Possible hint of life discovered on Venus

[admin]

Phosphine, a chemical long thought to be a signature of life, is floating around in the clouds of Venus. How did it get there?

Possible hint of life discovered on Venus : Read more

 

[Broadlands]

The problem is more than speculative evidence for some anaerobic microbe producing a phosphine signature. The problem goes back to where that microbe came from. The evolution of proteins and nucleic acids has to come first. How likely is that in clouds above Venus, or above anywhere...leading to a LUCA-type microbe living in the clouds?

 

[MM70RJ]

The problem is more than speculative evidence for some anaerobic microbe producing a phosphine signature. The problem goes back to where that microbe came from. The evolution of proteins and nucleic acids has to come first. How likely is that in clouds above Venus, or above anywhere...leading to a LUCA-type microbe living in the clouds?

To understand the evolution of proteins and nucleic acids, one needs to understand the planet history... although it may seem impossible to have this kind of process today, it is possible that in the past (1M of years ago) it was possible... who knows?!

 

[Broadlands]

It is not necessary to know anything more about the history of a planet other than it is in the so-called Goldilocks zone. A location where water is available but so is dry land with the Star's energy not too hot and not too cold. The initial peptide bonds for assembling the amino acids into chains need the input of energy and the removal of water. Not likely in clouds.

 

[Chem721]

Not likely in clouds.

The nature of living organisms as we know them, and likely elsewhere, requires the presence of large amounts of liquid water, to evolve and to exist. It is always essential since liquid water drives the formation of membranes, and the folding of proteins, and the diffusion of metabolites and waste products into and out of cells, to name just a few issues. Entire books have been devoted to the subject of water and chemicals regarding life. They usually have the word "biochemistry" in their titles.

You need large amounts of liquid water to support life anywhere. It is highly unlikely to survive, much less evolve, in the clouds of any planet.

 

[Broadlands]

Large amounts of water are not needed to get life started. Indeed the reverse. Once the first cells had evolved is quite different. Richard Dickerson made the situation clear when he wrote (back in 1978):

"The central problem in understanding how the polymers were formed on the primitive earth is understanding how reactions requiring both the input of energy and the removal of water could take place in the ocean."

Or in clouds?

 

[Chem721]

Large amounts of water are not needed to get life started.

One would have to question the meaning of "large amounts of water."

Whatever the case, in order for life to arise from "scratch", a substantial aqueous milieu would be required containing a vast assortment of chemicals in a stable thermal environment. Such conditions would be required in order to provide such a variety of chemicals in sufficient volume and dilution, and a stable, moderate temperature to allow for the vast assortment of complex chemical interactions required.

Life would never arise in a near chemical grid-lock of concentrated components. Such conditions would not allow for the rapid interplay of thousands of various chemicals required to kick-start life. The chemical kinetics of abiogenesis would be rather exacting, one should think. Only relatively dilute mixtures in considerable volumes of water, which are constantly mixed and replenished by thermal vents, are likely involved in such complex processes.

The nutrients and thermal stability are provided in the oceans of earth. Since photosynthesis did not arise until later, the nutrient source likely was from reduced compounds expelled from thermal vents, which also would provide for long term thermal stability (locally to the vents) within large, oceanic bodies.

It has been suggested that abiogenesis required a million years or more to develop into the most primitive replicating organism. It seems likely that such an environment would require a substantial body of water to hold all of the chemicals, as well as providing a very stable thermal condition for extended periods. Small bodies of water are also subject to more rapid changes in temperature, which would be detrimental to abiogenesis.

Large amounts of chemicals in large volumes of thermally stable water is the most likely scenario for abiogenesis anywhere.

As a side note : thermal extremophiles almost certainly arose from preexisting life forms which evolved under relatively mild temperature.

 

[Broadlands]

"Large amounts of chemicals in large volumes of thermally stable water is the most likely scenario for abiogenesis anywhere."

The problem remains for the formation of the initial bonds in any body of water that may have accumulated primordial amino acids. Heating and cooling with wetting and drying must take place....with added water (rain) to keep the locations from total dehydration. A difficult scenario, but so are all others.

The extremophiles at the base of the tree of life (LUCA) are not just thermophiles, they are also microaerophiles... Aquifex. Small amounts of free oxygen are needed.

 

[Chem721]

Heating and cooling with wetting and drying must take place

The most likely theories of abiogenesis require a continuous aqueous milieu at a stable, moderate temperature. Fluctuations in heating/cooling and drying would be random and/or relatively extreme events unsuitable for any complex organization of macromolecules to assemble into the first living cell. It cannot be ruled out that some of the chemicals used in abiogenesis underwent various processes before their incorporation, where "extremes" may have played a role. But the assembly and origin almost certainly occurred in a thermally stable solution of substantial volume.

Solid phases are believed to have played a major role, silicates being the most likely as they have surfaces with variable chemistries which can bind a variety of chemical species - ionized, polar and non-polar. Any chemical organization of such complexity on a solid surface could only occur when exposed to a fully liquid environment - the continuous capacity for diffusion of all the primary chemicals in water would be a major requirement for abiogenesis.

 

[Broadlands]

"The most likely theories of abiogenesis require a continuous aqueous milieu at a stable, moderate temperature."

All laboratory experiments are made under so-called "prebiotic conditions". The most likely theories and experiments are done indoors. They do not even require protection from intense solar UV. Nor do they require protection from oxidation by the ambient free molecular oxygen. The more successful ones (David Usher) have been done under heating/cooling, wetting/drying conditions. All needed for initial peptide or nucleotide bond formation. Solid phases (clay minerals) only add to the many complexities. Maybe the most likely answer (for the Earth) is Panspermia?

 

[Chem721]

The most likely theories and experiments are done indoors. They do not even require protection from intense solar UV.

Life arising in the oceans precludes any need for UV shielding.

The more successful ones (David Usher) have been done under heating/cooling, wetting/drying conditions. All needed for initial peptide or nucleotide bond formation.

Proteins are widely believed to have been a secondary development due to an initial RNA-based life form. Self-assembly of proteins and polynucleotides in liquids is documented.

Solid phases (clay minerals) only add to the many complexities.

The complexities involved are clearly not well established, and adding solid phases is just another element of complexity. That would hardly rule it out. Occam's razor is no where to be seen in this topic.

 

[Chem721]

Maybe the most likely answer (for the Earth) is Panspermia?

The panspermia concept is as unlikely as the magic wand notion. The shear forces of impact and ejecta, to say nothing of the heat involved, renders it highly unlikely, as does surviving the hazards of space weather for millions of years in a near vacuum. And then you go through it again with the heat of entry, and the shear and heat of impact. And then you must land in an area which contains all of the minerals and nutrients required to survive and propagate. It makes adding solid surfaces appear rather simple by comparison. Besides all that, panspermia simply puts the origin and its complex chemistry somewhere else.

 

[Broadlands]

Chem721. You are now grasping at straws? What is most likely believed is science by consensus and that has always been irrelevant.

"Life arising in the oceans precludes any need for UV shielding" A common misconception. Amino acids (appearing from anywhere) would need to combine with others to make peptide and polypeptide bonds that initially can only be done away from the oceans. RNA/DNA exposed to the full and more intense UV flux of the young Sun. This would be true even for the source(s) of Panspermia. There is no viable way around the need for peptide and nucleotide bonds to get cellular life underway. That's parsimony. Please re-read what Richard Dickerson wrote...posted yesterday. And don't forget what the LUCA (Aquifex) is telling us. There was oxygen very early on and enough for a minimal ozone screen. Venus in the clouds has none of this.

 

[Chem721]

What is most likely believed is science by consensus and that has always been irrelevant.

That is a statement quite impossible to accept. What is most likely believed is science by consensus, which usually is correct, at least in my experience. You sound like a contrarian, which some appreciate. All of the known laws of physics and major observations in science are based on consensus. How could science progress otherwise? It cannot.

"Life arising in the oceans precludes any need for UV shielding" A common misconception.

Clearly UV cannot penetrate very far in water. You know this. So any developing chemistry on its way to life would be in water anyway, but would have to be deep enough to shield it from UV, or nothing will arise. Very simple. That is why most insist, as do I, that life arose in the oceans, at least deep enough to avoid UV. It is clearly the optimal solution. As noted, the oceans also provide nutrients and thermal stability for an aqueous-based abiogenesis.

There is no viable way around the need for peptide and nucleotide bonds to get cellular life underway,

With a doctorate in biochemistry, I am well aware of the need for peptide bonds in proteins, and phosphodiester bonds (your "nucleotide bonds") in polynucleotides. However, it seems likely that there was no protein in the earliest life forms, with many accepting RNA genomes (i.e. RNA-coding) and RNA mechanistic-based life forms. We could go on for hours, but it will soon become circular. Getting pretty close already.

Please re-read what Richard Dickerson wrote...posted yesterday.

Who is Richard Dickerson? He does not appear on this thread.

 

[Broadlands]

With a doctorate in biochemistry? Who is Richard Dickerson? https://en.wikipedia.org/wiki/Richard_E._Dickerson

You keep confusing cellular life with the origins of proteins and nucleic acids before there was any life. That is where the primitive amino acids and the bonds between them become important... and creates the dilemma expressed by Dickerson.

Consensus science is rarely right with respect to controversial subjects. "The improver of natural knowledge absolutely refuses to acknowledge authority, as such. For him, skepticism is the highest of duties; blind faith the one unpardonable sin. Thomas Huxley

 

[Chem721]

With due respect, I am not confusing anything.

On the other hand, you have thrown out quite a bit of information which appears somewhat disjointed, offering no real approach to a course for abiogenesis. Things about hot and cold temperatures and drying things out and small volumes being required. Many are comments that do not seem to result in any conclusion. But certainly some would say this should not diminish your posts since no one else has any conclusion for it either. Start up notions yes, finished product, no.

The origin of biopolymers is clearly fundamental regarding the abiogenesis of life, and its evolution to modern life with Crick's notion of the Central Dogma of Molecular Biology:

DNA -> RNA -> protein

One cannot rationally consider the origin of modern life without considering these polymers first and foremost, and existing prior to life itself. Any other approach would be irrational. One must start with the biochemicals BEFORE cellular life can arise. There should be no confusion in this regard whatsoever.

And I looked up the wiki article. It was very brief and mentions Dickerson's work with B-DNA, which defines the double helix of DNA at atomic resolution. It goes on to mention his work in complexes between DNA and drugs or proteins, and the 'Dickerson dodecamer". This work is clearly secondary to Watson and Crick. There was no mention as to some defining principle(s) on the origin of life.

Seeing his name on a book of Protein Chemistry, I do recall it now. A reference to an article in Scientific American has his story about "Chemical Evolution and the Origin of Life", but I cannot read it without paying for it. Please inform me as to his "dilemma".

 

[Chem721]

And don't forget what the LUCA (Aquifex) is telling us.

This was an issue I neglected to mention in one of your last posts. It is quite revealing to your concepts of abiogenesis. LUCA is already a fully formed "central dogma life form". It cannot offer more on abiogenesis than any microbes living today, actually. We need to get from self-replicating polymers to replicating cells bound up in membranes. LUCA must have appeared long after the first life form arose. There is nothing there regarding a starting point, only relationships.

 

[Chem721]

There is nothing there regarding a starting point, only relationships.

While waiting for your reply to my request about the "dilemma", I had to revisit the notion of an "RNA World", to brush up on the concept. Wiki (1) defines it as:

"....a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existence of this stage. "

and goes on to note:

"....the evidence for an RNA world is strong enough that the hypothesis has gained wide acceptance. The concurrent formation of all four RNA building blocks further strengthened the hypothesis."

End quotes.

One might suppose that your concept of consensus in science (i.e. wide acceptance) renders this hypothesis null and void - i.e. purely blind faith? Could be.

However, there is strong evidence to support such an origin, and it clearly would mean, if true, that DNA and protein followed RNA via cellular evolution, not abiotic, chemical evolution. Once again, LUCA cannot address such aspects. It is too far removed from the original chemistries.

I do hope you have something good for me, I do like dilemmas. Time will tell.

(1) https://en.wikipedia.org/wiki/RNA_world

 

[Broadlands]

Ok Chem721... Yes, a great deal has been "thrown out". And you have been parsing it in your replies., as have I. That makes it difficult to find a defining issue with respect to the origins of life in the clouds of Venus, much less on the surface of the Earth. You are not correct that LUCA must have appeared after the first life.... It WAS the first life...a full biological organism by definition and by consensus. Aquifex a microaerophile in an anoxic world.

It has been the precursor biochemicals and conditions that led to a LUCA that have been under discussion here.

Once more.. prebiotic "life" (those 'original chemistries') required prebiotic materials of which one was inorganic carbon made into amino acids. e.g. The Miller-Urey hypothesis. These are (were) the "building blocks" of life that compounds that were in need of some protection from the early Sun's enhanced UV radiation... as the peptide bonds tried to have the carboxyl join the amino group and release water....in the presence of water??. That is the Dickerson dilemma. And it remains one.

Hypothetical stages and wide support are not 'strong' evidence, but opinion in need of support.

 

[Chem721]

You are not correct that LUCA must have appeared after the first life.... It WAS the first life...a full biological organism by definition and by consensus. Aquifex a microaerophile in an anoxic world.

In order to accept LUCA as the first life form, you must reject the RNA world. You say that LUCA is accepted by consensus agreement, but this after you ran the notion through the ringer. Who was it? Oh yes, "blind faith the one unpardonable sin". Thomas Huxley.

There is increasing acceptance of the RNA world in consensus estimates, so something must be wrong in one of these consensus notions. I would bet the ranch on the RNA world for various reasons :

Pure logic suggests that the formation of such an incredibly complex mechanism as central dogma in "one go" is beyond extremely unlikely. It requires the simultaneous encapsulation of three remarkably complex polymers, DNA, RNA, and protein, all linked up by a three-letter nucleotide code for sequential amino acids forming the 3-D structure of proteins with precise functions. As you must know, modern life is incredibly complex chemistry.

And all the membranes, and membrane proteins, and those of intermediary metabolism, with all their co-factors neatly in place, all pre-coded abiotically and then neatly tucked into one cell, all at the same time to give rise to LUCA. And it all runs on ATP, presumably via some form of electron transport (itself highly complex), again all combining in "one go". I am just getting started on all that is required to get LUCA going, all in "one go". And then there is the stereochemistry involved. A whole new wrinkle as there are so many varieties for life to choose from. Do we go with D or L amino acids? D or L for that co-factor. etc. And LUCA can tell you how? Doubtful is an extreme understatement.

Certainly more complex schemes have been considered, but this one is so far over the top one might be required to bring in the "magic wand" to accomplish it.

Totally inconceivable. The original life form almost certainly had a much less complex organization, one which could arise by many fewer mechanisms than those required to form LUCA from scratch. Of course the RNA world defies any notions of LUCA being the original life form, and it almost certainly was not.

The vast complexity to make LUCA requires hundreds of preformed enzymes and mechanisms, to say nothing of structural elements, with all of them encoded in DNA, all in one-go? It defies all logic and deductive reasoning. You brought up blind faith, it would seem too many that to buy into such a hypothesis requires that, and a whole lot more.

If you read through the Wiki article on LUCA, it mentions nothing about it being the first life form, only that it is the last universal life form common to modern life. Indeed, it tends to support my conclusion that it is not the first life form with this quote:

"Its genetic code was likely based on DNA, so that it lived after the RNA world."

They seem to believe in an RNA world where life first arose. You must reject that world if you believe LUCA to be the first living organism. Tough choice for you? It is a slam dunk for me.

Here is a quote from the opening paragraph from wiki on an RNA World :

"The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existence of this stage."

Recall the existence of RNA-based enzymes in modern life. They and transfer RNAs are remnants of that world.

You might want to give this a read:

https://en.wikipedia.org/wiki/RNA_world

A slower, less complex origin for life is much more likely. Evolving central dogma from an RNA-based life form is almost infinitely easier to believe than LUCA from scratch.

 

[Broadlands]

"...in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins."

That's the point where the bonds between primitive amino acids are required. The Dickerson dilemma. A long way from there to a last universal common ancestor... a hyperthermophile that is also a microaerophile. Aquifex species are aerobic hyperthermophiles that use elemental sulfur, hydrogen, and trace amounts of oxygen to live in ecosystems that today are near hot hydrothermal vents (Stetter, 1991). In the early Archean the Cyanobacteria had yet to appear to provide any oxygen. And elemental sulfur is unstable under reducing conditions.

Small amounts of free oxygen in an Archean world said to be anoxic. The clouds above Venus?

"Water is indispensable for life as we know it to emerge. But at the same time, water elimination (condensation, polymerisation) is one of the most common reactions in metabolism underpinning the synthesis of cells. The reverse reaction, water addition, is hydrolysis and can be chemically destructive to many essential biomolecules. Through hydrolysis, water literally works against the synthesis and accumulation of polymers at life’s emergence." William Martin

 

[Chem721]

Through hydrolysis, water literally works against the synthesis and accumulation of polymers at life’s emergence." William Martin

Using water as negative pressure for abiogenesis is rather strange, since it is the one, single component that drives all of the folding of proteins, the formation of membranes, the diffusion of nutrients and waste products, to name just a few of its many required activities. And the amounts of water which are present that are unrelated to metabolism are nearly infinitely higher. It would almost seem that William Martin believes life is a solid-state format.

Since you completely failed to provide any support for LUCA being the first living organism, and make no mention of the complexities involved for its direct formation, and the almost certain need for precursors, there is no reason to continue this exchange.

The greatest mystery to most biochemists is the origin of central dogma. Linear information transcribed into 3-D mechanisms. It is inconceivable to have been derived from an abiotic process. For that matter, it seems almost impossible to exist at all. It ranks with the Big Bang as one of the greatest mysteries in all of science.

But I understand your lack of explanations. No one else has them, so why should you?

 

[Broadlands]

"Using water as negative pressure for abiogenesis is rather strange, since it is the one, single component that drives all of the folding of proteins."

And water is the one single component that must be removed to begin biogenesis from the initial abiotic 'building blocks'... The Dickenson dilemma again. That's the one problem you seem to consistently refuse to admit is an important requirement for life, along with the simultaneous need for protection from intense solar UV radiation that would impinge on proteins and nucleic acids as they were drying. And then on the first cells and later the Cyanobacterial stromatolites in need of light in the visible spectrum.

I agree that it all seems improbable, almost impossible...but here we are trying to jam the square peg into a round hole in the clouds above Venus because of phosphine speculated to have been derived from some anaerobic bacteria... a very long way from their origins in those clouds.

 

[Broadlands]

David: Hamstrung: " until we are able to explain 'what is the source of life' in a living organism." Good point. Maybe we need to explain what life is before explaining its source?
In the clouds of Venus it has been assumed (suggested?) that life is an anaerobic organism that had already gone though the source. A big leap.