Space Plankton.

[Mazon Del]

Someone else said that Dragon hasn't docked with the Russia segment.

[Idobox]

Absolutely. If it wasn't plausible on Earth, it wouldn't be significantly more plausible somewhere else. What I'm getting at is the fact that, usually, evolution doesn't result in more complex life completely replacing simple life. If simple self-replicating RNA was a thing on Earth a few billion years ago, I'd expect some of it to still be around in that original form, or something closely resembling it. Not as a mechanism in a comparatively complex bacterium, but free-replicating in organic ooze. However, we don't see anything like that outside of the lab, despite suitable environments being available.

Ocam's razor cuts both ways here. If life on Earth started from a bacterium, then we wouldn't expect to find a precursor. We would also expect absolutely all life to have a common origin. Abiotic origin would allow for multiple ancestors. Panspermia makes a lot of things a lot simpler.

But this is just what makes me lean weakly towards panspermia. What I'd like to see is a lot more research done on Mars, since it's the only likely origin besides Earth. Even simply knowing more about its formation, and gauging whether it could have been habitable early enough to allow for life to start there, evolve into something complex enough to survive travel, and hitch a ride to Earth in time would be a great start. As you've pointed out, it'd need a considerable head start for necessary adaptations. Of course, jackpot would be finding actual life there, confirming common origin, and making sure that it's not a modern contamination. But that might be too much to hope for.

Not obvious at all. Self-replicating RNA, or whatever the first replicators were might be grossly out-competed by archae and simple bacterias, and we simply all descend from the first organism with a membrane, while those without were wiped out.

Viruses, especially retroviruses, look a lot like what a possible descendent of self-replicating RNA strands could have become when much better replicating machines were available.

Also some organelles used to be independent organisms (I'm thinking chloroplasts and mitochondria) but are never observed outside cells anymore.

Finally, panspermia doesn't fit that well with the common origin. If life managed to survive the trip once 2 or 3 billion years ago, it should have been able to do it a few more times since then, and we should observe microorganisms popping out with no apparent ancestor from time to time.

Panspermia is still totally possible, I just don't think the common ancestor is such a strong argument in its favor.

Edited August 20, 2014 by Idobox

[Kryten]

Someone else said that Dragon hasn't docked with the Russia segment.

US and Russian segments use different port designs. Only Progress, Soyuz and ATV have russian ports.

[Mazon Del]

Finally, panspermia doesn't fit that well with the common origin. If life managed to survive the trip once 2 or 3 billion years ago, it should have been able to do it a few more times since then, and we should observe microorganisms popping out with no apparent ancestor from time to time.

I don't think that is a particularly good argument as it presupposes that there are more than one life bearing locations within range for seeding, additionally it presupposes that any new organism would be equally (or even better) suited towards life on Earth as one of the others. It is quite possible that we are being lightly dusted with foreign organisms somewhat constantly, but our own biology is so firmly established that the other things cannot take hold. An example of this being say a virus from a different world than our seedworld shows up on Earth, it is unlikely (but within the realm of possibility) that it would be able to utilize ANY Earth based biology to reproduce. Generally speaking all the low hanging fruit in terms of resources are generally speaking 'occupied'. We don't exactly have world spanning pools of the building blocks of life sitting around as food. Granted, a few places can be described as such, but the likelihood of the bit of life finding that location upon reaching Earth by chance is about as likely as the thing hitting Earth itself after eons in space.

That said, scientists HAVE discovered some bacteria-like things that they are unable to find how and when they split off from the rest of our biological timeline. The reigning theory is that it could be an example of another form of life that grew on Earth, but was just mostly isolated. I'd need to google about it, but every couple months it reaches the upper pages of reddit in a TIL. But it could also be panspermia.

[KerikBalm]

What I'm getting at is the fact that, usually, evolution doesn't result in more complex life completely replacing simple life.

I don't agree with this statement. We have no examples of a Eukaryote without mitochondria (or similar organelles derived from them, ie mitosomes and hydrogenosomes), or of a "Eukaryote"/Archea with symbiotic alphaproteobacteria.

We have no small brained bipedal apes. We have no more non-avian therepods, we have just 2 examples of jawless fish, just a handful of examples of non-tetrapod sarcopterygian fish.

Something retaining the ancestral form is only retained if the ancestral niche has been continuously maintained, and a form was viable in that niche without going extinct.

There are still fish in the sea after tetrapods evolved not because of some conservation of a primitive form, but because of conservation of the niche for "fish".

But tetrapods evolved from coastal sarcopterygian, and those are all gone, out competed by the actinopterygians.

If a new, possibly more complex, organism evolves and outcompetes the old, the old is gone... bye bye.

If simple self-replicating RNA was a thing on Earth a few billion years ago, I'd expect some of it to still be around in that original form, or something closely resembling it. Not as a mechanism in a comparatively complex bacterium, but free-replicating in organic ooze. However, we don't see anything like that outside of the lab, despite suitable environments being available.

#1) We have plenty of examples of RNA genomes

* viral in nature, or intracellular and alternates between RNA and DNA, as in the case of retrotransposons)

#2) What we developed in a lab used what we found in nature as a starting point

#3) No such environment is available due to

*extreme competition from bateria and archea

*ubiquitous RNAses that digest RNA, which if you work in a molecular/cellbiology/biochemistry lab, you'll know is a major problem when working with RNA, and to have RNAse free conditions, you basically need sterile conditions

#4) Absensce of evidence is not evidence of absence - we haven't even identified most of the cellular species on Earth. Just taking samples of seawater and sequencing the ribosomal RNA yields truly astounding numbers of sequences indicating vast numbers of undescribed species that we haven't isolated.

For all we know, a self replicating RNA might be among those, as the catalytic part of a ribosome is RNA. Given all the undescribed nucleic acids we can find floating around, we may have an acellular self replicating RNA population for all we know. Such a thing would be very difficult to show, given the RNAse problems. To reconstitute the collection in vitro would be great, but there are far too many permutations of the RNA combinations to try, and the conditions to try, that without some better "hints" to constrain the search... it will have to remain a "maybe"

#5) The genetic code is not "universal", we observe variations on it here on Earth, the most distantly related lineages have the most differences. Given that the code would have become fixed at about the time you would start encapsulating protein synthesis machinery, these differences in lineages strongly imply that Earth life is descended from a cross section of the first cellular life. If a single species of bacteria were to have landed here from mars, it would likely have colonized the planet and adapted to outcompete any new arrivals before any new arrivals came, and we would not observe these differences in the genetic code.

These genetic code differences, to me, show that Earth has a diversity that started when the very first cell started. I highly doubt that if cellular life started elsewhere from RNA precursors, that we would be seeing the differences in the geneti code that we see today.

Ocam's razor cuts both ways here. If life on Earth started from a bacterium, then we wouldn't expect to find a precursor. We would also expect absolutely all life to have a common origin. Abiotic origin would allow for multiple ancestors. Panspermia makes a lot of things a lot simpler.

How does Occam's razor apply here, it favors the simplest explanation.

1) Life started on earth, but the acellular replicating precursor is not around any more/we can't find an example

2) Life started elsewhere, then came to earth, but the acellular replicating precursor did not come and we can't find any example of new life arriving from space

I'm choosing 1) as the simplest explanation that Occam's razor favors

But this is just what makes me lean weakly towards panspermia. What I'd like to see is a lot more research done on Mars, since it's the only likely origin besides Earth. Even simply knowing more about its formation, and gauging whether it could have been habitable early enough to allow for life to start there, evolve into something complex enough to survive travel, and hitch a ride to Earth in time would be a great start. As you've pointed out, it'd need a considerable head start for necessary adaptations. Of course, jackpot would be finding actual life there, confirming common origin, and making sure that it's not a modern contamination. But that might be too much to hope for.

Well, there is another possible Origin... Venus...

Its likely Venus had oceans, in fact, it seems likely there was a breif time period when all the terrestrial planets except Mercury had oceans. Venus's didn't last long, they were disappearing as Earth's were forming... but the progressively worsening conditions on venus may have favored the formation of extremophiles that could survive the journey.

Also, some theories on abiogenesis focus on thermodynamic properties + that nucleic acids absorb strongly in the UV range, of rely on thermal cycling (as used in modern PCR) that requires temperatures to be high enough to separate two strands -likely during the day- (life now has an enzyme to do that, we don't use it in the lab, we just heat and cool for each round of replication) and then cool down enough for annealing again -likely during the night-

These "light based" explanations look stronger and stronger the closer one gets to the sun...

If life started on Venus before its oceans boiled off... well, I don't know how we'd ever find evidence of that.. I'll just say, its plausible - but due to the observations about the genetic code, I'm sticking with life starting right here on Earth.

[lajoswinkler]

As I've predicted.

http://news.discovery.com/space/private-spaceflight/sea-plankton-on-space-station-russian-official-claims-140821.htm

"Russian source" - never trust that. Never.

[rtxoff]

"Russian source" - never trust that. Never.

That's rude.

[magnemoe]

Yeah, they launch Dragon over the Atlantic, so that could be it. But how would contamination get onto Russian part of the station, where only Soyuzes and Progresses dock?

Droplets with plankton freezes then boil in vacuum and get trust towards the Russian parts, perhaps in part of docking mechanism or the hardpoint the arm uses to grab it with.

Far more probably than air currents.

[K^2]

That's rude.

That's objective.

[Nibb31]

It still sounds far-fetched. I would wait for some sort of confirmation or third-party analysis of the samples.

[lajoswinkler]

That's rude.

No, it's perfectly objective. Russian media is full of crap. It's a remnant of the Soviet propaganda system. They fabricate a lot of stuff which are then spread around by other news outlets.

You might think USA media is horrific, but it's nothing compared to Russia.

[Javster]

Don't they mean air currents carried the stuff to the rocket, which went to the ISS, which was then found?

[Belphegor]

i believe the ISS was launched on an old seabed somewhere in kazachstan, which is now a desert. could it be that the kicked-up dust and hybernated plankton attached itself to the vessel?

[Vanamonde]

Let's leave politics and national characters out of it, please.

[Kryten]

I think we can all agree that if the best qualification you can get for a source is 'lives in generally the right country', it's probably rubbish. Remember this wasn't 'a source within russia's space agency', just 'a source within russia'; could have been Pravda for all we know.

i believe the ISS was launched on an old seabed somewhere in kazachstan, which is now a desert. could it be that the kicked-up dust and hybernated plankton attached itself to the vessel?

Khazakstan hasn't been underwater for a long, long time. All of central Asia's been basically where it is now for tens of millions of years.

[Janet]

Well, if you forget about evolution but focus on adaptation, then we have seem to have structures that we don't use that come into play when conditions are right. Think about the first creature that crawled out of water and up onto the stump! And took a breath! I am writing a sci fi novel about a claustrophobic guy who has to rescue an injured man on the ISS and to do so has to put on a helmet to pass between a shuttle and the ISS (the entrances were both destroyed in an explosion), and I was tempted to have him just pull off the helmet and take a breath, and discover that he could breath and live on whatever is out there. I didn't do that, but it sure was tempting.

The plankton apparently have done it--and I don't believe they went into some kind of dormancy and have now revived; look, life doesn't stay still, it lives, or dies. They lived. You have to think they reproduced. Since there's no Planned Parenthood for plankton, yet.