BBC Focus Magazine

[Isee]

Was thinking (as I was doing the dishes funny enough)
It is well known that water is necessary for life, as we know it to exist. I assume it is because it is most neutral liquid right?
If so, is it just most neutral from our point of reference? I mean there is nothign stopping life using acid or liquid methane right? Afterall Water is corrosive to certan things also, so it's just a frame of refernece and is arbitrary non? Or is water really so special that no other liquid can replace it?

I mean we successfully substitute all sorts of materials in industries and creations. And so far the nature has been able to do everythign we can with a lot more finesse...

Just pondering

[Liam Sheppard]

well extremophiles are able to live in conditions previously thought to be uninhabitable, so I imagine that life could evolve to exist using other chemicals other than oxygen and water.

It was thought that sunlight was needed to create life but that has since been disproved.

[Shadowwolf]

Probably related to us being carbon based life and carbon plays well with other elements like oxygen and hydrogen.

[...]

water is the main ingredient for the sustenance of life as we know it but there are other liquid solvents, as this is the main atribute of water for life, that could possibly take its place, i think it was carl sagan that theorised an ammonia base life back in the 70s

[M Paul Lloyd]

I think its the hydro-carbon element that favours water as our main 'fluid' but life may simply have evolved to take advantage of what was most abundant on the early Earth? Meanwhile on some other world with seas of ammonia Carl Sagan's alternative might, possibly have a cahnce, but I'm sure I recall someone pointing out that water has very special qualities that set it apart from other liquids, in as much as it expands as it freezes and as a solid floats in its own liquid state. If it didn't the Earthwould be a frozen ice covered ball.

[Flakkarin]

There are a lot of properties unique to water that actually makes it essential to life (on this planet at least). I don't know of another liquid that has as many of these properties that would make it suitable. A few of these properties are:
- High specific heat. Specific heat is the amount of energy required to change the temperature of a substance. Because water has a high specific heat, it can absorb large amounts of heat energy before it begins to get hot. It also means that water releases heat energy slowly when situations cause it to cool. Water's high specific heat allows for the moderation of the Earth's climate and helps organisms regulate their body temperature more effectively.
- Water conducts heat more easily than any liquid except mercury. This fact causes large bodies of liquid water like lakes and oceans to have essentially a uniform vertical temperature profile.
- Water molecules exist in liquid form over an important range of temperature from 0 - 100° Celsius. This range allows water molecules to exist as a liquid in most places on our planet. This is important due to water's important use as;
- A universal solvent. It is able to dissolve a large number of different chemical compounds. This feature also enables water to carry solvent nutrients in runoff, infiltration, groundwater flow, and living organisms.
- High surface tension. In other words, water is adhesive and elastic, and tends to aggregate in drops rather than spread out over a surface as a thin film. This phenomenon also causes water to stick to the sides of vertical structures despite gravity's downward pull. Water's high surface tension allows for the formation of water droplets and waves, allows plants to move water (and dissolved nutrients) from their roots to their leaves, and the movement of blood through tiny vessels in the bodies of some animals.
- High latent heat of evaporation gives resistance to dehydration and considerable evaporative cooling.
- Unique hydration properties towards biological molecules (particularly lipids, proteins and nucleic acids) that determine their three-dimensional structures, and hence their functions, in solution. This hydration forms gels that can reversibly undergo the gel-sol phase transitions that underlie many cellular mechanisms.
- Water ionizes and allows easy proton exchange between molecules, so contributing to the richness of the ionic interactions in biology.
- The density maximum at 4°C and low ice density means that all of a body of water (not just its surface) is close to 0°C before any freezing can occur. Also the freezing of rivers, lakes and oceans is from the top down, so insulating the water from further freezing and allowing rapid thawing, and density driven thermal convection causing seasonal mixing in deeper temperate waters.

(from http://www.physicalgeography.net/fundamentals/8a.html and http://www.ozh2o.com/h2phys.html)

[Shadowwolf]

There you go, water is one of those 'jack of all trades' chemicals.

Cheers Mrs Flakk

[M Paul Lloyd]

Yep, indeed as I said, or was going too.. .... I very much agree with the above.

[Isee]

Thanks Flakk, but are all thos equalities necessary for life?
I doubt it.
The qualities listed are certainly very welcome to organisms on earth, but i get the feeling we have the causality confused here. Organisms on earth have evolved to take advantage of these qualities. It is not qualities that allowed life. At least that's how i see it.

If the most abundant liquid on earth was sulfuric acid. Would we not still have trees, bugs and animals? just with very different properties and organs or would there be something fundamentally flawed with that?

[Flakkarin]

Some of the things in the list are obviously environmental, but others are biological, and I think this is why we can't use anything but water. Other liquids don't possess the properties necessary to internal functions - for example surface tension as a transport mechanism through the (strikingly different) bodies and modes of life of the plants and animals.
This one:

- Unique hydration properties towards biological molecules (particularly lipids, proteins and nucleic acids) that determine their three-dimensional structures, and hence their functions, in solution. This hydration forms gels that can reversibly undergo the gel-sol phase transitions that underlie many cellular mechanisms.

Could probably be expanded into very complex reasons why water is indispensable. Although I'm not an expert, if we take lipids an an example, cell walls rely on the properties of water:

Many molecules are hydro-phobic or -philic because of the strong polarization of the water molecule.

Oops, er, now I have to go somewhere. The universal solvent property of water cannot also not be under-estimated. I get your point about the causality, but life requires complexity, and, in general, things to come together, and I find it hard to imagine without water.
Can someone add to this?

[Nails]

Great answer Flak, as always.

I would just like to add the property of water to readily dissociate into H+ and OH-, which does improve its ability to act as a universal solvent but also means that the ions can be used in chemical reactions without needing the initial input of energy to split the molecule.

Conversely, the molecule is remarkebly stable due to the oxygen atom being bound so readily to at least one hydrogen atom.

[Thinker]

Although there are many extremophiles that survive in areas with no water, surely this is still only a product of evolution, which in it's earlier stages started in the oceans. I would guess that water is the ideal place for life to start, but once evolution has had it's wicked way, organisms are free to evolve as they please.

Mind you, saying that, look at the Xenomorph (Internecivus raptus/Lingua foeda acheronsis)!

[The Beige Avenger]

Although there are many extremophiles that survive in areas with no water....

What are they?

[Thinker]

Here's an example:

http://science.nasa.gov/science-news/sc ... 01sep98_1/

[The Beige Avenger]

Absolutely fascinating...

...but, correct me if I'm wrong, I'm understanding the article to have said that the bacteria were revived after ~3 years on the moon i.e. they went into a dormant state whilst in the lunar environment rather than 'lived' in the environment.

[Thinker]

As I originally stated

Although there are many extremophiles that survive in areas with no water....

[Shadowwolf]

Ahhh but I think the context here is life existing and living without the need for water. Whilst those bacteria managed to remain in stasis for three years and technically survive without water, they needed water to actually be active. Otherwise they would just remain in stasis and be indistinguishable from dead, possibly until going beyond reconstitution and being permanently dead.

Are there any examples of bacteria surviving in a living, active state sans water?

[Healerman]

Bacteria are routinely preserved in the frozen and the dehydrated state. Bacterial survival under these conditions is no great surprise. (It is, in fact, regrettable that we are contaminating non-terrestrial environments in this way, and future science may well curse us for doing so.) Surviving exposure to unfiltered solar radiation was the hard part.

To the very best of my knowledge, there is no life that is viable without water. The question is, can, and indeed has, life evolved elsewhere that is not water based? The jury is out.

[M Paul Lloyd]

Tardigrades anyone? Or Water Bears if you prefer, been around for some 530 million years (so they have survived a few major extinctions) and apparently capable of tolerating temperatures from +151 to -328 degrees Centigrade whilst being immune to most levels of radiation considered harmful to other life forms along with the ability to survive 1000 times more UV, they have even been exposed to the vacuum of space at 260 kilometres altitude and survived.
Tough little multi-celluar critters if you ask me.

[The Beige Avenger]

As I originally stated

Although there are many extremophiles that survive in areas with no water....

Indeed, again correct me if I'm wrong, but I don't believe Streptococcus is an extremophile... the implication I took (my misinterpretation) was that there exists some extreme-loving bacteria that somehow exist without water and AFAIK, there is no life that we know of that can exist without water so I'd be really interested to know if that info is out-dated... biology is moving so quickly.