Author Topic: Oldest fossils ever discovered raises question of life on Mars  (Read 9652 times)

Offline Star One

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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.

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“Up until now the oldest stromatolites have been from Western Australia and they are roughly 3,500 million (3.5bn) years [old],” said Clark Friend, an independent researcher and co-author of the research. “What we are doing is pushing the discovery of life earlier in Earth’s history.”

The discovery, says Friend, also raises questions about the possibility of life on other planets.

“If we have got life at 3,700 million (3.7 bn) years on Earth, did it exist on other planets - because Mars, for example, 3,700 million years ago was wet,” he said.

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Dartnell agrees that the discovery could help researchers explore whether life was once present on other planets. “The Martian surface today is very cold and dry, but around the time that these ancient layered rocks formed in Greenland, Mars was itself a much warmer and wetter, and thus habitable planet,” he said. While finding stromatolites with robotic landers or even manned missions is likely to be challenging, says Dartnell, if stromatolites are present, they could offer a wealth of information. “On Mars, we’d expect stromatolites, even as old as 3.5-3.8 billion years, to be better preserved than on Earth as Mars hasn’t experienced geological processes like plate tectonics,” he said.

https://www.theguardian.com/science/2016/aug/31/oldest-fossils-on-earth-discovered-in-37bn-year-old-greenland-rocks-stromatolites

Here's the Nature paper.

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature19355.html
« Last Edit: 09/01/2016 06:55 AM by Star One »

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4.1 billion years ago, there were oceans on Venus as well. Just saying  ;)

Offline ugordan

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4.1 billion years ago, there were oceans on Venus as well. Just saying  ;)

Maybe.  Even if you ignore the hellish environment any attempt at surface exploration would encounter, since Venus does not have plate tectonics but is thought to overturn its entire crust periodically, finding any fossils might be a challenge.

Offline Bob Shaw

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The best place to look for Venus fossils will be anywhere but Venus, where the weather and geology are terrible. Ice caps, glaciers and shadowed points on Earth, the Moon and Mercury can preserve and sort incoming material better than any other locations. Rather than looking for needles in a haystack, you seek fossil-bearing meteorites among those to be found on the 'shores' of ice where it has sublimated away. People do this already on Earth, and it wouldn't be impossible to do this robotically elsewhere.

Speaking of which, an upside of Global Warming here may be the deposition of meteorites as glaciers retreat - though, oddly, I've never seen any mention of meteorites in moraines etc - perhaps early Iron Age people grabbed all the irons!

Offline Bob Shaw

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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.


The flip side of that is, will we find that all local life is/was a close relative? A lot of stuff has been exchanged between the bodies of the Solar System as a result of impacts, and these used to be far larger and more common than nowadays. Now, as for exoplanets...

Offline Star One

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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.


The flip side of that is, will we find that all local life is/was a close relative? A lot of stuff has been exchanged between the bodies of the Solar System as a result of impacts, and these used to be far larger and more common than nowadays. Now, as for exoplanets...

There was some theory I saw proposed in a New Scientist article last year that there may be a direction of travel in the spread of life in the Milky Way. But obviously you have to find other life first.

Offline redliox

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I'm sure there could be fossils on Mars. This discovery just says it is possible. There is more likely to be fossils on Mars as opposed to living organisms; if anything it is a matter of finding where to look first.
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Offline Star One

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I'm sure there could be fossils on Mars. This discovery just says it is possible. There is more likely to be fossils on Mars as opposed to living organisms; if anything it is a matter of finding where to look first.

The only place I could see life surviving on Mars is in its caves and caverns.

Offline kevin-rf

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I'm sure there could be fossils on Mars. This discovery just says it is possible. There is more likely to be fossils on Mars as opposed to living organisms; if anything it is a matter of finding where to look first.

The only place I could see life surviving on Mars is in its caves and caverns.

Extreme life on earth is found underground in rock without any caves and caverns. When drilling for oil, they find microorganisms in the sludge that comes out of the drill holes. The drill holes go very deep. The same can be true on Mars. 
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Online Dalhousie

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Speaking of which, an upside of Global Warming here may be the deposition of meteorites as glaciers retreat - though, oddly, I've never seen any mention of meteorites in moraines etc - perhaps early Iron Age people grabbed all the irons!

Probably too many other rocks in moraines.  Here's one from a retreating glacier in Ladakh.  Good lucking finding a meteorite in that lot! ;)
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Online Dalhousie

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The best place to look for Venus fossils will be anywhere but Venus, where the weather and geology are terrible. Ice caps, glaciers and shadowed points on Earth, the Moon and Mercury can preserve and sort incoming material better than any other locations. Rather than looking for needles in a haystack, you seek fossil-bearing meteorites among those to be found on the 'shores' of ice where it has sublimated away. People do this already on Earth, and it wouldn't be impossible to do this robotically elsewhere.

It's a good idea, although as I understand it, the high gravity and thick atmosphere make it very difficult to eject material from Venus.  The lack of atmosphere on Mercury and the Moon mean that meteorites arrive there with velocities of km/s, which isn't good for preservation.  You need an atmosphere to lose them down.

Also to consider is that meteorites have a life time in space.  No Mars meteorite has yet been discovered which was ejected more than 20 million years ago.

So this leaves finding a very ancient meteorite from Venus on Earth in an ancient sedimentary succession.  Not possible, but extremely improbable.  Very few meteorites in ancient successions are known, although the are occasionally recognised.
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Offline Bynaus

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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.

Well, if you take the age of the fossils, 3.8 Ga, then it's not that fast. Almost the same amount of time between the formation of the planet and the first fossils as between the Cambrian explosion and today... And Earth was apparently habitable (cool, with running water and possibly an ocean) quite early on (=~4.4 Ga).

Offline Star One

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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.

Well, if you take the age of the fossils, 3.8 Ga, then it's not that fast. Almost the same amount of time between the formation of the planet and the first fossils as between the Cambrian explosion and today... And Earth was apparently habitable (cool, with running water and possibly an ocean) quite early on (=~4.4 Ga).
There was an article recently putting forward the view in a very recent New Scientist that life could have arisen on Earth multiple times.

https://www.newscientist.com/article/mg23130870-200-life-evolves-so-easily-that-it-started-not-once-but-many-times/
« Last Edit: 09/03/2016 07:10 AM by Star One »

Offline redliox

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There was an article recently putting forward the view in a very recent New Scientist that life could have arisen on Earth multiple times.

https://www.newscientist.com/article/mg23130870-200-life-evolves-so-easily-that-it-started-not-once-but-many-times/

There could be some truth to it, but the problem is it would have happened so far back that the heavy bombardment coupled with plate tectonics wiped out the evidence...save perhaps some genetic information in mitochondria and ancient cells.  We may find more evidence for the evolution of ancient life by studying DNA as opposed to fossils in some cases.

On Mars, there may be a chance, if it had life or Earthly-borne life, of it being preserved in a few regions.
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Online high road

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Not necessarily.  Life could be emerging all the time. Going from simple life to complex life seems to be very difficult, as it took the better part of the lifetime of the earth to do it once. So new protolifeforms could be getting devoured by more developed life before it gets a chance to evolve into a successful creature.

Offline jgoldader

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There was an article recently putting forward the view in a very recent New Scientist that life could have arisen on Earth multiple times.

https://www.newscientist.com/article/mg23130870-200-life-evolves-so-easily-that-it-started-not-once-but-many-times/

Ahh, New Scientist.

It's certainly plausible that there were many biogenesis events on Earth, but all evidence (DNA phylogeny) points towards one completely dominating to the extent that those organisms wiped out all the others.

One interesting hypothesis involves RNA-based life, which is possible but for which we've really never looked.  It is described in Peter Ward's book "Life As We Do Not Know It." We could have a shadow biosphere all around us that our DNA bias has caused us to ignore.
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Online Dalhousie

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There was an article recently putting forward the view in a very recent New Scientist that life could have arisen on Earth multiple times.

https://www.newscientist.com/article/mg23130870-200-life-evolves-so-easily-that-it-started-not-once-but-many-times/

Ahh, New Scientist.

It's certainly plausible that there were many biogenesis events on Earth, but all evidence (DNA phylogeny) points towards one completely dominating to the extent that those organisms wiped out all the others.

One interesting hypothesis involves RNA-based life, which is possible but for which we've really never looked.  It is described in Peter Ward's book "Life As We Do Not Know It." We could have a shadow biosphere all around us that our DNA bias has caused us to ignore.

RNA life probably preceded DNA life, and was probably ancestral to it.

I would have thought the RNA life, if still extant would be visible through ribosomal RNA testing of soils etc.  But I will have to read Ward's book, he is a stimulating writer (and speaker for that matter).
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Offline Star One

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It rather seems like the discovery of evidence concerning fossil life on Mars would be much less surprising than finding current life on the planet.

Offline Mongo62

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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.

Online high road

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There was an article recently putting forward the view in a very recent New Scientist that life could have arisen on Earth multiple times.

https://www.newscientist.com/article/mg23130870-200-life-evolves-so-easily-that-it-started-not-once-but-many-times/

Ahh, New Scientist.

It's certainly plausible that there were many biogenesis events on Earth, but all evidence (DNA phylogeny) points towards one completely dominating to the extent that those organisms wiped out all the others.

One interesting hypothesis involves RNA-based life, which is possible but for which we've really never looked.  It is described in Peter Ward's book "Life As We Do Not Know It." We could have a shadow biosphere all around us that our DNA bias has caused us to ignore.

RNA life probably preceded DNA life, and was probably ancestral to it.

I would have thought the RNA life, if still extant would be visible through ribosomal RNA testing of soils etc.  But I will have to read Ward's book, he is a stimulating writer (and speaker for that matter).

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.

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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Online 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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Online 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 »
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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.

Online 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 »

Online 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.

Online 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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Online 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".

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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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Offline Mongo62

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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.

I like all of his writing. I think Peter Ward is a tremendous writer, who should be a lot better known than he is. His books DO tend to make the readers emotionally uncomfortable, though. For example The Medea Hypothesis, which lays out his anti-Gaia hypothesis that the Earth's biosphere is not stable, and keeps "trying" to revert to a microbe-dominated state with no higher life forms. Sounds a bit crazy, but he presents a lot of evidence in support of the idea.

This would possibly explain the Fermi Paradox, though, if biospheres containing higher life forms almost always revert to single-celled systems. And after the book was published, additional support for the hypothesis was found, in the form of fossils of an early multi-cellular organism ecosystem (~2.2 billion years ago) which died out shortly afterwards, with the Earth reverting to only single-celled organisms for over a billion years afterward.

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

That date is no longer accepted, the bulk of the meteorite is now thought to be 4.091 billion years old: Oldest Mars Meteorite Younger Than Thought. The carbonate matrix containing the putative micro-fossils would have been deposited some time after this, but it seems to be very difficult to date.
« Last Edit: 09/07/2016 01:46 PM by Mongo62 »

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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.
Well some intelligent species has to be the first to the party. It might be that we are the first to evolve and that the others will be along in short order. It's it kind of contrary to the Copernican principle but humans may be the first intelligent life at least in our little corner of the galaxy. I've heard some pretty interesting arguments that the universe is still pretty young and that we may have evolved close to the earliest our universe could support complex life. There are what about three generations of stars? The first generation was needed just to make the elements needed for life. Then things had to calm down a bit too. A close by supernova isn't good for life. For the first part of universe's existence it was uninhabitable for intelligent life. The question is when did it become habitable? If that happened not too long ago then intelligent life could be common but hasn't had time to become common.

Offline llanitedave

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The best answer to the Fermi Paradox that I've come across states simply that once a technological species advances enough to be able to use fusion power, then a planetary gravity well is no longer attractive to them.  A planet cannot easily provide the variety and availability of raw materials that the small icy bodies can, so that advanced life is more likely to inhabit the Oort Cloud equivalents of star systems.  A dominant, advanced species can expand to populate an entire galaxy without bothering  itself with any of the inner planets.

As for the Rare Earth hypothesis, I suspect that Ward and Brownlee's thesis is close to correct, but maybe for different reasons than they argued.  The number of ways that life can evolve without having to invent eukaryotic structures and multicellular tissues makes me think that life like ours probably arose by nothing more than pure dumb luck.  No real specific obstacles need be evoked.
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Oldest fossils ever discovered raises question of life on Mars
« Reply #43 on: 03/01/2017 06:12 PM »
Here's an update on this matter and a note of caution is struck.

World's oldest fossils found in Canada, say scientists

Quote
But not everyone is convinced by the new study, not least Frances Westall, an expert on ancient fossil bacteria at the French national centre for scientific research. “The thing that bothers me most about these structures is the fact that they all seem to be extremely oriented. They are parallel to each other and microbes don’t grow parallel to each other,” she said.

Westall said it remains possible that the haematite structures were formed as a result of the high temperatures and pressures experienced by metamorphic rocks. What’s more, she points out, the newly discovered filaments are far larger than the oldest known well-preserved microbial filaments previously found in 3.33bn-year-old rocks – a surprise given the lack of oxygen in the environment in which the newly proposed fossils are thought to have originated. “In an environment without oxygen, microbes grow – but they grow very slowly and they are small,” she said.

“What I am not saying is that there could not have been life at 3.8bn years ago,” Westall added. “But in rocks that have been so altered, like these have been, I think that morphological traces are unlikely to remain.”

Others, too, remain cautious, if more optimistic. David Emerson, a geomicrobiologist and expert in modern iron-oxidising bacteria at the Bigelow Laboratory for Ocean Sciences in the US said that the structures do not look like what would be expected from modern bacteria, but that he found it compelling that filaments are found in groups, suggesting a colony of microbes. But, he added, “I don’t think there is a smoking gun here that says this is clearly biological.”

https://www.theguardian.com/science/2017/mar/01/worlds-oldest-fossils-found-canada-say-scientists-quebec-haematite-377bn-428bn-years
« Last Edit: 03/01/2017 10:14 PM by Star One »

Offline Alpha_Centauri

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An aerobe oxidising iron? At this time? Surely that's not what the hydrothermal vent hypothesis is about?
« Last Edit: 03/01/2017 08:29 PM by Alpha_Centauri »

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Here's an update on this matter and a note of caution is struck.

World's oldest fossils found in Canada, say scientists

Quote
But not everyone is convinced by the new study, not least Frances Westall, an expert on ancient fossil bacteria at the French national centre for scientific research. “The thing that bothers me most about these structures is the fact that they all seem to be extremely oriented. They are parallel to each other and microbes don’t grow parallel to each other,” she said.

Westall said it remains possible that the haematite structures were formed as a result of the high temperatures and pressures experienced by metamorphic rocks. What’s more, she points out, the newly discovered filaments are far larger than the oldest known well-preserved microbial filaments previously found in 3.33bn-year-old rocks – a surprise given the lack of oxygen in the environment in which the newly proposed fossils are thought to have originated. “In an environment without oxygen, microbes grow – but they grow very slowly and they are small,” she said.

“What I am not saying is that there could not have been life at 3.8bn years ago,” Westall added. “But in rocks that have been so altered, like these have been, I think that morphological traces are unlikely to remain.”

Others, too, remain cautious, if more optimistic. David Emerson, a geomicrobiologist and expert in modern iron-oxidising bacteria at the Bigelow Laboratory for Ocean Sciences in the US said that the structures do not look like what would be expected from modern bacteria, but that he found it compelling that filaments are found in groups, suggesting a colony of microbes. But, he added, “I don’t think there is a smoking gun here that says this is clearly biological.”

https://www.theguardian.com/science/2017/mar/01/worlds-oldest-fossils-found-canada-say-scientists-quebec-haematite-377bn-428bn-years

I'd also note that the succession is poorly dated, it could be as old as 4.23 Ga, or as young as 3.77 Ga.  Now 3.77 isn't really young, but it is comparable with other, also rather questionable, evidence for life in the Isua greenstone belt in Greenland (3.8 Ga)
« Last Edit: 03/02/2017 04:18 AM by Dalhousie »
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Offline Req

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The best answer to the Fermi Paradox that I've come across states simply that once a technological species advances enough to be able to use fusion power, then a planetary gravity well is no longer attractive to them.  A planet cannot easily provide the variety and availability of raw materials that the small icy bodies can, so that advanced life is more likely to inhabit the Oort Cloud equivalents of star systems.  A dominant, advanced species can expand to populate an entire galaxy without bothering  itself with any of the inner planets.

When I first read about Hair and Hedman's work and the Fermi paradox, it occurred to me that there is a very simple explanation, and that is that FTL travel and communication is not possible in this universe.  What Hair and Hedman talk about is completely true and does not rely on FTL at all from a topical perspective, but the motivation to expand and build such a galactic empire doesn't exist.

Think about it, our galaxy is over 100,000 light years in diameter.  The closest star to us is 4 light years away.  What motivation does this empire have to exist if there's a practical upper limit of 0.1c for travel and 1c for comms?  No trade, no military support, and not even the ability to have a central authority to drive any kind of imperative(such as colonize the entire galaxy.)  Let's say this authority is "conveniently" located near sag A*, it still takes over 50,000 years for any new directive to propagate, and that's assuming no response is necessary.  Let's say our friends at Proxima Centauri need something from us.  We won't even know for 4 years, and it'll take another 40 for us to get it there.

An entire solar system of raw materials is an awful lot.  It's not clear to me that the need for more space to live in or raw materials to consume alone would motivate such a civilization(or many civilizations) to expand across an entire galaxy given almost any amount of time.
« Last Edit: 03/02/2017 03:41 AM by Req »

Offline CuddlyRocket

An entire solar system of raw materials is an awful lot.  It's not clear to me that the need for more space to live in or raw materials to consume alone would motivate such a civilization(or many civilizations) to expand across an entire galaxy given almost any amount of time.

Think culture. The more sentient beings there are the more scientists, engineers and artists there are and the faster is scientific, technological and artistic advancement, to everyone's benefit, and which can be spread by radio. A one-in-a-trillion genius would appear every 100 generations on a planet of 10 billion, but ever generation on 100 such planets.

Then there's competition. Do you want those folks over there - who might even be of a separate species - to be colonising the galaxy spreading their weird ideas and genes and eclipsing your own? Think of the dash for empire among European powers in the 19th century. We might think we're too advanced to fall prey to such motivations, but so did many of them!

Offline meekGee

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The best answer to the Fermi Paradox that I've come across states simply that once a technological species advances enough to be able to use fusion power, then a planetary gravity well is no longer attractive to them.  A planet cannot easily provide the variety and availability of raw materials that the small icy bodies can, so that advanced life is more likely to inhabit the Oort Cloud equivalents of star systems.  A dominant, advanced species can expand to populate an entire galaxy without bothering  itself with any of the inner planets.

When I first read about Hair and Hedman's work and the Fermi paradox, it occurred to me that there is a very simple explanation, and that is that FTL travel and communication is not possible in this universe.  What Hair and Hedman talk about is completely true and does not rely on FTL at all from a topical perspective, but the motivation to expand and build such a galactic empire doesn't exist.

Think about it, our galaxy is over 100,000 light years in diameter.  The closest star to us is 4 light years away.  What motivation does this empire have to exist if there's a practical upper limit of 0.1c for travel and 1c for comms?  No trade, no military support, and not even the ability to have a central authority to drive any kind of imperative(such as colonize the entire galaxy.)  Let's say this authority is "conveniently" located near sag A*, it still takes over 50,000 years for any new directive to propagate, and that's assuming no response is necessary.  Let's say our friends at Proxima Centauri need something from us.  We won't even know for 4 years, and it'll take another 40 for us to get it there.

An entire solar system of raw materials is an awful lot.  It's not clear to me that the need for more space to live in or raw materials to consume alone would motivate such a civilization(or many civilizations) to expand across an entire galaxy given almost any amount of time.
Motivation is indeed the critical piece, for exactly these reasons.

What you need to do is replace "first evolved species" with "first evolved species that is inherently wired to expand" and the then argument remains the same.

So yeah, the first 1000 species may not propagate due to lack of motivation, but #1001 will, and then you can overrun the galaxy pretty quickly even with 0.01c or 0.001c
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Offline Ben the Space Brit

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Just a bit of context: This time is before the presumed 'Late Heavy Bombardment' that theory says created most of the Moon's (and presumably Mars's too) crater fields, which was about 3.8Gya. It has been previously assumed that this would have basically liquefied Earth's surface.

Taking this into consideration, it is probably going to be statistically difficult to find more samples on Earth, let alone the other terrestrial planets.
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Online Dalhousie

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Just a bit of context: This time is before the presumed 'Late Heavy Bombardment' that theory says created most of the Moon's (and presumably Mars's too) crater fields, which was about 3.8Gya. It has been previously assumed that this would have basically liquefied Earth's surface.

Taking this into consideration, it is probably going to be statistically difficult to find more samples on Earth, let alone the other terrestrial planets.

Assuming the old dates are correct of course. There are a few pre LHB rocks in the Acasta complex in Canada.  Plus individual mineral grains in Australia and elsewhere.

Mars has preserved more of it's pre LHB crust.

IF these finds are genuinely biological and IF the rocks as as old as claimed then two things are possible.

1) Conditions during the LHB were not as severe as thought and some life survived through it. or 2) Life appeared twice.
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Offline Req

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The best answer to the Fermi Paradox that I've come across states simply that once a technological species advances enough to be able to use fusion power, then a planetary gravity well is no longer attractive to them.  A planet cannot easily provide the variety and availability of raw materials that the small icy bodies can, so that advanced life is more likely to inhabit the Oort Cloud equivalents of star systems.  A dominant, advanced species can expand to populate an entire galaxy without bothering  itself with any of the inner planets.

When I first read about Hair and Hedman's work and the Fermi paradox, it occurred to me that there is a very simple explanation, and that is that FTL travel and communication is not possible in this universe.  What Hair and Hedman talk about is completely true and does not rely on FTL at all from a topical perspective, but the motivation to expand and build such a galactic empire doesn't exist.

Think about it, our galaxy is over 100,000 light years in diameter.  The closest star to us is 4 light years away.  What motivation does this empire have to exist if there's a practical upper limit of 0.1c for travel and 1c for comms?  No trade, no military support, and not even the ability to have a central authority to drive any kind of imperative(such as colonize the entire galaxy.)  Let's say this authority is "conveniently" located near sag A*, it still takes over 50,000 years for any new directive to propagate, and that's assuming no response is necessary.  Let's say our friends at Proxima Centauri need something from us.  We won't even know for 4 years, and it'll take another 40 for us to get it there.

An entire solar system of raw materials is an awful lot.  It's not clear to me that the need for more space to live in or raw materials to consume alone would motivate such a civilization(or many civilizations) to expand across an entire galaxy given almost any amount of time.
Motivation is indeed the critical piece, for exactly these reasons.

What you need to do is replace "first evolved species" with "first evolved species that is inherently wired to expand" and the then argument remains the same.

So yeah, the first 1000 species may not propagate due to lack of motivation, but #1001 will, and then you can overrun the galaxy pretty quickly even with 0.01c or 0.001c

It doesn't seem unlikely to me that such an imperative may originally exist, it just seems unlikely that it would persist over millions of years, during which time each colony is more or less irrelevant to one another.

Given that the speed of light is more accurately expressed as the speed of causality, when you start talking about galactic scales, they are literally irrelevant to each other in the sense that they don't even exist to each other in their current states, and won't for tens of thousands of years.

Edit to remind that I consider the notion that FTL is not possible as a hypothetical, and what I'm saying pre-supposes that it's not possible as a potential explanation to the Fermi paradox.
« Last Edit: 03/04/2017 04:57 AM by Req »

Offline Star One

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Complex Life Could Be Vastly Older Than Thought

Quote
It was around 1.6 billion years ago that a community of small, bright red, plantlike life-forms, flitting around in a shallow pool of prehistoric water, were etched into stone until the end of time. Or at least until a team of Swedish researchers chipped their fossilized remnants out of a sedimentary rock formation in central India.
Research published this week in PLoS Biology suggests this collection of ancient, newly analyzed fossils—unearthed a few years back—are in all likelihood red algae. If that proves true, it would imply that complex, multicellular life evolved a lot earlier than previously thought—and that the evolutionary family tree of life on Earth might need a major pruning.

https://www.scientificamerican.com/article/complex-life-could-be-vastly-older-than-thought/#

Offline Star One

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Oldest fossils ever discovered raises question of life on Mars
« Reply #53 on: 03/17/2017 06:35 AM »
Fossil or inorganic structure? Scientists dig into early life forms

Quote
An international team of researchers discovered that inorganic chemicals can self-organize into complex structures that mimic primitive life on Earth.

Florida State University Professor of Chemistry Oliver Steinbock and Professor Juan Manuel Garcia-Ruiz of the Consejo Superior de Investigaciones Cientificas (Spanish National Research Council) in Granada, Spain published an article in Wednesday's edition of Science Advances that shows fossil-like objects grew in natural spring water abundant in the early stages of the planet. But they were inorganic materials that resulted from simple chemical reactions.

This complicates the identification of Earth's earliest microfossils and redefines the search for life on other planets and moons.

"Inorganic microstructures can potentially be indistinguishable from ancient traces of life both in morphology and chemical composition," Garcia-Ruiz said.

Scientists had seen hints of this in past lab work, but now through Steinbock and Garcia-Ruiz's research, it is clear that this also happened in nature.

https://m.phys.org/news/2017-03-fossil-inorganic-scientists-early-life.html

As if such identifications weren't complicated enough already on Earth with access to a fully equipped laboratory, let alone on a distant world with just the instruments of an in situ rover or lander to call on.
« Last Edit: 03/17/2017 06:39 AM by Star One »

Offline Star One

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And here we have early life pushed back even further in time and implications for life on other planets. This brings it to the era of the late heavy bombardment, but this particular sample shows no signs of forming in such extreme conditions.

Life on Earth could be nearly four billion years old, suggests new fossil discovery

Quote
Life on Earth could be nearly four billion years old, new fossil evidence suggests.

Researchers analysed rocks found in Saglek in northern Labrador, Canada, which were dated to at least 3.95 billion years ago. At that time, the Earth was still relatively young – it was formed about 4.5 billion years ago – and was probably still being bombarded by asteroids.

Tests on grains of graphite found in the sedimentary rocks found that they had been produced by living organisms, thought to be single-celled plants capable of photosynthesis.

Quote
The discovery has two implications for the search for extra-terrestrial life. One is that the earlier life is found to have begun on Earth, the more likely it is that it will be found elsewhere.

The other is that it increases the amount of time it took for complex life and intelligent life to form on Earth, which might mean that is a relatively rare occurrence – although little can be deduced from a sample size of one

It is thought photosynthesising life would have arisen after a more primitive form, which if correct would push the date of the origin of life on Earth back further. “It looks like they [life-forms] arose pretty much as soon as they could,” Dr Sutton said.

http://www.independent.co.uk/news/science/life-on-earth-four-billion-years-old-new-fossil-paleontologists-a7968336.html

Offline jak Kennedy

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And very few rock outcrops date from those timescales. Lots of evidence will have been destroyed.

Offline Star One

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I would have linked to the paper but the link isn’t working. I wonder if they’ve jumped the gun on this and the paper hasn’t been published yet?

Offline as58

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I would have linked to the paper but the link isn’t working. I wonder if they’ve jumped the gun on this and the paper hasn’t been published yet?

I guess is was supposed to be embargoed until this evening, as is usual for articles that will be published in Nature on Thursday.

Offline Star One

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I would have linked to the paper but the link isn’t working. I wonder if they’ve jumped the gun on this and the paper hasn’t been published yet?

I guess is was supposed to be embargoed until this evening, as is usual for articles that will be published in Nature on Thursday.

Thanks. I didn’t know when Nature publishes their articles.

Offline M.E.T.

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So it took 4 billion years from the first appearance of life to the development of intelligence. Seems like we have identified the difficult and/or unlikely step in the process, and it is not the origin of life. It is the appearance of intelligent life.

We may well be the first.
« Last Edit: 09/27/2017 03:37 PM by M.E.T. »

Offline Ben the Space Brit

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@M.E.T.

Not entirely correct. It has taken 4 billion years to reach us. However, there are few obvious spaceborne artefacts and arguably no macroscopic planetary surface artefacts that would survive even a few million years. So, barring the discovery of an artificial moon or something similar, there is no obvious way to tell if intelligent life arose and subsequently went extinct even as recently as the end of the Neogene epoch.
« Last Edit: 09/27/2017 02:52 PM by Ben the Space Brit »
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Offline DrRobin

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Not often on this forum when a microbiologist like me has something substantive to contribute! First, let's see what the data really are here when the paper is released. It's pretty common for leaked press reports to mangle things. Second, it's alway good to be a bit skeptical when people are pushing up against the limits of what can reasonably be inferred from the data. It sounds like they have found chemical signatures suggestive of biological origin, which is not the same as, say, actual microfossils. That said, there is some value in considering how long things took to appear on Earth relative to the "lifespan" of sun-like stars. Signs of bacterial life can be found in rocks almost all the way back to when the Earth cooled enough to allow liquid water. On the other hand, eukaryotic cells (which have much more complex internal structures) do not appear until more than a billion years after that, and abundant, complex multicellular eukaryotes take more than a billion years after that. Technological intelligence takes "only" a few hundred million years after that (leaving aside the question of what steps come _after_ us). And as the Sun continues to brighten over time, in less than a couple billion years more, the Earth will no longer be able to sustain liquid water, so in the one example we have to work with, Earth will have spent most of its time in the Habitable Zone populated with single-celled life, but technological intelligence was a bit of a close call. Hope is that by studying the chemistry of promising targets over the next few decades (Mars subsurface, Europa, Titan, Enceladus, and perhaps spectroscopic analysis of extrasolar planets), we'll get a better idea of how likely life might be elsewhere.

Offline vjkane

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Not often on this forum when a microbiologist like me has something substantive to contribute! First, let's see what the data really are here when the paper is released. It's pretty common for leaked press reports to mangle things. Second, it's alway good to be a bit skeptical when people are pushing up against the limits of what can reasonably be inferred from the data. It sounds like they have found chemical signatures suggestive of biological origin, which is not the same as, say, actual microfossils. That said, there is some value in considering how long things took to appear on Earth relative to the "lifespan" of sun-like stars. Signs of bacterial life can be found in rocks almost all the way back to when the Earth cooled enough to allow liquid water. On the other hand, eukaryotic cells (which have much more complex internal structures) do not appear until more than a billion years after that, and abundant, complex multicellular eukaryotes take more than a billion years after that. Technological intelligence takes "only" a few hundred million years after that (leaving aside the question of what steps come _after_ us). And as the Sun continues to brighten over time, in less than a couple billion years more, the Earth will no longer be able to sustain liquid water, so in the one example we have to work with, Earth will have spent most of its time in the Habitable Zone populated with single-celled life, but technological intelligence was a bit of a close call. Hope is that by studying the chemistry of promising targets over the next few decades (Mars subsurface, Europa, Titan, Enceladus, and perhaps spectroscopic analysis of extrasolar planets), we'll get a better idea of how likely life might be elsewhere.
While I'm *not* and expert like Dr. Robin in this field, one could argue that after life itself, photosynthesis and the development of complex eukaryotic cells are the key events leading to complex life.  I seem to remember that photosynthesis may have evolved more than once (experts, please correct!) but complex cells evolved just once.  So we might have to modify Drake's equation to include chance that life arises and then for the chances that complex, energy intensive cells arise.  Of course, since we have an N of one, establishing statistical confidence intervals on our estimates is a bit tricky.   :)

Offline as58

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Now that 18:00 GMT has passed, the embargo is over.

Nature News: http://www.nature.com/news/oldest-traces-of-life-on-earth-may-lurk-in-canadian-rocks-1.22685
The original research article: http://dx.doi.org/10.1038/nature24019

edit: a lot of scepticism in that Nature News article...
« Last Edit: 09/27/2017 06:37 PM by as58 »

Online KelvinZero

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Intelligence emerged very quickly right at the end, with multiple diverse candidates. Octopuses are pretty intelligent. So it sort of seems that intelligence also happens all the time once you get to that point.

There was a long time in the middle where life did nothing of much interest. Eg maybe becoming multicellular was the big hurdle, or the evolution of eukaryotes (something about a cell with its various components inside a membrane)

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

There is an interesting statistical phenomenon that when you have a set of fairly unlikely events within a given interval, and you consider only cases where all the events happened to happen, then they tend to distribute themselves fairly evenly, even if one of the events is a billion times less likely than the other.

It is sort of like: If you throw a dart and it hits the center ring of the dart board, then it does not matter if your usual accuracy is to hit somewhere on the board or to throw it over your shoulder. If it hits the center then its probable location will evenly distributed.

So looking at that timeline, it could well be that photosynthesis, eukaryotes and multicellular life are all unlikely to happen on a given planet, but there is no way, from just the timeline, to tell if one of them happens fairly often and one does not occur in multiple universes. We only see the sample where they all happened. That could be enough to divide the timeline into 4 (very roughly) equal-sized sections.
« Last Edit: 09/27/2017 10:12 PM by KelvinZero »

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