Earth with liquid outer core, which was known as the Iron Catastrophe. The
convicting of the liquid core had created a dynamo that generated the Earth’s magnetic field.
The magnetic field protected the Earth atmosphere from being blown away by the solar wind.
The carbon dioxide gas was formed from volcano eruptions and was emitted into the
atmosphere. Then, it dissolved in water to dissolve minerals on the Earth’s crust. This process
helped reduce the amount of carbon dioxide gas in the atmosphere and kept the temperature
of the Earth from getting too hot. The melted iron core led to volcano eruption that emits the
sunken carbon dioxide gas that had been trapped in the mineral phases back into the
atmosphere and helped keep the Earth from getting too cold.
As a result, carbon dioxide is considered to be one of important molecules on Earth. People
need to fully understand the roles of carbon dioxide in the atmosphere regulation. Due to
global warming issue, many people have had bad impressions about this molecule. If the all the
carbon dioxides are removed from the atmosphere, the temperature on the Earth will drop and
global warming maybe go away. However, people will have to deal with a new problem: the
temperature will be too cold to survive. On the other hand, if human keeps increasing the rate
of carbon dioxide emitted into the atmosphere, this will cause the temperature of this planet to
increase higher and higher. The water on Earth evaporates into water vapor phase just like
what happens on Venus. Thus, the temperature will get too hot for human to survive.
Therefore, it is very crucial for every one of us to not only prevent the rate of carbon dioxide
secreted from increasing but also maintain the proper amount of this gas so that we do not
have to deal with another Ice Age.
Work cite
(1) "Causes of Climate Change." Climate Science Investigations South Florida -. Nasa, n.d.
Web. 13 Feb. 2014.
(2) C.D. Keeling, R.B. Bacastow, A.E. Bainbridge, C.A. Ekdahl, P.R. Guenther, and L.S.
Waterman, (1976), Atmospheric carbon dioxide variations at Mauna Loa Observatory,
Hawaii, Tellus, vol. 28, 538-551
(3) Coffey, Jerry. "Atmosphere of Mars." Universe Today. N.p., 19 Dec. 2008. Web. 13 Feb.
2014.
(4) Coffey, Jerry. "Atmosphere of Venus." Universe Today. N.p., 7 May 2008. Web. 13 Feb.
2014.
(5) "Global Climate Change." Forest Forever. N.p., n.d. Web. 13 Feb. 2014.
(6) "On This Day – June 11 : The Scottish Chemist Joseph Black Discovered Carbon Dioxide
on This Day in 1754- Learn Chemistry." Learn Chemistry Enhancing Learning and
Teaching. Royal Society of Chemistry 2014, n.d. Web. 13 Feb. 2014.
(7) Thauer, R. K., “Biochemistry of Methanogenesis: a Tribute to Marjory Stephenson”,
Microbiology, 1998, Volume 144, pages 2377-2406