Author Topic: Oldest fossils ever discovered raises question of life on Mars  (Read 9171 times)

Offline Star One

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Are we saying that life on Mars never progressed beyond the RNA stage?

Offline QuantumG

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Aren't (some) viruses RNA life?

The kind of RNA life biologists are interested in is the kind that doesn't require enzymes made from protein. i.e., the "RNA World" hypothesis is that the enzymatic activity required for life is possible using self catalysed reactions.
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Offline Dalhousie

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I am surprised that nobody has mentioned ALH84001 yet. There is still debate about whether the meteorite contains biogenic fossils or not. In my opinion, some of the evidence is very hard to explain by non-biological means. So it's quite possible that we already have fossil Martian life in our hands.

Some hints in other meteorites also. The problem is, like the Viking data, the evidence is not particularly strong.

Even the evidence for life in the Pilbara and 3.5 Ga - which is much stronger than in ALH84001 - has been questioned.  Erroneously in my view.

So I suspect there to be a push back against the Greenland paper shortly.  If you can't make your scientific name finding something, make it by criticising someone who has.....
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Offline Dalhousie

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Aren't (some) viruses RNA life? Even on that scale, life forms that are able to interact and take what they need to survive from life forms that dominate the planet, would have a huge competitive advantage over alternative RNA life that would have to compete without being able to profit from that dominant life form.

Or alternatively, such life would fill up a niche where it can survive because it does not have to interact with us to survive, so by definition it would not be found anywhere near our kind of life. And it would have an evolutionary benefit in keeping 'us' away, so it's probably quite toxic to us.

Think about it: something in a location harder to find, less likely to be habitable (to our preconceptions) and very likely less identifiable as life than snotites. We wouldn't even know where to start looking.

Yes, some viruses have RNA rather than DNA, those responsible for HIV for example. 

Are they alive? Good question.  They transmit genetic information, but can reproduce only with external help and do not metabolise. Like prions, which reproduce within RNA or DNA, they have some but not all the properties of life.

You would look for RNA life by looking for unusual RNA signatures in scans of soil, water, etc.  Or unusual metabolic activity.

RNA life is probably less reproductively fit than DNA life, it thus may well be extinct.
« Last Edit: 09/04/2016 11:47 PM by Dalhousie »
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Offline coypu76

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I may be mistaken, but if I understand correctly prions do not require nucleic acids to replicate.  Prions are proteins that, while chemically identical to healthy proteins, are folded differently than their healthy counterparts.  Their misfolded morphology becomes a template which causes healthy proteins to misfold, thus replicating the prion.

Offline Dalhousie

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I may be mistaken, but if I understand correctly prions do not require nucleic acids to replicate.  Prions are proteins that, while chemically identical to healthy proteins, are folded differently than their healthy counterparts.  Their misfolded morphology becomes a template which causes healthy proteins to misfold, thus replicating the prion.

That's right, no nuclear acids, no metabolism, just reproduction - creepy isn't it?
« Last Edit: 09/05/2016 03:09 AM by Dalhousie »
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Offline QuantumG

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I may be mistaken, but if I understand correctly prions do not require nucleic acids to replicate.

Fundamental dogma of biology, man. DNA -> RNA -> Protein. Prions interfere with the last step to amplify their variation, but without the production machinery they have nothing to replicate from.
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Offline coypu76

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Fundamental dogma of biology, man. DNA -> RNA -> Protein. Prions interfere with the last step to amplify their variation, but without the production machinery they have nothing to replicate from.

Considering that the prion diseases we know can rot your brain, creepy indeed!

Offline jgoldader

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In my (very non-medical) thinking, I view prions as akin to a virus, in that they can't reproduce on their own.  They "take over" properly folded proteins as viruses take over a normal cell's mechanisms in order to reproduce.  Maybe, they are just in a class by themselves.

On tests for finding RNA life--yes, IIRC Ward discusses this, and says while RNA life might have been here first, and may still be here, because of the requirement of DNA for "life as we know it," researchers look for DNA.

Ward's "Life As We Do Not Know It" and his other book "Rare Earth" (co-authored with Don Brownlee, who taught one of the best classes I ever took) are very good reading indeed for folks interested in the possibility of life elsewhere.  But fair warning, Rare Earth is a bit soul-crushing for those who want intelligent life to be common.
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Offline woods170

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In my (very non-medical) thinking, I view prions as akin to a virus, in that they can't reproduce on their own.  They "take over" properly folded proteins as viruses take over a normal cell's mechanisms in order to reproduce.  Maybe, they are just in a class by themselves.

On tests for finding RNA life--yes, IIRC Ward discusses this, and says while RNA life might have been here first, and may still be here, because of the requirement of DNA for "life as we know it," researchers look for DNA.

Ward's "Life As We Do Not Know It" and his other book "Rare Earth" (co-authored with Don Brownlee, who taught one of the best classes I ever took) are very good reading indeed for folks interested in the possibility of life elsewhere.  But fair warning, Rare Earth is a bit soul-crushing for those who want intelligent life to be common.
Regarding the soul-crushing: the notion that intelligent life is common was thoroughly crushed in my freshman year. By a biologist-turned-astronomer no less...

Offline Star One

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Oldest fossils ever discovered raises question of life on Mars
« Reply #30 on: 09/05/2016 11:47 AM »
In my (very non-medical) thinking, I view prions as akin to a virus, in that they can't reproduce on their own.  They "take over" properly folded proteins as viruses take over a normal cell's mechanisms in order to reproduce.  Maybe, they are just in a class by themselves.

On tests for finding RNA life--yes, IIRC Ward discusses this, and says while RNA life might have been here first, and may still be here, because of the requirement of DNA for "life as we know it," researchers look for DNA.

Ward's "Life As We Do Not Know It" and his other book "Rare Earth" (co-authored with Don Brownlee, who taught one of the best classes I ever took) are very good reading indeed for folks interested in the possibility of life elsewhere.  But fair warning, Rare Earth is a bit soul-crushing for those who want intelligent life to be common.

Problem with this kind of argument is as we only have one example to look at it it's relatively easy for people to extrapolate however they wish to make the argument either way. I've heard people take basically the same set of facts and argue it both ways.

This keeps occurring in different fields of study. It happened before with exoplanets & other types of planetary system that weren't thought possible to exist. Yet lo & behold nature has other ideas.
« Last Edit: 09/05/2016 11:52 AM by Star One »

Offline KelvinZero

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Ward's "Life As We Do Not Know It" and his other book "Rare Earth" (co-authored with Don Brownlee, who taught one of the best classes I ever took) are very good reading indeed for folks interested in the possibility of life elsewhere.  But fair warning, Rare Earth is a bit soul-crushing for those who want intelligent life to be common.
There could also be a soul crushing element to finding other intelligent life. Suppose it is a signal from 100 lightyears away. That implies there are millions of intelligent species.. and none of them ever achieved open ended colonisation.. so we almost certainly won't either.

More likely we will spot life at a great distance in the form of an expanding sphere of vanishing stars or galaxies. That can be depressing or scary depending how near they can approach light speed. In any case we might be gazing at our own ultimate limits.

Offline Dalhousie

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Ward's "Life As We Do Not Know It" and his other book "Rare Earth" (co-authored with Don Brownlee, who taught one of the best classes I ever took) are very good reading indeed for folks interested in the possibility of life elsewhere.  But fair warning, Rare Earth is a bit soul-crushing for those who want intelligent life to be common.

Mind you "Rare Earth" is very dated now. Something he acknowledges.
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Offline jgoldader

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Ward's "Life As We Do Not Know It" and his other book "Rare Earth" (co-authored with Don Brownlee, who taught one of the best classes I ever took) are very good reading indeed for folks interested in the possibility of life elsewhere.  But fair warning, Rare Earth is a bit soul-crushing for those who want intelligent life to be common.

Mind you "Rare Earth" is very dated now. Something he acknowledges.

Oh, the book is getting on in years, yes.  It's a darned good read, though.  I don't keep up on the geological stuff or paleobiology that much, so if that's dated, I'd not know.  Their astronomy, as I recall it, is still sound.  There was the follow-on book "Life and Death of Planet Earth" which might have updated the biology and geology some.  It's unusual for *any* book to make me emotional, much less a science book, but both made me sad. 

The main thesis of Rare Earth, that complex metazoan life (animal life) is rare, seemed awfully strong to me.  Rather than animal life being preordained, Ward and Brownlee presented an argument that it's the unlikely outcome of many mass extinctions and chance events (e.g., the development of oxygen metabolism is clearly not essential to all life, but *is* essential to animals on Earth).  They do claim simpler life is more likely, so maybe the dominant lifeform of the universe is methanotropic archaea or something.  Discovery of bona fide Martian microbial fossils would be a very powerful data point in favor of the Rare Earth hypothesis.  In fact, you might expect to find bacteria pretty much anywhere there are the raw materials and energy, like in the icy outer planet moons.

If I had to pick a single scientific question to know the answer to, it would be the Fermi paradox.  It would be interesting (yet probably not terribly useful) to know how the universe got started, and likewise to know how life got going here.  But understanding the Fermi paradox is all about the future.  You can have a solution to the Fermi paradox if the universe is full of algae, but with ourselves, as intelligent animals, being unique.  That would also make me sad, and I hope it's not the case, but my opinion isn't relevant to what's actually going on.
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Offline Dalhousie

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Ward's "Life As We Do Not Know It" and his other book "Rare Earth" (co-authored with Don Brownlee, who taught one of the best classes I ever took) are very good reading indeed for folks interested in the possibility of life elsewhere.  But fair warning, Rare Earth is a bit soul-crushing for those who want intelligent life to be common.

Mind you "Rare Earth" is very dated now. Something he acknowledges.

Oh, the book is getting on in years, yes.  It's a darned good read, though.  I don't keep up on the geological stuff or paleobiology that much, so if that's dated, I'd not know.  Their astronomy, as I recall it, is still sound.  There was the follow-on book "Life and Death of Planet Earth" which might have updated the biology and geology some.  It's unusual for *any* book to make me emotional, much less a science book, but both made me sad. 

It was the astronomy part that was most dated, as it still assumed that planetary systems are rare (unfortunate given the exoplanet revolution that was already underway when it was written). 

if you like Ward's writing, you should try Gorgon, all about the amazing mammal-like reptiles of the Permian and the Permo-Triassic extinction.
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Offline jgoldader

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Ward's "Life As We Do Not Know It" and his other book "Rare Earth" (co-authored with Don Brownlee, who taught one of the best classes I ever took) are very good reading indeed for folks interested in the possibility of life elsewhere.  But fair warning, Rare Earth is a bit soul-crushing for those who want intelligent life to be common.

Mind you "Rare Earth" is very dated now. Something he acknowledges.

Oh, the book is getting on in years, yes.  It's a darned good read, though.  I don't keep up on the geological stuff or paleobiology that much, so if that's dated, I'd not know.  Their astronomy, as I recall it, is still sound.  There was the follow-on book "Life and Death of Planet Earth" which might have updated the biology and geology some.  It's unusual for *any* book to make me emotional, much less a science book, but both made me sad. 

It was the astronomy part that was most dated, as it still assumed that planetary systems are rare (unfortunate given the exoplanet revolution that was already underway when it was written). 

if you like Ward's writing, you should try Gorgon, all about the amazing mammal-like reptiles of the Permian and the Permo-Triassic extinction.

Thanks for the rec!  I tried to find it on Amazon, and "peter ward gorgon" shows it's not available for Kindle, and also gave a suggestion of a sexy volleyball bikini.  :o  He does have a book out from a year or two ago called "A New History of Life," and I'm getting that...instead of the bikini.   ;D
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Offline Star One

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Oldest fossils ever discovered raises question of life on Mars
« Reply #36 on: 09/07/2016 12:36 AM »
Ward's "Life As We Do Not Know It" and his other book "Rare Earth" (co-authored with Don Brownlee, who taught one of the best classes I ever took) are very good reading indeed for folks interested in the possibility of life elsewhere.  But fair warning, Rare Earth is a bit soul-crushing for those who want intelligent life to be common.

Mind you "Rare Earth" is very dated now. Something he acknowledges.

Oh, the book is getting on in years, yes.  It's a darned good read, though.  I don't keep up on the geological stuff or paleobiology that much, so if that's dated, I'd not know.  Their astronomy, as I recall it, is still sound.  There was the follow-on book "Life and Death of Planet Earth" which might have updated the biology and geology some.  It's unusual for *any* book to make me emotional, much less a science book, but both made me sad. 

It was the astronomy part that was most dated, as it still assumed that planetary systems are rare (unfortunate given the exoplanet revolution that was already underway when it was written). 

if you like Ward's writing, you should try Gorgon, all about the amazing mammal-like reptiles of the Permian and the Permo-Triassic extinction.

Found  this which is an oldish but satisfying critique of this theory.

http://www.dailygalaxy.com/my_weblog/2011/01/the-rare-earth-theory-logic-and-math-says-were-not-alone-in-universe.html
« Last Edit: 09/07/2016 12:39 AM by Star One »

Offline Torbjorn Larsson, OM

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Those fossil candidates seem to impress many, compared to the slow consensus of the 3.5 Ga stromatolites. So maybe we will see references to 3.8 Ga fossils soon.

Makes you wonder if this indicates that as soon as a planet finishes forming, that providing conditions are right life will spring up ASAP. Considering that it's now believed life could have started on Earth 4.1 billion years ago, so very early on.

Make that 4.3 Ga. Earth had a habitable ocean > 4.3 Ga, [ http://www.minsocam.org/msa/ammin/toc/2015/open_access/AM100P1355.pdf , fig. 17], several molecular clocks date the first split between Bacteria and Archaea > 4.2 Ga [ http://www.timetree.org/search/pairwise/2/2157 ], and the current first fossil candidate is > 4.1 Ga [ http://www.pnas.org/content/early/2015/10/14/1517557112.full.pdf ]. Those are all consistent finds by the way, the fossil candidate carbon isotope ratio is spot on the photosynthesis Calvin cycle - bottle neck RuBisCO enzyme - ratio, potentially confirming the split date since Archeaa doesn't use the Calvin cycle for CO2 fixation. (It is in fact much better carbon isotope consistency than Isua organics - not associated with the putative stromatolites, what I know of - due to the zircon encapsulation, confirming the metamorphic nature of Isua rocks. But as for the Isua fossil candidates, repetition is local as of yet, and they lack external context which the Isua find do not.)

Maybe you are referring to the dates that Isua has forced onto the late bombardment hypothesis, moving its consensus 4.1 - 3.8 Ga interval towards the Apollo ejecta clustering date of 4.1 Ga?

Besides putting that hypothesis in tension, it is now in tension with the geological record of both Earth and Moon. The > 3.8 Ga zircons all lack the typical impact shock fractures that you can see in zircons related to the 2.1 Ga Vredesfort crater. And (while I have not yet read it) the latest result on the Imbrium crater has increased both size and ejecta zone, making the contamination question of the Apollo samples even more pointed.

And of course the other planet systems show nothing like the late migration that would be associated with the late bombardment. An early Jupiter-Saturn resonance would result in the same system architecture, but also remove the data tension. One late Imbrium impactor wouldn't be a finetuned result.

But even if the late bombardment really existed, life appears to have survived it easily. That is what Abramov et al models suggest, with or without an ocean evaporator impact.


Offline Torbjorn Larsson, OM

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That Rare Earth hypothesis seems daft, you can chose your selection to get any likelihood between 0 and 1, so what could you test in the future besides your current opinion?

Astrobiologist consensus is that life is common, it emerged so early here. (The scientific use of an individual is called a type case, and the processes involved can be studied over time. Earth is a common type case for many sciences.) Biologist consensus is that language capable life is uncommon, since it is a rare trait.

I am surprised that nobody has mentioned ALH84001 yet. There is still debate about whether the meteorite contains biogenic fossils or not.

There is no science debate though. As for the 4.1 Ga fossil candidate, the find lack repetition and context, so it would be a candidate at most. But all the proposed biomarkers had abiotic confounds. Notably the reverse condition applies for the 4.1 candidate, the abiotic confounds have been rejected, so the debate should move there.

The ALH84001 meteorite is 4.4 Ga, which is before the martian 4.1 - 3.8 Ga habitable window that is currently considered.

Are we saying that life on Mars never progressed beyond the RNA stage?

That is unlikely. A separation between genetic storage and expression evolves in models as soon as you introduce parasites.

Aren't (some) viruses RNA life?

The kind of RNA life biologists are interested in is the kind that doesn't require enzymes made from protein. i.e., the "RNA World" hypothesis is that the enzymatic activity required for life is possible using self catalysed reactions.

There are lots of cellular RNA that are protein independent in the genetic machinery (rRNA, tRNA, introns). However, protein expression should have evolved early on, since the codons have affinity for their amino acids.

As a result the RNA/RNA cell ("RNA World") would have been a fleeting thing, while the RNA/protein cell would have some life span. (See above on the ecology that would promote evolution of DNA or something similar. It would take some time.)

Koonin has suggested that some ancient viral clades evolved from his three stages of RNA to DNA evolution. The +ssRNA (positive single strand RNA) viruses could have evolved from a cell having the linear mRNA genes of a RNA/protein cell. The retroviruses could have evolved from a cell having a circular DNA as partial storage with the reverse transcriptase in the cycle between linear RNA strands with protein expression and safe memory. And of course some early dsDNA viral clade could have evolved from early ancestors of the pure DNA/protein cell of the LUCA.

Prions are not considered evolutionary life forms by medical doctors in the way viruses can be. (Or at least that is what I have been told by one doctor.) While their topological fold reproduction can evolve in the usual biological sense to use new protein templates, their expression is a mess. Prion tangles are calcified protein clumps of varying "trait expression".

Offline Dalhousie

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Those fossil candidates seem to impress many, compared to the slow consensus of the 3.5 Ga stromatolites. So maybe we will see references to 3.8 Ga fossils soon.

Well, there was only ever a small number of people who were not impressed by the Pilbara stromatolites, the chief instigator of which is now dead.  Plus the Greenland paper has only just come out - less than a week - so give the nay sayers time to regroup.

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