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as far as we know life cannot survive without water. even in enviroments such as sulfur, there are still traces of water to support life

As far as we know life WHICH EVOLVED ON EARTH cannot survive without water. Even in environments such as sulfur, there are still traces of water to support life. <=fixed

 

We're talking about aliens here.

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As far as we know life WHICH EVOLVED ON EARTH cannot survive without water. Even in environments such as sulfur, there are still traces of water to support life. <=fixed

 

We're talking about aliens here.

 

Wikipedia (see alternative biochemistry) proposes life in solvents other than water. They list the solvents in order of their likelihood of supporting some kind of life. Ammonia, methane, hydrogen fluoride, formamide, methanol, hydrogen sulfide, and hydrogen chloride, but all are far inferior to water as a solvent. So, I think it is safe to say that if, or when, THEY arrive here, there will be a high probablity THEY are water-carbon based, because water and carbon are very common and better at supporting life.

 

http://en.wikipedia.org/wiki/Alternative_biochemistry#Non-water_solvents

 

"Some of the properties of water that are important for life processes include a large temperature range over which it is liquid, a high heat capacity useful for temperature regulation, a large heat of vaporization, and the ability to dissolve a wide variety of compounds. Water is also amphoteric, meaning it can donate and accept a proton allowing it to act as an acid or a base. This property is crucial in many organic and biochemical reactions, where water serves as a solvent, a reactant, or a product. There are other chemicals with similar properties that have sometimes been proposed as alternatives. Additionally, water is the only compound listed here that is less dense as a solid (ice) than as a liquid. This is why bodies of water freeze over but do not freeze solid (from the bottom up). If ice were denser than liquid water (as is true for nearly all other compounds) then large bodies of liquid would slowly freeze solid, which would not be conducive to the formation of life."

Edited by Airbrush
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Airbrush, something inside me really wants to disagree with you on this, Life on the earth evolved in water, it would highly unlikely we would look at another solvent and say "wow that looks like it would be better for life than water", how could it? We are evolved to live on a planet with liquid water, Earth life suffers from a chauvinism, water and carbon chauvinism. From the inside looking out any other type of life seems unlikely. How ever life that evolved in sulfuric acid at high temperatures might see it differently and be absolutely amazed at life on a cold planet covered in an inert liquid like water.

 

Ammonia does a few things better than water does, dissolving metals is one of them. On a planet with liquid ammonia oceans even the things we see as problems for liquid ammonia life might be a plus from the stand point of liquid ammonia life forms, maybe they will be made up of boron or boron/nitrogen polymers ....

 

Or maybe we are being far too speculative, I for one would be flabbergasted if an alien space craft came our way piloted by anything other than carbon based, water solvent, oxygen breathing life forms but even then I still say it would be unlikely they could use or would want to use our planet...

 

Thinking way outside the box.... polylipids instead of proteins .

 

Methane

A mixture of hydrocarbons, such as the methane/ethane lakes detected on Titan by the Cassini spacecraft, could act as a solvent over a wide range of temperatures but would lack polarity. There is debate about the effectiveness of methane as a medium for life compared to water or ammonia.[14] While water is a far better solvent than methane, enabling easier transport of substances in a cell,[15] methane's lesser chemical reactivity allows for the easier formation of large structures akin to proteins.[16] Isaac Asimov, the biochemist and science fiction writer, suggested that poly-lipids could form a substitute for proteins in a non-polar solvent such as methane or liquid hydrogen.[17]

 

Possible evidence for this form of life was identified in 2010 by Darrell Strobel of Johns Hopkins University; an over-abundance of molecular hydrogen in Titan's upper atmospheric layers, which leads to a downward flow at a rate of roughly 1025 molecules per second. Near the surface the hydrogen apparently disappears, which may imply its consumption by methanogenic life forms.[15][18][19] Another paper released the same month showed little evidence of acetylene on Titan's surface, where scientists had expected the compound to accumulate; according Strobel, this is consistent with the hypothesis that acetylene is being consumed by methanogens.[15] Chris McKay, while agreeing that presence of life is a possible explanation for the findings about hydrogen and acetylene, has cautioned that other explanations are currently more likely: namely the possibility that the results are due to human error, or to the presence of some as-yet unknown catalyst in the soil.[20] He noted that such a catalyst, effective at 95 degrees K, would in itself be a startling discovery. [20]

Edited by Moontanman
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....I for one would be flabbergasted if an alien space craft came our way piloted by anything other than carbon based, water solvent, oxygen breathing life forms but even then I still say it would be unlikely they could use or would want to use our planet...

 

Thinking way outside the box.... polylipids instead of proteins .

 

I wish I could be as broad-minded as you are Moontanman, but after reading what Wiki had to say about "alternative biochemistry" I am rather pessimistic about the likelihood of non-carbon-water-based life. I would bet on carbon-water for intelligent life. There may well be other kinds of extremophile life out there, but not with intelligence and not as common as carbon-water life.

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I wish I could be as broad-minded as you are Moontanman, but after reading what Wiki had to say about "alternative biochemistry" I am rather pessimistic about the likelihood of non-carbon-water-based life. I would bet on carbon-water for intelligent life. There may well be other kinds of extremophile life out there, but not with intelligence and not as common as carbon-water life.

 

 

Extreme life forms, I like the idea, it would a mirror of our earth, it makes a odd kind of sense that only one or two types of life might be viable past very primitive cells. The Rare Earth theory assumes that most life is simple bacterial type. Of all the cell lines present on the earth, only one is thought to have developed into complex animals and plants.

 

If aliens land I'd make the same bet... But when we get to Titan will strange plants and animals great us?

Edited by Moontanman
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. Or, they could communicate via smells.

 

Olfactory communication would be so inefficient. Not only is smell slower than sound, it is even debatable whether the message will reach the receiver. I think the alien life forms would probably be some kinds of advanced bacterial colony with combined photosynthetic and digestive functioning.

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As far as we know life WHICH EVOLVED ON EARTH cannot survive without water. Even in environments such as sulfur, there are still traces of water to support life. <=fixed

 

We're talking about aliens here.

 

 

hmm u make a good point but there are such a large amount of species on this planet that evolved from different chemical reactions based on water that i think that race would have been the same. if that were true that not all life needs water there could be life on venus wich i dout

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hmm u make a good point but there are such a large amount of species on this planet that evolved from different chemical reactions based on water that i think that race would have been the same. if that were true that not all life needs water there could be life on venus wich i dout

 

The biggest problem with Venus is not the lack of water but the pressure and temperature. I'll explain: Start with the assumption that life is based on chemistry as opposed to some weird, novel physics that we have never heard of. Chemical life will almost certainly be based on carbon because carbon can make incredibly complex molecules and other elements cannot. We don't know what life is, but we know that it is something complex. And if you want complex chemistry, you are stuck with carbon.

 

What does this mean? It means that any environment where carbon compounds are regularly destroyed will be inhospitable to life. And in general, anything that destroys chemical bonds will be inhospitable to life. So we can ask ourselves, what sort of things destroy chemical bonds? Well, some examples include high radiation, high temperature and high pressure. When you cook something, the "cooking" process consists of breaking carbon bonds (which is why cooked food is easier to digest). You can also cook things with pressure, because pressure breaks molecular bonds too.

 

Anyway, long story short, Venus has both high pressure and high temperature, and that environment will break most chemical bonds, and in particular, it will break carbon-carbon bonds. Thus making Venus inhospitable to life, without having to invoke any argument about water.

 

Cheers,

Daniel.

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There's a lot of speculation here so I thought I'd chime in. There is a big difference between what's possible and what's likely. (especially if we are talking about aliens that visit Earth)

 

It is possible that alien life could be silicon based for example, however it's more likely it will be carbon based. This is because organic chemistry is vast and I think you would need that level of diversity and complexity for life to form. This isn't a human construct, it is nature and one thing we assume is that the laws of nature (physics) are the same everywhere in the universe. So there is a greater chance that alien life will be carbon based.

 

It is possible that alien life will use amonia instead of water for instance, but as far as I'm aware water is one of the best solvents around, more things dissolve in water and more of those things w/w dissolve in water making it more versatile (think what blood has to carry in it). Water might even be more common that ammonia seeing as commets are big lumps of ice and most of the planets in our solar system have water on them, but don't quote me on that. I think it's more likely then that alien life will need water.

 

So although it doesn't preclude other possibilities I think it is far more likely that alien life will be carbon based and will use a water based solvent.

 

 

As for technology and communication, if our assumption that the laws of physics are the same everywhere in the universe is true then it is likely aliens will have discovered the same laws. They will understand mathematics, logic, analysis, binary etc... They will have built transmitters recievers, sensors, lasers, clocks, measuring rods etc... and other similar technologies. These things are not human concepts they are based on physical principles, it's how we use them that makes them human, they only become human when we turn them into ipods, TV's, DVD players, PS3's.

 

So aliens may communicate by touch or smell or grafting DNA (carbon based) but they will most likely use EM transmission as well. If they're advanced enough to come visit us then they will have studied physics including the entire EM spectrum, they will have their version of radio telescopes, they will have studied the universe in x-ray, UV, microwave etc... Seti for example do not analyse the whole EM spectrum, they only look at a small part of it which they have decided is more likely to be sent by an alien species wanting to communicate. Aliens would recognise similar signals from us.

 

What will they do when/if they get here. Base on what we know (us) it is more likely they will be carbon/water based life, they will be altruistic, they will have a history of science and discovery and will have developed technology. In order to do this they will need to be organised, they will need rules and laws, they will need to be civilised, they will need training and education, they will have their version of goverment and politics. And that might mean a tyrannical totalitarian autocratic disgrace like N.Korea, but lets face it N.Korea would never have developed technology on its own because to do that you need to be civilised and all the other things I mentioned. Any alien race like that would have half its population in gulags and the other half will be almost starving to death. They would never develop the means to get here.

 

It's unlikely that we would be the first alien species they will have encountered, they would probably belong to or be policed be a body comprising all the 'worlds' they have relations with. If they were like N.Korea they would probably be under the eye of neighbouring societies and would not come all this way to kill us for fear of reprisals.

 

Even if they are immensely intellectually superior to us they will still recognise our intelligence, would they destroy us? I don't think so. Would they rape our planet of its natural resources? Probably not, there are 7 other planets for them to choose from. They would most likely be as fascinated with us as we would be with them and they would probably want to trade.

 

That's my opinion, like I said I'm not ruling out other possibilities just saying what I think is more likely.

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hmm u make a good point but there are such a large amount of species on this planet that evolved from different chemical reactions based on water that i think that race would have been the same. if that were true that not all life needs water there could be life on venus wich i dout

 

 

It depends on whether or not there is a suitable solvent for the temps and pressures on Venus, silicone (not silicon) chemistry is capable of at least some complex chemicals at the temps involved but there really doesn't seem to be a solvent to replace water although concentrated sulfuric acid comes close.

 

 

The biggest problem with Venus is not the lack of water but the pressure and temperature. I'll explain: Start with the assumption that life is based on chemistry as opposed to some weird, novel physics that we have never heard of. Chemical life will almost certainly be based on carbon because carbon can make incredibly complex molecules and other elements cannot. We don't know what life is, but we know that it is something complex. And if you want complex chemistry, you are stuck with carbon.

 

No you are not stuck with carbon, silicon, boron, nitrogen/phosphorus, boron/nitrogen, and few other chemicals can under the right conditions form complex molecules. Not as complex as carbon in most cases as far as we know but we only know our one little planet...

 

What does this mean? It means that any environment where carbon compounds are regularly destroyed will be inhospitable to life. And in general, anything that destroys chemical bonds will be inhospitable to life. So we can ask ourselves, what sort of things destroy chemical bonds? Well, some examples include high radiation, high temperature and high pressure. When you cook something, the "cooking" process consists of breaking carbon bonds (which is why cooked food is easier to digest). You can also cook things with pressure, because pressure breaks molecular bonds too.

 

Not true, even at high temps carbon still makes complex molecules, life, earth life, can and does thrive at temps as high as 300 degrees C pressure makes this possible. I think this suggests that all that is really needed is a solvent and carbon just might be able to step up to the plate at quite high temps and that ignores things like silicones. Just because we don't see silicone molecules complex enough for us to see how they could be alive doesn't mean they couldn't develop life with chemicals quite dissimilar to what we know as carbon life.

 

 

Anyway, long story short, Venus has both high pressure and high temperature, and that environment will break most chemical bonds, and in particular, it will break carbon-carbon bonds. Thus making Venus inhospitable to life, without having to invoke any argument about water.

 

Cheers,

Daniel.

 

There are other possibilities, we just don't see them on the Earth although Thomas Gold suggests that at temps and pressures deep with in the Earth silicone life might thrive today. He sites evidence of silicone biochemistry deep in the earth is his book the Deep Hot Biosphere.

 

There's a lot of speculation here so I thought I'd chime in. There is a big difference between what's possible and what's likely. (especially if we are talking about aliens that visit Earth)

 

This I cannot necessarily agree with, all we know is earth life, earths version of carbon life, we really don't know what is possible in other planets environments.

 

It is possible that alien life could be silicon based for example, however it's more likely it will be carbon based. This is because organic chemistry is vast and I think you would need that level of diversity and complexity for life to form. This isn't a human construct, it is nature and one thing we assume is that the laws of nature (physics) are the same everywhere in the universe. So there is a greater chance that alien life will be carbon based.

 

I'm pretty sure the smart money is on carbon as the basis of life but we really don't know enough about what might go one in very high temperature high pressure environments, such environments can change the very nature of how chemicals react, we have no idea if this would allow life based on other chemistries but it's sure thing that other chemistries work in unknown ways in radically different environments.

 

Then you have very low temp environments, silicon (not silicone) might be just the ticket at such low temps as Titan, methane or ethane as a solvent. Both temps and pressures can radically change how chemicals react, we just don't know enough to rule out these possibilities under radically different conditions....

 

It is possible that alien life will use amonia instead of water for instance, but as far as I'm aware water is one of the best solvents around, more things dissolve in water and more of those things w/w dissolve in water making it more versatile (think what blood has to carry in it). Water might even be more common that ammonia seeing as commets are big lumps of ice and most of the planets in our solar system have water on them, but don't quote me on that. I think it's more likely then that alien life will need water.

 

The idea of more things necessary for life dissolves in water is biased, all we know about is life dissolved in water, life that evolved to live in ammonia might look at water say exactly the same thing... I do think you have a very good point in that in any environment that would hold liquid ammonia would also almost certainly have water, possibly a mix of the two and oxidation would eventually destroy the ammonia but the idea that comets are made of ice and therefor water is more abundant is flawed due to the fact that frozen hydrogen compounds are called ice and comets are made up of many different ices.

 

So although it doesn't preclude other possibilities I think it is far more likely that alien life will be carbon based and will use a water based solvent.

 

I don't any data to refute that assertion other than a lack of data to confirm it either...

 

As for technology and communication, if our assumption that the laws of physics are the same everywhere in the universe is true then it is likely aliens will have discovered the same laws. They will understand mathematics, logic, analysis, binary etc... They will have built transmitters recievers, sensors, lasers, clocks, measuring rods etc... and other similar technologies. These things are not human concepts they are based on physical principles, it's how we use them that makes them human, they only become human when we turn them into ipods, TV's, DVD players, PS3's.

 

 

Almost certainly true...

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No you are not stuck with carbon, silicon, boron, nitrogen/phosphorus, boron/nitrogen, and few other chemicals can under the right conditions form complex molecules. Not as complex as carbon in most cases as far as we know but we only know our one little planet...

 

Saying that you are stuck with carbon is approximately true. Carbon is magnitudes better than any other atom. Silicon is probably #2, but it doesn't hold a candle to carbon. So, although I guess silicon-based life is permitted by the laws of physics, the probabilities are heavily stacked against it. When I say "you are stuck with carbon" I am speaking loosely, and the statement is to be an approximation to the truth.

 

Not true, even at high temps carbon still makes complex molecules, life, earth life, can and does thrive at temps as high as 300 degrees C pressure makes this possible.

 

You are missing the forest for the trees. High pressure, temperature and radiation all break carbon bonds (btw, extremes in pH do too, I forgot about those). As you go toward higher pressure, temperature or radiation, the environment becomes less hospitable, and any life becomes more and more difficult. Extremophiles on earth have to come up with various creative ways to deal with these challenges, like running heat pumps to keep their internal temperature lower than the outside.

 

Incidentally, my understanding is that hyperthermophiles actually thrive on temperatures up to about 100 degrees C, and not the 300 C that you get in the vents themselves. For comparison, the temperature on the surface of Venus is 460 C. Maybe there is life on the surface of Venus, but you have to understand that the conditions there really hare fundamentally inhospitable for carbon bonds. It is entirely reasonable to look at a chemistry textbook, find out what things break carbon bonds, and then say that environments with a lot of that are inhospitable for carbon bonds.

 

 

Just because we don't see silicone molecules complex enough for us to see how they could be alive doesn't mean they couldn't develop life with chemicals quite dissimilar to what we know as carbon life.

 

Just so I know, are you a chemist? I am not a chemist, I am a physicist. If you are a chemist I will take your word for it, but my understanding of chemistry is that silicon really is a much poorer choice than carbon because the valence electrons are less bound to the atom, making it more difficult to build complex molecules without them falling apart. This argument is independent of what we see directly on earth.

 

As a physicist, I can make another argument based on elemental abundance: Carbon is far more common in the universe than silicon. The most common atoms in the universe after H and He are C, N an O, and the most common molecules after molecular hydrogen are CH4, NH3 an H2O. Purely from elemental abundance, these molecules are logical choices for life, and their chemical properties together certainly gives them a lot of weight as the best candidates in our search for extraterrestrial life.

 

 

There are other possibilities, we just don't see them on the Earth

 

As a scientist, I am more interested in what is probable than what is possible. A surprising number of things are technically possible. I don't think that silicon life is prohibited by the laws of physics. But saying that something is not necessarily impossible does not automatically make it likely or interesting. It is possible that there is an alien spaceship parked at the L3 point of Mercury, but looking for it is not a very intelligent way to search for alien life.

 

This I cannot necessarily agree with, all we know is earth life, earths version of carbon life, we really don't know what is possible in other planets environments.

 

We know the laws of physics, and we know quite a lot about chemistry. Physical laws are universal, and understanding them can go a long way in guiding us in the search for alien life.

 

Both temps and pressures can radically change how chemicals react, we just don't know enough to rule out these possibilities under radically different conditions....

 

This is a strong statement to make. I'd like to know if you are a chemist. Since only a chemist should be able to make a blanket statement about whether we know enough chemistry or not to reach these conclusions.

 

I don't any data to refute that assertion other than a lack of data to confirm it either...

 

Earlier in this post I offered some data backing up the assumption of life based on C, N, O based on elemental abundance in the universe.

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First, to those who have explained why carbon is the most likely basis for life and why certain conditions are more hostile or favorable to protecting the chemical bonds, thanks.

As for technology and communication, if our assumption that the laws of physics are the same everywhere in the universe is true then it is likely aliens will have discovered the same laws. They will understand mathematics, logic, analysis, binary etc... They will have built transmitters recievers, sensors, lasers, clocks, measuring rods etc... and other similar technologies. These things are not human concepts they are based on physical principles, it's how we use them that makes them human, they only become human when we turn them into ipods, TV's, DVD players, PS3's.

Sure, "they" might have discovered the same physical laws, etc. but the question is how they manage culture and divide labor. If they are security-conscious, they may keep their scientists separate from others in their populations and promote other kinds of culture to help other factions of the population specialize in other kinds of work. If they sent being to Earth, these being might be specialized in accomplishing a mission and lack any capacity for ethical restraint or open communication and philosophical reflection. In that case, they might just be totally instrumental in getting whatever it was that they came for and doing so with as little contact as possible. If they are into the power of covert operations, like so many humans are, I doubt their presence would even be noticed.

 

 

Even if they are immensely intellectually superior to us they will still recognise our intelligence, would they destroy us? I don't think so. Would they rape our planet of its natural resources? Probably not, there are 7 other planets for them to choose from. They would most likely be as fascinated with us as we would be with them and they would probably want to trade.

That would be nice, but what if they were very ethnocentric, to the point of measuring terrestrial life in terms of deviation from their own planetary ecology, which they revered as being perfect? If they were intelligent photosynths, they might consider animal life barbaric and frightening and prefer to replace it with fungus and bacteria for its consumption and composting functions. They might want to genetically engineer terrestrial plants and trees with their own brain-type structures and communication mechanisms so that plant-life on both planets could exist in interactive harmony.

Edited by lemur
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Saying that you are stuck with carbon is approximately true. Carbon is magnitudes better than any other atom. Silicon is probably #2, but it doesn't hold a candle to carbon. So, although I guess silicon-based life is permitted by the laws of physics, the probabilities are heavily stacked against it. When I say "you are stuck with carbon" I am speaking loosely, and the statement is to be an approximation to the truth.

 

 

Like I've said before the safe money is on carbon. But as I pointed out there are some scientists that acknowledge that chemistry can be quite different at various temps and pressures, Thomas Gold explained this in his book "The Deep Hot Biosphere" and no I'm not a chemist but chemistry is one of my real life interests, but no i am not a chemist by any possible definition... I'm JAFO

 

You are missing the forest for the trees. High pressure, temperature and radiation all break carbon bonds (btw, extremes in pH do too, I forgot about those). As you go toward higher pressure, temperature or radiation, the environment becomes less hospitable, and any life becomes more and more difficult. Extremophiles on earth have to come up with various creative ways to deal with these challenges, like running heat pumps to keep their internal temperature lower than the outside.

 

Incidentally, my understanding is that hyperthermophiles actually thrive on temperatures up to about 100 degrees C, and not the 300 C that you get in the vents themselves. For comparison, the temperature on the surface of Venus is 460 C. Maybe there is life on the surface of Venus, but you have to understand that the conditions there really hare fundamentally inhospitable for carbon bonds. It is entirely reasonable to look at a chemistry textbook, find out what things break carbon bonds, and then say that environments with a lot of that are inhospitable for carbon bonds.

 

 

I misspoke when I said 300C while lots of vents spew out bacteria laced very hot and full of dissolved minerals super critical water at up to 400C so far the highest temp we have been able to grow bacteria has been 122C and while some seem to think it will go up drastically as we explore this habitat so far it's just speculation. but I do indeed agree that if there are any non carbon extreme life forms they will be at best just another odd bacteria like life form. Complex life is likely to be carbon based and using water as a solvent and breathing oxygen. But like what we call extremophiles on earth thses other life forms will be very interesting and might prove very valuable.

 

 

Just so I know, are you a chemist? I am not a chemist, I am a physicist. If you are a chemist I will take your word for it, but my understanding of chemistry is that silicon really is a much poorer choice than carbon because the valence electrons are less bound to the atom, making it more difficult to build complex molecules without them falling apart. This argument is independent of what we see directly on earth.

 

Silicon chemistry would have to proceed at very low temps and is almost certainly very unlikely,,, lol. But silicone chemistry is more likely and much tougher, so inert it would have to be at very high temps Issac Asimov ( a real biochemist) suggested that silicone life in concentrated sulfuric acid at very high temps might be possible. Under high pressure chemistry is different than it is at low temps. The super critical water is an example of this, water turning to ice at extreme pressure even at well above freezing temps is another example of how pressure can change the basic properties of chemicals. Thomas Gold says that under extreme pressure like that deep in the earth could suggest silicone life there and sited some geological deposits of quartz and some metals, gold and silver, as being possibly the result of a similar biological process that results in gold and silver being found in hydrocarbon deposits, early gold miners often used veins of carbon as leaders to find gold and silver due to this effect.

 

As a physicist, I can make another argument based on elemental abundance: Carbon is far more common in the universe than silicon. The most common atoms in the universe after H and He are C, N an O, and the most common molecules after molecular hydrogen are CH4, NH3 an H2O. Purely from elemental abundance, these molecules are logical choices for life, and their chemical properties together certainly gives them a lot of weight as the best candidates in our search for extraterrestrial life.

 

This I cannot argue with, the trace elements they need could vary between biospheres but you are probably correct in the main players in all but extreme cases... I think it's very telling that on the Earth silicon is far more common than carbon but we are still carbon...

 

 

 

As a scientist, I am more interested in what is probable than what is possible. A surprising number of things are technically possible. I don't think that silicon life is prohibited by the laws of physics. But saying that something is not necessarily impossible does not automatically make it likely or interesting. It is possible that there is an alien spaceship parked at the L3 point of Mercury, but looking for it is not a very intelligent way to search for alien life.

 

I like the speculative.

 

 

We know the laws of physics, and we know quite a lot about chemistry. Physical laws are universal, and understanding them can go a long way in guiding us in the search for alien life.

 

 

 

This is a strong statement to make. I'd like to know if you are a chemist. Since only a chemist should be able to make a blanket statement about whether we know enough chemistry or not to reach these conclusions.

 

No I'm not a chemist but other people who are have said these things, I believe them from examples of real differences in chemistry at different temps and pressures.

 

 

Earlier in this post I offered some data backing up the assumption of life based on C, N, O based on elemental abundance in the universe.

 

And I agree with in it's basics...

Edited by Moontanman
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While we're talking about alternative chemicals for life, how about aromatic compounds? Can we make complex aromatic compounds without carbon?

 

 

were getting off topic people. this thread is about first contact with aliens

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On a related note. I think we're spending too much time concentrating on Mars. I think we should drop a couple of baloons on the cloud tops of Venus. I said earlier that the Venusian surface is too hot, but the cloud tops (about 50km up) are actually the most Earth-like environment in the solar system, with a temperature and pressure about the same as the earth.

 

There is microbial life in the clouds of earth. It is conceivable that life might have appeared on Venus before it got too hot, and that it might have survived in the clouds. I'm sure that's worth a single mission with a few baloons.

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The idea of more things necessary for life dissolves in water is biased, all we know about is life dissolved in water, life that evolved to live in ammonia might look at water say exactly the same thing... I do think you have a very good point in that in any environment that would hold liquid ammonia would also almost certainly have water, possibly a mix of the two and oxidation would eventually destroy the ammonia but the idea that comets are made of ice and therefor water is more abundant is flawed due to the fact that frozen hydrogen compounds are called ice and comets are made up of many different ices.

 

 

I don't any data to refute that assertion other than a lack of data to confirm it either...

 

 

 

I don't quite know what you mean by "life dissolved in water", What I am saying is that water is the best carrier. A wider variety chemicals can dissolve in water than any other solvent and more of each of those chemicals w/w can disolve in water (on average). This makes water the best medium for supporting complex chemistry.

 

The data you need to confirm that carbon based life is more likely can be found in a library, simply compare the amount of shelf space given to either organic or inorganic chemistry. Organic chemistry is vastly bigger than inorganic chemistry (which silicon is only a small part of).

 

So when you consider that water and carbon are two of the most abundant chemicals in the universe (as DanielC said) and water provides a base for a lot of the complex carbon chemistry to take place you have all the data you need to make the assertion that carbon and water are more likely to give rise to alien life.

(EDIT: whilst I was writing this you posted a reply, I think we are agreed here that water/carbon life is more likely but not the only possibility)

 

I think that if we ever met an alien race we would be quite surprised at the similarities we share, physically, biologically, culturally, artistically, technologically, scientifically etc etc... The single biggest threat an alien race could bring to Earth is disease (bacteria and virusus) which is also the biggest threat we pose to them.

Edited by between3and26characterslon
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I don't quite know what you mean by "life dissolved in water", What I am saying is that water is the best carrier. A wider variety chemicals can dissolve in water than any other solvent and more of each of those chemicals w/w can disolve in water (on average). This makes water the best medium for supporting complex chemistry.

At STP or in general?

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I don't quite know what you mean by "life dissolved in water", What I am saying is that water is the best carrier. A wider variety chemicals can dissolve in water than any other solvent and more of each of those chemicals w/w can disolve in water (on average). This makes water the best medium for supporting complex chemistry.

 

This is demonstratively not true. Liquid Ammonia dissolves some important metals better than water is an easy example. Beings that evolved on a planet with liquid ammonia would see liquid ammonia was the perfect solvent.

 

 

The data you need to confirm that carbon based life is more likely can be found in a library, simply compare the amount of shelf space given to either organic or inorganic chemistry. Organic chemistry is vastly bigger than inorganic chemistry (which silicon is only a small part of).

 

So if we were some other sort of life could we would still see evidence of the vastness of organic chemistry and know we were far less likely than carbon life?

 

 

 

So when you consider that water and carbon are two of the most abundant chemicals in the universe (as DanielC said) and water provides a base for a lot of the complex carbon chemistry to take place you have all the data you need to make the assertion that carbon and water are more likely to give rise to alien life.

(EDIT: whilst I was writing this you posted a reply, I think we are agreed here that water/carbon life is more likely but not the only possibility)

 

Yes we do agree on that.

 

I think that if we ever met an alien race we would be quite surprised at the similarities we share, physically, biologically, culturally, artistically, technologically, scientifically etc etc... The single biggest threat an alien race could bring to Earth is disease (bacteria and virusus) which is also the biggest threat we pose to them.

 

There are people who think that even our "humanoid" appearance is likely to be repeated, not like on star trek of course but more like the whole general shape, under this definition even a theropod dinosaur comes close to being humanoid. Much like when vastly different animals are shaped in a similar way due to environmental adaptations. Fish, sharks, Ichthyosaurs, dolphins, and even some squid take on the fast torpedo shape powered by fins.

 

I have my doubts that disease organisms are likely to be capable of infecting life from another planet unless life is so very specific that all life is identical with carbon chemistry it seems unlikely that all life on all planets would be closely related enough to be cross infective very often if at all.

 

 

I am not a chemist (I'm a physicist), but my understanding is that water is a good medium in general due to its polar nature. But a chemist would be better able to explain this.

 

 

For our type of life you are correct, water's polar nature is important for life that evolved in water but life that evolves in, say... liquid methane, polylipids, if I remember correctly, would do better in non polar liquids.

 

While I agree that the safe bet is for carbon/water that breathes oxygen. I think we will find some interesting chemistries in unusual locations if nothing else...

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On a related note. I think we're spending too much time concentrating on Mars. I think we should drop a couple of baloons on the cloud tops of Venus. I said earlier that the Venusian surface is too hot, but the cloud tops (about 50km up) are actually the most Earth-like environment in the solar system, with a temperature and pressure about the same as the earth.

 

There is microbial life in the clouds of earth. It is conceivable that life might have appeared on Venus before it got too hot, and that it might have survived in the clouds. I'm sure that's worth a single mission with a few baloons.

 

 

i do believe there was once life on mars since it had an earth-like magnetic field and similar atmospere.

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I'd agree that alien pathogens are unlikely to be a problem. Pathogens tend to lose many of their vital genes because the host provides the needed chemicals, and so they are dependent upon as specific type of host. Also sometimes pathogens depend on specific proteins to be able to carry out the infection. However, regular dirt bacteria might do nasty things to the aliens. On the other hand, the immune system will attack pretty much anything that is not self.

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For our type of life you are correct, water's polar nature is important for life that evolved in water but life that evolves in, say... liquid methane, polylipids, if I remember correctly, would do better in non polar liquids.

 

I do not believe this is correct. Can you make a chemical argument to support your claim? As I understand it, the polar nature of water makes it better suited as a medium to transport ions, which in turn is going to be the basis of any kind of energy transport that is based on chemistry.

 

I have seen some very compelling chemical arguments that polar liquids really are best. They are better for dissolving nutrients (whatever this life form considers a nutrient) and for exchanging ions (which any chemical life needs to do to transport energy). There are other useful properties of water that come from its polar nature. For example, the fact that ice floats is important to keep the oceans liquid. Using a liquid where ice sinks can very easily lead to the oceans freezing over. Water also has an amazing heat capacity, making it very useful as a way to smooth temperature changes. Water also has a fairly wide range of temperatures where it is liquid. Thus water will be liquid in a wider range of possible planets, and it will be more resistant to climate changes in the planet.

 

There are other molecules that have some or nearly all of these properties, but they are quite rare in the universe. Remember my comment about elemental abundance, with CH4, NH3 and H2O being the most common molecules after molecular hydrogen.

 

Daniel.

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This is demonstratively not true. Liquid Ammonia dissolves some important metals better than water is an easy example. Beings that evolved on a planet with liquid ammonia would see liquid ammonia was the perfect solvent.

 

That may be true but I'm not saying that everything disolves better in water, I'm saying that more things disolve in water and more can disolve before water becomes saturated (not in all cases but in general)

 

So if we were some other sort of life could we would still see evidence of the vastness of organic chemistry and know we were far less likely than carbon life?

 

Yes, point taken, but given how unlikely it is that we will in the foreseeable future make contact with alien life I think that non carbon based ETI is so unlikely that we should not devote too much time to it.

 

There are people who think that even our "humanoid" appearance is likely to be repeated, not like on star trek of course but more like the whole general shape, under this definition even a theropod dinosaur comes close to being humanoid. Much like when vastly different animals are shaped in a similar way due to environmental adaptations. Fish, sharks, Ichthyosaurs, dolphins, and even some squid take on the fast torpedo shape powered by fins.

 

We may look very similar as well, I wasn't so much suggesting physical appearance more that when we look deeper we will find similarities eg. scientific theories, politics, art, cultures etc...

 

I have my doubts that disease organisms are likely to be capable of infecting life from another planet unless life is so very specific that all life is identical with carbon chemistry it seems unlikely that all life on all planets would be closely related enough to be cross infective very often if at all.

 

On the other hand given the number of different types of bacteria and the rate at which they reproduce and therefore mutate I think it still poses the biggest risk to both us and them. From our point of view it wouldn't have to affect us directly to be a problem, suppose all our wheat crops became infected or even worse something which affected pollinating insects.

 

 

 

For our type of life you are correct, water's polar nature is important for life that evolved in water but life that evolves in, say... liquid methane, polylipids, if I remember correctly, would do better in non polar liquids.

 

While I agree that the safe bet is for carbon/water that breathes oxygen. I think we will find some interesting chemistries in unusual locations if nothing else...

 

I think if we are talking about intelligent life which, through scientific understanding and political organisation, can build space ships that are capable of travelling the vast distances needed to reach alien life and communicate when they get there they really have to be carbon/water based. There are millions of species on earth and only one species (us) have developed to the point we're able to have this conversation. I don't think you'd get enough variety in non carbon/water based life to get that one species.

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