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Thread: What do you think is the most likely explanation for the Fermi paradox?

  1. #451
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    Quote Originally Posted by Noclevername View Post
    If it doesn't have many differences, then it indicates (not concludes) a shared origin.

    I think it depends more on the nature of the differences than how many. A judgement call.
    If there are significant points of commonality, there will be arguments that the alternate life had a common ancestor and was out-competed.

    Examples could be DNA-based life with six, vs four, bases: one could argue that all Earth life started with six, but all current life’s ultimate common ancestor was the one which lost the extra bases. Similarly, one could argue that life using alternative amino acids (IIRC, there are about 500 possible amino acids) had a common origin and was beaten in the evolutionary game.

    Non-DNA/non-RNA life would be a bit harder to argue as having a common origin.
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    Quote Originally Posted by swampyankee View Post
    If there are significant points of commonality, there will be arguments that the alternate life had a common ancestor and was out-competed.

    Examples could be DNA-based life with six, vs four, bases: one could argue that all Earth life started with six, but all current life’s ultimate common ancestor was the one which lost the extra bases. Similarly, one could argue that life using alternative amino acids (IIRC, there are about 500 possible amino acids) had a common origin and was beaten in the evolutionary game.
    If it still exists as life on Mars, then it wasn't out competed. It was a successful adaptation to Martian conditions.
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    Quote Originally Posted by Noclevername View Post
    If it still exists as life on Mars, then it wasn't out competed. It was a successful adaptation to Martian conditions.
    Yes, but the argument could be it originated on Earth, where it was out-competed.
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    Quote Originally Posted by swampyankee View Post
    Yes, but the argument could be it originated on Earth, where it was out-competed.
    Or, maybe (they'll argue) life originated on Mars, and our little mutant variation could only survive under Earth's cushy, easy, energy-and-resource-rich conditions. The truly tough survivor strains were the triumphant OG life on Mars, Earth life is merely a big leftover fish in a little pond. Marsupials to the Martian placentals. A "B" grade looks good on a report card of all D's, but it's still not an A!
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    But life without DNA would not prove that life was ubiquitous, as it still took hundreds of millions of years for life to develop, so there's a large window of many stages of development where proto-life might have been shared between worlds by lithopanspermia. So it may not be a truly independent origin, and still does not show that life is easily created and thus ubiquitous in the Universe. Earth and Mars are too close together, we contaminated each other too easily.

    Now, finding life in an outer planets ice moon would be a different story! That would really give ubiquitous life a big boost.
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    Quote Originally Posted by Noclevername View Post
    But life without DNA would not prove that life was ubiquitous, as it still took hundreds of millions of years for life to develop, so there's a large window of many stages of development where proto-life might have been shared between worlds by lithopanspermia. So it may not be a truly independent origin, and still does not show that life is easily created and thus ubiquitous in the Universe. Earth and Mars are too close together, we contaminated each other too easily.

    Now, finding life in an outer planets ice moon would be a different story! That would really give ubiquitous life a big boost.
    I don't see it'd be any different to finding life on Mars. You have the same problem of proving its independent origin.

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    Quote Originally Posted by kzb View Post
    I don't see it'd be any different to finding life on Mars. You have the same problem of proving its independent origin.
    It would be less likely to have made it to Earth, or vice versa.

    I suspect that there would be an argument that any life found in the Solar System, if it uses vaguely similar biochemistry, had a common origin with terrestrial life. Finding life in Titan's oceans using non-polar solvents would probably not be subject to the same arguments, but I'd also not be surprised if some people would argue that it wasn't real life as it didn't have DNA.
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  8. #458
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    Quote Originally Posted by kzb View Post
    I don't see it'd be any different to finding life on Mars. You have the same problem of proving its independent origin.
    Ice moons would be harder to contaminate. They're too far away to have been hit by rocks from Earth or Mars. Life or proto-life would be most likely to have started there by itself.
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    Quote Originally Posted by Noclevername View Post
    Ice moons would be harder to contaminate. They're too far away to have been hit by rocks from Earth or Mars. Life or proto-life would be most likely to have started there by itself.
    I would think that if we discovered life based on DNA and the same amino acids we use, we would start from the the assumption that they were of common origin, and the issue with the icy moons would be, how did it get there? By contrast, if it was completely different life, there would still be the suspicion for Mars that it might have been related at an early stage. For the icy moon that assumption probably would not be made.


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    As above, so below

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    Quote Originally Posted by swampyankee View Post
    It would be less likely to have made it to Earth, or vice versa.

    I suspect that there would be an argument that any life found in the Solar System, if it uses vaguely similar biochemistry, had a common origin with terrestrial life. Finding life in Titan's oceans using non-polar solvents would probably not be subject to the same arguments, but I'd also not be surprised if some people would argue that it wasn't real life as it didn't have DNA.
    "Less likely" is not the same thing as proof beyond reasonable doubt.

    I agree with your second para, I think you have it about right there, except the bit about non-DNA life. If it fulfills the definition of life there shouldn't be a problem with accepting alternatives to DNA.

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    Quote Originally Posted by Noclevername View Post
    Ice moons would be harder to contaminate. They're too far away to have been hit by rocks from Earth or Mars. Life or proto-life would be most likely to have started there by itself.
    How do you know? Prove it beyond reasonable doubt.

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    Quote Originally Posted by kzb View Post
    How do you know? Prove it beyond reasonable doubt.
    Meteors from Earth impacts can reach Mars' surface. It is the next planet upward in the Solar gravity well, and relatively close.

    The outer planets and their moons are too far away for Earth-origin meteors to plausibly reach. They would have to climb much higher in the Sun's gravity well. An Earth impact would not have sent intact life-bearing material that far, because an impact energy strong enough to do so would also likely have vaporized that material.
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    Quote Originally Posted by Jens View Post
    I would think that if we discovered life based on DNA and the same amino acids we use, we would start from the the assumption that they were of common origin, and the issue with the icy moons would be, how did it get there? By contrast, if it was completely different life, there would still be the suspicion for Mars that it might have been related at an early stage. For the icy moon that assumption probably would not be made.


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    We could, but we would have to also consider the likelihood of life spontaneously developing from other forms other than DNA and the amino acids that make up this. If life as we know it is formed from the "most likely" mixture of compounds then it would be also reasonable to assume life may spontaneous develop on other worlds which have similar chemistry to our own, we don't have to assume panspermia has to occur. If life can spontaneously develop from a multitude of mixtures of compounds then the chemistry may not have to be so consistent to our own. Either way, life may well have developed here on Earth due to panspermia and if found on other worlds this maybe the case also. But, if we can get a better understanding of what is actually required for "life" to spontaneuosly develop then we can make better assumptions about all of this and it may well turn out that panspermia, though possibly occurring many times, is not that essential for life to develop elsewhere.

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    Quote Originally Posted by Noclevername View Post
    Meteors from Earth impacts can reach Mars' surface. It is the next planet upward in the Solar gravity well, and relatively close.

    The outer planets and their moons are too far away for Earth-origin meteors to plausibly reach. They would have to climb much higher in the Sun's gravity well. An Earth impact would not have sent intact life-bearing material that far, because an impact energy strong enough to do so would also likely have vaporized that material.
    That's not proof in my book. Anyhow, if it is all about the sun's gravity well, how do you know we are not all descended from Europa life?

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    Quote Originally Posted by kzb View Post
    That's not proof in my book.
    What would be?
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    Meteors from Earth impacts can reach Mars' surface. It is the next planet upward in the Solar gravity well, and relatively close.
    SNC meteorites are thought to be igneous rock from Mars, found on Earth.

    http://cdsads.u-strasbg.fr/abs/1994Metic..29..757M

    https://en.wikipedia.org/wiki/Martian_meteorite

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    Quote Originally Posted by Noclevername View Post
    What would be?
    I'm not sure to be honest, and that is exactly why I am raising it as an important consideration.

    As I said, I am looking forward to all the arguments about it when some life (or microfossils) is finally found on Mars. My suspicion is that it won't definitively settle the question of independent origin. Some will say yes and some will say no.

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    Quote Originally Posted by Roger E. Moore View Post
    SNC meteorites are thought to be igneous rock from Mars, found on Earth.

    http://cdsads.u-strasbg.fr/abs/1994Metic..29..757M

    https://en.wikipedia.org/wiki/Martian_meteorite
    Yes and the President of the USA fronted the NASA discovery of life on Mars if you remember !

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    Quote Originally Posted by kzb View Post
    I'm not sure to be honest, and that is exactly why I am raising it as an important consideration.

    As I said, I am looking forward to all the arguments about it when some life (or microfossils) is finally found on Mars. My suspicion is that it won't definitively settle the question of independent origin. Some will say yes and some will say no.
    You said "reasonable doubt". I don't think that not having any standard to measure up to fits that description. I feel like you will express doubt no matter what I say or show.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    You said "reasonable doubt". I don't think that not having any standard to measure up to fits that description. I feel like you will express doubt no matter what I say or show.
    The reason is you are presenting a case based on "balance of probabilities", not "beyond reasonable doubt".

    Balance of probabilities won't do for this question. It is too important and it will cause mass debate.

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    Quote Originally Posted by kzb View Post
    The reason is you are presenting a case based on "balance of probabilities", not "beyond reasonable doubt".

    Balance of probabilities won't do for this question. It is too important and it will cause mass debate.
    So, I can't satisfy you no matter what I say. Noted.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by kzb View Post
    I'm not sure to be honest, and that is exactly why I am raising it as an important consideration.

    As I said, I am looking forward to all the arguments about it when some life (or microfossils) is finally found on Mars. My suspicion is that it won't definitively settle the question of independent origin. Some will say yes and some will say no.
    I doubt it will either, but I think, as I wrote earlier, that I think the specific situation will lead to accepted theories one way or the other. For example, if (hypothetically!) we discover a T Rex. fossil on Mars, then it will be pretty clear that it got there (or here) somehow, and that it's related to earth (perhaps a hoaxer astronaut). While if we discover life that is based on some entirely different molecules than the ones we use, then the hypothesis will naturally be that it evolved independently.
    As above, so below

  23. #473
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    Quote Originally Posted by cosmocrazy View Post
    We could, but we would have to also consider the likelihood of life spontaneously developing from other forms other than DNA and the amino acids that make up this. If life as we know it is formed from the "most likely" mixture of compounds then it would be also reasonable to assume life may spontaneous develop on other worlds which have similar chemistry to our own, we don't have to assume panspermia has to occur. If life can spontaneously develop from a multitude of mixtures of compounds then the chemistry may not have to be so consistent to our own. Either way, life may well have developed here on Earth due to panspermia and if found on other worlds this maybe the case also. But, if we can get a better understanding of what is actually required for "life" to spontaneuosly develop then we can make better assumptions about all of this and it may well turn out that panspermia, though possibly occurring many times, is not that essential for life to develop elsewhere.
    I'm not sure, I thought initially from the "but" at the beginning of the post that you were disagreeing with you, but I think I can pretty much agree with everything you wrote so maybe there was something unclear about what I wrote, either that or you were just adding something. In any case, I basically agree.
    As above, so below

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    Every planet in this solar system (and probably every smaller body as well) has been contaminated with complex organic molecules from the same sources: comets, interstellar objects, carbonaceous meteorites, etc. It appears the Kuiper Belt is rich with organic materials such as tholins created from less complex molecules like CO2, based on cometary studies. Every planet and every moon, everything has been hit with this stuff, over and over. Further, studies indicate that ejected mass from Earth from giant impacts is capable of spreading organic material from Venus to Mars, as well as from Mars to Earth. Interstellar objects are also capable of bringing organic material to the solar system (ALIENS!). This will complicate efforts to "prove" independent life development. Comets on their way inward to or outward from the Sun can pick up Earthly (or Martian, or Titanian) microbes, DNA, RNA, amino acids, etc., and dump it somewhere else

    ===

    https://arxiv.org/abs/1801.10254
    Implications of Captured Interstellar Objects for Panspermia and Extraterrestrial Life
    Manasvi Lingam, Abraham Loeb (Submitted on 30 Jan 2018 (v1), last revised 13 Oct 2018 (this version, v3))

    We estimate the capture rate of interstellar objects by means of three-body gravitational interactions. We apply this model to the Sun-Jupiter system and the Alpha Centauri A\&B binary system, and find that the radius of the largest captured object is a few tens of km and Earth-sized respectively. We explore the implications of our model for the transfer of life by means of rocky material. The interstellar comets captured by the "fishing net" of the Solar system can be potentially distinguished by their differing orbital trajectories and ratios of oxygen isotopes through high-resolution spectroscopy of water vapor in their tails.

    ===

    http://cdsads.u-strasbg.fr/abs/2005AsBio...5..483G
    Impact Seeding and Reseeding in the Inner Solar System
    Gladman, Brett; Dones, Luke; Levison, Harold F.; Burns, Joseph A.
    Astrobiology, Volume 5, Issue 4, pp. 483-496.
    Publication Date: 08/2005

    Assuming that asteroidal and cometary impacts onto Earth can liberate material containing viable microorganisms, we studied the subsequent distribution of the escaping impact ejecta throughout the inner Solar System on time scales of 30,000 years. Our calculations of the delivery rates of this terrestrial material to Mars and Venus, as well as back to Earth, indicate that transport to great heliocentric distances may occur in just a few years and that the departure speed is significant. This material would have been efficiently and quickly dispersed throughout the Solar System. Our study considers the fate of all the ejected mass (not just the slowly moving material), and tabulates impact rates onto Venus and Mars in addition to Earth itself. Expressed as a fraction of the ejected particles, roughly 0.1% and 0.001% of the ejecta particles would have reached Venus and Mars, respectively, in 30,000 years, making the biological seeding of those planets viable if the target planet supported a receptive environment at the time. In terms of possibly safeguarding terrestrial life by allowing its survival in space while our planet cools after a major killing thermal pulse, we show via our 30,000- year integrations that efficient return to Earth continues for this duration. Our calculations indicate that roughly 1% of the launched mass returns to Earth after a major impact regardless of the impactor speed; although a larger mass is ejected following impacts at higher speeds, a smaller fraction of these ejecta is returned. Early bacterial life on Earth could have been safeguarded from any purported impact-induced extinction by temporary refuge in space.

    ===

    http://cdsads.u-strasbg.fr/abs/2015A%26A...583A...1L
    Inventory of the volatiles on comet 67P/Churyumov-Gerasimenko from Rosetta/ROSINA
    Le Roy, LÚna, et al.
    Astronomy & Astrophysics, Volume 583, id.A1, 12 pp. (A&A Homepage)
    Publication Date: 11/2015

    Context. The ESA Rosetta spacecraft (S/C) is tracking comet 67P/Churyumov-Gerasimenko in close vicinity. This prolonged encounter enables studying the evolution of the volatile coma composition.
    Aims: Our work aims at comparing the diversity of the coma of 67P/Churyumov-Gerasimenko at large heliocentric distance to study the evolution of the comet during its passage around the Sun and at trying to classify it relative to other comets.
    Methods: We used the Double Focussing Mass Spectrometer (DFMS) of the ROSINA experiment on ESA's Rosetta mission to determine relative abundances of major and minor volatile species. This study is restricted to species that have previously been detected elsewhere.
    Results: We detect almost all species currently known to be present in cometary coma with ROSINA DFMS. As DFMS measured the composition locally, we cannot derive a global abundance, but we compare measurements from the summer and the winter hemisphere with known abundances from other comets. Differences between relative abundances between summer and winter hemispheres are large, which points to a possible evolution of the cometary surface. This comet appears to be very rich in CO2 and ethane. Heavy oxygenated compounds such as ethylene glycol are underabundant at 3 AU, probably due to their high sublimation temperatures, but nevertheless, their presence proves that Kuiper belt comets also contain complex organic molecules.

    ===

    https://en.wikipedia.org/wiki/Carbonaceous_chondrite
    Last edited by Roger E. Moore; 2019-Jun-28 at 02:18 AM.

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    I'm not saying it would be impossible to tell if a world biology developed independently from any other, just that it will be awkward if Martian fossil microbes turn out to look remarkably like Earthly Precambrian fossil microbes. Panspermia? Convergent evolution? Aliens? Does life follow the same developing molecular pathways from world to world? Many of the same complex hydrocarbons are found on both Earth and Titan; can life develop in similar ways whether water-based or methane based? We just don't know.

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    Quote Originally Posted by Roger E. Moore View Post
    I'm not saying it would be impossible to tell if a world biology developed independently from any other, just that it will be awkward if Martian fossil microbes turn out to look remarkably like Earthly Precambrian fossil microbes. Panspermia? Convergent evolution? Aliens? Does life follow the same developing molecular pathways from world to world? Many of the same complex hydrocarbons are found on both Earth and Titan; can life develop in similar ways whether water-based or methane based? We just don't know.
    I agree. I don't think I would say "awkward," but it would be a fascinating discovery that would stimulate a lot of new thinking about why it was so. And yes, the suggestions you made would be candidates for why it happened.
    As above, so below

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    Quote Originally Posted by Jens View Post
    I agree. I don't think I would say "awkward," but it would be a fascinating discovery that would stimulate a lot of new thinking about why it was so. And yes, the suggestions you made would be candidates for why it happened.
    "Awkward" was said tongue-in-cheek. But yeah, weird. Almost want to see it.

    LATE ADD: Really just want to see a Martian fossil of anything. Anything.
    Last edited by Roger E. Moore; 2019-Jun-28 at 02:39 AM.

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    Quote Originally Posted by Jens View Post
    I'm not sure, I thought initially from the "but" at the beginning of the post that you were disagreeing with you, but I think I can pretty much agree with everything you wrote so maybe there was something unclear about what I wrote, either that or you were just adding something. In any case, I basically agree.
    Yes sorry, the but should have been replaced with "to add". I wasn't disagreeing with you I meant just to add. Apologies.

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    Quote Originally Posted by Noclevername View Post
    So, I can't satisfy you no matter what I say. Noted.
    That's not what I am saying at all. I am just saying that it is going to be a lot more difficult than balance of probabilities arguments.

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    Quote Originally Posted by Roger E. Moore View Post
    I'm not saying it would be impossible to tell if a world biology developed independently from any other, just that it will be awkward if Martian fossil microbes turn out to look remarkably like Earthly Precambrian fossil microbes. Panspermia? Convergent evolution? Aliens? Does life follow the same developing molecular pathways from world to world? Many of the same complex hydrocarbons are found on both Earth and Titan; can life develop in similar ways whether water-based or methane based? We just don't know.
    The thing is, going by current thinking on abiogenesis, this is precisely what we should find on Mars.
    At any rate we should find them if abiogenesis is as common as hypothesized.
    All experiments point to nucleic acids and amino acids as the starting point for life, and this goes for both Earth and Mars.
    After that the prokaryotes would develop along very similar lines. Conditions on early Mars were similar to those on early Earth.

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