Panspermia, anyone?

[Clonus]

Re: Panspermia, anyone?

 

Except that's also the Creationist arguement' date=' that abiogenesis without Divine Intervention is just too improbable.[/quote']

 

Not really. Merely being improbable is not enough of a reason to reject a hypothesis. But it is reason to prefer a more probable explanation. Life originating elsewhere and somehow making it here adds one improbability (life originating) and adds it to another, (life originating elsewhere and then managing it to make it all the way here). Space is obviously not swarming with life because if it was, it would be easy to find. I think that must mean it is difficult for life to traverse interstellar distances and it would have to. The Creationist arguement on the other hand, is dependant on assuming divine intervention as a given rather than estimating the probability involved, (because, after all, the probability of divine intervention is inestimable).

[Kristopher]

Re: Panspermia, anyone?

 

Not really. Merely being improbable is not enough of a reason to reject a hypothesis. But it is reason to prefer a more probable explanation. Life originating elsewhere and somehow making it here adds one improbability (life originating) and adds it to another' date=' (life originating elsewhere and then managing it to make it all the way here). Space is obviously not swarming with life because if it was, it would be easy to find. I think that must mean it is difficult for life to traverse interstellar distances and it would have to. The Creationist arguement on the other hand, is dependant on assuming divine intervention as a given rather than estimating the probability involved, (because, after all, the probability of divine intervention is inestimable).[/quote']

 

Also, what he said.

[L. Marcus]

Re: Panspermia, anyone?

 

Occam's Razor, and that.

[McCoy]

Re: Panspermia, anyone?

 

Well' date=' actually, no, I'm not making the same argument, at all. [/quote']

 

Not really.

 

Occam's Razor' date=' and that. [/quote']

 

Yes, it is the same arguement, and saying "It's not! It's not! It's not!" doesn't change that.

 

Merely being improbable is not enough of a reason to reject a hypothesis. But it is reason to prefer a more probable explanation. Life originating elsewhere and somehow making it here adds one improbability (life originating) and adds it to another' date=' (life originating elsewhere and then managing it to make it all the way here). Space is obviously not swarming with life because if it was, it would be easy to find.[/quote']

Define "easy." AFAIK we have sent ONE experiment to Mars looking for life, and it had ambiguous results. There is a probe on the way to Mars now to repeat that experiment, and the insterment to examine that atmosphere of extrasolar planets is under construction.

 

What we do know is that the longer we look at interstellar nebula, the more complex organics we find, and that some metorites contain amino acids. We've found the raw ingredents for life outside Earth, what we don't know is how to create life on or off Earth.

 

How many places do we need to find life before panspermia becomes, in your opinions, a viable hypothesis?

 

All of this is at this point an attempt to plot a curve from a single point. Again, we have insufficent data to eliminate either hypothesis.

[L. Marcus]

Re: Panspermia, anyone?

 

There is a search underway for living things that differ from the "mainstream" -- it might be pertinent to the current discussion. Scientific American's Are Aliens Among Us?

[McCoy]

Re: Panspermia, anyone?

 

Space is big, and we're not:

 

http://www.exploratorium.edu/ronh/solar_system/

Yet current consenses theory is that everything in the Solar system that isn't hydrogen was formed in one or more super-novi. What are the odds of these heavier elements accreating into the pre-solar nebula in the first place?

 

Now add to this the hypothesis that all water on the planet, enough to cover three fourths of the surface, is currently believed to have come form comet impacts.

 

Space is big, yet meteors hit the atmosphere daily.

 

The fact that you consider an event improble doesn't mean it didn't happen.

[Clonus]

Re: Panspermia, anyone?

 

Yes' date=' it is the same arguement, and saying "It's not! It's not! It's not!" doesn't change that.[/quote']

 

Really? So how do you estimate the relative probability of divine intervention?

 

 

Define "easy." AFAIK we have sent ONE experiment to Mars looking for life, and it had ambiguous results. .

 

If space was filled with life we wouldn't have to go to Mars to find it it. We'd be finding it in moon rocks and meteorites. The only reason why they went to Mars in particular looking for life is because they have a sneaking suspicion that life needs liquid water and Mars probably had liquid water once upon a time.

[Kristopher]

Re: Panspermia, anyone?

 

Yes' date=' it is the same arguement, and saying "It's not! It's not! It's not!" doesn't change that.[/quote']

 

Let's see... someone making an argument based on relative probabilities (derived from basic issues of the size of space and the mechanics involved) is "making the Creationist argument that improbable = impossible", and three different people disagreeing with your assesment equals a childish outburst of irrational objection?

 

I guess I shouldn't be surprised, though.

 

I'm not going to play a little game of "Is so! - Is not!" with you. It's been explained in detail by more than one of us why it's not the same argument, and if you want to keep believing it is, I think that tells the rest of us more about your thinking than about anything else.

 

Define "easy." AFAIK we have sent ONE experiment to Mars looking for life' date=' and it had ambiguous results.[/quote']

 

The results from Viking weren't ambiguous, really. Basic inorganic soil chemistry accounts for the one seemingly-positive result, and the others came up negative.

 

http://en.wikipedia.org/wiki/Viking_program#Results_of_the_Biological_Experiments

 

There may be life on Mars, but there wasn't life in the soil where the Viking program tested it.

 

What we do know is that the longer we look at interstellar nebula' date=' the more complex organics we find, and that some metorites contain amino acids. We've found the raw ingredents for life outside Earth, what we don't know is how to create life on or off Earth.[/quote']

 

Amino acids and complex organics != life. You can get amino acids from very simple nonbiotic chemistry. Even if comets or other bodies delivered complex organics to Earth, which seems very plausible, it would not be life, and it would not be panspermia.

 

Furthermore, the conditions for life as we know it simply do not exist in deep space, anywhere, that I've ever heard of. The conditions are simply too hostile. For Earthlike life, you need Earthlike conditions in terms of tempature range, pressure range, density, protection from radiation, etc -- see below for more on how this makes panspermia a longshot at best.

 

How many places do we need to find life before panspermia becomes' date=' in your opinions, a viable hypothesis?[/quote']

 

How many places we find life doesn't have anything to do with the viability of panspermia. The only thing that would make panspermia viable is if we find very very similar life on more than one body -- life that can be shown without a doubt to have evolved from the same ancestors. Otherwise, finding life all over the solar system only shows us that life is very common and will reliably come about given the right conditions.

 

All of this is at this point an attempt to plot a curve from a single point. Again' date=' we have insufficent data to eliminate either hypothesis.[/quote']

 

At this point, life originating on Earth is a bit more than a hypothesis -- it's here, and originating here is the simplest answer to how it came to be here. Occam's Razor, as already pointed out.

 

At this point, panspermia is a longshot hypothesis. Not only would life have to survive the Rube Goldberg process of getting here across space as explained in detail more than once in this thread, it would also have to have gotten to Earth within a relatively small window in time, beginning with the existance of liquid water in sufficient places and volumes, and ending before the first signs of life perhaps 3.8 billion years ago.

 

Life that comes from elsewhere and ends up thriving on Earth, also needs to come from someplace with conditions within the range of environments found on Earth during the time it arrived, and has to be able to survive the journey, and has to be able to adapt to changing conditions on Earth between then and now.

[Clonus]

Re: Panspermia, anyone?

 

Yet current consenses theory is that everything in the Solar system that isn't hydrogen was formed in one or more super-novi. What are the odds of these heavier elements accreating into the pre-solar nebula in the first place?

 

High. Heavier elements are more massive. If pre-solar nebulae form in the first place (and we can actually see them forming in lots of places, notably the Pleides), then heavier elements are less likely to escape the gravitational pull.

 

Now add to this the hypothesis that all water on the planet, enough to cover three fourths of the surface, is currently believed to have come form comet impacts.

 

Um...so?

 

Space is big, yet meteors hit the atmosphere daily.

 

Leading us to the conclusion that space has lots of rocks in it. As it happens we've looked at space, and it turns out that space has lots of rocks in it.

 

The fact that you consider an event improble doesn't mean it didn't happen.

 

Ah but that's not the issue. The issue is whether an even more improbable event is preferable as an explanation to one which merely seems improbable. Panspermia can't be ruled out at this time but there's no real support for it either. We haven't found earthlike-life in space, and there are reason to think that space would be very inhospitable to it so until we do, there's no particular reason to think that Earth-like life didn't originate on Earth.

[Kristopher]

Re: Panspermia, anyone?

 

Yet current consenses theory is that everything in the Solar system that isn't hydrogen was formed in one or more super-novi. What are the odds of these heavier elements accreating into the pre-solar nebula in the first place?

 

A) High, as they're heavier, and more likely to be end up in an area of higher gravitation, as Clonus explained.

 

Has nothing to do with life being able to arise or exist in a nebula.

 

Now add to this the hypothesis that all water on the planet' date=' enough to cover three fourths of the surface, is currently believed to have come form comet impacts.[/quote']

 

Yes...and? Again, has nothing to do with the question of whether there was life on those comets.

 

Space is big' date=' yet meteors hit the atmosphere daily. [/quote']

 

And of all of them we've recovered, only one has ever shown even a hint of life, it came from right next door to Earth, and the maybe-fossils inside it were far more likely to be nonbiological in origin.

 

The fact that you consider an event improble doesn't mean it didn't happen.

 

No, but that doesn't change the fact of how rediculously improbable it was. See previous posts for all the stacked improbable events that have to all come to pass for panspermia to work just once, let alone be the origin of all life everyone as it is according to some advocates of the idea.

[McCoy]

Re: Panspermia, anyone?

 

There is a search underway for living things that differ from the "mainstream" -- it might be pertinent to the current discussion. Scientific American's Are Aliens Among Us?

Yep. Very interesting. Discovery of survivors on Earth of a different abiogenesis event would disprove the common ancestory hypothesis, and be evidence for the "life originated here" hypothesis.

[McCoy]

Re: Panspermia, anyone?

 

Really? So how do you estimate the relative probability of divine intervention?

Probability of divine intervention: unknown, insufficent data.

 

Probability of spontaneous abiogeneis on Earth: unknown, insufficent data.

 

Probability of life originating elsewhere and traveling to Earth: unknown, insufficent data.

 

No matter who's opinions are dogmatically stated as capital T Truth, none of these can be ruled out by the available data.

[McCoy]

Re: Panspermia, anyone?

 

The results from Viking weren't ambiguous' date=' really. Basic inorganic soil chemistry accounts for the one seemingly-positive result, and the others came up negative. [/quote']

The experimenters predicted one result for if life were present, another if it was not. They got a third, unexpected, result. Without repeating the experiment, current explanation of the unexpected result is a best-guess hypothesis.

 

Furthermore' date=' the conditions for life as we know it simply do not exist in deep space, anywhere, that I've ever heard of. The conditions are simply too hostile. For Earthlike life, you need Earthlike conditions in terms of tempature range, pressure range, density, protection from radiation, etc [/quote']

Through evolution, life adapts to changing conditions. Conditions at the time we first have evidence of life on Earth were nothing we would recognize as "Earthlike" today. Extremeophiles exist on Earth in pressures, temperatures, and radiation levels many times higher than was predicted possible before they were discovered. On Earth, life seems to exist where ever there is liquid water, even if that water is superheated, under several atmospheres of pressure, or in a nuclear reactor. I don't think we've fully reached the limits of the conditions under which Earth-life can survive.

[Kristopher]

Re: Panspermia, anyone?

 

The experimenters predicted one result for if life were present' date=' another if it was not. They got a third, unexpected, result. Without repeating the experiment, current explanation of the unexpected result is a best-guess hypothesis.[/quote']

 

There were three experiements, one came up positive, the other two came up negative. The best way to explain that overall observation is that the one positive is the result of nonbiological soil chemisty.

 

Through evolution' date=' life adapts to changing conditions. Conditions at the time we first have evidence of life on Earth were nothing we would recognize as "Earthlike" today. Extremeophiles exist on Earth in pressures, temperatures, and radiation levels many times higher than was predicted possible before they were discovered. On Earth, life seems to exist where ever there is liquid water, even if that water is superheated, under several atmospheres of pressure, or in a nuclear reactor. I don't think we've fully reached the limits of the conditions under which Earth-life can survive.[/quote']

 

None of the life we've found on Earth, or would expect to have found in the early conditions on Earth, could originate or survive in any of the conditions we've seen in open space, even in nebulas. There's no liquid water, for starters.

[Kristopher]

Re: Panspermia, anyone?

 

Probability of spontaneous abiogeneis on Earth: unknown, insufficent data.

 

Probability of life originating elsewhere and traveling to Earth: unknown, insufficent data.

 

Probability of latter, far lower than probability of former, due to multiple extra very-low-probability steps of getting life from elsewhere to Earth.

[Zeropoint]

Re: Panspermia, anyone?

 

I've read that a strain of bacteria has been found on Earth which uses hydrogen peroxide rather than water as the basis for its cellular fluid--a bit of a shock to the scientific community, which hadn't realized that anything like that was possible. The same article also pointed out that the results indicated by the Viking probe could be the result of this type of life: adding water would result in a brief spike of biological activity, then the bacteria would rupture and die, because of the water they were absorbing.

 

Yeah, that's right--we sent out a mission to dig up innocent Martian life and kill it!

[McCoy]

Re: Panspermia, anyone?

 

None of the life we've found on Earth' date=' or would expect to have found in the early conditions on Earth, could originate or survive in any of the conditions we've seen in open space, even in nebulas. There's no liquid water, for starters.[/quote']

As the aformentioned Scientific American article points out, the experts in the field have yet to agree on a definition of life, much less what conditions it could survive under or under what conditions it might have originated. The first life on Earth probably could no more survive under curent "Earthlike" conditions than it could submerged in a bucket of bleach. I think it is established that spontaneous abiogenesis under "Earthlike" conditions today is improbable to the point of impossible. All experiments to try to stimulate abiogenesis under hypothetical former Earth conditions have failed. One possibility is that we are missing a factor, a missing ingredient if you will, and once we add that we'll see abiogenesis attempts succeeding right and left. But another possibility is that abiogenesis requires conditions that cannot be duplicated on Earth, now or in the past.

 

I do not insist on the warm nebula hypothesis, simply mention it as a possibility where a condition not available on Earth, microgravity, might, emphasis on might, cause complex organics to behave differently than they do on Earth. Is microgravity the key to abiogenesis? Unlikely, can't be ruled out with the current data.

 

Viable bacteria have been recovered from the moon and from inside salt crystals millions of years old. Bacteria seem to be more robust than you think. Simplier life forms may be even tougher.

[McCoy]

Re: Panspermia, anyone?

 

I've read that a strain of bacteria has been found on Earth which uses hydrogen peroxide rather than water as the basis for its cellular fluid--a bit of a shock to the scientific community, which hadn't realized that anything like that was possible. The same article also pointed out that the results indicated by the Viking probe could be the result of this type of life: adding water would result in a brief spike of biological activity, then the bacteria would rupture and die, because of the water they were absorbing.

 

Yeah, that's right--we sent out a mission to dig up innocent Martian life and kill it!

And peroxides are found, admittedly in trace amounts, in the Martian atmosphere.

 

Free oxygen, methane with no vulcanism, what they use to say were signatures of life before we found them on Mars. Maybe that's whay we haven't found Martian life so far, we're just refusing to recognize it.

[Kristopher]

Re: Panspermia, anyone?

 

Disagree' date=' the universe is about 99.a google of 9's per cent "somewhere else," so I would hardly call that even odds.[/quote']

 

A better response to this, actually: yes, it is. Which is exactly why it's so vanishingly unlikely that life from anywhere else would happen to end up here, instead of in the other 99.99~% of the universe.

[Kristopher]

Re: Panspermia, anyone?

 

As the aformentioned Scientific American article points out, the experts in the field have yet to agree on a definition of life, much less what conditions it could survive under or under what conditions it might have originated. The first life on Earth probably could no more survive under curent "Earthlike" conditions than it could submerged in a bucket of bleach. I think it is established that spontaneous abiogenesis under "Earthlike" conditions today is improbable to the point of impossible. All experiments to try to stimulate abiogenesis under hypothetical former Earth conditions have failed. One possibility is that we are missing a factor, a missing ingredient if you will, and once we add that we'll see abiogenesis attempts succeeding right and left. But another possibility is that abiogenesis requires conditions that cannot be duplicated on Earth, now or in the past.

 

I do not insist on the warm nebula hypothesis, simply mention it as a possibility where a condition not available on Earth, microgravity, might, emphasis on might, cause complex organics to behave differently than they do on Earth. Is microgravity the key to abiogenesis? Unlikely, can't be ruled out with the current data.

 

Viable bacteria have been recovered from the moon and from inside salt crystals millions of years old. Bacteria seem to be more robust than you think. Simplier life forms may be even tougher.

 

Yes, from inside tiny pockets of water inside salt crystals, IIRC. And that's downright hospitible compared to tens of millions of years in interstellar space. A few years on the moon is a weekend hike compared to that long hypothetical trip from here to there.

 

The problem with the nebula idea is that they're just not dense enough for anything as complex as even primitive life to get going there.

 

We've got a decent idea of what the environment was like on early Earth, simply because of the rocks it left behind. And that's nothing like you'll find anywhere in space, away from large bodies. The difference in environments is in all likelihood just too severe for life evolved out in "the dark" -- cold, thin, microgravity -- to survive down in a big gravity well, with its relatively hot and dense and heavy conditions. And even if it could, it would have been something so different from what we find on Earth as far back as we can "see", that it's very unlikely to have changed into what we have on Earth now -- the leap from whatever it would have been then to the liquid-water-based stuff we have now is immense. The chemistry necessary for out there, is just too different from the chemistry we see here, and see traces of as far back as we can tell. Even far back before the O2 buildup, when Earth's atmosphere was full of CO2 and CH4 and whatnot, and the oceans were full of disolved iron, conditions were still so unlike anything you'll find out in space that life falling in from some hypothetical interstellar origin just wouldn't have had much of a chance to survive, even if it survived the journey and the impact.

 

So really, all that pretty much eliminates anything other than another large body as even a hypothetically possible origin of life on Earth. And that gets us back to the problem of how it gets up out of that gravity well intact, survives tens of millions of years in space, happens to get here instead of the other 99.99~% of the universe, survives landing here on Earth, and adapts before it dies out.

[Kristopher]

Re: Panspermia, anyone?

 

And peroxides are found, admittedly in trace amounts, in the Martian atmosphere.

 

Free oxygen, methane with no vulcanism, what they use to say were signatures of life before we found them on Mars. Maybe that's whay we haven't found Martian life so far, we're just refusing to recognize it.

 

Note: I did not say that there isn't life somewhere on Mars, or that there never was life on Mars.

 

I did say:

 

A) That Viking didn't find life, based on the overall results of three experiments conducted, and that instead the best explanation for the observations is nonbiological soil chemistry.

 

That life on Mars is immaterial to the question of panspermia, unless it is very, very similar to life on Earth in terms chemistry and genetics. In fact, if it's chemically different, and/or genetically unconnected, panspermia becomes even more unlikely, because we have two seperate strains of life, unrelated, right next door to each other.

[Clonus]

Re: Panspermia, anyone?

 

Probability of divine intervention: unknown, insufficent data.

 

Probability of spontaneous abiogeneis on Earth: unknown, insufficent data.

 

Probability of life originating elsewhere and traveling to Earth: unknown, insufficent data.

 

No matter who's opinions are dogmatically stated as capital T Truth, none of these can be ruled out by the available data.

 

Panspermia ISN'T ruled out. There's just nothing to support the idea and it adds whatever the problems are with life originating to the problems associated with somehow getting life into space, across interstellar distances and onto a planet in shape to start replicating.

[McCoy]

Re: Panspermia, anyone?

 

Yes' date=' from inside tiny pockets of water inside salt crystals, IIRC. And that's downright [i']hospitible[/i] compared to tens of millions of years in interstellar space.

And surviving a million years inside a tiny pocket of water inside a salt block several meters accross buried underground differs from surviving a million years inside a tiny pocket of water inside a salt block several meters accross drifting through deep space exactly how?

 

We know a lifeform from Earth survived exposuer to deep space virtually unprotected, we know some Earth lifeforms survived being cut off from any contact with the outside enviroment for a very, very long time. I think we have established the possibility that a natural "suspended animation chamber" could transport life-as-we-know-it across at least interplanetary distances.

 

The problem with the nebula idea is that they're just not dense enough for anything as complex as even primitive life to get going there.

Again, I do not insist on the warm nebula hypothesis, just point out that your dismissing it as impossible requiresassumptions not based on the currently available data. You may be right, you are probably right, but to state as you do as fact that it is impossible requires more knowledge of the nature of life than any Earth-human possesses at this time.

 

We've got a decent idea of what the environment was like on early Earth' date=' simply because of the rocks it left behind. And that's nothing like you'll find anywhere in space, away from large bodies. The difference in environments is in all likelihood just too severe for life evolved out in "the dark" -- cold, thin, microgravity -- to survive down in a big gravity well, with its relatively hot and dense and heavy conditions. And even if it could, it would have been something so different from what we find on Earth as far back as we can "see", that it's very unlikely to have changed into what we have on Earth now -- the leap from whatever it would have been then to the liquid-water-based stuff we have now is [i']immense[/i]. The chemistry necessary for out there, is just too different from the chemistry we see here, and see traces of as far back as we can tell. Even far back before the O2 buildup, when Earth's atmosphere was full of CO2 and CH4 and whatnot, and the oceans were full of disolved iron, conditions were still so unlike anything you'll find out in space that life falling in from some hypothetical interstellar origin just wouldn't have had much of a chance to survive, even if it survived the journey and the impact.

So many assumptions!

 

We've seen life on Earth adapt to temperatures of 761° F (678° K) and pressures of 283 atmospheres. (Or contrarywise, if black smokers were the site of abiogenesis, as one current hypothesis suggest, it has adapted from 761° F and 283 atmospheres down to 32 ° F (273° K) and 1 atmosphere.) Are current Earth-surface conditions closer to deep sea or deep space? Is 273° K closer to 678° K or 3° K? (Keep in mind also that the "temperature" of the cosmic microwave background radiation is a function of the age of the universe, which was some half to two thirds as old as it is now when the Sun and Earth formed. Someone ask Cancer what the temperature of deep space was 6 billion ybp, I've misplaced the formula.)

 

Keep in mind also that the earliest traces of life, "as far as we can tell" is deposits with isotope ratios preferred by current lifeforms, no clue to the structure and very little lue to the metabolism of that earliest life.

[Cancer]

Re: Panspermia, anyone?

 

It is worth pointing out that the conditions needed for life to start no longer exist on Earth: all the photosynthetic organisms poisoned the atmosphere with all that oxygen.

 

That is, in fact, why it is so difficult to guess how life got started: we don't have a secure picture of the initial environment.

 

oops, more later, time to go lecture on exactly this subject!

[McCoy]

Re: Panspermia, anyone?

 

Note: I did not say that there isn't life somewhere on Mars' date=' or that there never was life on Mars. [/quote']

Never said you did. That was more of an oblique answer to

Space is obviously not swarming with life because if it was' date=' it would be easy to find. [/quote']

 

That Viking didn't find life' date=' based on the overall results of three experiments conducted, and that instead the best explanation for the observations is nonbiological soil chemistry. [/quote']

No, the Viking experiments didn no give the expected results, and the best guess hypothesis is that unexpected nonbiological soil chemistry was the reason. Until the Phoenix probe does the experiment to confirm or deny it, it remains a hypothesis, not an explanation.