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Life in the Universe – Astrobiology


Studies into the origin and the evolution of life on earth, coupled with the discoveries in the terrestrial biosphere which ranges from extremophilic microbes to the evolution of intelligence has played a crucial role in the thoughts and prospects of life in areas of the cosmos (Chyba & Hand, 2005). This paper, therefore, is a discussion of the possibility of life elsewhere other than on earth in the universe. This discussion will be done by looking into the various ways through which science searches for extraterrestrial life, the conceptualization of life with respect to the universe, the universe that can support life, the habitable zones of the galaxy based on current science, and then make a conclusion.

Search for and the conceptualization of life

According to Mix (2009) and Chyba & Hand (2005), there are three ways through which science is used for the search of extraterrestrial life. These are in situ searches done within the solar system, spectral examination for the chemicals of life within planetary atmospheres, and the search for evidence of extraterrestrial technology. Ideally, and for these searches to be successful, they have to be done within the confines of an agreed and definite comprehension of life in the universe. However, and given that science doesn’t have evidence of life or how and what life is or ought to be in within the confines of space, such a ‘guide’ is not available.

As a result, scientists have to rely on ‘life as we know it’ (Chyba & Hand, 2005), in the searches for life within the universe. Based on ‘life as we know it’ the concept underlying herein is that life is based on liquid water, a combination of elements referred to as biogenic, and a source of free usable energy (D. J. Des & Walter, 1999; Chyba & Hand, 2005). The common biogenic element for life is carbon. Given that carbon and usable energy are common, but not ubiquitous, through the entire solar system, but liquid water appeared, in some time to be only limited to the earth, the search for life within the universe came to be the search for liquid water. Based on ‘life as we know it’, liquid water is an absolute requirement for life on earth, which explains NASA’s “follow the water” slogan for the Mars exploration program (Allamandola, 2013; Shostak, Bennett & Jakosky, 2007).

The need for liquid water is based on the requirement for an internal medium through which life-support process, for example dissolving molecules and chemical reactions, may occur. Based on the ability of water to form hydrogen bonds with polar solutes, water is referred to as the universal solvent (LoPresto, 2013). Nevertheless, alternatives do exist like liquid ammonia, for it’s possible to build bio-molecules with ammonia as the solvent (Allamandola, 2013). Even though most polar solvents are stable liquids in temperatures colder than water, which slows down biochemical reactions given the dependence of chemicals reactions with temperature, in high pressure as in Jovian planets, it’s possible for ammonia to remain in liquid form up to critical temperatures (Allamandola, 2013).

Universe compatible with life

The idea of life in the universe is furthered by the fact that extraterrestrial biology of the universe beyond the earth is in various important aspects similar to the experience on earth. This, however, has not been the case and in particular, Aristotle presented a radical dichotomy between the earth and the heavens with his reasoning being founded on the observation that objects in the terrestrial space, objects followed a straight line towards or away from the center of the universe. As a result, Aristotle argued the earth must be spherical, which is in line with observations, and centered on the center of the universe. However, objects in the heavens move in circles about the earth and thus, they obey different laws physically. As a result, such objects are made not only of four elements but five, with quintessence being the fifth (Shostak et al., 2007). However, Newton has demonstrated that the same laws apply t the heavens as on earth.

Despite the earlier confusions, and the insufficient knowledge of the universe in modern science, it is inarguable that the universe appears to be remarkably fine-tuned for support of life as we know it (Chyba & Hand, 2005). The anthropic principle can at times be used to support this fact. One of these principles argues that the universe is designed in a way that it should support observers at some stage (Chyba & Hand, 2005). However, and given that this argument is based on the observer bias, it is challenged by the argument that, probably the earth occupies a privileged place in terms of supporting life as we know it. Nevertheless, this is challenged by the Copernican principle that the earth occupies no privileged position in the universe.

The habitable zone of the galaxy

Both the physical constant values and laws of the terrestrial zone could be compatible with intelligent life however, it could be that most of the areas within the galaxy that have been thought to be habitable and capable of supporting intelligent life have turned out to be not so. This as lead to the developed of the ‘belt of life’ idea, which argues that there is an area in the galaxy where intelligent life can be found (Chyba & Hand, 2005). This area has been referred to as the Galactic Habitable Zone (GHZ) and this idea holds that, outside this area, complex life would be unlikely and have no evolution change.

The three key parameters in the definition of GHZ are metallicity, the closed frequency of supernovae, and stellar age (Chyba & Hand, 2005). The metallicity of a parent star is crucial as it determines whether there is a formation of a solar system. Stellar metallicity is directly proportional to the density of stars which increases towards the center of the galaxy. Thus, the habitability of a solar system increases with decreasing galactic radius. Supernovae appear to impact on the habitability of planets within ˜10 parsecs of the event (Chyba & Hand, 2005; Mix, 2009). Based on these aspects, it is argued that about 10% of stars formed within the galaxy have the GHZ.


Three ways are available for searching extraterrestrial life; in situ searches done within the solar system, spectral examination for the chemicals of life within planetary atmospheres, and the search for evidence of extraterrestrial technology. Given that science doesn’t have evidence of life or how and what life is or ought to be within the confines of space, scientists have to rely on ‘life as we know it’ on earth. Liquid water has predominated searches for life in space given it’s a major requirement for the sustenance of life-supporting processes. To refine such searches, scientists have narrowed down to universes habitable of life and galactic habitable zones.


Allamandola, L. J. (2013). Life and the Universe: From Astrochemistry to Astrobiology. NASA Ames Research Center, Moffett Field CA.

Chyba, C. F., & Hand, K. P. (2005). ASTROBIOLOGY: The Study of the Living Universe. Annual Review Of Astronomy & Astrophysics43(1), 31-74. doi:10.1146/annurev.astro.43.051804.102202

J. Des, M., & Walter, M. R. (1999). Astrobiology: Exploring the Origins, Evolution, and Distribution of Life in the Universe.Annual Review of Ecology and Systematics, 397.

LoPresto, M. (2013). Life in the Universe: An Interdisciplinary Seminar Course. Journal of College Science Teaching, 42(5), 14-19.

Mix, L. J. (2009). Life in Space: Astrobiology for Everyone. Cambridge, Mass: Harvard University Press.

Shostak, S., Bennett, J., & Jakosky, B. (2007). Life in the Universe. University of Colorado, SETI Institute.

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