Abiogenesis Update

[Skeptic Ginger]

I had a reason to review the current state of the science of abiogenesis recently and it seemed worth sharing.


2009:The Origin of Life
A case is made for the descent of electrons

In this article we present a view gaining attention in the origin-of-life community that takes the question out of the hatchery and places it squarely in the realm of accessible, plausible chemistry. As we see it, the early steps on the way to life are an inevitable, incremental result of the operation of the laws of chemistry and physics operating under the conditions that existed on the early Earth, a result that can be understood in terms of known (or at least knowable) laws of nature. As such, the early stages in the emergence of life are no more surprising, no more accidental, than water flowing downhill….

…Since 1953, we have found many of the same simple organic molecules in meteorites, comets and even interstellar gas clouds. Far from being special, then, the simplest of the molecules we find in living systems—life’s building blocks—seem to be quite common in nature…
…The next major advance came in the early 1980s, when Thomas Cech and Sidney Altman showed that some RNA molecules can act as enzyme-like catalysts. The frozen-accident argument was then replaced by a suggestive scenario in which something like RNA was assembled by chance, and was then able to fill twin roles as both enzyme and hereditary molecule in the run up to life…..

…Networks of synthetic pathways that are recursive and self-catalyzing are widely known in organic chemistry, but they are notorious for generating a mass of side products, which may disrupt the reaction system or simply dilute the reactants, preventing them from accumulating within a pathway. The important feature necessary for chemical selection in such a network, which remains to be demonstrated, is feedback-driven self-pruning of side reactions, resulting in a limited suite of pathways capable of concentrating reagents as metabolism does. The search for such self-pruning is one of the most actively pursued research fronts in Metabolism First research.
…At the very core of metabolism—the starting point for the synthetic pathways of all biomolecules—is a relatively simple set of reactions known as the citric acid cycle (also called the tricarboxylic acid cycle or the Krebs cycle). The cycle involves eight molecules, each a carboxylic acid (a molecule containing —COO groups). In most present-day life forms on Earth, the citric acid cycle operates to break organic molecules down into carbon dioxide and water, using oxygen to produce energy for the cell—in effect, ”burning” those molecules as fuel….The cycle can also operate in the opposite direction, taking in energy (in the form of high-energy electrons) and building up larger molecules from smaller ones….

…The important pattern to appreciate is that the primordial cycle provides the stability and starting materials that make an age of selection possible. We think it was at the transition to this stage that geochemistry began to take on the features of replication and selection recognized by Darwin as distinctive of life. After such an age has begun, it can maintain the complexity and diversity needed to explore for refinements—in efficiency, in adaptation to the geological environment or in specialized division of labor within communal systems. The same pattern repeated itself when the environment was changed by the accumulation of a destructive toxin—oxygen—that was produced by primordial organisms as a waste product. As they adapted, organisms did not abandon the reductive citric acid cycle, which we believe was the unique foundation for biosynthesis. Instead they acquired the ability to run the cycle in reverse, extracting energy from the breakdown of molecules similar to those the cycle formerly produced.

The science of our origins is moving right along. The Talk Origins page on abiogenesis was apparently last updated in 2001. The evolution deniers cite Talk Origins claiming there is no mechanism for 'selection' before the first complete organisms. But it appears there is evidence for a purely non-organic chemical 'selection' process that preceded RNA molecules and replication.

The authors of the above citation compare the problem to investigating the highway system. If you just took the current form, you might investigate asphalt, cars, oil and so on. Or you could instead start with mechanisms of movement and transportation. Then you might move on from walking to trails to horses and vehicles and roads and then to the highway system.

Instead of approaching the problem of abiogenesis by trying to find the mechanisms of replication, some scientists are looking at the chemical processes within the cell and looking for the pathway those process might have been involved in creating the first organic molecules. From there the line of inquiry is then to look at what might have happened next.

 

[Taffer]

Thanks, Skeptic Ginger (when did you change your name?), interesting stuff. I always enjoy your posts on this subject.

 

[JoeTheJuggler]

But it appears there is evidence for a purely non-organic chemical 'selection' process that preceded RNA molecules and replication.

The way I've often thought of it is if vessicles form and trap a bit of water and other molecules inside, they're already "selecting" for molecules that are more abundant. Some molecules will be more abundant based on non-organic chemical processes. (This might explain why amino acids are fairly ubiquitous.)

Of course, once you get a self-replicating molecule, that process would swamp selection based on those other processes.

I think the line between life and non-life will become blurrier and blurrier. It's all really just chemical/mechanical processes. There's nothing magical about life.

 

[John Hewitt]

I had a reason to review the current state of the science of abiogenesis recently and it seemed worth sharing.


2009:The Origin of Life
A case is made for the descent of electrons

The science of our origins is moving right along. The Talk Origins page on abiogenesis was apparently last updated in 2001. The evolution deniers cite Talk Origins claiming there is no mechanism for 'selection' before the first complete organisms. But it appears there is evidence for a purely non-organic chemical 'selection' process that preceded RNA molecules and replication.

The authors of the above citation compare the problem to investigating the highway system. If you just took the current form, you might investigate asphalt, cars, oil and so on. Or you could instead start with mechanisms of movement and transportation. Then you might move on from walking to trails to horses and vehicles and roads and then to the highway system.

Instead of approaching the problem of abiogenesis by trying to find the mechanisms of replication, some scientists are looking at the chemical processes within the cell and looking for the pathway those process might have been involved in creating the first organic molecules. From there the line of inquiry is then to look at what might have happened next.

Could you please give the source of these quotations.

 

[Cainkane1]

If it happened here it happened elsewhere. Who wants to go to Europa with me?

 

[TheDoLittle]

If it happened here it happened elsewhere. Who wants to go to Europa with me?

No, thanks. As an American, I can't imagine staying at the ultimate hostile Europian Hostel!

 

[blobru]

Could you please give the source of these quotations.

The line-break might've caused a glitch in the OP's. Here's the fixed link:

Origin of Life: A case for the descent of electrons.

 

[Skeptic Ginger]

The line-break might've caused a glitch in the OP's. Here's the fixed link:

Origin of Life: A case for the descent of electrons.

Thanks. I usually check my links but not always.

 

[Skeptic Ginger]

The way I've often thought of it is if vessicles form and trap a bit of water and other molecules inside, they're already "selecting" for molecules that are more abundant. Some molecules will be more abundant based on non-organic chemical processes. (This might explain why amino acids are fairly ubiquitous.)

Of course, once you get a self-replicating molecule, that process would swamp selection based on those other processes.

I think the line between life and non-life will become blurrier and blurrier. It's all really just chemical/mechanical processes. There's nothing magical about life.

What I found especially interesting was the trend in the attack on evolution theory by the IDer/Creationists. Since their attacks are always "that's impossible" rather than evidence based, I have read a few times now that because natural selection can't occur until you have a life form, abiogenesis is impossible.

But I see natural selection pressures as not specifically related to a living organism surviving to reproduce. Rather, I view natural selection as anything that amplifies a gene sequence. It seems a no brainer you might also have selection pressures amplifying an inorganic molecule in transition to creating an organic one, amplifying the organic molecule in transition to becoming replicating RNA and so on.

 

[Skeptic Ginger]

Thanks, Skeptic Ginger (when did you change your name?), interesting stuff. I always enjoy your posts on this subject.

Thanks for the compliment. My name was getting confused with another forum member so I changed it.

 

[JoeTheJuggler]

But I see natural selection pressures as not specifically related to a living organism surviving to reproduce. Rather, I view natural selection as anything that amplifies a gene sequence. It seems a no brainer you might also have selection pressures amplifying an inorganic molecule in transition to creating an organic one, amplifying the organic molecule in transition to becoming replicating RNA and so on.

I agree.

We shouldn't transfix on survival and death of organisms as the sole objects of selection. (Simple archaebacteria don't really die anyway, since the result of cell division for them are two "daughter cells" that replace the one parent cell.)

Instead, I think the emphasis should be on relative abundance. I like to think of a vessicle trapping stuff in water as the selector that gives you a random sample of the relative abundance of molecules in the water.

When the vessicle grows to a microtubule and then breaks off ("reproduces") the more abundant molecules will again be selected. But that's just a convenient way of thinking about it for me. You could say the same thing about any random sample of the water even without anything like a proto-cell.

I think we'll find that there is no hard and fast line between abiotic chemistry and life. And I think this blurring is also why there won't likely be a newspaper headline saying "Life on Mars Discovered" (unless, of course, we find something readily recognizable, like a cell with organelles) or "It's Certain: There Is No Life on Mars". Instead we'll just get more and more confident in one or the other conclusion.

ETA: And the ID/Creationist argument you mentioned is at heart an argument from ignorance. Just because we once didn't know how non-life could evolve into life (that is, how evolution works on non-biotic chemistry) doesn't in any way support their explanations.

 

[Soapy Sam]

... it appears there is evidence for a purely non-organic chemical 'selection' process that preceded RNA molecules and replication.

SG-
Given the carboxylic acids obviously are organic chemicals in the strict sense, you might want to find alternatives to the highlighted phrase for use with creationists. They're confused enough already. In fact, avoiding the word "organic" altogether is usually a timesaver when discussing abiogenesis.

 

[Skeptic Ginger]

SG-
Given the carboxylic acids obviously are organic chemicals in the strict sense, you might want to find alternatives to the highlighted phrase for use with creationists. They're confused enough already. In fact, avoiding the word "organic" altogether is usually a timesaver when discussing abiogenesis.

Being in the infectious disease field and not in the molecular chemistry field, such distinctions are not a concern to me. Most people (assuming biochemists are in the minority) may know organic and inorganic as names. The lay public if they have at least pondered abiogenesis, are likely to know one needs to go from inorganic to organic to living organisms. I doubt many people have much interest in the details of the molecules.

I agree with you that accuracy is important. I often distinguish between a "challenge dose" of Hep B vaccine vs a "booster dose" of vaccine even though the vaccine dose itself is the same. But I do that because I have a goal in mind. I don't want to add to the erroneous belief one needs Hep B vaccine booster dose and I know people recall things differently years after the fact. I'm hoping by calling it a "challenge dose" years later people will not have modified their memories and come to believe booster doses are needed. So I'd expect to speak the details correctly, for example, if I were talking to biochem students. But I don't see why such a detail would ever matter to a lay person simply pondering the evidence for or mechanism of abiogenesis.


So I'll accept your advice if you would please explain to me the specific goal you have in mind. Confusing Creationists further isn't clear to me without a bit more specifics. Technical correctness can sometimes get in the way of effective communication. A lot of skeptics/science types don't understand that concept and see technical errors as very important when such errors may not be depending on the folks you are communicating with.


Dang, my edit disappeared. Trying again....

I would think molecular details matter when you are communicating with a group like biochem students. But I don't think such pedantic issues matter if you are merely communicating with laypersons contemplating abiogenesis.

 

[Skeptic Ginger]

duplicate deleted

 

[Sideroxylon]

What I found especially interesting was the trend in the attack on evolution theory by the IDer/Creationists. Since their attacks are always "that's impossible" rather than evidence based, I have read a few times now that because natural selection can't occur until you have a life form, abiogenesis is impossible.

But I see natural selection pressures as not specifically related to a living organism surviving to reproduce. Rather, I view natural selection as anything that amplifies a gene sequence. It seems a no brainer you might also have selection pressures amplifying an inorganic molecule in transition to creating an organic one, amplifying the organic molecule in transition to becoming replicating RNA and so on.

It's been a while since I read 'The Selfish Gene', but didn't Dawkins describe selection working on crystals?

Thanks for the posts - I'm enjoying the read.

 

[bokonon]

Skeptic Ginger -

Our "DNA - Proof of God?" thread over in R&P is becoming more sciencey and less philosophical, so I thought I'd see if maybe it might make more sense to continue it here. I re-read the article you linked, and I understand how, if that line of inquiry turns out to provide a comprehensive explanation for abiogenesis, it might be possible to find life beginning fairly commonly throughout the universe.

Even in that article, though, the authors write

Whereas most scientists believe, on the basis of Cech and Altman’s work, that life went through an early RNA-dominated phase (dubbed “RNA World”), the “RNA First” scenario has again a quality of frozen accident.

Certainly, even more extreme versions of "frozen accident" have not been falsified. It remains on the table as a viable hypothesis, though it is not an especially promising direction for research, and I doubt many scientists today are pursuing it.

Of RNA First or Metabolism First, I'd place my money on MF too, but even there one has to propose a way to get from metabolism to RNA. That's a big step. Simply proposing MF can provide a possible framework, but the devil is still in the details.

What if a critical step requires a very rare substrate, which surfaced like a diamond four billion years ago and then was once again subsumed? That scenario, or dozens of others like it, could make life a rare and unlikely occurrence, even if MF turns out to be the method used (and I think that's likely).

I'm not even sure if any researcher has managed to get a Krebs cycle working outside a cell, and it would seem to me that that would be a necessary first step toward validating the MF framework. If anyone else is more informed, a link would be much appreciated.

 

[Skeptic Ginger]

I posted an answer in the other thread before reading your post here, so take that one as applying to a different aspect of the discussion.

In the meantime, I found this fascinating article that I believe contributes a lot to the abiogenesis questions, including some facts about viruses I was totally unaware of.

Astrobiology Field Reports: Are Canadian Lake Structures Biological or Chemical?

Okay, cool, you may be thinking. Advanced DNA work done in the field. But why viruses? Surely no-one thinks viruses are building the Pavilion Lake microbialites.

"Viruses amplify life," Suttle says. "For every living organism that you find, there's many, many more viruses that infect that organism." On average, there are a million bacteria in a milliliter of water. And 10 million viruses.

What's more, although the genome of an individual virus is relatively small, "Collectively, viruses probably have about 90 percent more genetic information than we find in the three domains of life" combined, Suttle says. Let's go over that again: 90 percent of the genes found in viruses are not found in cellular organisms.

For example, "Other lifeforms only have double-stranded DNA. Viruses have double-stranded DNA, single-stranded DNA, positive-sense single-stranded RNA, negative-sense single-stranded RNA, double-stranded RNA. They have every possible combination of nucleic acids for passing along genetic information." They're quite versatile.

So if you want to look for life on another world, you'd do well to learn how to hunt for viruses, Suttle suggests. "They're like a biosignature for other living organisms."

Work on the smallest number of genes needed to make up a life form have used viruses. I think they are down to 9 genes. But in general, viruses are viewed as needing cells to replicate. But that doesn't mean it was always so. Nor does it mean that viruses don't exist which replicate without parasitic activity. It could just be that viral pathogens or viruses that have come to our attention use cells to reproduce.

This research suggests that maybe there are trillions or more viruses out there that replicate outside of cells. Maybe there are RNA fragments still around that we've yet to detect which reflect a step in the abiogenesis process and we just didn't know about yet.


This companion story was also interesting but less directly so regarding the abiogenesis process:

What Do You Call a Microbialite?.

 

[shadron]

The way I've often thought of it is if vessicles form and trap a bit of water and other molecules inside, they're already "selecting" for molecules that are more abundant. Some molecules will be more abundant based on non-organic chemical processes. (This might explain why amino acids are fairly ubiquitous.)

Of course, once you get a self-replicating molecule, that process would swamp selection based on those other processes.

I think the line between life and non-life will become blurrier and blurrier. It's all really just chemical/mechanical processes. There's nothing magical about life.

This kind of reminds me of cdk007's video about simulating clock evolution. The very first clocks that just happen to come together at random are simple pendulums; Once there is a mechanism for them to work against the randomness of their lives they immediately take over the environment they are in. cdk007 points out, as sort of an after-thought, that each of the stages of improve clocks takes over very quickly from the previous stage, and the possibility of finding "transitional" clocks (those with the improved works but not yet as accurate as older clocks) in any kind of fossil strata of any transitional age would be exceedingly small.

cdk007's video about this is here:

 

[Skeptic Ginger]

....
Certainly "frozen accident" would not be inevitable. RNA First would probably not be inevitable. Metabolism First might or might not be inevitable, but the burden of proof is on the one making the positive claim, and in my opinion the evidence is nowhere near there.

And until the real answer is known, it may still turn out to be "none of the above".

If you'd prefer to continue this conversation in your "Science and Technology" thread, we can do that. As I said when I revived it today, the recent discussion here has seemed to center less on philosophy than on science.

I'm not familiar with the "frozen accident".

I'm convinced abiogenesis was inevitable given the composition and conditions on our planet at the time it occurred, and, think it is inevitable that said conditions are not unique to our planet. I think it is much more likely that abiogenesis is not so unique as to be a one time event in the entire Universe.

I fail to see why the default position is superior, that unless demonstrated otherwise, we should go with the one time event. Since I reject magical and god explanations for reasons I've defended in other threads, we can say that abiogenesis occurred once. But once again, it seems most rational thinkers consider only the narrow point of view that this is all the information we can put into our conclusion basis.

How many other events in the Universe have we observed that were one time events? I can't think of any.

The composition of the planets and other bodies in the Universe is fairly consistent. Why shouldn't that support the conclusion that a one time abiogenesis event is much less likely than that we should find the conditions and events to not be a one time event?

 

[bokonon]

I'm not familiar with the "frozen accident".

It's mentioned on page 2 of your original link:

The essential legacy of the Primordial Soup was twofold: It simplified the notion of the origin of life to a single pivotal event, and then it proposed that that event—the step that occurred after the molecules were made—was a result of chance. In the standard language, life is to be seen, in the end, as a “frozen accident.” In this view, many fundamental details about the structure of life are not amenable to explanation. The architecture of life is just one of those things.

I fail to see why the default position is superior, that unless demonstrated otherwise, we should go with the one time event.

"Law of parsimony" and that's where the evidence points today.

There is no indication that life arose more than once on earth. All terrestrial life uses DNA for reproduction and as a template for protein synthesis. All proteins are built from left-handed amino acids; all cells use right-handed sugars for energy.

There is no evidence that life arose outside of life on earth. Products of metabolism which would suggest photosynthesis are not seen in the spectrographs of any of the heavenly bodies we've analyzed.

Simply assuming abiogenesis happened elsewhere is more than a leap of faith, it's a hop (simple chemical reactions are all that's required for abiogenesis / invariably result in abiogenesis), skip (those chemical reactions are found on other planets), and a jump (those planets are sufficiently like earth to allow life to form) of faith.

How many other events in the Universe have we observed that were one time events? I can't think of any.

We don't know of any other Earth-like planets. No other planets in our solar system have a single large moon, or an atmosphere which contains water vapor. I'm a one-time event; so are you.

 

[Aepervius]

Just a nitpick , our spectrographic analysis are nowhere near precise enough to be able to pinpoint any exoplanet (except maybe the nearest) and state what you said. The heavenly body we can look at are at most the suns, and we already knew that life was unlikely on those. Comparing to the number of sun we know there is an exoplanet and the number of sun in our own galaxy (or the universe) then you quickly see that we can't draw any conclusion yet as have only looked at 1 or 2 sand corn on the long, long beach.

Secondly assuming abiogenesys may have happened elsewhere is not a leap of faith. If the same condition as earth hapenned on another planet , it is only a question of probability. Assuming our planet is so special in the whole universe that the condition was not reproduced by any other suns in any other galaxy , is *the* anthopomorphic leap of faith.

The bottom line is that we don't knowq either way, life could be teeming in our neighborhood, or we could really be that lucky (?) to be the only one in the universe. We have at the moment NOT enough info to conclude either way. We have OTOH enough info to say that if this is a chemical processus only, then the law of probability govern it.

 

[Skeptic Ginger]

...
Secondly assuming abiogenesys may have happened elsewhere is not a leap of faith. If the same condition as earth hapenned on another planet , it is only a question of probability. Assuming our planet is so special in the whole universe that the condition was not reproduced by any other suns in any other galaxy , is *the* anthopomorphic leap of faith.....

Exactly.

 

[Skeptic Ginger]

...

There is no indication that life arose more than once on earth. All terrestrial life uses DNA for reproduction and as a template for protein synthesis. All proteins are built from left-handed amino acids; all cells use right-handed sugars for energy.

It is reasonable to hypothesize that if life had arisen more than once on the early Earth, an exchange of genetic material between microorganisms (which occurs extensively today) could have washed out the evidence.

...There is no evidence that life arose outside of life on earth. Products of metabolism which would suggest photosynthesis are not seen in the spectrographs of any of the heavenly bodies we've analyzed.

Have you missed all the discoveries from the Mars explorers? While there is no direct evidence yet, past life on the planet has not been ruled out and is still consistent with what we've seen so far.

...Simply assuming abiogenesis happened elsewhere is more than a leap of faith, it's a hop (simple chemical reactions are all that's required for abiogenesis / invariably result in abiogenesis), skip (those chemical reactions are found on other planets), and a jump (those planets are sufficiently like earth to allow life to form) of faith.

We don't know of any other Earth-like planets. No other planets in our solar system have a single large moon, or an atmosphere which contains water vapor. I'm a one-time event; so are you.

Surely you recognize the limits of our ability to observe and the vastness of the Universe?

 

[bokonon]

It is reasonable to hypothesize that if life had arisen more than once on the early Earth, an exchange of genetic material between microorganisms (which occurs extensively today) could have washed out the evidence.

Circular reasoning. "Exchange of genetic material" is only possible if the microorganisms doing the exchanging already share a common template, and the common template (DNA) implies a common origin, which implies life arose once.

Have you missed all the discoveries from the Mars explorers? While there is no direct evidence yet, past life on the planet has not been ruled out and is still consistent with what we've seen so far.

I don't think I've missed anything significant. They've found evidence of liquid water. They've found no evidence of life.

While we believe liquid water is a necessary condition for life, I don't believe (and doubt most scientists believe) it is a sufficient condition. Perhaps if the origin of life on earth was extraterrestrial (some variant of the panspermia theory), then liquid water will prove to be sufficient, and life will be common elsewhere (though in that case, our ability to discern the conditions under which life originally arose would take a big hit).

Some hypotheses about the origin of life require oceans, and a single large moon such as we have. The collision which we believe created our moon could have been a unique event in the universe. It gave us an extra-large molten iron core (which helps shield us from ionizing radiation that could destroy the molecules required for life), and (scientists believe) hundred-mile tides which would have concentrated pre-biotic chemicals on the early earth. What if such a lucky collision is actually a requirement for abiogenesis? What if a specific mineral matrix about which we know nothing today was also required, to act as a pre-life "enzyme" to a critical step in early metabolism?

I'll say again WE DON'T KNOW what conditions are required for life to begin. There are some good ideas, but none of them have approached the level of accepted theory.

Surely you recognize the limits of our ability to observe and the vastness of the Universe?

Yes, and some people take that abject ignorance as a license to indulge in baseless speculation about what may be happening in galaxies long ago and far away. Legitimate speculation is based on what we know, not on what we don't know, and since we don't know how life began or how many earthlike planets the universe contains, projections of extraterrestrial life remain currently in the realm of science fiction rather than science.

 

[bokonon]

assuming abiogenesys may have happened elsewhere is not a leap of faith. If the same condition as earth hapenned on another planet , it is only a question of probability.

And we have no way of evaluating that probability. We don't know what the range of extra-solar planetary variability might be. Outside of a twin born of the same parents, what is the probability that another person lived who had the same DNA that you have? Is it a leap of faith to presume that you might be unique?

 

[noreligion]

While we believe liquid water is a necessary condition for life, I don't believe (and doubt most scientists believe) it is a sufficient condition.

You're right but not the way you think. Most scientists in biology (and oher disciplines) do not think H₂O is a sufficient condition for life they believe it is a requirement for life as we know it and the only other possible substitute (for another kind of life) would be H₂F.

 

[Skeptic Ginger]

Circular reasoning. "Exchange of genetic material" is only possible if the microorganisms doing the exchanging already share a common template, and the common template (DNA) implies a common origin, which implies life arose once.

This is not something I made up or read about on a non-scientific site. The exchange of genetic material on the early Earth is a serious hypothesis based on the genetic evidence. I'll see if I can find you the research which has the supporting evidence for the hypothesis.

In addition, there are at least 4 mechanisms by which microorganisms exchange genetic material. This occurs across species and occurs very commonly. There is no circular reasoning going on here at all. Take your foot out of your mouth and consider looking into these things before commenting if it is something you were previously unaware of. I read a lot on this topic and while I certainly don't guarantee getting everything right, I do know the difference between an evidence supported (but not proven) hypothesis ond one that is pure speculation.


Here are a couple examples (sorry, you'll need to find your own links for the moment):
Aravind, L., R. L. Tatusov, Y. I. Wolf, D. R. Walker, and E. V. Koonin. 1998. Evidence for massive gene exchange between archaeal and bacterial hyperthermophiles. Trends in Genetics 14:442-444.

Doolittle, W. F. 1999. Lateral genomics. Trends in Biochemical Sciences 24: M5-M8.

Gogarten, J. P., E. Hilario, and L. Olendzenski. 1996. Gene duplications and horizontal gene transfer during early evolution. Pages 267-292 in Evolution of Microbial Life (D. McL. Roberts, P. Sharp, G. Alderson, and M. Collins, eds.) Symposium 54. Society for General Microbiology. Cambridge University Press, Cambridge.

I don't think I've missed anything significant. They've found evidence of liquid water. They've found no evidence of life.

If water is the only evidence you are aware of, you've missed some significant evidence, methane outgassing detection and some carbonite structures.

...What if such a lucky collision is actually a requirement for abiogenesis? What if a specific mineral matrix about which we know nothing today was also required, to act as a pre-life "enzyme" to a critical step in early metabolism?

If that plus even more was required for abiogenesis, the Universe is still vast enough that such a combination would be very unlikely to be unique.

I'll say again WE DON'T KNOW what conditions are required for life to begin. There are some good ideas, but none of them have approached the level of accepted theory.

They still would be expected to recur given the size of the Universe.

Yes, and some people take that abject ignorance as a license to indulge in baseless speculation about what may be happening in galaxies long ago and far away.

Non sequitur

Legitimate speculation is based on what we know, not on what we don't know, and since we don't know how life began or how many earthlike planets the universe contains, projections of extraterrestrial life remain currently in the realm of science fiction rather than science.

We know abiogenesis occurred once. We know we haven't observed enough of the Universe to say it only happened once. The more logical default here is it would have happened more than once given the composition and size of the Universe.

It is much more unlikely abiogenesis happened only once. So the position of 'evidence first' would start with the more likely event of the Earth not being unique, not the other way around.

 

[Taffer]

Circular reasoning. "Exchange of genetic material" is only possible if the microorganisms doing the exchanging already share a common template, and the common template (DNA) implies a common origin, which implies life arose once.

Um. No it doesn't.

 

[Skeptic Ginger]

And we have no way of evaluating that probability. We don't know what the range of extra-solar planetary variability might be. Outside of a twin born of the same parents, what is the probability that another person lived who had the same DNA that you have? Is it a leap of faith to presume that you might be unique?

Your "no way" of evaluating that is a very poor conclusion. You are ignoring all we do know about the likely conditions for abiogenesis, but more importantly, all we do know about the consistency we find throughout the Universe we have observed.

For example before we were able to observe planets orbiting other stars, some people would have maintained the position only our Sun had planets until we observe other planets. Others would have taken the default position the existence of planets around the one sun we can observe is evidence planets are likely until we observe numerous stars and don't find planets.

Now that we have gained the ability to detect planets, which default position turned out to be right? The more logical hypotheses, not the hypothesis denying logic until absolute proof is obtained.

 

[noreligion]

It's amazing to me that some people without the slightest knowledge of chemistry assume they can understand abiogenesis and actually think they have a valid criticism. If they really want to show abiogenesis isn't possible or that it wasn't an inevitability from the moment of the big bang, they really should run their mouth less and seek education in the necessary field. Astrobiology or biochemistry (even plain vanilla chemistry) would be an excellent place to start.

 

[Skeptic Ginger]

Re: the evidence found by our probes supporting the hypothesis we may eventually find life, past or present, on Mars (Note: I'm not claiming these are evidence of life, only that things we've found are possible evidence of life, other explanations are not ruled out):

The discovery of methane outgassing sparked interest in current active life as a source. The discovery of perchlorate did not mean life was unlikely as was first reported. (documentation of these findings is readily available)

Links to the following can be found on the Wiki page bibliography.

72nd Annual Meteoritical Society Meeting (2009)
CAN METHANOGENS GROW IN A PERCHLORATE ENVIRONMENT ON MARS?

Results and Discussion: Methane concentrations varied with species and perchlorate salt tested. However, all four methanogens produced substantial levels of methane, even in the presence of 1.0wt% perchlorate salt. In all cases, there were no differences in methane concentrations at 0 and 0.1wt% perchlo- rate salt. In most cases, 1.0wt% perchlorate salt resulted in lesser amounts of methane, at least initially. There are at least two pos- sible explanations for this. The higher perchlorate concentrations may be inhibiting methane production by the methanogens, but with time some of the methanogens are adapting. A second ex- planation would be that methanogenesis is not being inhibited, but the methane being produced is being oxidized by the perchlo- rate. In preliminary experiments where methane was added to tubes containing perchlorate salt solutions, there was no decrease in methane concentration with time. This would seem to rule out the second explanation. Whatever the explanation, the results reported here indicate that the perchlorates discovered by the Phoenix Lander would not rule out the possible presence of methanogens on Mars.

EVIDENCE FOR ANCIENT MARTIAN LIFE. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth, and C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.

Three SNC meteorites ranging in age from 4.5 Ga. to 1.3 Ga. to 165 m.y. contain features suggestive of past biogenic activity on Mars [1,2]. Because we do not know what past martian life looks like or its physical or chemical properties, the only tools or criteria which the scientific community have to evaluate evidence of past life is to use evidence for early life on earth. There are features within ALH84001’s carbonate globules and the preterrestrial aqueous alteration phases of Nakhla and Shergotty which have been interpreted as possible evidence for past life on early Mars [1,2].

Spider-Ravine Models and Plant-like Features on Mars - Possible Geophysical and
Biogeophysical Modes of Origin; PETER K. NESS1 and GREG M. ORME2; JBIS vol 55, 2002

The Martian South Polar region of Mars is littered with crypto-organic structures, structures that look like trees and plants. They vary in shape, size and colour seasonally and some may disappear over winter.
A number of models for their origin are proposed and discussed:
(1) Dry venting of CO2 gas and dust up joints.
(2) Head-ward erosion: Fluid derived from sub-surface layers is expelled up fissures eroding joints to create tributaries capped with mud-like material and/or ice.
(3) ModifiedClathrate-hydratemodel:Structuresformastheoutsideoftheflowchills. (4) Hydrothermal-typesources,and (5) Magmapressurizesoverlyingfluids,expellingmud-likematerial,hydrothermalfluidsorbasalt. Some complex ‘spiders’ may revert to ravines in the summer.
The morphology of ‘spiders’ appears to be controlled by bedding and local jointing of the rocks; implying that expelled fluids are derived from within a few hundred metres of the Martian surface. Some spider-ravines modify, some destroy and others create crust in a dynamic near-surface process that mimics subduction zones. Ancient forms of these structures have had a more extensive coverage.
Some valley networks may be formed by similar processes.
We consider the possibility that organic material, microbes, or even simple plants might co-exist with these inorganic models.

There are a number of papers on these structures. This one was the most thorough.


For a review of the Alan Hills meteorite findings:
The meteorite evidence, despite being inconclusive and downplayed by many researchers after the initial paper was published, nonetheless still has evidence beyond "water":

A NASA research team of scientists at the Johnson Space Center and at Stanford University has found evidence that suggests primitive life may have existed on Mars more than 3.6 billion years ago.
The NASA-funded team found the first organic molecules thought to be of Martian origin; several mineral features characteristic of biological activity; and possible microscopic fossils of primitive, bacteria-like organisms inside of an ancient Martian rock that fell to Earth as a meteorite. This array of indirect evidence of past life will be reported in the August 16 issue of the journal Science, presenting the investigation to the scientific community at large to reach a future consensus that will either confirm or deny the team's conclusion.

Another discussion of the perchlorate problem:
Martian Life Or Not? NASA's Phoenix Team Analyzes Results

Perchlorate is an ion, or charged particle, that consists of an atom of chlorine surrounded by four oxygen atoms. It is an oxidant, that is, it can release oxygen, but it is not a powerful one. Perchlorates are found naturally on Earth at such places as Chile's hyper-arid Atacama Desert. The compounds are quite stable and do not destroy organic material under normal circumstances. Some microorganisms on Earth are fueled by processes that involve perchlorates, and some plants concentrate the substance. Perchlorates are also used in rocket fuel and fireworks.
Perchlorate was discovered with a multi-use sensor that detects perchlorate, nitrate and other ions.

Before I'm taken out of context here, the point is not that we have found evidence of ET life, the point is we've found evidence conditions and chemicals found on Earth associated with life are probably common in the Universe.

 

[bokonon]

It is reasonable to hypothesize that if life had arisen more than once on the early Earth, an exchange of genetic material between microorganisms (which occurs extensively today) could have washed out the evidence.

Circular reasoning. "Exchange of genetic material" is only possible if the microorganisms doing the exchanging already share a common template, and the common template (DNA) implies a common origin, which implies life arose once.

This is not something I made up or read about on a non-scientific site. The exchange of genetic material on the early Earth is a serious hypothesis based on the genetic evidence. I'll see if I can find you the research which has the supporting evidence for the hypothesis.

I think you're missing my point. I'm not disputing that exchanges of genetic material took place in the past. Such exchanges are still taking place today.

My point is that, in order for such exchanges to be meaningful, they must happen between organisms which already use the same kind of genetic material -- DNA. This is true even in the case of viruses, which can hijack a host using RNA and compel the host to do the replicating. They're still using the same template, the same code for translating nucleic acid chains into protein chains.

If life arose independently more than once on this planet, it seems unlikely that each of those independent lines would have converged on DNA as the method for codifying genetic information. That's as implausible as discovering life on another planet which happens to speak English.

My point, therefore, is that it doesn't really makes sense to say that such an exchange might have somehow obscured an independent origin, since a common origin would be required in the first place for that kind of an exchange.

If water is the only evidence you are aware of, you've missed some significant evidence, methane outgassing detection and some carbonite structures.

Methane and methane outgassing is common in Oort cloud comets. I don't regard it as evidence of life, even though here on Earth it CAN be produced by rotting organic material. Carbonite structures are only more evidence of water, not evidence of life.

If that plus even more was required for abiogenesis, the Universe is still vast enough that such a combination would be very unlikely to be unique.

You continue to say this, even though you admit you can't say what "even more" might be required for abiogenesis. Your argument is essentially just "the universe is a big place; anything's possible." If it's vast enough to spawn multiple instances of abiogenesis, is it vast enough to spawn multiple instances of intelligent life? Multiple instances of homo sapiens? Multiple instances of English-speaking cultures? Multiple Shakespeares? Multiple interstellar versions of Hamlet? If not, why not? Isn't it vast enough? How would you know? How could you know?

They still would be expected to recur given the size of the Universe.

Even though you don't know what they are, you're confident that this statement is true. I'm amazed.

We know abiogenesis occurred once. We know we haven't observed enough of the Universe to say it only happened once. The more logical default here is it would have happened more than once given the composition and size of the Universe.

I've seen nothing that makes this "more logical" except your unwavering faith in the vastness of the universe. But we're really just repeating ourselves, and I'm sure we both have better things to do. I'll continue to follow this thread, and comment on new facts and speculations, but I hope I've said all I'm going to say on "It's BIG! It's REALLY REALLY BIG! HUGE!"

 

[bokonon]

Think again

 

[bokonon]

Think better

 

[Skeptic Ginger]

If life arose independently more than once on this planet, it seems unlikely that each of those independent lines would have converged on DNA as the method for codifying genetic information.

This is an odd conclusion. Evolution has resulted in successful traits evolving more than once in many cases. If DNA is the most successful option then it is logical this is the system which will evolve over and over.

Methane and methane outgassing is common in Oort cloud comets. I don't regard it as evidence of life, even though here on Earth it CAN be produced by rotting organic material. Carbonite structures are only more evidence of water, not evidence of life.

Despite putting my comments in bold, you still ignored them.

"Before I'm taken out of context here, the point is not that we have found evidence of ET life, the point is we've found evidence conditions and chemicals found on Earth associated with life are probably common in the Universe."

Water is not evidence of life either. But the more components of what we think it entails for life to evolve, the more common life is likely to have evolved. There are many conditions on Mars, not just liquid water, that add to the likelihood life on Earth is not likely to be unique in the Universe.

your argument is essentially just "the universe is a big place; anything's possible, if we have evidence of something existing in the Universe the possibility that thing is unique in all the Universe is near zero".

Fixed that for you.

 

[quixotecoyote]

Reported for an uncivil exchange with yourself.

 

[bokonon]

Evolution has resulted in successful traits evolving more than once in many cases. If DNA is the most successful option then it is logical this is the system which will evolve over and over.

Unbelievable.

It isn't just DNA, it's the code: UAA -> Stop, CUx -> leucine, etc.

I don't think you'll find any reputable scientists who would support your claim that this precise system might have evolved independently "over and over".

Eyes evolved independently many times on earth. They have a multitude of forms, and are even tuned to perceive different wavelengths of light. Which eye is "most successful"? Why aren't they all the same? For the same reason horses and butterflies aren't the same: because they evolved independently.

If life evolved on earth many times independently, I'd expect to see different templates for passing along a genetic code, different metabolic paths for making proteins, rather than the sort of conformity which we actually observe.

the universe is a big place, if we have evidence of something existing in the Universe the possibility that thing is unique in all the Universe is near zero

So you must also believe that somewhere, in another galaxy far, far away, AG Shakespeare wrote AG Hamlet, which can be read on an AG iPhone developed by AG Steve Jobs. Because we have evidence that such a thing exists in the Universe, so (by your lights) the possibility it's unique to this planet is near zero.

 

[Aepervius]

And we have no way of evaluating that probability. We don't know what the range of extra-solar planetary variability might be. Outside of a twin born of the same parents, what is the probability that another person lived who had the same DNA that you have? Is it a leap of faith to presume that you might be unique?

Abiogenesis base (and life) is only chemical reaction. Unless you pretend there is something else to boot it up (gods or whatever) which is unique to earth, then SIMILAR conditions somewhere else can lead to similar life form rising up. Or different life form. Heck on our own planet there could have been competitive abiogenesis , some of which failed to settle and the RNA/DNA based won the competition.

I am not sure what you are arguying that life must be 100% identical ? I am certainly not arguying that. Even if the other life form was absed on DNA/RNA like us, with the different condition (and thus different pressure selection), evolution would lead to different life form.

 

[Aepervius]

If life evolved on earth many times independently, I'd expect to see different templates for passing along a genetic code, different metabolic paths for making proteins, rather than the sort of conformity which we actually observe.

We don't know how many metabolic path , or way to pass genetic code there is. We only know two. That does not mean there isn't other, but before asserting they exists, they would have to be demonstrated to be existing. Please show me the biologist pretending there are other way, before I slap them with a "falsification" fish in the face, french style. It isn't up to us to demonstrate that only one way exists (which is impossible to do), it is up to other to falsify the hypothese and demonstrate the other way, or present their hjypotheses of other way, and make up a life form using those.

Fact is, we know of only DNA based life form and RNA based life form (which parasite and steal the cellular machinery of the DNA based life formn to reproduce). Fact is we don't know if it is the only path possible (due to the chemistry) or if there are many others. All we can conclude is : that was the path favorized on earth.

 

[bokonon]

Abiogenesis base (and life) is only chemical reaction. Unless you pretend there is something else to boot it up (gods or whatever) which is unique to earth, then SIMILAR conditions somewhere else can lead to similar life form rising up.

Since we don't know what caused it to boot up, it may well be that what caused it to boot up was unique to Earth. Maybe it required a huge nearby moon creating 100-mile tides every 10 hours, when the Sun was precisely the temperature it was then, and the ocean chemistry was precisely what it was, and even then there was only a half-inch of mineral matrix, in a single location which has since been subsumed, which provided the necessary catalytic surface for a key reaction, plus other special conditions which no one has even imagined...

And maybe it doesn't require anything extraordinary, and somebody will be cooking it up in a lab before Christmas.

Until we do know what caused it to boot up, or find evidence that it's booted up more than once, I don't think there's any reason to assume it's commonplace.