Study Puts Hole In Comet Theory Of Life's Origin 204
Astervitude writes "A new study by US and Japanese scientists has put a serious dent into one version of the popular panspermia theory that credits comets for bringing the seeds of life to Earth. Surveys conducted by the University of Arizona, the National Astronomical Observatory of Japan and others now show that objects from the main asteroid belt between Jupiter and Mars were largely responsible for the period of Late Heavy Bombardment that ended 3.9 billion years ago. UA Professor Emeritus Robert Strom believes that no more than 10 percent of the Earth's water comes from comets and any oceans then extant would have been 'vaporized by the asteroid impacts during the cataclysm.'" Interesting, because this directly contradicts the Nova mini-series Origins that just finished running on PBS. Science never stops moving.
But then again... (Score:2, Insightful)
Re:Why (Score:5, Insightful)
> than to assume that life started here on Earth?
Two reasons:
1) We have some idea of the early conditions on Earth - but maybe
we have a hard time believing that those were conducive to
forming life from scratch. If life started elsewhere then there
is almost no limit to the range of concievable temperatures, pressures,
gravity, radiation and chemical environments in which it might
ultimately have formed.
2) Time: Is the Earth old enough for that very early phase of going
from completely non-biological materials to DNA, cell walls, etc?
If not - then panspermia explains that by saying that life was
around in some other place LONG before the Earth was formed.
So panspermia allows for a scientific explanation of life's formation
that is perhaps more plausible than formation on early Earth.
Re:So why does this contradict panspermia? (Score:5, Insightful)
Yes, but, as you point out, the Problem with the Idea of Panspermia is that it does not explain how life arose -- it just shifts the blame for it (as it were) elsewhere.
Re:So why does this contradict panspermia? (Score:3, Insightful)
Re:Why (Score:3, Insightful)
that is perhaps more plausible than formation on early Earth.
Scientific? Sounds to me like you have a untestable theory for the origins of life. You can test components of the theory, but ultimately you always be able to say... well sure it came from somewhere else, but it's been millions/billions of years and all of the concrete evidence has been washed away.
Re:Heh. (Score:5, Insightful)
Re:Why (Score:3, Insightful)
Re:Why (Score:3, Insightful)
If we find a perfectly good explanation for the origins of life on Earth - then that is still not proof that life actually did start here.
That means that Panspermia is unfalsifyable - which is a bad thing for a scientific theory. All you can do is to presume that it's false until someone proves otherwise.
But the previous post questioned why Panspermia could possibly be of any help in explaining the origin problem. I merely pointed out the theoretical possibility that Panspermia might some day be an important explanation of how this happened.
If you somehow managed to utterly PROVE that life could not possibly have originated on early Earth, science would be in deep trouble without something like the Panspermia theory which allows one to hypothesise other sets of conditions and longer timescales.
Suppose we found evidence that life could not have formed without some particular chemical compound that cannot ever have existed at earthly temperatures and pressures? Then you'd be forced to admit that life started elsewhere. In a sense, you could prove panspermia by showing that life could not have come from early earth. Given that there is demonstrably life here now, you'd have proven that it had to have come from elsewhere.
A true test of Panspermia would require us to find another planet - perhaps one very similar to Earth and to demonstrate that life here and life there shared striking similarities that could not have arisen by chance. For example, if both life forms had similar long stretches of 'junk' DNA. You'd be unable to show that the 'life originated on earth' theory was true anymore because by symmetry, it might have arisen on planet-X and travelled here instead of the other way around.
So Panspermia might be proved, conclusively. If we found evidence of life on (say) Mars and could demonstrate that this life bore striking resemblances to Earthly life. You'd then be forced to admit that the overwhelmingly most likely explanation was that life could travel from one planet to another. You'd still be left with the question of whether it originated on Earth, on Mars or in some yet other place...but the idea that life could be formed in one place and travel to another would be demonstrably true.
Science never stops moving (Score:2, Insightful)
Science never stops moving? (Score:4, Insightful)
A good case in point is evolution, where if you don't mention it in a glowing light on
Re:So why does this contradict panspermia? (Score:1, Insightful)
The size and age of the universe are meaningless if you don't have any other informaton to go on.
The universe could have been a billion times larger and a billion times older, and still had no life in it, if the chance of life developing were sufficiently small. If the chance of life developing were zero, then you could have an infinitely large universe of infinite age, and it would contain no life. That's simple mathematics.
So, basically, you looking at the universe and saying "wow, it's big, no wonder there's life" is no more meaningful than a creationist looking at the universe and saying "wow, it's big, that proves God exists". Neither of you is making a comment with any scientific content or value whatsoever.
We simply don't have the data to draw any conclusions about the likelihood of life having developed here, or elsewhere. We don't have the data to draw any conclusions at all about how common life is likely to be in the universe; basically, it is just as plausible that our world is unique, as that there is some form of life in every galaxy.
Let's wait for science to find some evidence before we start jumping to conclusions, okay?
Re:So why does this contradict panspermia? (Score:2, Insightful)
Life will find a way, and given the scope of the universe, even if such systems were uncommon, as you stated, there would still be numorous possibilities.
some quick math tells me that even if a habitat suitiable for life was 0.1%, there would still be 150000000000000000000 locations in the universe.
0.01% gives 15000000000000000000
both these numbers to me are very nice, but still to optimistic.
Lets just say that solar systems like our own were only
Of course, all of this remains speculative, and massively over optemistic, until we start reaching for the stars.
But i will continue to say, that given the scope of the universe, the time avaliable and lifes adaptability, I believe life will be a very common occurance throughout the universe, it may just not be in the way of anything that would resemble life to us.
Re:We have three different non-competing models he (Score:4, Insightful)
I mean, vaporizing something like a person would pretty much destroy them, but it doesn't do much to eliminate individual atoms, it just moves them around. So the ocean itself might be turned into water vapor, but then where does that all go?
I'm sure a big enough impact could blow matter up into space, where it'll float away never to bother the busy earth again, but I would think that most matter gets propelled outwards from an impact, not up. So wouldn't a meteor hitting an ocean just spread the water around?
Re:Why its not turtles all the way down (Score:3, Insightful)
That's a very interesting argument. I would suspect, however, that Z is such a small number as to swamp all the other terms. A panspermic chunk must gain enough velocity to escape the gravity well of its planet AND star yet not have so much velocity that it doesn't get captured by our Sun's gravity well (yet not penetrate too deeply into the Sun's gravity well that the chunk gets baked). And life on the chunk must survive its ejection from its home planet.
Moreover, the effective value of N can't be that large, since panspermic chunks from only nearby stellar system have any hope of reaching Earth. The umpteen hundred million planets on the other side of the galaxy don't contribute much to the population of chunks floating about. My guess is that the probability of a chunk getting to Earth is worse than proportional to 1/d^3 -- stars twice as far away have less than 1/8 the chance of delivering a chunk here. I say 1/d^3 to reflect the combination of 1/d^2 projection of objects over distance times 1/d for the slow accumulation of damage over millions of years of floating in interstellar space. Thus, I'd bet the effective N is not high at all (less than 10 to 100). Moreover, N will be small unless Px is nearly 1 so that many local star systems spawn endogenous life. But if Px is near 1 for a large population of local planetary systems, then why should we think that Pe is very small. And if Pe isn't tiny, then we're back to a high chance of endogenous life on Earth.
Even the Tx/Te ratio isn't as high as it might seem since Px was zero at the beginning of the universe because there were no heavy elements. Only after a sufficient number of supernovae and second generation stellar systems formed would Px rise. In fact the Earth's relatively late arrival probably means that Pe is higher than the Px of older systems born before the galaxy accumulated as much heavy elements. Tx is also down-modulated by life-destroying events. If life formed on a planet that was then sterilized by a supernova, gamma ray burst, etc. billions of years before Earth became habitable, then such a high Px planet would be unlikely to contribute much to the chance of spawning life on Earth. It seems like the ratio of Tx/Te might only 10 to 50 or so.
Finally, even if Px > Pe, there's the assumption that life arising on these high Px planets can survive on Earth. One might suggest that a high Px planet is like a lush tropical environment -- very conducive to life -- and that Earth's postulated low Pe status makes Earth relatively desert-like. What is the likelihood that a life form adapted to a high Px, tropical planet, would survive on a low Pe, desert world? I'm not saying life can't adaptt, only that not all high Px worlds spwan life than can survive on Earth. This likelihood that Earth might be effectively uninhabitable by life from a high Px world means the effective Px is lower (or Z is even worse).
I agree with (and enjoyed) your arguments about N, Tx/Te, Px/Pe, but I seriously doubt that the numerical values of these ratios trumps the incredibly small probabilities of an interstellar transfer of a viable lifeform. My suspicion is that Z has a very very large negative exponent that outweighs these other terms.
Until we can visit other planets in other star systems, we'll have a hard time estimating all these numbers. And, ultimately, the panspermia theory is impossible to falsify as we can never prove it did not happen, only that it has a relatively low probability of having happened.
Re:Genesis Therories (Score:5, Insightful)
Which is why it's important for people to learn about science before tehy accept its knowledge. Just like it's important for us to learn about religion. Not just to learn the science, like reading it in _Discover_ magazine, or to learn the religion, like reading it in a bible. But we need to learn how the "knowledge system" works: its history, its failures, its successes, its alternatives and their histories. Just like we don't need to learn enough science to be scientists in order to appreciate science (and our world that it explains), we don't need to become experts in the discipline, to become scientists or clerics. We need to understand what the strengths and limitations are, and what it means when a scientist or a cleric says "we know", "I believe" or "this is". Otherwise, we're just faking it, and we will make all kind of mistakes, without ways to recover. And that's very dangerous, considering how powerful are these ways of knowing, whether they're right or (especially when) they're wrong.
Re:Panspermia vs. GOD vs. Evolution vs. Creationis (Score:4, Insightful)
Many of the plaintiffs in lawsuits against idiotic creationist "equal time" laws have been religious figures. Do not make the assumption that all religious people buy into the creationist agenda.
Re:Genesis Therories (Score:2, Insightful)
That's just because such "theories" either ignore any inconvenient facts, or revise the "theory of Creation" so that it is impossible to disprove (and then pretend that's what the "theory" said all along). Eventually, they can say (like you did) that their theory has been stable longer than the physically-testable theories, and is therefore somehow "better".
You obviously haven't read much about the Church of the FSM. Part of their Articles of Faith is that the FSM continually adjusts reality so that you can neither prove nor disprove its existence - much like the fanatics who insist that the Bible is the literal truth say that their "ever-truthful" God created the world thousands of years ago, complete with all the physical evidence that makes us think it is billions of years old.
Re:So why does this contradict panspermia? (Score:2, Insightful)
Obviously the percentage chance of life forming in the universe cant be 0%, our own existance proves that. Given the enormity of the universe, and the incomprehensibly long periods of time given (the big bang is theorized to be almost 14 Billion years ago), even something that has only a 0.000000000000000000000001% chance becomes almost a certainty.
It only really becomes amazing when you get into intelligent life forming, given that you must have not only life, but incredibly complex life forms in many different variations with symbiotic connections to other life forms.
Then when you get into technologically advanced life. We as humans could never have developed technology without fire. So a species could be as intelligent as us, even more intelligent, but would never develop technology if they, for example, lived in an atmosphere that was not as coducive to fire as ours, or lived underwater.
Each one of these steps, from single-cellular life, to complex life forms, to intelligent life forms, to technologically capable life forms, to civilization, are exponentially less likely than the one preceding it. It is concievable that the universe is teeming with single-cellular life, but that our planet is the only one which has reached the (as far as we know) uppermost stage of complexity. But, once again, given the enormity of the universe & the lengths of time available, they each become almost a certainty.
The fact that we dont understand today how life originates doesnt mean that we can never understand. Only a couple generations ago we didnt have the slightest clue about the nature of matter, gravity, light, or electricity, does that mean that our forefathers were incapable of understanding these concepts? Of course not. We are no more intelligent than they were, just better informed. Just as our descendants will (hopefully) be about the things we dont understand today.
Re:Science never stops moving? (Score:3, Insightful)
Such as?
Sure, right now it's the best idea going, but that doesn't mean it's the end of the conversation. Yet questioning it all usually does end the conversation.
I would be interested to know exactly what about evolution you would like to question? That organisms have changed over time? That such changes happen naturally? That the changes result in variety, and from that variety some organisms turn out to be better able to reproduce than others?
Evolution is a very, very simple idea. Once we realised that the Earth is old enough for small variations to have resulted in large changes over millions of years, evolution is pretty self-evident.
Re:So why does this contradict panspermia? (Score:2, Insightful)
Re:So why does this contradict panspermia? (Score:3, Insightful)
If the chances are one in a hundred trillion trillion trillion, and you have 9 hundred trillion trillion trillion trials, it can be expected to happen nine times.
Essentially impossible is just a way for people to discount the improbable, because realistically, it's either impossible or not. There isn't any middle ground.