Problem Set 1
The Search for Life
For millions of years, man has looked to the sky in wonder and the question has always been asked, “Are we alone or is there life out there on another planet?” Investigation into this very question is essential in the continuation of the development of the human race. The discovery of life on another planet could answer many difficult questions that we are faced with, such as, how did life on Earth begin? How did we evolve to be where we are today? It may also tell us where we could be in the future as well as provide the opportunity for many great advances in medicine, the economy and technology, not to mention science.
A well-known theory of how life began on Earth is known as the Primordial Soup Theory. This theorises that chemicals found on earth mixed with energy (possibly lightning) created amino acids, commonly referred to as the building blocks of proteins (Premordial Soup Theory, (n.d.)). These then were able to form into unicellular organisms, which over time, evolved into the species recognisable today.
Firstly, what is defined as life? According to many textbooks, reports and scientists, there are a number of things that make up living organisms and are in common across all living things. Living organisms possesses the ability to utilise energy from the environment around it for its own use (Astrobiology Magazine, 2007). This can be done in various different ways, plants use a process called photosynthesis to absorb light energy from the sun through chlorophyll molecules and give the plant energy to convert CO2 into glucose and O2 (Reece, et al., 2011). Animals obtain energy from other organisms such as plants and smaller organisms, which allow many chemical and organic processes within the body to continue, keeping the organism alive.
However according to Professor Cleland of the University of Colorado, life on earth is just one example of life and therefore cannot be used to make a valid definition of ‘life’ (Cleland, (n.d.)). This poses many problems when it comes to space exploration. On Earth, life requires carbon as it is found in many of the chemicals and substances that make up living organisms (Reece, et al., 2011). This is due to the elements structure, which allows it to bond with many other atoms, creating very complex and unique molecules (Reece, et al., 2011).
Water, H2O, has been coined as ‘the molecule that supports all life’. Cells are 70 – 95% made of water so already it is clear that water is essential for life as we know it, to exist (Reece, et al., 2011). The properties of water are also incredibly important to the existence of life on earth. Water is exposed to the forces of hydrogen bonding due to its bent shape and thus its electronegativity allowing for hydrogen bonds to form. This hydrogen bonding allows water molecules to be very cohesive. This is one very important properties of water which allows life on Earth as it allows water to travel against gravity through thousands of water-conducting cells in plants, from the roots to the leaves. The molecule bonds to the cell wall, while still maintaining hydrogen bonds between other water molecules, keeping the substance together (Reece, et al., 2011).
Water also helps to moderate the air temperature as it absorbs heat from the atmosphere around it and then releases the heat when the air is cooler. This process does not significantly change the overall temperature of the water due to its specific heat (Reece, et al., 2011). This means that marine life on Earth live favourable conditions, as the temperature is kept very stable. Another property of water is that it is much less dense as a solid than a liquid (ice floats). This is due to hydrogen bonding and when water temperatures reach 0°C the water molecules freeze into a lattice structure allowing for more space between the molecules than when water is in its liquid form and thus being less dense.
It is for these various reasons the search for life in the universe usually begins with the search for water. Of course, there are other indicators, which can give signs of life, which can be viewed here from Earth. Firstly the size of a planet is important as it determines the level of gravity that is forced upon the planet. A larger planet will exert more gravity and therefore an atmosphere can be formed which provides protection from radiation coming from the sun. As well as this, the likelihood of liquid water being present is much higher as it does not evaporate into space and life may form on the planet’s surface. However smaller planets with very little atmosphere, such as Mars, may exhibit life underground where they are shielded from this radiation and water may be present.
The Goldilocks Zone is also a very important characteristic of a planet to consider. The Goldilocks Zone is defined as a zone in space, which allows for liquid water to exist. This means that the planet is neither to hot, nor too cold. Earth is found in the Goldilocks Zone and clearly supports life. Therefore it is predicted that for life to form on another planet, the planet must be in a Goldilocks Zone. However this is only one component, the planet must be solid, and as stated before, a suitable size and of course show evidence of water.
In conclusion, life as we know it requires many certain aspects for its survival on other planets. It is recommended that the search should begin on solid planets within the Goldilocks Zone in other galaxies however the scientists must take into account the size of the planet. If a small planet is seen as being suitable for life, investigations must take place underground. Water will be the first marker that life may exist on the planet, particularly liquid water.
Bibliography
Astrobiology Magazine. (2007, November 30). Life's Working Definition: Does It Work? (S. Watanabe, Editor, & Astrobiology Magazine) Retrieved February 28, 2014, from NASA: http://www.nasa.gov/vision/universe/starsgalaxies/life%27s_working_definition.html
Cleland, C. E. ((n.d.)). Life without Definitions. Retrieved February 28, 2014, from http://abrc.montana.edu/cls/CarolCleland.pdf
Premordial Soup Theory. ((n.d.)). Retrieved February 28, 2014, from Leiwen's Origin of Life: http://leiwenwu.tripod.com/primordials.htm
Reece, J., Meyers, N., Urry, L., Cain, M., Wasserman, S., Minorsky, P., et al. (2011). Campbell Biology (9th Edition ed.). (B. Wilbur, Ed.) Australia: Pearson Australia Group Pty Ltd.
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