I dug this up from somthing I cobbled together earlier this year. Once I started finding out about water, it appeared more and more like it is the only substance capable of supporting life. Nothing else will do.<Ol> <Li>Simple structure <Li>Low molecular weight <Li>Polar molecule disolves polar solutes - The water molecule is an isosceles 105 degree triangle. The hydrogen bonding gives the molecule both ionized and covalent states for structural integrity. With its unusually high dipole moment, water is sometimes called a universal solvent because it surrounds each solute ion with a polar shell, shielding them from the electrostatic forces of other ions. <Li>Water has the highest surface tension of any liquid except mercury. <Li>Water's cohesion from hydrogen binding each of four neighboring water moleculesmost of the time. <Li>Highest specific heat of any liquid moderates temperature fluctuations, increasing usefullness as a habitat. Aids in an organism's homeostasis. <Li>Highest heat of fusion and vaporization moderates environments, again providing a suitable habitat. <Li>Water remains liquid over a wider temperature range than most other substances. Since metabolism requires a liquid environment for the exchange of ions, this gives life a better shot than other solvents. <Li>At the phase change of heat of fusion at STP, water is one of the only substances that is less dense as a solid than as a liquid. This unusual property insulates water from freezing solid when the temperature temporarily drops below the freezing point, such as our winter. Without this property freezing would go clear to the bottom of the environment, an environment hostile to life. The ice on the surface insulates the water undneath from further freezing. <Li>The metabolic characteristics of a body of water are affected by density changes. Since water is densist at 4 decress Celsius, warmer layers lower down create a density gradient that lifeforms take advantage of for life processes. <Li>Water is one of the very few inorganic liquids. <Li>Water is the only solution that occurs naturally as a solid, liquid, and a gas, sometimes in the same environment. <Li>Water is one on the only substances to expand when it freezes at STP. <Li>Water has the greatest thermal conductivity of any liquid for life processes except for mercury. <Li>Water has a high transparency which allows life driving sunlight to penetrate to greater depths, increasing the size of the habitat. <Li>Water resists compression. <Li>Water is highly mobile throughout the biosphere. <Li>Water is an efficient transmissoin medium for sound, which some lifeforms take advantage of. <Li>Water has a very low vaporization pressure <Li>Water joins organic molecules and is given off when the catabolize. </Ol>
what about duodium(sp?) or tritium(sp?), surely more dense lifeforms can survive in them like a nitrogen based lifeform
Ok, what about them? Give me one of them that has a large number of these attributes: simple structure and thereby low molecular weight, an excellent polar solvent, high specific heat, high cohesion, high surface tension, high specific heat, high transparency, high mobility, wide range between heat of fusion and heat of vaporization, decreases density after heat of fusion, efficiently transmits sound, low vaporization pressure, and links organic molecules during catabolism and anabolism? Oh, and this tritium must of course have a few such properties of its own as well since it will not have all that water has. Then you can say it does as well as water.
vslayer, what you may be missing are the implications of each of these attributes. Consider just two: The water molecule is an isosceles 105 degree triangle. This, in combination with charge imbalances within the silica tetrahdra and alumina octahedra of clay minerals, leads to the hydrophilic properties of clays. These may well have been responsible for the emergence of self replicating molecules (i.e. life). Cairns-Smith, a chemist at the University of Glasgow, proposed this in 1966. A simple review of the concept, with further links, may be found here. http://originoflife.net/crystals/ At the phase change of heat of fusion at STP, water is one of the only substances that is less dense as a solid than as a liquid. Without this property Earth and life would never have recovered from Snowball Earth episodes. One could write a book on the implications.
If I remember correctly, Deuterated water actually reacts ever so slightly more slowly than normal water. Its not a matter of density, what matters with water and life is reactivity and energy gradients.
