Essay code: B10/C4
Carbon Dioxide, a Simple but Miracle Molecule
Carbon dioxide is an essential constituent of the Earth atmosphere. If oxygen atom is
considered to be the most important element required for the sustainability of life, then its
carbonic form (carbon dioxide) should be 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 increasing
concentration in the atmosphere that may relates to global warming. However, without carbon
dioxide, the Earth could not provide a suitable environment to develop and support life.
Throughout the history, carbon dioxide plays different roles in regulation of the Earth climate
though different methods. Plus, photosynthesis also requires carbon dioxide as one of the
reactant. Therefore, it is very important to learn about the roles of carbon dioxide in the
atmosphere in order kto have better understandings about the Earth climate and what can be
done to protect it.
Carbon dioxide is discovered in the seventeenth century by a Scottish chemist named
Joseph Black (6). On June 11, 1754, upon his experiment with lime stone he discovered a gas
which he called “fixed air” turned out to be carbon dioxide molecules. His wonderful discovery
of this molecule enhanced scientists’ knowledge about the Earth’s atmosphere at that time.
Carbon dioxide is a naturally occurring molecule its structure is one carbon formed double bond
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. First of all, this molecule in gas state can dissolve minerals on Earth. Through
acid/base reaction, the carbon dioxide gas dissolves in water and produce carbonic acid (Equation
1). Part of the increasing concentration of CO2 were absorbed by the ocean and formed carbonic
acid, which increased the acidic of the ocean. Many studies find some sea creatures were
influenced by the increasing CO2. More 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 cations Ca2+. This reaction help reduce the amount of carbon dioxide in the
early Earth climate (Equation 2).
H2CO3  H+ + HCO3- (Equation 1)
CaCO3 + H2CO3 -> Ca2+ + 2 HCO3- (Equation 2)
Secondly, through the redox reaction of carbon dioxide and water, a new molecule was
introduced to Earth’s early atmosphere. This process is also known as photosynthesis and it may
contribute to the major step for the appearances of many possible lives on the planet (Equation
3). About two billion years ago, Cyanobacteria appeared on Earth and have the ability to do
photosynthesis. This organism absorbs carbon dioxide and water and react in the presence of
light to produce oxygen. Another example is methanogenesis (Equation 4), a process of redox
reaction that gives rise to methane and produce energy by reducing carbon dioxide using
hydrogen gas (7). Methane is one of the most significant greenhouse gases because it provides
an ultraviolet shield for the earth from the sun and regulates the earth climate (7).
2nH2O + 2nCO2 + light -> 2(CH2O)n + 2nO2 (Equation 3)
CO2 + 4H2 -> CH4 + 2H2O (Equation 4)
Carbon dioxide together with methane, is a very important greenhouse gas of the Earth
atmosphere. These greenhouse gases act as a bubble shield to protect the Earth from the
incoming solar radiation (5). Ultraviolet in the run rays have high energy and can destroy living
tissues and form gene mutation if not blocked. The greenhouse gases like carbon dioxide,
methane, and water vapor absorb the ultraviolet radiation in sun rays; solar radiations with lower
energies are 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 helps keep 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 sun light.
This process takes out the carbon dioxide in the atmosphere by converting it into organic carbons
and stores them in the deep ocean. In addition, the maximum density of the seawater is about 4
degree Celsius; hence, top layer cold water will sink underneath the warmer water and with the
dissolved carbon dioxide. Due to these processes, the carbon dioxide is stored in the deep ocean
until upwelling occurs, which will reintroduce the 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 in Equation 1. Carbonic acid will once again react with
limestone to produce calcium and bicarbonate ions that will run off into river and then back to
the ocean. In the ocean, the calcium and bicarbonate ions will be further precipitated by the 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, it is essential to bring
up the Earth neighbor planets: Venus and Mars. Both planets used to have water molecules but
unlike Earth they went a different path. 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 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 will
disappeared. Carbon dioxide in the atmosphere of Venus does not have water to dissolve with,
since all the water molecules are in gas state. So the amount of carbon dioxide in Venus
atmosphere rocketed (4). Ultimately, Venus has too much carbon dioxide, no liquid water, and
the temperature is too hot to support live.
Mars is about 1/3 the size of the Earth and is further away from the Sun than the Earth,
therefore, Mars has a lower temperature than Earth (3). Also, the activity of volcano on Mars is
decreasing, which leads to less amount of carbon dioxide introducing into the atmosphere. The
temperature on Mars will continues to decrease until the core of Mars loses its ability to create
magnetic field (3). Without the magnetic field, Mars will loses most of its atmosphere to the solar
wind since the protection from the magnetic field no long exist and this consequently leads to a
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 conclusion is 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 due to the appropriate distance from the Sun. In the early
history of Earth, the iron with high density sank into 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 first formed from the
volcano eruptions and then rose into the atmosphere. Then, it was absorbed by the seawater
and later was able to dissolve minerals on the Earth’s crust. The absorption by the seawater
greatly reduced 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 which had been trapped in the mineral phases back into the
atmosphere and that process helped to keep the Earth from getting too cold.
The conclusion is that carbon dioxide can be considered as one of important molecules on
Earth. Many People need to fully understand the roles of carbon dioxide in the atmosphere
regulation in order to have a correct view of how this molecule impact Earth. 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 the issue
of global warming would became global cooling. People will have to deal with that 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. Seawater would absorb a big part of the carbon dioxide in the
atmosphere and it will cause the low PH level and affect many sea organisms. The water on Earth
maybe 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.
(Relating CO2 with Mars and Venus is somewhat a fresh topic. There are many more negative
impact of high concentration of CO2 on Earth can be included. Overall a great essay)
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