"habitable zone"...?

[zdiddy]

I don't understand what people mean by the "habitual zone" of a star. Ok, so for any lifeform that ever has existed here on Earth, they could only live in this zone. But how can we assume that under different conditions, life couldn't exist elsewhere? We aren't perfectly adapted to live in the "habitual zone's" conditions because of coincedince of some overlying prerequisites for life, we are adapted because this is where we evolved.

Further, how can we even assume that water is necessary for life to occur? I realize that water is essential to the makeup of cells, but our cells are like that because we DID have water. Who can tell if other liquids and other elements can be replaced with billions of years of trial and error via evolution? Why is it assumed that conditions like those on Earth are needed to support life? I see why some sort of atmosphere is necessary, but why couldn't a lifeform be supported by another kind of gas, not oxygen or co2?

Ultimately, my argument is that we are not equipped to live in the habitual zone of the Sun by coincedince, it's actually quite the opposite. I think that if we do find life elsewhere (and I think it exists, whether or not we will is a tossup question) it will be radically different than what we know.

Someone tell me where I go wrong here, because I'm sure I'm missing something.

[Infinity Watcher]

I'm going to put a quick disclaimer on this post: the amount I know about (not even sure of the correct term so here's a guess) exobiology could be written on the back of a postage stamp and still leave room for name and address so take the following for what it's worth:

Firstly I assume you mean "habitable zone" rather than habitual (something of a nitpick but just for the sake of the search function on the boards I thought I'd throw it in).

As far as the actual post goes water is actually quite unusual so it is very good at what it does as a solvent and it's specific heat capacity (good for CSF and carrying heat away from brains and other important organs) but we can't be absolutely sure but I think to a degree we're looking for water as an indicator for life simply because we know that life can form depending on water, anything else is likely to be "life Jim, but not as we know it" to quote Spock from Star Trek.

We don't have the Enterprise (well we do or more accurately did (Wikipedia seems to indicate it was never brought back into service) but it's a space shuttle and somewhat short on Warp capabilities) We have to look for things visible from a distance that indicate life and water is a good place to start simply because it is so good at what it does from a chemical perspective similarly with O2 and CO2 they work well due to their chemistry (respiration pathways etc) and we know it can work, since it does, so it seems like a good place to start. Maybe one of the chemists on this board could fill in on the unique properties of water: Van der Waals forces and so forth, since I can't remember enough to be coherent beyond it being kind of unusual in some ways such as actually being liquid at its molecular mass.

As to what people mean by the "habitable zone" (which I think was the main question) it is fairly predicated on life as we know it (Which as I say above for various reasons is a good place tos tart looking if one were so inclined to do so) and is effectively a place where if you were to dump you or I on a planet in that region there is the potential that we might survive if the planet was suitable Wikipedia (http://en.wikipedia.org/wiki/Habitable_zone) has a reasonable article on it: it describes the habitable zone as being one where water could remain liquid and is dependant on such things as the luminosity of the star.

It doesn't mean it is the only place life could it exist but it is a fairly good indication of where "life as we know" it could exist (but see the criticism on the Wiki page about Europa like worlds)

Does that help at all?

[zdiddy]

actually it did. i was thinking that people assumed those were the necessary conditions for life, as opposed to the conditions that we KNOW can support life.

and also thanks for clearing up the terminology. that's why my searches weren't turning anything up

[Dr Nigel]

I don't understand what people mean by the "habitual zone" of a star.

More commonly known as the "habitable zone" or ecosphere. Its size and extent (depth) will vary according to the size, surface brightness and surface temperature of the parent star.


Ok, so for any lifeform that ever has existed here on Earth, they could only live in this zone. But how can we assume that under different conditions, life couldn't exist elsewhere?

Because there are certain things about which we can have a fair degree of confidence: life requires that a range of chemical reactions happen. If it is too hot, chemistry gets very difficult to control. If it is too cold, many reactions won't happen at all, and those that do will happen very slowly.

Similarly, life (even hypothetical life) cannot survive in conditions of extreme ionising radiation (because few materials can).


We aren't perfectly adapted to live in the "habitual zone's" conditions because of coincedince of some overlying prerequisites for life, we are adapted because this is where we evolved.

OK, which means that, since there is no detectable life on Venus or Mars, we can conclude that these conditions (i.e. in the habitable zone) are more likely to lead to a wide range of evolved life forms, assuming it can get started in the first place.


Further, how can we even assume that water is necessary for life to occur? I realize that water is essential to the makeup of cells, but our cells are like that because we DID have water. Who can tell if other liquids and other elements can be replaced with billions of years of trial and error via evolution?

Because, chemically, water is absolutely unique. It is volatile, but not so volatile that it remains liquid in only a narrow range of temperatures. This is due to the intermolecular interactions within any body of water.

In turn, this is due to water's chemistry.

Water is an amazingly versatile solvent. No other known substance is able to dissolve so many different compounds.

Again, this is due to water's chemistry.

The unique properties of water arise from two factors:
(1) the water molecule is not linear (i.e. the H-O-H does not form a straight line, but an angle. IIRC this is around 100-110°).
(2) oxygen is significantly more electronegative than hydrogen. This means that the electrons that comprise the bonds spend more time near the O nucleus than they do near the H nucleus.

Consequently, the water molecule is polar (one side of it is a little bit +ve, while the other side is a little bit -ve). This has a whole range of useful consequences that I shan't go into here and now.


Why is it assumed that conditions like those on Earth are needed to support life? I see why some sort of atmosphere is necessary, but why couldn't a lifeform be supported by another kind of gas, not oxygen or co2?

Because the chemistry that happens on Earth is most favourable for the properties of life (metabolism, replication, a boundary and so on).


Ultimately, my argument is that we are not equipped to live in the habitual zone of the Sun by coincedince, it's actually quite the opposite. I think that if we do find life elsewhere (and I think it exists, whether or not we will is a tossup question) it will be radically different than what we know.

But if we encounter life that is not life as we know it, how will we recognise it? Personally, I feel it is more likely that, if we encounter ET life, it will resemble life on Earth to at least some extent (e.g. be carbon-based, use water as a solvent, have something rather like DNA etc.)


Someone tell me where I go wrong here, because I'm sure I'm missing something.

I think the only thing you're missing is background knowledge of chemistry and biochemistry. The trouble is, there's no shortcut.

[Infinity Watcher]

actually it did. i was thinking that people assumed those were the necessary conditions for life, as opposed to the conditions that we KNOW can support life.

Well as with a lot of things, different people mean different things when they use it and like I say the chemistry of water is quite complex so there are reasons for assuming that complex life is likely to use it and certainly everything on earth uses water in some form or another so the assumption that water is necessary for life is not a bad one and may well turn out to be factually correct but the thing is that even assuming life not based on water could form (for which at present we have no evidence it must be stressed) would be completely different so what would you look for: even a really advanced civilisation might not be visible from here (and in fact in some ways as we get more advanced we get quieter: transmissions become more directed and so forth).

So if you are trying to decide where life could form you have to look at what life seems to require, unfortunately we only have the one sample at the moment so we have to assume that any life is similar to terrestrial life (since it appears dependant on chemical reactions for which it would be quite difficult to substitute other chemicals) this necessarily leads to the habitable zone: where those conditions can form and at present we really have no idea about whether non-water based life could come into existance: we don't even fully understand the way that life formed on Earth what we do know is it did and therefore it could and if it could here it might be able to elsewhere, (which doesn't mean that it did, just that it could)

[Dr Nigel]

D'oh! Infinity Watcher posted while I was composing.

[Infinity Watcher]

D'oh! Infinity Watcher posted while I was composing.
You were somewhat more lucid than I was though since I think my post is a bit unclear.

[zdiddy]

thanks both of you, really cleared things up. i wish i paid better attention in high school science :(

[m1omg]

More commonly known as the "habitable zone" or ecosphere. Its size and extent (depth) will vary according to the size, surface brightness and surface temperature of the parent star.



Because there are certain things about which we can have a fair degree of confidence: life requires that a range of chemical reactions happen. If it is too hot, chemistry gets very difficult to control. If it is too cold, many reactions won't happen at all, and those that do will happen very slowly.

Similarly, life (even hypothetical life) cannot survive in conditions of extreme ionising radiation (because few materials can).

OK, which means that, since there is no detectable life on Venus or Mars, we can conclude that these conditions (i.e. in the habitable zone) are more likely to lead to a wide range of evolved life forms, assuming it can get started in the first place.



Because, chemically, water is absolutely unique. It is volatile, but not so volatile that it remains liquid in only a narrow range of temperatures. This is due to the intermolecular interactions within any body of water.

In turn, this is due to water's chemistry.

Water is an amazingly versatile solvent. No other known substance is able to dissolve so many different compounds.

Again, this is due to water's chemistry.

The unique properties of water arise from two factors:
(1) the water molecule is not linear (i.e. the H-O-H does not form a straight line, but an angle. IIRC this is around 100-110°).
(2) oxygen is significantly more electronegative than hydrogen. This means that the electrons that comprise the bonds spend more time near the O nucleus than they do near the H nucleus.

Consequently, the water molecule is polar (one side of it is a little bit +ve, while the other side is a little bit -ve). This has a whole range of useful consequences that I shan't go into here and now.



Because the chemistry that happens on Earth is most favourable for the properties of life (metabolism, replication, a boundary and so on).



But if we encounter life that is not life as we know it, how will we recognise it? Personally, I feel it is more likely that, if we encounter ET life, it will resemble life on Earth to at least some extent (e.g. be carbon-based, use water as a solvent, have something rather like DNA etc.)



I think the only thing you're missing is background knowledge of chemistry and biochemistry. The trouble is, there's no shortcut.

if you have enough pressure , even ammonia will stay liquid in much wider range of temp. than water
also, chlorine can be on the place of oxyge in some biochemistries
i think these water+co2+oxygen are just "true dogmas" tha will be disproven over time just like the "100 percent true" dogma of flat stationary earth 2000 ya

and venus and mars are geologically almost dead planets, if, for example, Earth has chlorine atmosphere and HCL plus water oceans ,life will be still there, but with chlorine in place of oxygen in the molecular bonds, and breathing chlorine and drinking dilute HCl

DONT TEACH THAT BOY DOGMAS

[Noclevername]

i think these water+co2+oxygen are just "true dogmas" tha will be disproven over time just like the "100 percent true" dogma of flat stationary earth 2000 ya

Only if we find alien life that uses other chemistry.

[m1omg]

Only if we find alien life that uses other chemistry.

Humanity is extremly arrougant,We judge that life can use only water, carbon and oxygen, but we are struggling to get man second time to the moon and get unmanned little probe to Pluto.I don't think we will discover life until we invent interstellar travel.

[Ronald Brak]

I was going to write about the impossibility of life being anything but carbon based, but I don't have time because of a system crash caused by a computer virus.

[Dr Nigel]

Do not write it. [RUDE STUFF DELETED BY MODERATOR]

That's an ad hominem. What's your actual point?


Nature crached your computer because life can be different.

What evidence do you have to support this?


It is like writing speeds more than 1000 mph are impossible, that was thought of many early 20. century sciencist.

Not a valid analogy. The utility of carbon-based chemistry has been amply demonstrated. Just pick up any university-level organic chemistry text book.


Sry, I had to say you are closed minded earthcentrist:(.

Since you have not really supported your argument, I don't think you're in a position to accuse anyone of closed-mindedness.

Now, on to the actual point you made a few posts further up the thread:

I will grant that ammonia does remain liquid in a wide range of temperatures under higher pressure, but this does not change its chemistry fundamentally. There are several substances that become better solvents under high pressure (superfluid CO2 springs to mind), but this does not make them as versatile as water.

I'm not sure where you got the idea that CO2 is touted as essential for life; quite the reverse, in fact. Carbon is the most versatile element in terms of the kind of chemistry it takes part in. No other element can combine with a few others in so many different ways (well, hydrogen does, but it is only able to do so by attaching itself to carbon, oxygen or nitrogen). No other element can form long chains; no other element permits such a variety of structural geometries. With a bit of research, I could go on.

Thus, I conclude that life, in a form that we would be able to recognise, will be carbon-based, wherever it is found.

[m1omg]

But it could not breath oxygen for example, but another thing or live in another temperatures, water remains liquid even at high temperatures if pressure is high and metabolism - high temperatures life will have simply faster metabolism.Also, we proved and tested principles of organic chemistry just because we are carbon based lifeforms and we are most familiar with it.There is a great range of imo potentionally life forming compounds, of, for example, silicon at extreme temperatures, hybrid silicon-carbon, which is more plausible in milder temperatures...
Read Wikipedia, there is no fundamental reason that non carbon life is impossible.

And "impossible" is an arrogant word.You never know that is impossble until you explore every corner of the infinity universe.Some exotic life certainly is.And, remember, the universe is never what we expect and "plausible".

I apologise for the insult in my previous post, but, please dont be too close minded, our science is in diapers, we even do not know how to cure AIDS and cancer but we are claiming that other than carbon based life is impossible.We even dont understand the details of our biology and we are going to judge that life may exist only on the carbon base.Why?Just because it has not been yet found it doesnt mean that it doent exist.

And please dont start debunking Wikipedia as a band of jerks, Wikipedia is a most impressive information source for a non expert. Are you an expert to biochemistry?

[m1omg]

That's an ad hominem. What's your actual point?



What evidence do you have to support this?



Not a valid analogy. The utility of carbon-based chemistry has been amply demonstrated. Just pick up any university-level organic chemistry text book.



Since you have not really supported your argument, I don't think you're in a position to accuse anyone of closed-mindedness.

Now, on to the actual point you made a few posts further up the thread:

I will grant that ammonia does remain liquid in a wide range of temperatures under higher pressure, but this does not change its chemistry fundamentally. There are several substances that become better solvents under high pressure (superfluid CO2 springs to mind), but this does not make them as versatile as water.

I'm not sure where you got the idea that CO2 is touted as essential for life; quite the reverse, in fact. Carbon is the most versatile element in terms of the kind of chemistry it takes part in. No other element can combine with a few others in so many different ways (well, hydrogen does, but it is only able to do so by attaching itself to carbon, oxygen or nitrogen). No other element can form long chains; no other element permits such a variety of structural geometries. With a bit of research, I could go on.

Thus, I conclude that life, in a form that we would be able to recognise, will be carbon-based, wherever it is found.

So you agree with that, for example, carbon based life breathing chlorine is possible?

[korjik]

Dont forget that the four most common elements are hydrogen, helium oxygen and carbon, in that order. Water is probably the most common multi-element molecule there is. It seems unlikely that you can have life without there being some water around.

There is life on earth that dosent use oxygen, but uses sulfur compounds. but since most of these lifeforms are at the bottom of the ocean, there is plenty of water around.

[ToSeek]

Do not write it. [RUDE STUFF DELETED BY MODERATOR]
Nature crached your computer because life can be different.
It is like writing speeds more than 1000 mph are impossible, that was thought of many early 20. century sciencist.Sry, I had to say you are closed minded earthcentrist:(.

Name-calling and using profanity, even in abbreviated form, are both against the rules of this forum. Don't do it again.

ToSeek
BAUT Forum Moderator

[m1omg]

Name-calling and using profanity, even in abbreviated form, are both against the rules of this forum. Don't do it again.

ToSeek
BAUT Forum Moderator

I apologise.I have deleted it.Sorry, I will not do it again.

[Noclevername]

Humanity is extremly arrougant,We judge that life can use only water, carbon and oxygen, but we are struggling to get man second time to the moon and get unmanned little probe to Pluto.I don't think we will discover life until we invent interstellar travel.


Actually, no, many people do speculate about life based on other chemistries. We only know of one kind of life, and we look for that because it's the most convenient, and because we know it works.


And yes, unless somebody sends us a message I think we won't find life until we go look for it directly.

[Van Rijn]

Thus, I conclude that life, in a form that we would be able to recognise, will be carbon-based, wherever it is found.

Which also gets into definitions of life. For instance, I would consider a complex (organized) self-replicating machine that can operate and maintain itself in the "wild," and grows, adapts, and reproduces, to be life. I would recognize it by what it does. There is already room for argument on the definition of "life" and I expect it will become a more complex issue over time.

[m1omg]

Which also gets into definitions of life. For instance, I would consider a complex (organized) self-replicating machine that can operate and maintain itself in the "wild," and grows, adapts, and reproduces, to be life. I would recognize it by what it does. There is already room for argument on the definition of "life" and I expect it will become a more complex issue over time.

I think that we will able recognize all life, because of its reproduction , oherwise it is not life.
Look at this: http://en.wikipedia.org/wiki/Iron-sulfur_world_theory
http://en.wikipedia.org/wiki/Silicon_based_life#_note-1
"It is also possible that silicon compounds may be biologically useful under temperatures or pressures very different from the surface of a terrestrial planet, either in conjunction with or in a role less directly analogous to carbon.

A. G. Cairns-Smith has proposed that the first living organisms to exist were clay minerals - which were probably based on silicon.[3]"

[Noclevername]

Silicon can form complex molecules, just not as many or as complex as carbon. If there's no carbon-life to compete, it may be possible --assuming that silicon life can even exist, for which we have no evidence-- that less efficient S-life might survive and dominate a world, just as marsupials came to dominate Australia barring more competitive reproduction. But we do have evidence that C-life exists, so that's the main focus of our current searches.

[m1omg]

Silicon can form complex molecules, just not as many or as complex as carbon. If there's no carbon-life to compete, it may be possible --assuming that silicon life can even exist, for which we have no evidence-- that less efficient S-life might survive and dominate a world, just as marsupials came to dominate Australia barring more competitive reproduction. But we do have evidence that C-life exists, so that's the main focus of our current searches.

So you are saying, that, silicon-based life, can form, even prevail under certain conditions?That's exactly my opinion!I am not saying that it is abundant, just that it may exist, even prevail in certain conditions.

And what about silicon-carbon life?That is even more exotic - but also more plausible - than life based purely on one element (but even our carbon based life, that we are familiar with - utilizes some silicon compounds - for example, diatoms {and many other animals and plants} (biogenic silica);

http://en.wikipedia.org/wiki/Diatoms
http://en.wikipedia.org/wiki/Biogenic_silica

[Noclevername]

So you are saying, that, silicon-based life, can form, even prevail under certain conditions?That's exactly my opinion!I am not saying that it is abundant, just that it may exist, even prevail in certain conditions.

I'm saying it might exist, not that it necessarily can. We have no evidence that it can, but it's hypothetically possible.


And what about silicon-carbon life?That is even more exotic - but also more plausible - than life based purely on one element (but even our carbon based life, that we are familiar with - utilizes some silicon compounds - for example, diatoms {and many other animals and plants} (biogenic silica);

http://en.wikipedia.org/wiki/Diatoms
http://en.wikipedia.org/wiki/Biogenic_silica

"Plausible" is an unknowable quantity, since we have only one planet's example to go by. We may be the freaks of the galaxy, for all we know.

[m1omg]

I'm saying it might exist, not that it necessarily can. We have no evidence that it can, but it's hypothetically possible.



"Plausible" is an unknowable quantity, since we have only one planet's example to go by. We may be the freaks of the galaxy, for all we know.

True.But why are all on this forum trying say that non carbon based life is impossibe to zddidy.Simple high school chemistry didn't explain this.We simply don't know.

[Noclevername]

True.But why are all on this forum trying say that non carbon based life is impossibe to zddidy.Simple high school chemistry didn't explain this.We simply don't know.

No one on this thread has described noncarbon life as "impossible". Just that we know Carbon/water chemistry works, and that there are valid chemical/physical reasons why it works.

[Dr Nigel]

...assuming that silicon life can even exist, for which we have no evidence-- that less efficient S-life might survive and dominate a world, just as marsupials came to dominate Australia barring more competitive reproduction. ...

I think you meant "Si-life". S is the symbol for sulphur.

[Ilya]

So you agree with that, for example, carbon based life breathing chlorine is possible?
It would be possible on a planet which has much more chlorine than oxygen. The problemis how such planet would come into existence in the first place. Oxygen is the third most common element in the universe after H and He. Chlorine is several thousand times less abundant. How would an oxygen-poor, chlorine-rich planet ever form?

You might like this post I made on similar topic:
http://www.bautforum.com/showthread.php?p=663535#post663535

[Van Rijn]

True.But why are all on this forum trying say that non carbon based life is impossibe to zddidy.


We all have? Where? :) But, there have been points raised by posters about the advantages of carbon molecules and water, as well as the definition of life.

[Infinity Watcher]

This post is mostly to say "what Van Rijin said". Certainly I never meant to imply that we know that carbon based life is the only type of life possible (although I do think that for chemical reasons it is probably the most likely form of life as we know it (LAWKI) that we're likely to find (depending on how you define life and whether you include computer viruses and AIs in with life forms)

Also I was going to ask: the problem which strikes me with using Cl as an oxidising agent rather than oxygen would be one of transport. This has probably been thought out by someone so I'm asking what the solution is to it since my chemistry isn't good enough to answer it myself.

For terrestrial multicellular life, since diffusion is inadequate for gaseous exchange, it is necessary to use other methods of transportation: in humans we use iron based haemoglobin, some insects use a copper based compound instead but the principle is the same. Now the problem that strikes me is this: with Chlorine being a halide wouldn't any such bonds be much more stable so whilst uptake might be possible how would you decouple the chlorine at the tissues where it was actually needed? (I do note this doesn't present a problem for single-celled organisms but it seems as though this would put a crimp on anything more complex developing).

If an answer to this exists could someone with better chemistry come to my aid here or its going to be bugging me for ages!

[Dr Nigel]

But it could not breath oxygen for example,

Obligate anaerobes are known on Earth. "Breathing" is a function of large animals only. Any chemical reaction that (a) possesses a high delta-G (Gibbs free energy) and (b) can be coupled to other processes is likely to be used by life somewhere. We know that there are different options on Earth.


but another thing or live in another temperatures, water remains liquid even at high temperatures if pressure is high and metabolism - high temperatures life will have simply faster metabolism.

Well, of course I have to grant that it is possible. But I do not have to agree that it seems likely.

High-temperature chemistry doesm't only proceed faster. It makes a wider range of different products. This is what I meant several posts back when I suggested it was harder to control. Our current understanding of biochemistry indicates that nature has evolved some exquisite mechanisms for controlling chemistry in cells (an example I can suggest is the 17alpha- hydroxylase-17,20-lyase involved in the biosynthesis of steroid hormones - go to PubMed and do a search on that key word). These mechanisms work because of the prevailing chemical conditions in our cells. At significantly elevated temperatures, I am sure that they would not work, or at best they would not work anywhere near as well as they do at 37°C. Therefore, I stand by my conclusion that the control of intracellular chemistry at elevated temperatures is a significant challenge.


Also, we proved and tested principles of organic chemistry just because we are carbon based lifeforms and we are most familiar with it.

About 15 years ago, there were 11,000,000 known chemical compounds, of which 1,000,000 were inorganic and the remaining 10,000,000 were organic. I am sure that many more chemical compunds have been synthesised and characterised since then, but I am also sure that at least 90% of known compounds are organic, i.e. they are carbon-based.


There is a great range of imo potentionally life forming compounds, of, for example, silicon at extreme temperatures, hybrid silicon-carbon, which is more plausible in milder temperatures...
Read Wikipedia, there is no fundamental reason that non carbon life is impossible.

That is correct, there is no reason it is impossible. But there are several reasons for believing it to be unlikely.


And "impossible" is an arrogant word.

Isn't it a good thing I didn't use it, then.


You never know that is impossble until you explore every corner of the infinity universe.

That is not so. All science operates on the axiom that physical laws apply equally everywhere. Thus, chemistry is the same in the USA, the UK, France, the Moon, Neptune, and various exoplanets.

Taking this axiom to be true, you can deduce that something that you demonstrate to be impossible in the Solar system will be impossible elsewhere also. If you do not accept this axiom to be true, then you cannot draw any firm conclusions from anything you do, as you can convince yourself that moving the lab across the street might give you a different result.


Some exotic life certainly is.And, remember, the universe is never what we expect and "plausible".

I'm not sure what you mean by this.


I apologise for the insult in my previous post, but, please dont be too close minded,

If you study my previous posts, you will notice that they are comments on what seems most likely (based on a certain amount of background knowledge in chemistry and biochemistry). I do not believe my approach is closed-minded.


our science is in diapers,

On the contrary, I believe we have achieved a great deal. While there is still much to learn and many things to discover, our collective scientific achievements to date should not be dismissed so casually.


we even do not know how to cure AIDS and cancer

But, we know why they are so difficult to treat.


but we are claiming that other than carbon based life is impossible.

I haven't seen anyone make that claim in this thread.


We even dont understand the details of our biology

Speak for yourself. Collectively, there is a quite detailed understanding of our biology.


and we are going to judge that life may exist only on the carbon base.

Again, I have not seen anyone make that claim in this thread.


Why?Just because it has not been yet found it doesnt mean that it doent exist.

And just because it is logically possible, it does not necessarily follow that it is likely.


And please dont start debunking Wikipedia as a band of jerks, Wikipedia is a most impressive information source for a non expert.

Stange as it may seem to you, I have no intention of trying to gainsay Wikipedia on this topic.


Are you an expert to biochemistry?

Yes. My PhD is in biochemistry.

[m1omg]

Ok, but I why there are thermophiles that happily reproduce at 120 degress Celsius, if the bio processes cannot happen reliably about above 37 degress?Even on an average Earth's average desert or there opposite, we tropics there are even average temperatures above 38 degress, but life thrives here!

And by a high temperature life I mean that silicon based life may exist in high temperatures, that molucules essential for silicon based life cannot happen in the O2/CO2/N2/CH4 or whatever atmosphere of any body in the solar system, but Silane atmosphere.One problem is high temp. solvent...
And we STILL doesn't understand our biloogy because we dont know to cure diseases or how the brain exactly functions.And yes, you are an expert at biology..but cabon....

And tell me what fundamental psychyc law prohbits the existence of the non carbon-based life?

Sorry, I have no disrespect to you but I think that we cannot judge prematurely, the universe is here 15 000 000 000 years, we only about 100 000 and we spend 70 000 years of our existence in the Stone age, Sorry, I think that the real understanding of the nature will not be achieved soon...And far future generations of people will laugh at certain aspect of our culture and science just like we laugh at Geocentrism or Medival beliefs about Earth and astronomy.

[Van Rijn]

And tell me what fundamental psychyc law prohbits the existence of the non carbon-based life?


I'm curious. Who are you arguing with?

[Ilya]

Ok, but I why there are thermophiles that happily reproduce at 120 degress Celsius, if the bio processes cannot happen reliably about above 37 degress?

Who claimed that "bio processes cannot happen reliably about above 37 degress"?

[m1omg]

Dr Nigel

"High-temperature chemistry doesm't only proceed faster. It makes a wider range of different products. This is what I meant several posts back when I suggested it was harder to control. Our current understanding of biochemistry indicates that nature has evolved some exquisite mechanisms for controlling chemistry in cells (an example I can suggest is the 17alpha- hydroxylase-17,20-lyase involved in the biosynthesis of steroid hormones - go to PubMed and do a search on that key word). These mechanisms work because of the prevailing chemical conditions in our cells. At significantly elevated temperatures, I am sure that they would not work, or at best they would not work anywhere near as well as they do at 37°C. Therefore, I stand by my conclusion that the control of intracellular chemistry at elevated temperatures is a significant challenge."

If you mean only human cells, then sorry but if you mean every living cell then it's a nonsense...

[Noclevername]

If you mean only human cells, then sorry but if you mean every living cell then it's a nonsense...

He was just showing an example. Chemical processes in lifeforms work the way they do for specific physical reasons. These physical properties mean that chemical reactions work differently under different conditions, making it less likely for complex organics or their alternate-chemistry analogues to form, or to function in a manner consistent with life.

Extremophiles may be adapted to survive at higher/lower temperatures than most Terrestrial life, but there's no evidence that they originated under those conditions.

According to everything we know about chemistry and physics, carbon works best as the basis of biochemistry, and liquid water works best as a biosolvent. Other biochems might be possible, but they'd be less efficient, less stable, have less survival value and probably be unable to support a level of complexity needed for sentience or human-level intelligence.

[Grashtel]

Dr Nigel

"High-temperature chemistry doesm't only proceed faster. It makes a wider range of different products. This is what I meant several posts back when I suggested it was harder to control. Our current understanding of biochemistry indicates that nature has evolved some exquisite mechanisms for controlling chemistry in cells (an example I can suggest is the 17alpha- hydroxylase-17,20-lyase involved in the biosynthesis of steroid hormones - go to PubMed and do a search on that key word). These mechanisms work because of the prevailing chemical conditions in our cells. At significantly elevated temperatures, I am sure that they would not work, or at best they would not work anywhere near as well as they do at 37°C. Therefore, I stand by my conclusion that the control of intracellular chemistry at elevated temperatures is a significant challenge."

If you mean only human cells, then sorry but if you mean every living cell then it's a nonsense...
Read what he said again. He isn't saying that high temperature life is impossible or "bio processes cannot happen reliably about above 37 degress", he is just saying that it is hard for biological processes to work at high temperatures, which is why only a few extremophiles do live at high temperatures rather than normal bacteria doing so.

[Dr Nigel]

m1omg, I said that intracellular control of high-temperature chemistry is a significant challenge.

Extremophiles that reproduce at 100-130°C overcome this challenge by some very hefty adaptations. So much so that many of them cannot reproduce at lower temperatures (e.g. 60°C).

You are talking about higher temperatures still, temperatures at which silicon becomes a significant participant in chemical reactions.

A feature of all chemical reactions is something known as activation energy. This is the energy required for two molecules to react with one another. It has a different value for different reactions. If the two molecules don't have the required energy, they won't react no matter how often they bump into one another.

For example, the reaction between sodium and water has a relatively low activation energy (compared with the available energy at the kind of temperatures we humans find comfortable). Consequently, sodium reacts very readily with water. By contrast, the reaction between nitrogen and hydrogen has a much higher activation energy, so this reaction only happens to any significant extent at high temperatures and pressures.

Thus, the higher the temperatures, the more types of reaction become available to any particular molecule.

There is a second feature, possessed by all chemical compounds, which is sometimes referred to as thermodynamic stability. Different chemical compounds have different intrinsic stability, which will vary with temperature. For instance, many chemical reactions could have two possible products, one of which may be more stable than the other. For the sake of argument, call them A and B. Often the more stable product has a higher activation energy. So there will be some temperatures at which only A is formed, a range of temperatures at which both A and B are formed (in varying proportions) and some temperatures at which only B is formed. Industrial chemists use this feature to control the outcome of some reactions.

As further illustration, as an undergraduate I was assigned a project to synthesize econazole. While doodling away at possible mechanisms for one of the reactions in the synthesis, I hit upon two outcomes - one in which the desired product is formed, and one that formed a polymer of my synthetic intermediate. I mentioned this to the professor, who told me that the stuff can indeed polymerise, and will do so quite rapidly if it got hot. A sample of this stuff kept in a cupboard for a few weeks did indeed polymerise - it went from yellow, through orange to red and then to brown (indicating that the extent of conjugation within the molecule was increasing, and thus that the molecule was getting bigger).

So, back to the high-temperature life problem:

At significantly elevated temperatures (say, a few thousand degrees C), even if you can control what reactions occur (among the many possible ones), your product is unlikely to exist for very long unless it is intrinsically very stable. This limits the range of chemical compounds available to your organism.

Life as we know it here on Earth utilises many tens of thousands of different chemical compounds (and that's not counting proteins). I accept that life could exist in some basic form with fewer chemical compounds, but my conclusion remains:

Significantly elevated temperatures represent a significant challenge to the control of intrecellular chemistry, and thus life that we would be able to recognise is unlikely at very high temperatures.

[Dr Nigel]

...
And we STILL doesn't understand our biloogy because we dont know to cure diseases or how the brain exactly functions.And yes, you are an expert at biology..but cabon....

We know how many diseases occur. Many of them we can cure, by applying toxic chemicals. Penicillin, for instance, is toxic to many bacteria, but harmless to most eukaryotes. We know how many dozens of types of cancer occur. We understand how and, to a lesser extent, why it happens. But this is not the same as being able to kill only the cancerous cells. There are many therapies being investigated that act by killing cancer cells in a specific fashion, but there are complex and subtle interactions within the body that we do not yet understand, so many of these therapies will fail during clinical trial.

But there are still a great many aspects of human biology that we, collectively understand in great detail.


And tell me what fundamental psychyc law prohbits the existence of the non carbon-based life?

All I can do is quote my earlier post: "... there is no reason it is impossible. But there are several reasons for believing it to be unlikely."


Sorry, I have no disrespect to you but I think that we cannot judge prematurely, the universe is here 15 000 000 000 years, we only about 100 000 and we spend 70 000 years of our existence in the Stone age, Sorry, I think that the real understanding of the nature will not be achieved soon...

Understanding is not something that will suddenly happen one day. It is a long, slow journey. We have made a good start (after all, we have come so far) but we do not know how much further there is to go. But we are accumulating understanding all the while.


And far future generations of people will laugh at certain aspect of our culture and science just like we laugh at Geocentrism or Medival beliefs about Earth and astronomy.

Well, not in the same way. We laugh at geocentrism because all it takes to realise that the Earth is not the centre of things is to look at the behaviour of the sun, moon, stars and planets and think about what we are seeing. A heliocentric solar system could, in principal, have been deduced by the ancient Egyptians*, if they had had the idea of checking what they thought happened with what actually does happen. We recognise many Mediaevel beliefs as attempts to rationalise a largely inexplicable world. However, we now have a basic knowledge of how the universe works. Even if we are wrong, we have a reasonable approximation. Do we laugh at Newton, after the advent of general relativity? No, because his equations are still a reasonable approximation in many cases.


* I'm sure someone will correct me if there is a good reason why they couldn't...