Has there been any recent discussion about the theory of Panspermia? Hey, there appears to be some pretty good evidence that it may be possible, snip:

How probable is this idea? Any opinions? Any new information? I'm not advocating the theory, just curious as to what people think about it.

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Add it up:

1 comet per year, over 1/8 of the Earth's 4.7 billion years (something like 600,000,000 years), times the mass of a typical comet.

How many tons is that adding to the earth?

I'm just taking a stab at the 1/8 of the Earth's lifetime. Tell me more.

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Sure, there's plenty of stuff that's "in-coming" but does any of this "stuff" contain the seeds of life? This life would be exposed to radiation, cosmic rays and stellar winds. However, we do know that some bacteria might be able to survive these conditions. Also, what about the ability of life to survive in asteroids or comets that are somewhat shielded from these hazards?

So, is this whole idea completely out there in "la la land" or is it actually possible that it could have happened this way?

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I don't see this as a viable survival trait on the timescales we are discussing. For it to be viable for a life-form to survive millennia or more just to get to another star, one would expect some survival trait that at least allowed life to survive in a vacuum under extreme radiation for a while. While there may be some utility in the short term, long term exposure to interstellar radiation would be enough to kill life on the timescales we are discussing.

I personally doubt life could survive that long, however favorable the conditions. While some seeds have been germinated after an extended period (lotus seeds, I believe, over a thousand years old...) they share the traits of seedlings exposed to radiation: even the damage from background radiation from being in the ground for an extended period was enough after only a thousand years to mimic moderate radiation exposure in causing malformations; how much more an unprotected life-form outside of the Sun's magnetosphere?

And I am also aware of claims of reconstituting bacteria that are millions of years old; however, many of these were frozen and/or encased in halides within the surface of the earth. Again, ionizing radiation behaving as it does, it equals perhaps a few centuries of exposure in space.

As far as chemical and materials go - they can come from any source, as they all follow generally the same rules with regard to chemical reactions, and ultimately it is these rules that give rise to how and when life is able to form.

couple comments/questions i'd like to add for consideration...

1) wouldn't the impact of radiation be reduced significantly within the comet? certainly surface organisms would be damaged quickly, but inside the heart of the comet it may be a different story. if i'm not mistaken, water is what is generally used to shield human observers from radioactive rods in older model nuclear reactors (as well as for cooling).

2) we're talking about microorganisms perhaps even less complex than viri or bacteria, not seeds. would that make a difference in long-term viability?

overall, i've always thought the idea that the "spark" that started things off came from somewhere else we interesting, but it has obvious problems. first, it's probably not provable. second, it only pushes off the original start of life to some other planet. it is just as plausible to say that the amino acids lined up to form the first life here as it is somewhere else, actually moreso for here simply because that is the only true evidence we have to date (the evidence being life is proven here, unproven anywhere else). i'm afraid we may never know the answers to this particular issue.

taks

No level of shielding from material can protect against every type of radiation indefinitely. Some radiation will always get through, even through lead. Keep in mind how long comets must be floating through radiation in order to reach Earth. Could be millions of years, easily.

It could, but not necessarily.

To back you up, I think it would be more likely that the basic components of organic chemistry may have arrived on comets. I don't imagine any viable spores or seeds arrived. Then again, DNA could have been in comets and then hammered by cosmic rays so much that the coded ATCG chains could have been pulped into mush. Still, it would be a random stew of organic chemicals that could have been a crucible for life.

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Well, one premise is that the "building blocks of life" could easily have arrived via comets. From the article linked above:

Once thought to be simply silly, this idea seems to be gaining at least some supporters. Some take the idea even further suggesting that perhaps amino acid chains and even proteins might be able to exist in the cores of comets. Others go the whole nine yards and postulate that micro-organisms may even be able to survive a comet journey.

I came across this pro panspermia site Here's a part of what they have to say:

While panspermia certainly isn't a strong theory at this point, it could conceivably herald a quite a paradigm shift.

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I just don't see the "whole cell" theory ever gaining credence. One could conceive of a life-form that was able to withstand the rigors of space and the length of the trip, but then; how did it come about? How does natural selection operate when there is a million year or more stretch between events, and the organisms that "fail" this test face much more urgent pressures within their environment than surviving the death of their sun? Essentially, it would be evolution slowed a billionfold or more, as events would occur in disparate sites at disparate times, and the odds against finding another planet within an organisms viable lifetime is astronomical, no pun intended.

It would be much more likely that any viable organisms would be consumed by a sun than strike a viable planet, especially if in cometary form. Jupiter should be teeming with life. Life is tenacious, and sticks around whenever it gains a toehold, but this I think is a bit of a stretch, in addition to being a "dodge" of the chemical or life-origin question; an infinite regression, as one never gets to the original life this way: it always could have come "from space."

the same is true on the earth, with bacteria on/near the surface surviving for quite some time. inside a snowball, of significant size, you could easily see similar results. outside of the solar system, the radioactive picture is not nearly the same as it is close in to the earth. i don't think we can assume high levels of radiation "everywhere," which may imply such things need not suffer for long.

maybe, maybe not. i agree it may not have been necessary, but may have happened that way nonetheless. radiation also need not be a universal killer to all life forms. in the beginning, it may have helped turn primitive precursors into life, which you certainly mention... another unprovable, though plausible (i think) thought.

taks

I saw a Nova last night that had some interesting info about a sort of modified panspermia, not whole cells, but amino acids. (Making it panacidia, maybe? Or panamino-ism? Panamino sounds like someone from The Magic Flute, though.) It involved setting up a reaaally big gun and actually shooting at the amino acids, to see what the impact generally does to them.

According to that woman's experiment, they actually combine into peptides. Which make up proteins, which make up yours truly.

I think my SO is rather impressed with my psychic powers at this point, or else my scientific knowledge. 8) There was one transition in the program where I said, "Ooo, stroma-thingies!" before the scene even changed. Practically the next word out of the narrator's mouth was, "Stromatalites . . ." (I know I haven't spelled that right, but you know what I mean.)

Next week's NOVA is going to be about SETI, I think, from the ads. Do I even have to mention that I'll be watching it?

Izunya

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Comets lack something Earth has. A magnetic field. This mechanic is different than absorption by dense solids.

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oh i certainly realize that. i'm just making a suggestion that:

1) water, the primary component of comets, is an excellent absorber of radioactivity protecting things deep within the belly of large comets

2) radiation may not be a "universal" killer as it is with more advanced life which could be an impetus for the chemical precursor idea with radiation as the "spark" that started it all

and

3) comets are not necessarily exposed to high levels of radiation for millions of years due to their orbits out of the solar system.

again, suggestions for probable cause. unproven hypothesis at best for sure. probably unprovable.

taks

Much of the radiation I'm discussing is high velocity atomic nuclei aka "cosmic rays" which are persistently present in or out of a solar system. Additionally, while some water may help, a comet, judging by the Deep Impact results, would not be dense enough to protect much of anything. Comets might not survive to the ground in an atmosphere given the probability Tunguska was a comet, and the large atmospheric signatures of Shoemaker-Levy 9 on Jupiter.

The consistency would lead to an effect like a fuel-air bomb, with a powdery comet detonating like so much flour in a camp fire. Hard for any organism to survive that, much less carbon compounds.

Also, given the spectral results of Deep Impact as well, comets are not that much water, or other hydrogen compounds which can act as neutron absorbers from secondary radiation scattering.

If anything, I would expect a rain of carbon compound soot, the things that might make up some comets, to have been swept up by planets rather than as in the Oort cloud being left to slowly accumulate. It would fit the bill of externally derived and radiation selected carbon compounds without the catastrophic effects of high velocity impact with an atmosphere.

Yeah, cosmic radiation crosses hundreds of thousands of light-years. It passes through gravitational fields of stars, black holes, nebulae, dark matter, and raw space (which isn't exactly empty) and loses little energy.

You think a mile of ice is going to stop it?

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I think it will eventually be shown that it is possible for life to survive a comet impact. We know shock is no barrier, micro-organisms are very difficult to damage on the scale they exist. And heat can certainly be resisted. If micro-organisms could surive a lucky hop from say Mars to Earth then I think there is a chance that they could have survived the impact as well.

... but...

There is every reason to believe that the conditions that existed on the primordial Earth were condusive to the genesis of life without help from cosmic "seeding". Amino acids have geologic origins (like methane) and do not directly indicate the presence of (or guarantee the genesis of) life. Indeed only a small fraction of the amino acids that potentially rained down from the heavens have any direct relevance to life as we know it.

Finally the suggestion that life began on another planet and seeded Earth is tantamount to Creation theory becuase you then have to describe how life began on that planet, then the planet it was seeded from, and so on and so forth.

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if it's passing through all those things, neither will the earth's atmosphere! (life has managed here...)

hadn't realized that about deep impact, btw.

taks

Some bombard the Earth, but I did mention that we have a magnetic field.

Here's another mechanic at work. Cosmic rays don't hit here often, but when they do, they enter an active ecosystem where they may hit a DNA chain in an organism's cell nucleus. It does damage and causes a mutation. Most often, the mutation is fatal. Other times, it helps and gives that organism an edge and a better chance of passing it's advantage on.

Yeah, yeah, blah, blah, evolution and all that.

But the point is, that each living thing in an operating ecosystem lives for only a blink of evolutionary time and doesn't have much opportunity to get struck by cosmic rays. If they were frozen in a block of ice for a half billion years, they'd be the equivalent of a radioactive sponge.

The same batch of organisms--- frozen cells, spores, viral material--- has to survive the journey without the opportunity to reproduce.

8)

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my point was based on all the things mentioned, in particular the black hole. important since that's really what i was referring to...

taks

But my new point is that on a comet the same organisms get bombarded by radiation over a billion years or more, while in a thriving ecosystem, damage to DNA gets wiped or supported by evolution.

Reproduction cancels the damage. Frozen life forms just have their DNA eroded into unintelligible garbage.

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