Why is water essential to life

Sophie Balis-Harris                                                                                                12/1/09

                                                Why is water essential to life? 

             Nearly two months ago a satellite called Lcross crashed into the moon’s surface as part of a NASA experiment attempting to find water on the moon. The Lcross scientists hoped that locating and studying water on the moon will significantly aid in our understanding of the environment and conditions of the moon (1). The experiment was successful, scientists found over 2 dozen gallons of water after the impact, and some scientists believe that this discovery is "painting a really surprising new picture of the Moon.” (1) This is not the first time that water has been sought after (and found) in outer space, it has been long established that water is present on the planet Mars. These discoveries of the presence of water are not only considered to be important because it helps scientists understand the history of the planet but also because the presence of water indicates the presence of life. Water is viewed as one of the most essential elements to life, and the molecular structure of water is almost universally known. However I do not understand what makes water the ultimate medium of life, and why, despite all of our technology we have not been able to find a similar replacement for water? 

         Water is composed of two hydrogen atoms and one oxygen atom linked by a covalent bond, which are polar. Oxygen atoms in a water molecule have six valence electrons, two of which are shared with hydrogen atoms while four electrons remain unshared (2). Because of the polarity within the water molecule, hydrogen atoms are attracted to areas with high electron density which causes them to form a weak bond with the unshared oxygen electrons from neighboring water molecules (2). These hydrogen bonds are constantly breaking apart, causing the water molecules to perpetually re-form themselves (2). This means that water molecules are extremely interdependent, especially in the liquid and solid form, which seems to create qualities unique to water. 

        One of the most commonly known anomalies of water is the fact that ice floats, meaning the solid form of water is less dense than the liquid form- something that is uncommon in most chemical compounds (2). This occurs in water because of frequency of intermolecular bonding,   water molecules in a solid state are arranged in a lattice shape consisting of each oxygen atom sharing electrons with four hydrogen atoms (2). In the liquid state water molecules are far less ordered and tend to be clumped together. The lattice shape creates more open space between molecules than in the liquid state, which in turn causes water to both expand and become less dense in its solid state (2). 

        Another widely known characteristic of water is its high boiling and freezing points. Most similar compounds have boiling and freezing points that are considerably lower than water’s (2). This means that water has a much wider liquid range than similar substances. This also occurs due to molecular interdependence among water molecules, as hydrogen atoms in water molecules can bond more frequently than molecules in most hydrogen compounds. Usually when liquids have a high level of intermolecular attraction, they also have a high boiling point, this is because it requires much more energy to break the hydrogen bonds than in other compounds (3). Additionally, the high level of attraction between water molecules causes water to have surface tension. 

        These qualities are not merely interesting oddities, they are extremely important to maintaining the structure of the Earth. Our weather system is dependent upon the hydrologic cycle, in which water in the liquid state on earth evaporates and enters the atmosphere in the form of water vapor, then condenses back into liquid state and becomes precipitation which is distributed across the earth in different ways and re starts the process (4). However the hydrologic cycle would not be nearly as stable as it currently is without the high boiling and freezing points of water, small shifts in temperature (that occur when the sun rises/sets, etc) would create major changes in the hydrologic cycle (5). 

            The fact that ice floats is extremely important in maintaining ocean life. Currently when bodies of water freeze in the winter it creates a layer of ice on the surface, however if water became denser in its solid state the ice would simply sink to the bottom. Were ice to sink to the bottom of a body of water, it would cause more of the water to become cold and freeze and make aquatic life almost, if not entirely impossible in regions where bodies of water freeze over in the winter (2). 

            Not to sound trite, but perhaps water is considered to be the ultimate medium of life because 60% of the human body and 70% of planet earth is composed of water. The way that life is structured within our bodies, and the earth living without water would be impossible. It is the viscosity of water that allows the blood to flow through our veins, and nutrients to travel through the roots of a plant (6). Water provides sustatinability to life, without it our environment would be nearly constantly changing and most likely always hostile. We have no way of compreheding life without water, nor has there been any reason to believe that life can exist without water, and as we move forward in exploring new environments scientists's only recourse is to rely upon the symbols of life we aware of. The scientists who worked on the Lcross experiments hope that the water found on the moon could possibly support settlers on the moon, as it could be used as drinking water, but also split apart and converted for both rocket fuel and air to breathe (1). In this situation water is not representative of life, or living entities themselves but instead a means through which life can be sustained. 
Works Cited

1) http://www.nytimes.com/2009/09/29/science/space/29mars.html?_r=1&ref=space

2) http://www.britannica.com/EBchecked/topic/636754/water

3)http://www.elmhurst.edu/~chm/vchembook/163boilingpt.html

4)http://www.pbs.org/wgbh/nova/origins/essential.html

5)http://www.britannica.com/EBchecked/topic/278858/hydrologic-cycle

6)http://ga.water.usgs.gov/edu/capillaryaction.html