Thoughts on Abiogenesis

[FrumiousBandersnatch]

.. and yet Darwian evolution is not possible under the low temperatures and physically absent liquid water conditions on Titan's surface (and methane lakes).

Yet one particular NASA Ames Planetary scientists publishes papers on 'the possibility' of Titan based methanogenic 'lifeforms'? Why is that?

Why not? Darwinian evolution just involves reproduction with heritable variation & selection - no particular temperature or chemistry specifications... I agree that it seems unlikely, but I understand that simple metabolic pathways have been suggested for Titan with methane as a solvent. How realistic they are, I have no idea.

Yes .. a different definition to suit the particular context/environment under study .. Highlights what I've been saying about the importance of thoroughly categorising the natural environment as a first step .. which may/may not lead to concluding/diagnosing 'life' within that specific environment/context.

Life's definition is far from being established as a universal 'given' .. yet everyone throws around the term as though it is!?

I think there's been a general recognition that we can't be absolutely definitive about life for a long time; viruses still spark debate. There's an interview on the NASA site where an astrobiologist suggests that we shouldn't bother making definitions of life in advance of finding suitable candidates...

 

[Occams Barber]

I think there's been a general recognition that we can't be absolutely definitive about life for a long time; viruses still spark debate. There's an interview on the NASA site where an astrobiologist suggests that we shouldn't bother making definitions of life in advance of finding suitable candidates...

Perhaps we should keep it simple and apply a variant of the obscenity test:

I don't know what life is but I'll know it when I see it.​

On "I Know It When I See It" (yale.edu)

OB

 

[SelfSim]

By what is it determined that Darwinian evolution isn't possible there.

DNA/RNA molecules possess an outwardly negative charge which repeats along their backbones, which then allows DNA and RNA to dissolve and float freely in normally polarised liquid water. In this fluid medium, DNA and RNA can interact with other biomolecules, leading to complexity in biological systems.

For liquid-waterless bodies like Titan, where hydrocarbons dominate, molecules like DNA and RNA cannot dissolve in hydrocarbons.

In fact, any molecules with any sort of outward charge more or less 'goop' up in hydrocarbons. The so-called 'blueprints of life on Earth', (when modelled as 'encoded instruction based' DNA and RNA), cannot perform their translation/transcription functions on low temperature bodies with predominately liquid hydrocarbons.

IOW: it a chemical properties issue for any Titan-like environment.

 

[Ponderous Curmudgeon]

Perhaps we should keep it simple and apply a variant of the obscenity test:

I don't know what life is but I'll know it when I see it.​

On "I Know It When I See It" (yale.edu)

OB

I've been avoiding saying that, but it was an interesting definition.

 

[Occams Barber]

DNA/RNA molecules possess an outwardly negative charge which repeats along their backbones, which then allows DNA and RNA to dissolve and float freely in normally polarised liquid water. In this fluid medium, DNA and RNA can interact with other biomolecules, leading to complexity in biological systems.

For liquid-waterless bodies like Titan, where hydrocarbons dominate, molecules like DNA and RNA cannot dissolve in hydrocarbons.

In fact, any molecules with any sort of outward charge more or less 'goop' up in hydrocarbons. The so-called 'blueprints of life on Earth', (when modelled as 'encoded instruction based' DNA and RNA), cannot perform their translation/transcription functions on low temperature bodies with predominately liquid hydrocarbons.

IOW: it a chemical properties issue for any Titan-like environment.

@SelfSim

Thank you for explaining this in a way mere mortals like me can understand (seriously)

Is it possible that there is a combination of substitutes which are neither DNA/RNA or liquid water but could perform a similar function?

OB

 

[Astrid]

DNA/RNA molecules possess an outwardly negative charge which repeats along their backbones, which then allows DNA and RNA to dissolve and float freely in normally polarised liquid water. In this fluid medium, DNA and RNA can interact with other biomolecules, leading to complexity in biological systems.

For liquid-waterless bodies like Titan, where hydrocarbons dominate, molecules like DNA and RNA cannot dissolve in hydrocarbons.

In fact, any molecules with any sort of outward charge more or less 'goop' up in hydrocarbons. The so-called 'blueprints of life on Earth', (when modelled as 'encoded instruction based' DNA and RNA), cannot perform their translation/transcription functions on low temperature bodies with predominately liquid hydrocarbons.

IOW: it a chemical properties issue for any Titan-like environment.

Obviously life there would be different.

You didn't say why it could not evolve.

 

[SelfSim]

.. I agree that it seems unlikely, but I understand that simple metabolic pathways have been suggested for Titan with methane as a solvent. How realistic they are, I have no idea.

Do you have a reference there?

AFAIK, the closest anyone's come so far, for a Titan analogue, involved a lab made version of Titan's tholins, (carbon, hydrogen and nitrogen based), which was then made to dissolve in the kind of hydrocarbons that fill Titan’s lakes (using isopentane – a hydrocarbon from the same family as methane and ethane, that is liquid at room temperature). Once the tholins dissolved, the researchers (McKay etal) cooled the mixture, by diluting it with liquid ethane. Some of it remained dissolved. This is a far cry from the complexity needed for a template based replicator to do its thing .. (and in extremely low temperatures!)

The above tholin solubility experiment is far from being sufficient to plausibly assert a possibility of life's emergence on Titan in the prebiotic chemist's world. First of all, any living organisms would have to be able survive in Titan's lakes at extremely low temperatures, (as evidenced by ethane and methane's liquid state in the lakes). This is a frigid –183°C for ethane, and for methane –182°C. Reaction rates fall off exponentially with temperature, and would proceed way too slowly to maintain a so-called hypothetical 'lifeform' on Titan's surface.

For Earth-like 'life' to emerge, oxygen atoms would also have to be incorporated into the above tholin based organic molecules. (Almost every biological molecule we know of contains oxygen). As far as is currently known, neither Titan tholins, nor the hydrocarbon lakes, contain any oxygen.

Apart from the dissolution issue, the over-riding factor is that it is known that energy just isn't there, in the environment, without some major, (hypothetical, and perhaps ad-hoc) external model inputs, to feasibly accomplish the feat of those wishing Titan 'life' into existence.

 

[SelfSim]

Perhaps we should keep it simple and apply a variant of the obscenity test:

I don't know what life is but I'll know it when I see it.​

Y'know what .. IMHO, think that's still our best approach when compared against deploying specialised (and perhaps costly) life process detection equipment remotely, when there is no evidence basis, initially, for doing so.

Generalised surface survey equipment deployment is still the best strategy .. (ie: until the cost/launch masses of the alternatives drastically reduce).

Detection of 'samples of interest' is the necessary first step .. then comes sample isolation, followed by controlled analysis.

Deploying targetted searches (as though we know what we really don't know) has already been recognised by prebiotic chemists/geologists as being fraught with a good chance of mission failure .. particularly for the case where the sought after target, just isn't where some believed it might be.

 

[SelfSim]

Is it possible that there is a combination of substitutes which are neither DNA/RNA or liquid water but could perform a similar function?

Then what you'd mean by 'life' there would have to change .. and therefore the meaning of DNA/RNA also gets blown away at the same time (ie: is rendered meaningless).
What test equipment would you possibly deploy in advance, if one imagined that scenario was possible? I don't know .. Does anyone else?

I could make up a story to make some folk feel better there .. but there's way to much of that going on in the hunt for exo-life, (as well as other belief-based religions around these parts).

Please understand, I'm just trying to be completely (scientifically) honest and consistent here .. in the face of what is clearly: Unknown.

 

[SelfSim]

Obviously life there would be different.

What do you mean by 'life' there? .. (Namely because I don't understand what you mean).

You didn't say why it could not evolve.

Chemistry.
(See the more detailed explanations I've given in prior posts).

 

[Occams Barber]

Y'know what .. IMHO, think that's still our best approach when compared against deploying specialised (and perhaps costly) life process detection equipment remotely, when there is no evidence basis, initially, for doing so.

Generalised surface survey equipment deployment is still the best strategy .. (ie: until the cost/launch masses of the alternatives drastically reduce).

Detection of 'samples of interest' is the necessary first step .. then comes sample isolation, followed by controlled analysis.

Deploying targetted searches (as though we know what we really don't know) has already been recognised by prebiotic chemists/geologists as being fraught with a good chance of mission failure .. particularly for the case where the sought after target, just isn't where some believed it might be.

Sound familiar?

'A policeman sees a drunk man searching for something under a streetlight and asks what the drunk has lost. He says he lost his keys and they both look under the streetlight together. After a few minutes the policeman asks if he is sure he lost them here, and the drunk replies, no, that he lost them in the park. The policeman asks why he is searching here, and the drunk replies, “this is where the light is.”‘

OB​

 

[Bradskii]

This one showed up recently .. which I tend to think of as being a rather well considered and well modelled attempt which might lead to better analysis techniques of remotely sourced mass spectrographic data. Well worth the read, (IMHO):
Identifying molecules as biosignatures with assembly theory and mass spectrometry:

This: 'The search for alien life is hard because we do not know what signatures are unique to life...etc.' is a search for evidence of life. It actually says 'signatures'. In other words, that which will present itself as evidence of life. It has nothing at all to do with what the characteristics of life are.

And I agree with you, the evidence that there is an alien life form might be totally different to the evidence that terrestrial life forms exist. If all we are looking for is oxygen and water, then all we are determining is that conditions might be suitable for earth-like organisms. And methane might be an indication that earth-like organisms were present. So the search as it is currently being done is making the assumption that life elsewhere would be pretty similar to life here; Carbon based, utilising oxygen, requiring water etc. But to be honest, I'm not sure how else we could approach it at this point.

And evolution must be a feature of life anywhere. Otherwise...stasis. A life form would be a one off. And anything even multicellular, let alone conscious or even intelligent would literally be a result of that ol' creationism standby - the 747 in a junkyard. You cannot get complexity (something that exhibits most of the characteristics of life) without an evolutionary process. Simply not possible.

 

[SelfSim]

Sound familiar?

'A policeman sees a drunk man searching for something under a streetlight and asks what the drunk has lost. He says he lost his keys and they both look under the streetlight together. After a few minutes the policeman asks if he is sure he lost them here, and the drunk replies, no, that he lost them in the park. The policeman asks why he is searching here, and the drunk replies, “this is where the light is.”​

Good one for future reference .. I've been pummelled before with the search for the 'lost keys' metaphor ..

Sometimes the light shifts position too. Eg: just the other day I was reading a report that the hypothesised liquid water underneath Mars' (northern(?) polar ice cap has now been determined to be in temperatures way too low for liquid water to exist!
So what now happens to those near to deployment missions who have designed to dig underneath the icy surfaces at northern latitudes? (That latter idea happens to also trace back to 'Mr Titan Methanogens', (Chris McKay).

Also, I notice the Mars Insight mission is rumoured(?) to have been deemed as being a failure (internally to Nasa) due to various design issues including the failure of 'the mole' surface drill.
See that linked wiki entry there (I'll bet it doesn't stay up long, so I'll quote the relevant part):
(Oh .. this one also had McKay behind it ...)

InSight has internally been regarded as a failure by NASA's Planetary Science Directorate, with numerous problems since landing—including the failure of the mole to properly deploy, and a development schedule which ran over-budget and over-time.

 

[SelfSim]

This: 'The search for alien life is hard because we do not know what signatures are unique to life...etc.' is a search for evidence of life. It actually says 'signatures'. In other words, that which will present itself as evidence of life. It has nothing at all to do with what the characteristics of life are.

Oh yes .. it most certainly does!
The problem you're wrestling with is that life's characteristics are a function of its molecular constituents and their subsequent collective (macro-scale) functions.
Its a bottoms-up definition .. not a top-down one. By that I mean, the 'top down' definition approach has to assume that life exists elsewhere, is true, (usually because that's a commonly held belief). The problem there, is that is not yet known.
The 'bottoms-up' definition approach however, makes no such assumptions .. life is (and its definition) is a derived product of bio-chemistry and its environment, which is contextually evidenced but only in Earth's geo-atmospheric environment/biosphere.

And I agree with you, the evidence that there is an alien life form might be totally different to the evidence that terrestrial life forms exist. If all we are looking for is oxygen and water, then all we are determining is that conditions might be suitable for earth-like organisms. And methane might be an indication that earth-like organisms were present. So the search as it is currently being done is making the assumption that life elsewhere would be pretty similar to life here; Carbon based, utilising oxygen, requiring water etc. But to be honest, I'm not sure how else we could approach it at this point.

The flaw in the approach is specifically targeting looking for what we're familiar with .. often cited for reasons of being because we have no other plausible models to design searches for .. but the flaw in that, is the unstated apparent necessity to find life elsewhere .. regardless of the cost .. ie: 'hang science .. its more important to find what we believe must exist' .. Sound familiar? See the Hunt for the Holy Grail .. as its sometimes even referred to (eg: I've heard Michio Kaku explicitly call it that too .. not that he's anything close to what I'd call a reputable scientific reference source, mind you .. but he did state that ..).

And evolution must be a feature of life anywhere. Otherwise...stasis. A life form would be a one off. And anything even multicellular, let alone conscious or even intelligent would literally be a result of that ol' creationism standby - the 747 in a junkyard. You cannot get complexity (something that exhibits most of the characteristics of life) without an evolutionary process. Simply not possible.

From a theoretical viewpoint, (and Earth-life historical evidence), I mostly concur with your intent there. (We however, don't know anything about 'features of life elsewhere', so the term 'must', somewhat prematurely, only implies an Earth-life centric belief/attachment).

And yet we get qualified Planetary Scientists (like Chris McKay) publishing papers about how Evolution is possible in -180 degrees C, liquid organics based surface environments and in subsurface polar Martian polar icecap environments, which now appear as being too cold for liquid water! Go figure!

 

[Bradskii]

Oh yes .. it most certainly does!
The problem you're wrestling with is that life's characteristics are a function of its molecular constituents and their subsequent collective (macro-scale) functions.
Its a bottoms-up definition .. not a top-down one. By that I mean, the 'top down' definition approach has to assume that life exists elsewhere, is true, (usually because that's a commonly held belief). The problem there, is that is not yet known.
The 'bottoms-up' definition approach however, makes no such assumptions .. life is (and its definition) is a derived product of bio-chemistry and its environment, which is contextually evidenced but only in Earth's geo-atmospheric environment/biosphere.

The flaw in the approach is specifically targeting looking for what we're familiar with .. often cited for reasons of being because we have no other plausible models to design searches for .. but the flaw in that, is the unstated apparent necessity to find life elsewhere .. regardless of the cost .. ie: 'hang science .. its more important to find what we believe must exist' .. Sound familiar? See the Hunt for the Holy Grail .. as its sometimes even referred to (eg: I've heard Michio Kaku explicitly call it that too .. not that he's anything close to what I'd call a reputable scientific reference source, mind you .. but he did state that ..).


From a theoretical viewpoint, (and Earth-life historical evidence), I mostly concur with your intent there. (We however, don't know anything about 'features of life elsewhere', so the term 'must', somewhat prematurely, only implies an Earth-life centric belief/attachment).

And yet we get qualified Planetary Scientists (like Chris McKay) publishing papers about how Evolution is possible in -180 degrees C, liquid organics based surface environments and in subsurface polar Martian polar icecap environments, which now appear as being too cold for liquid water! Go figure!

I think we're talking past each other. But...

...it doesn't matter what the molecular constituents are of a life form. It has to react to the environment in which it finds itself. How could it not? It has to reproduce. In an evolutionary process. Or we're in junkyard 747 territory. It has to process energy in some way. There needs to be some sort of metabolism present.

I don't think that it's even possible to conceive of a life form that doesn't have at least some of the characteristics we use to define life. Certainly not the ones I just mentioned. I've been an avid reader of sci fi since I was a kid and I have never found a Pratchet or a Banks or a Clarke that could devise a form of alien life without it having the characteristics that we now use.

I think that the only time we're going to have a problem with the question 'is it alive' is when it comes to AI.

 

[SelfSim]

I think we're talking past each other. But...

No .. you are just not acknowledging the biochemical basis responsible for, say, metabolism. See the citric acid cycle here, for starters. Its all chemistry .. and it ends up producing life's metabolic functions in one way or another:

The citric acid cycle (CAC) – also known as the TAC cycle (tricarboxylic acid cycle) or the Krebs cycle – is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest components of metabolism and may have originated abiogenically. Even though it is branded as a 'cycle', it is not necessary for metabolites to follow only one specific route; at least three segments of the citric acid cycle have been recognized.

...

... it doesn't matter what the molecular constituents are of a life form.

Not so. .. See the citric acid cycle quote/link above, as an example.

It has to react to the environment in which it finds itself. How could it not? It has to reproduce. In an evolutionary process. Or we're in junkyard 747 territory. It has to process energy in some way. There needs to be some sort of metabolism present.

.. and in Earth-life there is .. its derived directly from the chemistry pertaining to the citric acid cycle.

.. I've been an avid reader of sci fi since I was a kid ..

I, personally, am inclined to think therein may lie the basis of the issue we have here(?)

I think that the only time we're going to have a problem with the question 'is it alive' is when it comes to AI.

Meh .. just adapt the definition to artificial contexts .. no problem.

 

[Bradskii]

No .. you are just not acknowledging the biochemical basis responsible for, say, metabolism. See the citric acid cycle here, for starters. Its all chemistry .. and it ends up producing life's metabolic functions in one way or another:

But you've just showed me an example of metabolism. I don't care what the biochemical basis for it is. The exact method and the consitituent parts and the specific process and chemicals involved don't matter in the slightest. It's a metabolic process. So we have metabolism. And therefore one of the characteristics of life.

Do you want to address the others?

 

[SelfSim]

But you've just showed me an example of metabolism. I don't care what the biochemical basis for it is. The exact method and the consitituent parts and the specific process and chemicals involved don't matter in the slightest. It's a metabolic process. So we have metabolism. And therefore one of the characteristics of life.

In the scientific context, the term you're using there, ie: 'metabolism', refers to the sum of all chemical reactions that also happen to occur in all 'living' organisms, (and is also referred to as digestion and the transport of substances into and between different cells).

The most prominent feature which happens to also be observed across all known organisms, is the set of carbolic acids, produced by the citric acid chemical reaction cycle. Because of the weight of evidence for this commonality, and simplicity of organic reactants which commence the cycle (citric acid is: C6H8O7 and has a molar mass of only 192.123 g/mol, which is less than many of the Mars GCMS molecules detected, IIRC?), the inference is drawn that the cycle was likely one of the earliest organic chemical reaction pathways to appear in the Earth context, prior to evolution (aka: abiogenetically relevant).

If this process cannot function in a given physical environment, for whatever reason, there can be no 'metabolism' present .. and therefore one of "life's" defining processes, is also absent. Where does that leave your linguistic usage of 'life' and 'metabolism' in such contexts/environments then? Would you just insist that because you want to use those words, that this then is evidence for the existence of life in those environments?

That you don't 'care about' these fact based evidences for Abiogenesis, I find as being a highly suspicious declaration. Its also equivalent to 'not caring about' Evolution's LUCA, or the fact of the common genetic code(?) Do they also 'not matter'?

 

[Bradskii]

In the scientific context, the term you're using there, ie: 'metabolism', refers to the sum of all chemical reactions that also happen to occur in all 'living' organisms, (and is also referred to as digestion and the transport of substances into and between different cells).

The most prominent feature which happens to also be observed across all known organisms, is the set of carbolic acids, produced by the citric acid chemical reaction cycle. Because of the weight of evidence for this commonality, and simplicity of organic reactants which commence the cycle (citric acid is: C6H8O7 and has a molar mass of only 192.123 g/mol, which is less than many of the Mars GCMS molecules detected, IIRC?), the inference is drawn that the cycle was likely one of the earliest organic chemical reaction pathways to appear in the Earth context, prior to evolution (aka: abiogenetically relevant).

If this process cannot function in a given physical environment, for whatever reason, there can be no 'metabolism' present .. and therefore one of "life's" defining processes, is also absent. Where does that leave your linguistic usage of 'life' and 'metabolism' in such contexts/environments then? Would you just insist that because you want to use those words, that this then is evidence for the existence of life in those environments?

That you don't 'care about' these fact based evidences for Abiogenesis, I find as being a highly suspicious declaration. Its also equivalent to 'not caring about' Evolution's LUCA, or the fact of the common genetic code(?) Do they also 'not matter'?

If there is no process within an organism that can be described as a metabolic process then how will that organism survive? Are you suggesting that converting food (in whatever form) into the energy required to run whatever processes are required and using the food to build the material from which the organism is made isn't a requirement?

 

[SelfSim]

.. (citric acid is: C6H8O7 and has a molar mass of only 192.123 g/mol, which is less than many of the Mars GCMS molecules detected, IIRC?) ..

Correction:
Chlorobenzene (detected) has a molar mass of 112.56 g/mol and its likely martian precursor, benzoic acid, has a molar mass of 112.12 g/mol.
(I just checked).