PDA

View Full Version : 'We can't imagine life without water'-but can YOU?


dropzone
01-06-2004, 09:20 PM
Actually, the guy on Nova said "liquid water" but that is too easy. Without ANY water. Other than that the field is wide open--any elements, any temperatures.

Here's your chance to play Alternate Gods. Argue about it. Hash out the details. Have FUN.

(Can you tell I'm bored with the same old topics in Great Debates?)

Aeschines
01-06-2004, 10:01 PM
Sure, I think it's quite possible. As a premise, let's grant that an evolved life form would need a fluid--water or gas--to be biologically viable. A rock monster or what have you may also be possible, but let's consider "juicy creatures" first, the only life we have on Earth.

All life forms (plants, animals, and protazoa) on Earth use water. (Not all require oxygen for respiration.) But here are some other possibilities:

1. Hydrogen fluoride (HF). It's possible that there are planets with HF oceans. Cold environment required.

2. Ammonia (NH3) on a cold planet or moon.

3. Methane (CH4) on a cold planet or moon.

4. Ethane (C2H6). There may be liquid ethane bodies on Titan, the largest moon of Saturn. It's cold there.

Any of these liquids has some nice goodies in it (carbon, nitrogen, and hydrogen) that could help life along.

Roches
01-06-2004, 10:11 PM
Not allowing any water is only marginally more restrictive than not allowing liquid water. The biochemical purpose of water is as a solvent -- the medium in which all structural and catalytic components of an organism are dissolved and in which all reactions take place. Since water vapor and ice can't act as solvents, allowing them (but not liquid water) doesn't make a difference. Life (as we understand it) is just as impossible in a world of ice as it is in a world with no water at all.

Even more so than water, I think life is impossible without carbon. Science fiction authors may play around with silicon-based and even more exotic organisms, but there are many reasons why I think life must be carbon-based. First, the chemistry of carbon-containing molecules (i.e. organic chemistry) is vastly more complex and varied than the chemistry of any other element. The very unique ability of carbon to form long chains with itself (concatenation) is one of the main reasons for this. Other elements can concatenate, but in a much more limited way than carbon. Even silicon, because of its larger atomic radius, has a hard time forming long chains with itself. Further, carbon reacts readily with a variety of other elements (H, O, N, F, Cl, etc.) that permit functionalization of carbon-based molecules. This allows them to have a much more diverse chemistry that is conducive to life. This ability is determined by the energies of the C-C bond and the bonds of carbon with other elements as well as other properties. These properties are set by physical laws, which are (to our knowledge) constant throughout the universe.

If you'll permit me to assume that all life must be carbon-based, then we can work with the question of whether water is the only possible solvent. Certainly, laboratory organic chemistry can easily be done in other solvents. The polarity of water and its ability to support acid-base reactions better than other potential solvents make it a very good choice, but I can't be sure it's the only choice. I think life might be possible in other, less polar solvents. The most likely possibilities would probably be polar aprotic solvents such as dimethyl sulfoxide. Perhaps even non-polar solvents such as methane or ethane could support a very exotic biological chemistry. As for heavier solvents such as hexane or benzene, or even something like acetic acid, I can't be certain that such a liquid could exist in large enough quantities to act as a solvent on a planet-wide scale.

Anyway, I don't think life without water is absolutely unimaginable. Life without a solvent certainly is.

Roches
01-06-2004, 10:21 PM
Aeschines: I think HF and NH3 would be poor choices (erm, unlikely to support the development of life). HF is strongly acidic and reactive with many classes of carbon compounds, which would severely limit the range of chemistry possible. That is, you could have acid-catalyzed reactions, but not base-catalyzed ones. Also, a lot of types of organic molecules just wouldn't develop because of the extensive halogenation that would occur. Conversely, ammonia would permit base-catalyzed reactions but disallow acid-catalyzed ones.

Methane and ethane are probably viable. Life on Earth has been very good at taking advantage of aqueous organic chemistry. Life on a methane world would probably be able to adapt to wholly non-polar chemistry.

I think DMSO is a really intriguing possibility. The polarity would allow a wide range of solutes, and the solvent could even participate in some reactions (though not as well as water can). Reduction of DMSO to dimethyl sulfide might even be used as a biological energy source provided the environment was right for it. I'm not sure how likely a world with DMSO oceans would be, though.

Bryan Ekers
01-06-2004, 10:32 PM
In the collection The Left Hand of the Electron, Isaac Asimov included an essay title "The Thalassogens", a term he coined for life-supporting liquids. In it, he discusses the subject at length, including postulating oceans of methane and ammonia and whatnot. Among other problems, the liquid range of temperature of most of these is too small. For example, at a pressure of one atmosphere, ammonia boils at -33 degrees C, and melts at -77 degress C, giving it a liquid "range" of only 44 degrees. Merthane's liquid range is even smaller (at one atmosphere) at about 21 degrees. Speculating on life existing in either of these requires a much steadier temperature than can be found on Earth. Water is more tolerable to temperature changes, staying liquid across a 100-degree range.

In all, I expect life-forms that evolved in an ammonia or methane environment would be far too vulnerable to temperature variation. One bad "season" where the temperature dipped 20 or so degrees would force mass extinctions. On Earth, we just put on coats.

dropzone
01-06-2004, 10:35 PM
[chemistry aside]

Okay, I know little about chemistry but my wife has worked as a chemist. One day I remarked that the emissions from a local refinery of some sort smelt just like french fries.

She said, "I guess there are only so many ways carbon compounds can be arranged."

Okay, that answer seemed okay for a while. Then it struck me. "I thought the ways carbon compounds can go together is nearly limitless."

"That's only so many ways."

[/chemistry aside]

Roches, don't get hung up on likelihoods of things like DMSO oceans. Remember, you are a demigod in this universe with almost limitless powers.

Roches
01-07-2004, 07:52 AM
dropzone: The argument goes something like 'the number of possible organic compounds is unlimited because you can always add something'. If you can make X, you can make X-CH3, and if you can make that, you can make X-CH2CH3, and if you can make that, you can make X-CH2CH2CH3, and so on. Or X-CH2CH2OH, or anything else you might imagine. So there is no 'most complex possible organic compound', and the size and diversity of organic chemicals is limitless.

eburacum45
01-07-2004, 09:41 AM
Aha! the chap who posed this question did not appear to specify that the life concerned evolved spontaneously; I can imagine a water based carbon intelligent lifeform designing silicon and metal explorer robots which have the capacity to self replicate and adapt to their environment; send enough of those out and ater a few million years they could be present on every solid object in the Galaxy.

Now if that could happen why could the same thing not conceivably happen spontaneously?
Abiogenic robots?
Spontaneously evolving microprocessors?

Given enough montmorillionite and enough time you never know...

dropzone
01-07-2004, 10:25 AM
Okay, wiseguy, I will throw in the "evolved spontaneously" rule. ;)

I'm just surprised nobody's cheated by having the creature create water while breaking down its food and then using it. "But the water didn't exist as water at first--it's just a waste product!"

bordelond
01-07-2004, 11:23 AM
For those interested in this topic: Harvard Neurologist Athena Andreadis wrote a popular science book titled To Seek Out New Life (http://www.amazon.com/exec/obidos/tg/detail/-/0517443031/ref=pd_sim_art_elt/104-5832484-2767110?v=glance) which discusses at length the ramifications of waterless environments and non-carbon-based molecules on the creation of life.

Central to Andreadis' theme are the same points that Roches and Bryan Eckers made above.

dropzone
01-07-2004, 01:18 PM
Would freezing the liquid methane or ammonia for a while kill the creature or just slow/stop its processes until conditions improved? Neither substance expands when it freezes so you needn't worry about cell walls (if it has them) breaking.

People, people, I'm disappointed that some of you are not getting into the spirit of this. You are taking the writings of a neurologist at face value? And a biochemist, even one whose sideline was imagining alternatives, is going to have blind spots and preconceptions imposed by his training about what is possible. You're as smart or smarter than they--let your imaginations soar! (Within the bounds of the exercise, of course.)

dropzone
01-07-2004, 01:24 PM
Aw, CRAP! She's a Trekkie?!?!? Does she explain how all that latex gets on people's faces? Or the predilection of alien life forms to have ridges on their foreheads?

Yeesh.

Hmmmm, OTOH, Wife would get into it and I can buy it used for $2.67.

bordelond
01-07-2004, 02:35 PM
Originally posted by dropzone
Aw, CRAP! She's a Trekkie?!?!? Does she explain how all that latex gets on people's faces? Or the predilection of alien life forms to have ridges on their foreheads?

...

People, people, I'm disappointed that some of you are not getting into the spirit of this. You are taking the writings of a neurologist at face value? ... You're as smart or smarter than they--let your imaginations soar!

1) I only mentioned the book as a suggestion for those interested in the subject. I wasn't using mention of the book as an argument. I'm not really debating here.

2) Don't knock the book until you've tried it. While Dr. Andreadis is fan of the various Star Trek shows as entertainment, she repeatedly and tenaciously eviscerated the shows' writers when they employ poor science (which is often).

3) "You're as smart or smarter than they"? I don't make that claim for myself. I can discuss this matter only at a very broad layman's level. I, for one, can't come up with the boiling and freezing points for various chemicals off the top of my head.

Loopydude
01-07-2004, 02:50 PM
I think a number of relatively inert polar solvents might fit the bill, as Roches brilliantly outlined above. The thing is, chemical reactions depend on basically two things: molecular motion, and proper configuration. I can't see much going on in the solid phase. In addition, I have a hard time picturing anything like a cell membrane developing in the gaseous phase. What would cause it to self-assemble, and what would keep it cohesive and support it against collapse? Maybe I lack imagination, but it's hard for me to conceive of "life" without some kind of compartmentalization, where something separated the substance of the living thing from its environment sufficiently to make it an identifiably discreet body of some sort. I've seen some whimsical pictures of imaginary aliens that floated in the atomosphere of a gas giant, either on wings or suspended from gas bladders of some sort. I could see something like these evolving from an ocean-based life form, but I just can't see how you get cells outside of a liquid environment. Sure, you can blow soap bubbles into the air, but only from a little tub of it in solution. Liposomes (or some analog) purely derived from and suspended in a gas? Seems pretty much impossible to me.

I agree with the bias towards looking for life where there's water. We've got pretty good evidence here on earth that life can arise spontaneously in a watery environment, and, even more exciting, there are or were other watery environments in the solar system. I'd put my money on the watery spots first.

An interesting question might be: Would we be able to recognize something as "alive" if it didn't fit some sort of cellular paradigm? I mean, energy beings or smart dust-devils or whatever? They might be too alien.

dropzone
01-07-2004, 04:41 PM
Careful, Loopy. You might start us down the road to another "Is fire alive?" discussion! ;)

(searching)

Hey! We've never had one!

ataraxy22
01-07-2004, 06:28 PM
I can't personally imagine a first generation lifeform (e.g. ex nihilo evolved lifeform) that doesn't require water, however I can certainly imagine a second generation (or beyond) lifeform, artificially created by the first generation lifeform that does not require water (and maybe not even matter).

Roches
01-07-2004, 07:05 PM
I did give some consideration to the 'spontaneous evolution' rule. Allowing an existing intelligent lifeform to design some organism that doesn't require water significantly increases the likelihood of it happening, because you eliminate the variable of the probability of abiogenesis occurring on this waterless planet. I think water tends to favor abiogenesis -- for example, oceans of water can support geothermal vents which give rise to a diverse chemistry at relatively high temperature.

Bordelond, speaking of boiling points, I suppose the boiling point of a potential solvent is a major factor. A high-boiling solvent will lead to reactions happening much more quickly, which makes abiogenesis seem more likely.

One other thing I just thought of is this -- does this planet have no water, or are small amounts present? (A hypothetical planet will probably have some liquid water if its average temperature is within 0-100C.) Without water, a lot of possible organic molecules (alcohols, carboxylic acids, ketones, etc.) probably won't form, which makes life far harder to imagine.

dropzone: I admit my training (in biological/organic chemistry) is going to lead to some preconceptions. I really can't imagine organic molecules that are entirely different than the ones we've already prepared. So I think what I'm considering here is more like "Would something similar to life as we know it be possible on a planet without water?" rather than "Is life possible without water?" I'm also working with the basic assumption that 'life' must consist of something analogous to life on Earth, with these very basic components:

- structural components (cell membranes, structural proteins)
- chemical components (mostly catalytic proteins/enzymes)
- data storage/genetic components (nucleic acids)

I suppose it's possible that something could be considered 'alive' that used an entirely different paradigm of life. I imagine extraterrestrial life as being very similar to life on Earth mostly because I don't think extraterrestrial chemistry is different than chemistry on Earth. But terrestrial chemistry has shown us some possibilities which could potentially, somehow, lead to 'living' things. For example, in a world where silicon or organic or some other semiconductors formed spontaneously, you might eventually get 'energy beings' that were essentially living computers. But I agree that planets with water are almost certainly the best place to look.

dropzone
01-08-2004, 12:09 PM
Yeah, it's a given that planets with liquid water are the best bets and I don't want my hard-earned tax dollars chasing the remote possibility of oddball lifeforms when we haven't found any more "normal" ones off off Earth, but this thread is is as much a Pitting of that guy I heard on Nova as it is a chance for youse guys to brainstorm. "We can't imagine life without liquid water," eh? Well, I know people who CAN! And some who can't. ;)

Cervaise
01-08-2004, 04:30 PM
Along the same lines as the writings by Andreadis and Asimov, chapter 17 Worlds Without End by planetary scientist John S. Lewis speculates about alternative biochemistries. As above, ammonia, liquid carbon monoxide, and various sulfur and hydrogen compounds are considered, and all are found to be inferior to liquid water for fulfilling the need for a solvent.First, why do we need a solvent? Because chemical reactions in general do not take place inside solids: they take place on surfaces, in solutions, and in gases. Surfaces are fine locations for molecules and atoms to sit in order to react with something else, such as gases or solutions. Gases are great places for rapid reactions. <However, c>omplex organic materials are for the most part intolerant of temperatures much above 373K <while most substances under 500K are> either something other than gases, or the substances decompose into simple molecules when they become gases. ... Further, in gases the density is typically a thousand times lower than that of a liquid solution. Collisions between molecules, which are essential to making reactions possible, are millions to billions of times less frequent in a given volume of gas than in the same volume of liquid. The complex products that are formed will generally be much less volatile than the reactants that make them: they will tend to condense and be unavailable for further reaction. Gases are a very poor medium for the chemistry of life.So we have to have a solvent, and it pretty much has to be a liquid. Water is far and away the best alternative. If we reject it, we're left with the second-best alternative, sulfur dioxide. (Actually, the second best is ammonia, but it will almost invariably be found with water.) Lewis proposes that liquid sulfur dioxide may plausibly be found beneath the surface of Io, for example.

He follows the same reasoning to conclude that carbon is the most preferable molecular building material, superior to sulfur, iodine, chlorine, and so on. Silicon, of course, is widely considered second best after carbon, and Lewis's analysis corroborates this. The OP doesn't demand that we exclude carbon, though.

So if we keep carbon, but reject water, we're talking about a limited-biosphere life form in an extremely alien environment, such as a hypothetical low-temperature sea under the surface of a volcanic world like Io. The substance of the sea would normally be frozen, but is kept in liquid form by high gravity and tidal action.

How's that for a starting point?

dropzone
01-08-2004, 05:43 PM
There you go!

Roches
01-08-2004, 08:43 PM
Well, like I said I think carbon is the only suitable basis of life. Silicon is a far, far second. Si-Si bonds are very difficult to make, and Si=Si double bonds are even more difficult. The likelihood of catalytic silicon-based macromolecules developing spontaneously would be far lower than for carbon. Even in a highly exotic environment. Further reasons for the necessity of carbon (and water) are given in the first few pages of Voet and Voet's Biochemistry. (This means I don't feel like looking for it, but I'll quote some if anyone really wants it.) Silicon-based life might be possible, but I don't think it could be adequately hypothesized with our (read: my) current understanding of Si chemistry. Maybe in the future we'll discover that silicon can do things we don't now know it can do.

If C is vastly better than Si, then Si is even more vastly than the next-best alternative. I honestly can't see chalcogens, pnictogens or halogens forming the basis of life. They simply cannot concatenate to the degree necessary to form catalysts. I suppose it might be vaguely possible to use a different catalytic paradigm for life that would emphasize inorganic catalysis -- this would take some of the emphasis off carbon, but it would be much less likely to arise spontaneously and would lack much of the specificity of organic catalysts.

Solvents:I can see how sulfur dioxide could be a decent solvent. I disagree with ammonia because of its reactivity. In the real world, ammonia-water oceans would be suitable for life, as has been mentioned, but the OP excludes that.

I hadn't thought of liquid CO, but that's very intriguing. Unfortunately I can't find a phase diagram, so I don't know what conditions would be required. But CO is an excellent feedstock for organic synthesis. CO oceans -- especially ones with abundant dissolved metals -- would give rise to all kinds of organic compounds. The compounds would be different than terrestrial biological molecules, but they could easily be catalytic. Assuming the right atmospheric conditions, any organisms that happened to evolve would likely be able to sustain themselves by oxidizing CO to CO2.

The only problem is that these organisms would be constantly surrounded by a fairly reactive substance. Keeping CO out would be a priority, and they would have to find a way to protect themselves against it. One idea: with all that CO around, perhaps they could use polymers instead of lipid membranes. A polyalkane or polyketone 'shell' could be used to keep out CO and sustain an internal environment of some other solvent.

It's not inconceivable that that solvent could be water. If there were hydrogen in the atmosphere, molecular hydrogen rather than water could be used as the hydrogen and proton source. And it's possible that some water could be produced as the byproduct of CO-based organic synthesis. This water could be used inside the organisms as a less reactive solvent -- and then a very different biochemistry would begin to appear. I don't think it violates the OP to introduce water after the beginning of life. Remember, most of the oxygen in the Earth's atmosphere is the result of life, so it's not inconceivable that an initially waterless planet could have water in abundance after a couple billion years of life.

Urban Ranger
01-19-2004, 04:10 AM
A highly unusual property of water is it can dissolve both organic and inorganic materials, plus it has a very high specific heat, and that it actually conducts electricity with impurities added.

So water is not as simple as a solvent, though that is a very important role.

eburacum45
01-19-2004, 06:13 AM
Well, if we must try to imagine life without water and carbon based organics, the we are looking at different kinds of self perpetuating complexity; this complexity also has to be self-replicating, with a capacity for storing information...
I have tried to imagine high energy life-like complexities, for instance in high temperature plasmas- the trouble is a high temperature seems to defeat the object of storing information, as high temperature conditions are generally chaotic.
Some geological events are quite complex, especially during the crystalisation phase; perhaps a low order life-like self-perpetuating complexity could emrge in certain exotic lavas out there in the universe somewhere;
(as I have depicted in this piece of fiction (http://www.orionsarm.com/xenos/Rheolithoids.html), without giving any real coherent details of course)
but I don't really expect that such life-like lava really exists, or if it does, it wil be short-lived and restricted to a narrow range of temperatures and chemistries,
while organic life can adapt to its environment and even modify it.

Lemur866
01-19-2004, 11:31 PM
One thing to consider are the relative frequencies of different elements in the universe, and on planets. If we look at volatile compounds, hydrogen is the most common, followed by helium, then a grab bag of carbon, nitrogen and oxygen, and then everything else.

So we can imagine that the most common compounds in the universe would be water, methane, and ammonia. But how common would liquid helium be? Sure there's lots of helium, but most of it is in stars. How much helium could there be in the Kuiper belt, and would conditions there permit liquid helium? Since we don't know much about liquid helium, we can imagine all sorts of interesting properties for life in a helium solvent without being too constrained by awkward facts.

Or do we already know too much? Any experts on liquid helium physics want to weigh in?

Urban Ranger
01-20-2004, 03:23 AM
I can't imagine liquid helium being a solvent, as helium is the most insert element there is.

Urban Ranger
01-20-2004, 03:55 AM
I can't imagine liquid helium being a solvent, as helium is the most insert element there is.

Lemur866
01-21-2004, 12:18 AM
Yes, helium is chemically unreactive. But that doesn't mean it can't act as a solvent, does it? Sure, the helium itself wouldn't be part of the chemistry of helium organisms, but perhaps there could be interesting superfluid properties of helium. Would any normal carbon organic chemistry be possible at liquid helium tempertures?

owlofcreamcheese
01-21-2004, 09:02 AM
how about life in the form of magnetic configurations in a star. its obvious to everyone that magnetic feilds can be used to store information, they also can be used to effect eachother and so interact and arrange themselfs.

of course this is unlikely to form life, but there are MANY stars out there and they are VERY big and VERY long lived.