[X] My Assistant

[jaredGalen]

Thought this article title was a little over the top, the kind of one you would
expect to see followed by lots of exclamation marks.

Interesting article though.

"IF LIFE exists on Titan, Saturn's biggest moon, we could soon know about it - as long as it's the methane-spewing variety. The chemical signature of microbial life could be hidden in readings taken by the European Space Agency's Huygens probe when it landed on Titan in January."

http://www.newscientistspace.com/article.ns?id=dn7716

[exoplanet]

I quote JRheling:

"Consider that some of 2004's top ten scientific discoveries (as rated by AAAI) concerned the chemical properties of WATER. If we don't yet understand H2O inside and out, forget about predicting life given some alternative chemical basis.

To put a spotlight on the problem, consider that a water molecule essentially consists of 15 particles, and so a pair of water molecules involves up to 435 interactions. Create a computer model of those two water molecules, and you have a lot of math to juggle. Fine, that's tractable, but make it 100 water molecules, and forget about it (although, admittedly, you could make simplifying assumptions -- not all of those interactions will amount to much). So simulating a water nanodroplet is a big task. This just goes to say that "brute force" computation cannot be the bridge between molecular chemistry and a hypothetical new kind of biology. And if water still holds secrets, you can see that no more-burly kind of chemical theory is in hand yet."

Thank you for your post. It is conceivable that if we do not know all the properties of water . . . how in the heck do we know what the limitations of life is. I am by no means from the astrobiological mindset, however, I do believe that from what has been discovered both from Cassini and Hyugens . . . a more complex probe/rover would be a highly rewarding endeavor for both NASA and ESA.

I would love to begin some very heated discussions about the surface and atmospheric chemistry of Titan and the implications to the possibility of life pro and con. It is already being discussed in some important scientific journals and I would like to begin the discussion here as well (Also, I don't have the $ to subscribe or a nearby university to access most of the recently published articles).

[JRehling]

I quote JRheling:

Rehling, but lots of people like to move the H!

I would love to begin some very heated discussions about the surface and atmospheric chemistry of Titan and the implications to the possibility of life pro and con.  It is already being discussed in some important scientific journals and I would like to begin the discussion here as well (Also, I don't have the $ to subscribe or a nearby university to access most of the recently published articles).

A fascinating (and speculative) topic is the issue: Given a planet with appropriate conditions (for life as we know it, or LAWIK), what is the probability that life will actually arise? Internet posts and books can be found postulating (or arguing, or hoping) that the number is very close to 1.0. (Of course, the definition of "appropriate" is a wildcard!) If I had to make a guess this instant, I would say the opposite, something very close to 0.0. But some basic key facts are:

a) We have no unbiased data. We know of one case of biogenesis, but that data point stems from the same basic fact that we are here to make that observation! This is the anthropic principle at work.

We have a merely-kinda biased data point in that life on Earth seems to have arisen very quickly -- it didn't just dawdle around and then suddenly happen at some time in the middle of Earth's history. Or did it? It's not quite a solid fact when life could have arisen. And in any case, if life on Earth could have arisen at any old time, but it happened to arise, say, in the first 1% of the time that it possibly could have, that is merely a suggestive finding -- not proof. There was a 1% chance it would have done so anyway. In fact, more than 1%, because we wouldn't be here to talk about it if biogenesis of bacteria had happened only a million years ago.

c) It doesn't happen VERY fast. You can't throw the right nonbiological compounds in a bucket for an hour and get bacteria to evolve. It doesn't happen in days, or weeks, and probably not in centuries. But with a bigger bucket? A Pacific Ocean sized bucket, and a million years? What about a thimble and a trillion years?

Let's try this model: Given a quantity of soup, and a span of time, how great does the product of those two numbers have to be for life to arise? We might guess that given twice the bucket size, we could expect life in half the time. This model is valid if biogenesis consists of enthalpy's little fingers twirling organic molecules like Rubik's Cube, "trying" to create biology and succeeding when the correct sequence occurs by chance, which is inevitable given enough molecules in enough oceans over enough time.

Is that a correct model? Surely on some level, but tempered by modularity. Life did not arise when the molecules making up a raccoon or a pine tree randomly fell into place. The cell was an intermediary step from which natural selection could proceed, and surely there are subcellular intermediate steps as well. But still, something had to arise that crossed the natural-selection barrier. This process is not well understood.

To work with a simple model, I took the random-compilation model and assumed that biogenesis took place when M molecules were placed together in the right linear sequence. In other words, if biogenesis were the sorting through of M! (M factorial) permutations, until the right one were found. Then, for planet-like values of ocean-bucket volume and geological time, what is the probability of biogenesis as a function of M?

That's surely not literally accurate, but the mathematics were instructive. If M were 2, then biogenesis would take place in a thimble in a fraction of a second. If M were very very large, biogenesis would take place in very vast space and very vast time. The question is, how does the probability of biogenesis (some of the key values of Drake's Equation) vary as a function of M? We don't get to alter M, the laws of biochemistry have determined it, but it is still interesting to see how Drake's Equation might depend upon the inherent laws of the universe.

The answer is, the probability (Pl) of biogenesis on a planet given a few eons is very near 1.0 for low values of M, and then as M grows it very abruptly switches to near 0.0. The switchover happens somewhere around 55 (to cosmological standards of approximation, the exponent you'd use to express the number of molecules in an ocean times the number of molecule-manipulations you'd have in an eon).

This is so based on speculation that no conclusions can be drawn, but it seems quite reasonable to me that biogenesis is a freakishly rare event -- lacking a way to clean up all of my questionable assumptions, we still get a basic truth -- if the number of elements in the minimum requisite biosufficient "thing" is less than about 50, the galaxy will be full of life. If it's more than about 60, we may be totally alone -- not one stinking bacterium in all the galaxies anyplace farther away than Voyager 1!

[AndyG]

a) We have no unbiased data. We know of one case of biogenesis, but that data point stems from the same basic fact that we are here to make that observation! This is the anthropic principle at work.

Firstly, on the anthropic principle: over recent history, the position of humans has been displaced by science and intelligent thought. For example, we've discovered that we're not at the centre of a finite universe (whose planets move in circles and are pushed by angels), the Sun isn't the only star with planets, our species isn't the be-all-and-end-all of all evolution... Science tends to work against the inate biases of anthropicism, and is (supposedly) designed to take a more objective viewpoint.

Work relating to Earth's pre-biosphere suggests that life started amazingly early...and perhaps even more than once. Consider: 4GA ago solar output was (what? 30%?) lower than it is today, the planet was bathed in UV, the centre of some extraordinary impact events, and yet life started in what, in geological terms, is almost the blink of an eye. I therefore have to take the alternative, much more optimistic view: if the processes that lead to cellular life get a chance, and the resources are available, then it will occur. On Earth or anywhere. Without a doubt in my mind. Sign me up for a low "M". ;-)

...if life on Earth could have arisen at any old time, but it happened to arise, say, in the first 1% of the time that it possibly could have, that is merely a suggestive finding -- not proof. There was a 1% chance it would have done so anyway. In fact, more than 1%, because we wouldn't be here to talk about it if biogenesis of bacteria had happened only a million years ago.

I can turn that around. Yes, there is an anthropic principle at work here, since we (as the intelligent species that does science) can study Earth's early history to some level. But there is nothing to particularly argue against the possibility that intelligence (with all its negative evolutionary costs regarding brain size & power, relative weakness in infants, etc.) could have arisen 50 or even 500 million years ago if evolutionary paths were different, and done the same thing. The indisputable fact is, when you look back in time and disregard the details and time taken for the soup-intelligence transition, life started in the few million years that conditions first allowed it to. That 1% chance you see as "luckily coming up" could (I'd even argue "should") be viewed as: life appears to be an inevitable byproduct of basic chemistry in any suitably large environments.

I would be much more pessimistic if the geological record showed (for example) a half billion years of "nothing much" before the soup-stage. But it doesn't.

(This is naturally a factor siezed on by panspermia-lovers. Personally I feel that space might be a good source for plentiful organic molecules, but nothing much more advanced than that. Life needs water. Water requires gravity and pressure.)

...the probability (Pl) of biogenesis on a planet given a few eons is very near 1.0 for low values of M, and then as M grows it very abruptly switches to near 0.0. The switchover happens somewhere around 55 (to cosmological standards of approximation, the exponent you'd use to express the number of molecules in an ocean times the number of molecule-manipulations you'd have in an eon).

This is so based on speculation that no conclusions can be drawn, but it seems quite reasonable to me that biogenesis is a freakishly rare event...

Not necessarily. The conclusions you can draw are:

A: M is low and there is inevitability.
B: M is higher and we are a statistical freak.

Our admittedly single-point data suggests inevitability. Which seems as reasonable to me as freakishness does to you! This probably means, in your model, that (for the Earth at least) M is low, or (more likely) comprised of numerous sub-factors whose independent M-lettes are low.

Obviously the only way to answer this question (and for the first time in human history we might be on the verge of doing this) is to widen our range of datapoints. Missions to Mars, Europa and the Venusian atmosphere to specifically search for life are (I'd argue) essential. A TPF in orbit in the next couple of decades would be good too!

Andy G

[JRehling]

[quote=AndyG,Jul 26 2005, 02:03 AM]Firstly, on the anthropic principle: over recent history, the position of humans has been displaced by science and intelligent thought. For example, we've discovered that we're not at the centre of a finite universe (whose planets move in circles and are pushed by angels), the Sun isn't the only star with planets, our species isn't the be-all-and-end-all of all evolution... Science tends to work against the inate biases of anthropicism, and is (supposedly) designed to take a more objective viewpoint.

[/quote]

Two things. One, of course, this sort of trend-analysis is suggestive, but not evidence. The facts that we once thought that the Earth was the center of the universe, and that it turned out not to be the case doesn't mean that it is impossible for the Earth to be unique in some other way.

Two, even so, on this level, the track record is not unidirectional from mankind-is-special to mankind-is-just-another-germ-on-just-another-rock. I can think of two dawning relevations that tilt the other way. One, the quantum mechanical fact that observers (in any case we have to latch onto, humans) can actually alter the outcome of an event by passively observing it -- this is still not understood, and would surely (?!) work just as well if some alien intelligence were the observer, but it still shows that we have a role that is more special than if a lump of dirt were in the lab in place of the scientist. This is still shocking to contemplate, and does work counter to the general trend you describe. In addition, the speculative paradigm regarding extraterrestrial intelligence had cause to wane, not wax, from 1900 to 1976. From the 17th through 20th centuries, sober individuals opined that places like Venus and Mars were appropriate hosts for civilizations and that numerous unknown planets would surely be the same, but the more we have gathered evidence from our solar system, the more we find that "earthlike" is a rare quality out there. Even with the Huygens landing, our discovery of channels coincided with the glum realization that the equatorial dark areas, which betting people might have guessed were seas, are remarkably Venus-looking rock-on-sand plains.

Of course, those two observations do not directly impinge upon the Pl question, but neither do heliocentrism, etc. Trends are just trends, and my only point here is, if nature is "trying" to foreshadow the answer to the Pl question, she is being a good mystery writer; there is foreshadowing on both sides.

[quote=AndyG,Jul 26 2005, 02:03 AM]Work relating to Earth's pre-biosphere suggests that life started amazingly early...and perhaps even more than once. Consider: 4GA ago solar output was (what? 30%?) lower than it is today, the planet was bathed in UV, the centre of some extraordinary impact events, and yet life started in what, in geological terms, is almost the blink of an eye.

[/quote]

That's not quite clear. The problem is, we have a subtraction to perform with two uncertain numbers: When did life arise, and when could it have. The uncertainty surrounding each number is pretty small, as a percentage, but because we're subtracting, the uncertainty surrounding the result is orders of magnitude. See for example:

http://www.livescience.com/forcesofnature/...arly_earth.html

It is credible that the Earth became habitable 4.2 or 4.3 GYA, with life not forming until 3.8 or 3.9 GYA -- and it is therefore credible (I'm not saying probable) that biogenesis here took 500 million years of random molecular combinations. If so, that's up to 11% of the time-since-creation, which casts doubt upon the notion that life started as soon as it could have. Admittedly, I chose the most extreme values to get that 11%, and the lowest value is arbitrarily close to 0% -- but we don't know. The math I laid out before suggests that either the real number was very close to 0%, or life is a pretty chancy thing, and if it's chancey, that's not far from saying (in terms of M) that it is almost miraculous.

[quote=AndyG,Jul 26 2005, 02:03 AM]I therefore have to take the alternative, much more optimistic view: if the processes that lead to cellular life get a chance, and the resources are available, then it will occur. On Earth or anywhere. Without a doubt in my mind. Sign me up for a low "M". ;-)
I can turn that around. Yes, there is an anthropic principle at work here, since we (as the intelligent species that does science) can study Earth's early history to some level. But there is nothing to particularly argue against the possibility that intelligence (with all its negative evolutionary costs regarding brain size & power, relative weakness in infants, etc.) could have arisen 50 or even 500 million years ago if evolutionary paths were different, and done the same thing.

[/quote]

The rise of intelligence is another matter, of course, and it's an interesting fact that vertebrates seem to have made such faltering progress towards it. The dinosaurs don't seem to have made moon landings despite tens of millions of years of having had nontrivial brains.

[quote=AndyG,Jul 26 2005, 02:03 AM]The indisputable fact is, when you look back in time and disregard the details and time taken for the soup-intelligence transition, life started in the few million years that conditions first allowed it to. That 1% chance you see as "luckily coming up" could (I'd even argue "should") be viewed as: life appears to be an inevitable byproduct of basic chemistry in any suitably large environments.

I would be much more pessimistic if the geological record showed (for example) a half billion years of "nothing much" before the soup-stage. But it doesn't.

[/quote]

Well, it may have been half a billion years. We don't have a clear word on that yet, and whether it was half a billion or half a million, that enormous difference would only impact modestly on what it means for M, and we surely don't have the tools now or later to rule out the half-million-years possibility.

[quote=AndyG,Jul 26 2005, 02:03 AM](This is naturally a factor siezed on by panspermia-lovers. Personally I feel that space might be a good source for plentiful organic molecules, but nothing much more advanced than that. Life needs water. Water requires gravity and pressure.)
Not necessarily. The conclusions you can draw are:

A: M is low and there is inevitability.
B: M is higher and we are a statistical freak.

Our admittedly single-point data suggests inevitability. Which seems as reasonable to me as freakishness does to you! This probably means, in your model, that (for the Earth at least) M is low, or (more likely) comprised of numerous sub-factors whose independent M-lettes are low.

[/quote]

I agree that we face these two possibilities and are currently stymied as to which has the evidence its way. We can demonstrate a lower bound on M by doing the "bucket" experiment, but we're left only saying that M must be more than 30 or something. (Avogadro's Number times a large number of interaction-opportunities.) My high-M guess is only a guess. But you must admit, it's a little dicey to stipulate that M is between 30 and 50 when all we know is that it's greater than 30.

[quote=AndyG,Jul 26 2005, 02:03 AM]Obviously the only way to answer this question (and for the first time in human history we might be on the verge of doing this) is to widen our range of datapoints. Missions to Mars, Europa and the Venusian atmosphere to specifically search for life are (I'd argue) essential. A TPF in orbit in the next couple of decades would be good too!
Andy G

[/quote]

Indeed, it is possible that, eg, a Europa ocean probe could definitively answer the Pl question! Not only in the positive (if life could be found and proven to require a separate biogenesis), but even in the negative (if it could be shown that such an ocean was a suitable habitat, but was nevertheless lifeless). That is, a negative result could give us a value of M that wouldn't quite prove the universe lifeless, but would give M a lower bound close to the value that would mean the universe is lifeless. Possible oceans of giant planet satellites probably give us our only chance to set a lower bound on M, while any test for the existence of a separate biogenesis would answer the question the other way.

It has been noted elsewhere that if we find life on Mars, it may tell us nothing philosophical if it turns out to have shared biogenesis with terrestrial life.

[MacAndrew]

Two things. One, of course, this sort of trend-analysis is suggestive, but not evidence. The facts that we once thought that the Earth was the center of the universe, and that it turned out not to be the case doesn't mean that it is impossible for the Earth to be unique in some other way.

Two, even so, on this level, the track record is not unidirectional from mankind-is-special to mankind-is-just-another-germ-on-just-another-rock. I can think of two dawning relevations that tilt the other way. One, the quantum mechanical fact that observers (in any case we have to latch onto, humans) can actually alter the outcome of an event by passively observing it -- this is still not understood, and would surely (?!) work just as well if some alien intelligence were the observer, but it still shows that we have a role that is more special than if a lump of dirt were in the lab in place of the scientist. This is still shocking to contemplate, and does work counter to the general trend you describe. In addition, the speculative paradigm regarding extraterrestrial intelligence had cause to wane, not wax, from 1900 to 1976. From the 17th through 20th centuries, sober individuals opined that places like Venus and Mars were appropriate hosts for civilizations and that numerous unknown planets would surely be the same, but the more we have gathered evidence from our solar system, the more we find that "earthlike" is a rare quality out there. Even with the Huygens landing, our discovery of channels coincided with the glum realization that the equatorial dark areas, which betting people might have guessed were seas, are remarkably Venus-looking rock-on-sand plains.

Of course, those two observations do not directly impinge upon the Pl question, but neither do heliocentrism, etc. Trends are just trends, and my only point here is, if nature is "trying" to foreshadow the answer to the Pl question, she is being a good mystery writer; there is foreshadowing on both sides.
That's not quite clear. The problem is, we have a subtraction to perform with two uncertain numbers: When did life arise, and when could it have. The uncertainty surrounding each number is pretty small, as a percentage, but because we're subtracting, the uncertainty surrounding the result is orders of magnitude. See for example:

http://www.livescience.com/forcesofnature/...arly_earth.html

It is credible that the Earth became habitable 4.2 or 4.3 GYA, with life not forming until 3.8 or 3.9 GYA -- and it is therefore credible (I'm not saying probable) that biogenesis here took 500 million years of random molecular combinations. If so, that's up to 11% of the time-since-creation, which casts doubt upon the notion that life started as soon as it could have. Admittedly, I chose the most extreme values to get that 11%, and the lowest value is arbitrarily close to 0% -- but we don't know. The math I laid out before suggests that either the real number was very close to 0%, or life is a pretty chancy thing, and if it's chancey, that's not far from saying (in terms of M) that it is almost miraculous.
The rise of intelligence is another matter, of course, and it's an interesting fact that vertebrates seem to have made such faltering progress towards it. The dinosaurs don't seem to have made moon landings despite tens of millions of years of having had nontrivial brains.
Well, it may have been half a billion years. We don't have a clear word on that yet, and whether it was half a billion or half a million, that enormous difference would only impact modestly on what it means for M, and we surely don't have the tools now or later to rule out the half-million-years possibility.
I agree that we face these two possibilities and are currently stymied as to which has the evidence its way. We can demonstrate a lower bound on M by doing the "bucket" experiment, but we're left only saying that M must be more than 30 or something. (Avogadro's Number times a large number of interaction-opportunities.) My high-M guess is only a guess. But you must admit, it's a little dicey to stipulate that M is between 30 and 50 when all we know is that it's greater than 30.
Indeed, it is possible that, eg, a Europa ocean probe could definitively answer the Pl question! Not only in the positive (if life could be found and proven to require a separate biogenesis), but even in the negative (if it could be shown that such an ocean was a suitable habitat, but was nevertheless lifeless). That is, a negative result could give us a value of M that wouldn't quite prove the universe lifeless, but would give M a lower bound close to the value that would mean the universe is lifeless. Possible oceans of giant planet satellites probably give us our only chance to set a lower bound on M, while any test for the existence of a separate biogenesis would answer the question the other way.

It has been noted elsewhere that if we find life on Mars, it may tell us nothing philosophical if it turns out to have shared biogenesis with terrestrial life.

To try and make a long story short: the definition of M, a number deriving from a specific mathematical model of biogenesis, is such that it, given the (scanty) available data, must be greater than 30, and such that it leads to a complete collapse of the probability of biogenesis around 55. But, at the same time, supposing that M is between 30 and 50 (the only "useful" values for a viable biogenesis) should be considered "dicey". So the Universe should be probably lifeless outside Earth.

All this is a logical fallacy, alas, very common in scientific thinking: confusing the mathematical model with the real world and incorrectly transferring tautological deductions from the former to the latter (in this case, using properties of M which tautologically derive from its mathematical definition to draw negative inferences about the possibility of biogenesis in the real Universe).

Of course, there is an INFINITE number of possible definitions of M where viable biogenesis in other worlds is confined to values between 30 and 50 (or 30 and 31, or 30.03 and 30.04 for that matter), but that shows nothing about the real possibility of biogenesis.