Life exists everywhere though it may not be "life" as we know it...
http://forums.parascientifica.com/viewtopic.php?f=24&t=5094
Be Well.
David
SA: Life as we don't know it
It is definitely worth considering that other options do exist besides water and carbon. Alternative biochemists speculate that there are several atoms and solvents that could potentially spawn life.
Carbon is the molecular glue of life, just add water and you’ve got life. Well, it’s not that simple but it does give a good general idea. The carbon/water combo even worked so well that we have trouble imagining anything else. But it’s definitely worth considering that other combinations exist besides carbon/water. There are many speculations about atoms and compounds that could potentially spawn life, in this article I will cover two of these compounds.
The first and most plausible carbon replacement is silicon.
Silicon was first mentioned as a base for life the by the Brittish chemist James Emerson Reynolds in 1893, in his opening address to the British Association for the Advancement of Science, He stated that because of the heat stability of silicon compounds might allow life to exist in very high temperatures. Comparable life would be the thermopiles, microbes that can live in temperatures from 40 to 113 degrees centigrade. So to our eye’s these life forms would be extremophiles, living in places that would be too hostile for any carbon based life.
Silicon is a likely candidate because it is very common in the universe and lies directly under carbon in the periodic table of elements, meaning that it shares much of it’s basic chemistry. For example carbon can form Methane(CH4) and Silicon can form Siliane(SIH4). Both elements can also form long chains, or polymers, which in fact are the building blocks of life. So theoretically silicone DNA could exist, since its stable enough.
There is tho, one possibly fatal characteristic to silicone based life, namely the way it reacts with oxygen. Where carbon reacts to the gas carbon-dioxide(CO2) silicone becomes Silicone-dioxide(SiO2) , a solid substance. So where CO2 is easily removed from the body SIO2 is not. Disposing of such a substance would pose a major respiratory challenge.
Silicone life is often depicted as a living rock or crystal, for example H. G. Wells wrote:
One is startled towards fantastic imaginings by such a suggestion: visions of silicon-aluminium organisms – why not silicon-aluminium men at once? – wandering through an atmosphere of gaseous sulphur, let us say, by the shores of a sea of liquid iron some thousand degrees or so above the temperature of a blast furnace.
As the silicone based life forms are nothing like us they still share one crucial factor, they are dependant of water for their biological processes. But the next possible life forms are not.
These life forms would go by the name of ammonia-based life.
This possibility was first suggested in 1954 by J. B. S. Haldane, speaking at the Symposium on the Origin of Life. He suggested that water could be replaced as a solvent by liquid ammonia(NH3).
Part of his observation was based on the behavior of ammonia, which behaves very similar to water only in lower temperatures, for example methanol( CH3OH) and it’s ammonia counterpart, methylamine( CH3NH2).
In fact ammonia can replace water in nearly all compounds found in terrestrial life. Making it hardly inferior to water. In fact there are probably as many different possibilities in carbon-ammonia as in carbon-water systems.
This suggests that life on ammonia-rich worlds such as gas giants (e.g. Jupiter) would be very possible without even a drop of water on the whole planet.
Liquid ammonia does have some striking chemical similarities with water. It is intact even better in dissolving organic substances then water. The main objection is that the liquid range of ammonia is -44 degrees centigrade and that that is too low for any life to thrive. This true but the liquid range is specified by the pressure of the planet which on earth is 1atm but for example on Jupiter or Venus where the pressure is 60atm the boiling point is ammonia becomes 98 degrees centigrade instead of minus -33 giving it a liquid range of 175 degrees meaning that ammonia based life doesn’t need to be low-temperature life at all!
A downside to ammonia based life is the way that its dissociates, or lets molecules fall apart into positive and negative ions. This prosess is crucial for acid-base reactions. In ammonia the positive ions would be the NH+ ion, being a very strong acid and deadly to life as we know it. But scientists do suggest that ammonia-based life forms may use other salts to regulate their functions than we do.
Also there is the problem of the density of ammonia, being almost identical to water it has still one flaw that pose a major restriction to the life, namely it’s solid form does not float on the liquid form like in water. In fact water is the only substance known to man where the solid is less dense then the liquid. The reason that this is a major problem is because this would mean that any ammonia-ice that would form would sink to the bottom of the liquid, flattening all life. Ice is also a good insulator, so while floating it keeps the water beneath at a constant temperature making is virtually impossible to freeze all the water. But when the ice sinks then it loses all its isolative properties and allows the water to freeze leaving no place for the life to evolve.
This would restrict the life to a planet where the temperatures are well above the ammonia freezing point for it to be a potential candidate for a water replacement.
Regarding these facts ammonia-based life would have the largest chance of forming and surviving on a hot planet with high pressure. If we combine it with silicone-based life then the chances of its forming would grow because silicone works well at high temperatures. Also the biological properties of these two substances would allow for an even more efficient way of photosynthesis and dissimilation.
Instead of O2 these life forms would breath H2, this seems catastrophic because hydrogen is very flammable but this is only the case in an O2 rich environment, if the atmosphere is actually mainly H2 it is in fact very stable. These life forms would thrive on gas giants like Venus and Jupiter
In this article we have only covered two of the large number of combinations and this leaves us with but one question; Are we looking in the right places? The SETI program specifically searches for earth like planets with water and oxygen and completely ignore all other possibilities . With the gigantic number of planets and a with different compounds, pressure and atmospheres it is very possible that other forms of life have evolved where carbon-based life would not stand a chance.
It’s even not beyond the realm of possibility that our first encounter with alien life will not be a carbon-based life form.
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