Carbon Dioxide, a Simple but Miracle Molecule

Essay code: B10/C4≠≠

Carbon Dioxide, a Simple but Miracle Molecule

Carbon dioxide is an essential constituentof 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 aboutits current level in the atmosphere that relates to global warming. However, without carbon dioxide, the Earth will not have the right temperature todevelop 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 260years ago by a Scottish chemist named Joseph Black (6). On June 11, 1754 while experimenting with limestone,he discovereda 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)). Thismoleculehas 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

Thisweak 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+ + HCO3-

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 dissolveit by turning into soluble Ca2+ cations.This reaction helps reduce the amount of carbon dioxide in the early Earth’sclimate.

CaCO3 + H2CO3 -> Ca2+ + 2 HCO3-

Secondly, 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 tothe appearances of many possible lives on the planet. About two billion years ago, Cyanobacteria appeared on Earth and started photosynthesis. This organism tookthe 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 gasfor 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 inthe 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 radiationaretrapped by the greenhouse gases and thenare reflectedor re-emittedback 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 factorto 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 densityis 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 storedinthedeep 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 calciumand bicarbonate ions that run off into river and then back to the ocean.In the ocean, the calcium and bicarbonate ionswill 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 Venusdisappeared. 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 losesmost of its atmosphere to the solar wind and this consequentlyleads 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 historyof 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 eruptionsand was emitted into the atmosphere. Then, itdissolved in water to dissolveminerals on the Earth’s crust. This process helpedreduce 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 dioxidesare 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