Another vote for panspermia

[chew_on_this]

Interesting article. I'm sure Steve will have a cow over it.<br /><br />http://www.sciam.com/article.cfm?chanID=sa007&articleID=00073A97-5745-1359-94FF83414B7F0000

 

[chew_on_this]

Some stars aren't so far apart. Take alpha centauri, 4 light years? Depends on the speed of the sample I suppose.

 

[igorsboss]

<font color="yellow">But no way could panspermia work for interstellar distances, as some enthusiasts claim.</font><br /><br />Way: Panspermia can not work over <i>today's</i> interstellar distances.<br /><br />Our sun was born in stellar nursery, where it was once in close contact with many sibling stars. If the cloud we came from contained chemolithicautotrophs (chemical or rock eaters) as part of the dust, then many solar systems may have been seeded from that same cloud. Our sun has been ejected from that nursery, and is now isolated.<br /><br />This theory requires at least one precursor garden world, ("Eden") to have once existed, and then subsequently shattered, to sow the seeds into the primordial cloud.<br /><br />The primary points of evidence supporting this model are:<br />1) The extremely early rise of life after Earth's formation. Since it is hard to create life from non-life, we would expect life to arise slowly, which it didn't.<br />2) The wet volcanic conditions on early Earth would have supported very simple chemoautotrophic or lithoautotrophic settlers.<br />3) The space-survival ability of bacterial spores makes this possible, but not likely.<br />4) Once any life is established, subsequent evolution through mutation and natural selection is sufficient to explain today's biodiversity.<br /><br />Corollaries:<br />a) Early-earth conditions are not a constraint for life to arise (from non-life). This process may have taken place in any "Eden" planet's environment.<br />b) We are cosmic weeds.

 

[earthseed]

An alternative scenario is for another star to pass close enough to the Sun for their Oort clouds to intersect. A life bearing meteorite is thus transferred from that star to our Solar System, and eventually makes its way to Earth.<br /><br />But given that life arose soon after our Solar System's formation, the window for this to happen is small. Then there is the extremely small probability for each required step - a big enough rock bearing life ejected far enough out from its planet, the small chance of it being perturbed enough from its orbit to be captured by our Sun, then the unliklihood of it reaching the Earth, then its life surviving the encounter. A big rock is required to protect life from radiation, but such a rock is more likely to be destroyed on impact.<br /><br />Then there is very low probability that another star will have life in the first place, at the moment it passed by our Sun.<br /><br />You can read a detailed analysis by Jay Melosh, who has done the most give transfer of life between planets a scientific basis. Conclusion: Extremely unlikey.

 

[igorsboss]

Alright, I'll clarify: Eden is a parent world, not a sibling world.<br /><br />"Eden" is the name I assign to the world on which life arose from non-life. (I ascribe no supernatural features to Eden.)<br /><br />Very roughly, the Earth is about 5Gy old, and the Universe is 15Gy old. During the 10Gy before Earth, life had plenty of time to slowly arose on Eden, and then to flourish. One day, Eden was completely obliterated, in a massive, planet-shattering impact event.<br /><br />Eventually, the remnants of Eden, the remnants of various supernovas, and some elements from the big bang, coalesced into a dust cloud. This eventually became our stellar nursery. During formation, Earth collected some of the remnants of Eden. By sheer luck, some chemoautrophic bacterial spores found conditions on proto-Earth just favorable enough to survive.<br /><br />The sun and sibling stars formed, then were ejected from the nursery. Our current isolation, and Earth's well-adapted inhabitants, preclude additional panspermic arrivals here.<br /><br />Although I don't have enough evidence to prove this, I think this model fits the available facts.

 

[earthseed]

Interesting scenario. I suppose the right kind of impact could make a planet explode such that a number of life-bearing framents were ejected. But tying this to the process that formed the solar system only makes things worse - the rocks have to hang around waiting for the Earth to form and become habitable. Every day increases the chances of being zapped by a particularly strong cosmic ray. Eden is better off exploding when the Earth is ready for it, which returns us to the standard panspermia scenario, except maybe there are a few more rocks to start with.<br /><br />There is still a long chain of improbabilities, starting with a rather unlikely impact.

 

[chew_on_this]

<font color="yellow">It would take anywhere from hundreds of thousands to millions of years to drift between stellar systems</font><br /><br />Who said anything about "drift"? Ejected material doesn't exactly drift. I think you're over-dramatizing to make your point. Try even .0001% light speed and it doesn't take long in the big picture ( />50,000 years). Spores snuggled nicely in a large chunk of planet could possibly survive.

 

[chew_on_this]

<font color="yellow">Article was pure speculation</font><br /><br />Didn't we go over this speculation thing already? Speculation is the beginning of science. Kinda like a hypothesis.

 

[igorsboss]

<font color="yellow">life on Mars that spread to the earth</font><br /><br />This is NOT what I contend. I don't see how this is possible.<br /><br />Postulate:<br />In order to initiate a transpermic event, the parent world must be a garden planet. It must have a very well established ecosystem, chock full of life.<br /><br />Facts:<br />* Earth and Mars are siblings; they formed at the same time.<br />* Life was on Earth when it was very young. (This is by far the most compelling evidence that life arrived here, instead of beginning here.)<br />* Early Evolution on Earth was very slow. Bacteria was present for well over 3 GY before the Cambrian explosion.<br /><br />Conclusions:<br />* Since early Terrestrial evolution was slow, it is reasonable that early Martian evolution was also very slow.<br />*Life on Mars would not have had enough time for evolution to produce a garden planet, before life was on the very young Earth.<br />* Since Earth is a known garden planet, it is far more likely that life has spread from Earth to Mars, rather than the other way around.<br /><br />However, given the Eden model above, Earth and Mars would have had about the same chances of being seeded with viable chemoautotrophic organisms during formation. Since early Mars was wet, I would expect life to have arose on early Mars. However, there was never a Martian "cambrian explosion" of higher life forms.<br /><br />The Eden model predicts that living Archea or Bacteria would be found somewhere on Mars today, and that Martian life forms somehow altered the early chemistry of Mars.

 

[igorsboss]

<font color="yellow">There is still a long chain of improbabilities, starting with a rather unlikely impact.</font><br /><br />No doubt! ...Yet at the end of the chain of improbabilities is one absolute certainty: Life existed on Earth when it was very young.<br /><br />Our task is to choose between these two chains of improbability:<br />1) Life began from non-life very quickly on early Earth, or<br />2) Earth was seeded with life from elsewhere, very shortly after formation.<br /><br />I think that creating life from non-life is too hard for #1 to possibly be true, leaving #2 as the only remaining natural conclusion.<br /><br />(Alternate supernatural conclusions exist, but none of them are falsifiable, so they are ignored here.)

 

[chew_on_this]

<font color="yellow">And it doesn't exactly navigate, either. "Drift" is a perfectly appropriate word.</font><br /><br />Hmmm..let's see... Drift:[v] wander from a direct course or at random. Don't see how this applies. This from the root of Drive, which also implies navigation. Not appropriate.<br /><br /><font color="yellow">And here I was thinking that you Panspermia folk were the ones fond of drama.....since I go for the boring old "simplest explanation". </font><br /><br />And that simple explanation is....? I would tend to believe a simpler explanation to life arising from non-life in such a short time span would be panspermia.<br /><br /><font color="yellow">Let's stick to the maximum reasonable speeds a meteorite is likely to attain in a ejection event: solar system escape velocity, or 13.6 km/sec....and that's pushing it. Most ejecta will remain within the stellar system.</font><br /><br />What's so unreasonable about 66,960 mph? I believe I saw a figure close to this attributed to a comet(?) or asteroid recently. <br /> <br /> <br /> <br /><br />

 

[earthseed]

crazyeddie, as you said earlier, the only way a rock will be ejected from a solar system is through gravitational assist from a giant planet. This is possible, but is another link in the chain of improbabilities.<br /><br />igorsboss, there may not be much connection between the time it took for bacteria to evolve into multi-cellular organisms, and the time it took for bacteria to form. We have no idea how that happened, so it is not valid to make conclusions about how probable it is. Given the only life we have ever observed is on Earth, any scientist working on its origin must assume, at least as a working hypothesis, that it arose here. If it arrived here from Venus or Mars, then it still arose in conditions similar to that postulated for early Earth, including the available time.<br /><br />Until we know a lot more, panspermia can only remain interesting speculation. We can't build a science from it.<br /><br />

 

[igorsboss]

<font color="yellow">We have no idea how (bacterial formation) happened</font><br /><br />Regardless of how it happened, if life arose quickly on the very early Earth, then it should have arisen multiple times in Earth's first billion years. Is there evidence of this?<br /><br /><font color="yellow">Given the only life we have ever observed is on Earth, any scientist working on its origin must assume, at least as a working hypothesis, that it arose here. We can't build a science from it.</font><br /><br />This "Eden" hypothesis has a definite implication for these researchers.<br /><br />Various experimenters have already found various interesting processes that can form cells from bubbles, and amino acids from lightning, and so on.<br /><br />Suppose someone created an experiment where life crawls out of a testtube, but the test-tube's chemical content fails to mimic the environment of the early Earth.<br /><br />If we assume that life arose on Earth, then this experiment could be rejected, because it failed to model Earth.<br /><br />However, if we allow the possibility of "Eden", a parent world, then that test-tube experiment could be accepted, so long as it models *any possible* natural world.<br /><br />This is the implication of the corollary I included in my first post:<br /><br /><font color="yellow">Early-earth conditions are not a constraint for life to arise (from non-life). This process may have taken place in any "Eden" planet's environment. </font>/safety_wrapper>

 

[igorsboss]

<font color="yellow">(igorsboss)Although I don't have enough evidence to prove this, I think this model fits the available facts. </font><br /><br /><font color="yellow">(crazyeddie)I won't say it's flat-out impossible.</font><br /><br />That's good enough for now. However unlikely it may be, it still remains a valid alternate model.<br /><br />Someday, when more evidence comes in, such as the discovery of life on another world, we can compare the models again.

 

[earthseed]

The multiple formation of life idea applies equally to panspermia - we could get rocks from different planets. The answer is once bacteria were estabished, any precursors to another life form became their lunch. Or a much less fit life form would be driven to extinction early on.<br /><br />Creating life from a pathway plausible on another planet, but not on early Earth, would definitely be a boost for panspermia. I would not argue that dogma about life must have formed on Earth should prevent research of this kind. So in this sense panspermia is a useful scientific hypothesis. But I expect most research will be based on life arising in Earth-like conditions, because almost all the data is here on Earth, and it is the simplest hypothesis, at least for now.

 

[chew_on_this]

<font color="yellow">Don't be obtuse. The simpler explanation is that life arose here, on Earth. </font><br /><br />That's debatable. Pretty easy to explain life arising by seed than by nothing. Of course, you then have to explain the seeds' beginning but that isn't the point.<br /><br /><font color="yellow">By the way....no comet, or any object, has EVER been observed to be entering the solar system from interstellar space. </font><br /><br />Boy, we've been looking for so long too. What a hoot!<br /><br /><br /><br />

 

[igorsboss]

<font color="yellow">The multiple formation of life idea applies equally to panspermia - we could get rocks from different planets. The answer is once bacteria were estabished, any precursors to another life form became their lunch. Or a much less fit life form would be driven to extinction early on. </font><br /><br />Yup.<br /><br /><font color="yellow">Creating life from a pathway plausible on another planet, but not on early Earth, would definitely be a boost for panspermia. I would not argue that dogma about life must have formed on Earth should prevent research of this kind. So in this sense panspermia is a useful scientific hypothesis. But I expect most research will be based on life arising in Earth-like conditions, because almost all the data is here on Earth, and it is the simplest hypothesis, at least for now.</font><br /><br />Agreed. Excellent. I don't mind being second simplest.<br /><br />BTW, I prefer that this particular model be referred to as the "Eden" hypothesis, with "transpermia" as one of the features of the model, to distinguish it from panspermia.<br /><br />Panspermia supposes certian things with which I disagree, such as life always having existing everywhere.

 

[robnissen]

"By the way....no comet, or any object, has EVER been observed to be entering the solar system from interstellar space."<br /><br />I thought I read once, that one of the famous comets from the 70's 80's or 90's flew by the sun so fast, that it was headed straight out of the solar system. Unfortunately, I could not find anything about that comet when I just googled it, but if my recollection was correct, wouldn't that mean that that comet, in fact, came from outside of our solar system?

 

[chew_on_this]

Don't recall the comet but I would imagine if it had the velocity to leave, yes, it could have come from outside our solar system. Unless of course the sun was gravity assisting it on it's way.

 

[sirfer]

Well all this talk of panspermia is nice but it doens't really answer the question of how life even formed from non-life...it just shifts the attention somewhere else

 

[earthseed]

Well, igorsboss, our views seem to be converging, perhaps with a different view of the lilkihood of panspermia.<br /><br />Literally, panspermia means "seeds everywhere", but it is now used to mean the transfer of life between stars at whatever rate. The Fred Hoyle fan club gives it a much deeper meaning with an infinitely old universe, the source of all species (ie. no evolution), diseases from space, etc, but we can consign that to science fiction.

 

[igorsboss]

<font color="yellow"> but we can consign that to science fiction.</font><br /><br />Yet another member of the set of non-falsifiable theories.

 

[earthseed]

I disagree with you there. The Hoyle theory is indeed scientific in the sense that it is falsifiable. And it is entirely false.

 

[thebigcat]

Pausing to ponder this whole concept, I am reminded of the kind folks of the 19th century who saw the Italian word for "Channels" and decided that it was imminantly necessary to send missionaries to Mars so that the undoubtedly immoral denizens could find salvation before their civilization was destroyed by drought. The reason that I am reminded of this that I see arguing about the theory of Panspermia, which is an attempt to explain how a rock which came from Mars could contain something suggestive of life, as containing much more un-suggested speculation than fact-based hypothesizing.<br /><br />There are too many things that we don't know yet. While Spirit and opportunity have found some remarkable things on Mars, they were not equipped with strong enough microscopes to image objects the size of bacteria, so we are going to have to wait a little longer to find out just what those little things are. We are also going to have to wait until we can land some sort of ice-penetrating sensor package on Europa to see whether there is any life there. <br /><br />There are quite a few more thiings we are going to have to wait upon in order to be able to even argue the point intellegently, armed with facts instead of prejudices. <div class="Discussion_UserSignature"> </div>

 

[earthseed]

The facts, or at least calculations by a reputable scientist (Jay Melosh), are that it is possible for a meteor impact on Mars to deliver bacterial life intact to Earth. Whether there was ever any bacteria there in the first place is entirely a different matter. As you say, we are a long way from knowing that.<br /><br />You can read these papers on Martian Transpermia or the much less likely Interstellar Panspermia.