Does Water Really Have To Mean Life?

bigweenie asks: "With the frozen mud on the Moon's pole and the springlike seepage of water out of the lowest valley walls of Valles Marinaris, everyone seems to have a heightened urgency and hope to find life on the Red Planet (past or current). My question is, what is the link between water and life? What exactly is the biochemical, environmental, evolutionary, physiological and, God forbid, logical evidence that water is suggestive of life? All the Mars 'search for life' experts have spent the last 20 years proving life can exist anywhere under almost any conditions; no oxygen, no H2O, etc. I wish to know the real hard data and analyses that defines the relationship between water and life, and how optimistic should we be about life on Mars just because it is there in abundance." Assuming that other life exists, it is possibility of extra-terrestrial life similar to earth-life that provide a good deal of momentum to our collective interest. Since water is an absolute necessity for Earth based life, it is assumed that the presence of it elsewhere may mean the presence of lifeforms closer to what we know and understand.

Comments

Water for Life

[fremen]

Water has quite a few properties that make it REALLY useful for life.

The thing about water is that it has a tremendous polarity associated with it. The oxygen atom tends to be electronegative, pulling the electrons away from the hydrogen atoms. Why is this important? The polarity of the molecule makes water an EXCELLENT solvent, meaning that things dissolve in it easily. This means that water can transport atoms between cells more efficiently.

Perhaps the most important effect of this polarity is the hydrophobic aspect of water. The polarity of the water molecules make it adhere to other water molecules when in the presence of non-polar molecules, such as organic chemicles (which is why oil and water do not mix). This is CRITICAL for the formation of cell membranes. Cell's have a layer of lipids on the outside that are held together by the hydrophobic pressure of water molecules.

Another benefit of water's polarity is that it floats when frozen. This keeps it from accumulating on an ocean floor where it can never melt, taking valuable things that are dissolved within the molecules with it. Since ice floats, it can theoretically melt and refreeze in a fairly constant pattern, assuming the planet is warm enough. If water didn't float, we would have never left the first ice age!

I would think that any highly polar molecule would work similarly to water, but very few exist. The biggest problem is that most of them are normally either gasseous or solid. Some are too complex to expect them to normally form in large enough quantities to support life. I'll grant that there is no way we could know everything about life and the universe, but it's a safe bet to guess that life will be involved with water.

For more information, go to Google and search for 'water biochemistry'. Enjoy.

Alternative Forms of life

[The Iconoclast]

Ok, now for some alternative Biochemistries!!

-Silicon Based Life: This would be based upon silicon instead of carbon. We (and evrything else living on earth) are based on Carbon. Why? Because carbon just so happens to have a valence shell of 4 electrons meaning that it can accept 4 more electrons or donate 4 more electrons. This leads carbon being able to form all sorts of nifty compounds such as rings (benzene, sugars) and chains (hydrocarbons, starches, proteins). Silicon also has 4 valence electrons, so theoretically, it could form all sorts of nifty compounds, too. However, because of some quantum chemistry issues, silicon does not perform quite as well as carbon in forming chains and rings. Silicon is much better for forming nifty crystals as we all know :-).

-Sulfur breating life: We breathe oxygen. Why? Because in order to release the energy stored in fats, sugars, and protiens, they must be oxidized (burned) and we use oxygen to do that. Even plants use oxygen (in small amounts) to metabolize the sugars they produce from photosynthesis. There are forms of life on Earth that do not use oxygen at all, these are chemotrophs (chemical eaters) who live in volcanic vents on the ocean floor and such. They tend to combine and split different chemicals to release the requisite energy for life. Some of them use Sulfur as an oxidizer instead of oxygen. Theoretically Carbon Monoxide, ozone, or even a halide (Chlorine, florine, bromine) could be used.

-Ammonia bathed life: Water is incredibly important for us, because as mentioned earlier, it is an excellent solvent for all the chemical reactions that make up life to occur. Also as mentioned earlier, there are not too many simple molecules that are liquid and polarized at decent temperatures. Water is one of them. Ammonia (NH3) is another. However, ammonia is slightly less polarized than H20 and therefore it doen't quite work as well as water. Other things like like hydrochloric acid might work, but it is a bit strong of a solvent :-) Things like benzene and hydrocarbons and liquid chlorine are not polarized so they really wouldn't work.

As for other things (energy-based life, etc.), although we cerainly do not know enough to completely rule out this type of life, chances are that any based on vastly different chemistry from our own (or NOT chemistry) would find it difficult to communicate with us.

By the way, I am a physics student, so this is a small step down for me (just kidding :-). I did watch lots of Nova and stuff when I was younger.

A wealthy eccentric who marches to the beat of a different drum. But you may call me "Noodle Noggin."