5 ms·

This could make more plausible the theory that life on Earth is coming from space and then it evolved from there, rather than being born from scratch on Earth.

by fosk 12y ago

3rd3 12y ago
By Occams Razor, however, it’s probably better to assume that it formed spontaneously on Earth: "Just turning on the spark in a basic pre-biotic experiment will yield 11 out of 20 amino acids." [1] [1]: https://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment https://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment
- thret 12y ago
  This is conjecture. We don't really know how many billions of years it takes to spontaneously evolve life. Panspermia may well be a much simpler vector.
- alanh 12y ago
  Hmm, I wonder if Occam's razor is really applicable. Is it simpler for life to form on multiple planets, or one and spread? I would guess your interpretation is more likely, but I suppose we don't know
  - 3rd3 12y ago
    It’s applicable if one hypothesis is simpler than the other. Panspermia simply defers the origin of life elsewhere and now you have to explain how seeds survived travelling through the hostile environment of space and impacting on Earth, which complicates it quite a bit.
    - tjradcliffe 12y ago
      Ockham's razor is either useless, or a special case of Bayes' Rule. People argue endlessly about it because they fail to recognize they are assuming different priors. If the Urey experiment is reasonably representative of conditions on primordial Earth, no further work is required to get amino acids. So for some people P(terrestrial primordial amino acids) is ~1 If the Murchison meteor and other evidence is correct, amino acids are common in the universe. Data from the Philae lander may tell us more about this. So for some people P(extra-terrestrial primordial amino acids) is ~1 Nor are these exclusive groups. It appears amino acids aren't all that hard to make, so they may have both fallen from the sky and been created on Earth. But... amino acids are not life. There is a further step that is required for the actual pan-spermia hypothesis: the synthesis of more complex molecules, like RNA and DNA. If you think P(RNA|amino acids) ~ 1 then pan-spermia becomes at best irrelevant: not impossible, but not very interesting. If you think P(R/DNA|amino acids) ~ ε then pan-spermia becomes very important, because it is far more likely than not that life on Earth is due to RNA or DNA that descend from an original synthesis that happened elsewhere. Evidence suggests RNA synthesis given amino acids is not very probable. I don't believe it has ever been observed to happen spontaneously the way amino acids are spontaneously synthesized in the Urey experiment. So pan-spermia cannot be dismissed on the basis that it is uninteresting. DNA propogating itself across the universe is also not very probable, so the two hypotheses remain in competition, and it isn't obvious which is more plausible. Pan-spermia requires things like "DNA can survive re-entry." So the OP is correct: discovering that DNA can survive re-entry makes "Life originated elsewhere" more plausible. You'll notice I never used the word "simplicity" in any of this. There is no simplicity: only probability and plausibility. Evidence is more or less probable. Propositions are more or less plausible. Bayes' rule is the only way to update our beliefs consistently, such that no matter what order we get the evidence we come to the conclusion.
      - deleted 12y ago
        [deleted]
- jonahrd 12y ago
  From the same article: "The Murchison meteorite that fell near Murchison, Victoria, Australia in 1969 was found to contain over 90 different amino acids, nineteen of which are found in Earth life."
- ajcarpy2005 12y ago
  There's Occam's Razor but then there's also things like Gravity. Gravity happens on all planets/masses. It could be that life formed on Earth and also forms other places. It could be that the life on Earth has been interbred on a genetic level (think virus insertion of bacteria-based epigenetics) Perhaps for life to really thrive we need very specific planetary conditions (such as Earth-like but for different life with different chemistries they may thrive under different planetary conditions) but the more basic modules of life could be quite plentiful in comparison to what we think of as full-fledged organisms. There is some evidence of bacteria on other planets and in space even. (although scientists are being careful not to rule out contamination from Earth)
- duaneb 12y ago
  Occam's razor is only useful if it removes complexity. Since amino acids can form just as easily on comets, for instance, how is it any more plausible to form on earth? All our water comes from comets; it would be ludicrous to think it's not also a source of organic material. Indeed, Philae confirmed that organic molecules were abundant on the comet on which it landed. Now whether RNA came from a comet is another story, and one that will probably be very difficult to answer, given the lack of archeological evidence. And finally, what does it matter where our RNA came from? Our roots are in these tiny, self-assembling structures. That's the miracle. It's not like we're surrounded by other solar systems that may be candidates for precursors to our life: either life sat around in a very primitive form for probably billions of years before coming to rest at earth, or it formed somewhere in the vicinity of our solar system.
- deleted 12y ago
  [deleted]
alevskaya 12y ago
It's still quite unlikely. The original biochemistry needed a liquid aqueous environment to form and replicate, and you won't find that condition outside of a reasonably deep gravity well in a solar habitable zone. Only Venus, Earth, and Mars would be plausible candidates inside the Solar System for an early incubator of life, and relatively speaking, there wasn't all that much matter transferred between these bodies. Early life probably wasn't as tough as modern bacteria, and likely used something less robust than DNA. The problem with the idea that life could have originated from outside the solar system is that Earth has a laughably small "absorption cross-section" with respect to matter ejected from another solar system, plus the fact that it's very unlikely any information-bearing polymer could survive the integrated radiation flux over its long subrelativistic journey between the stars.
DanBC 12y ago
The other interesting theory is smashing comet ice onto a barren Earth gives you amino acids. http://www.bbc.co.uk/programmes/b04pkvpq http://www.bbc.co.uk/programmes/b04pkvpq 28mins30secs http://www.newscientist.com/article/dn24199-crack-a-comet-to-spawn-the-ingredients-of-life.html http://www.newscientist.com/article/dn24199-crack-a-comet-to...
- lotsofmangos 12y ago
  I have an outside bet with myself that we will find basic life on comets that are using the tail as a dispersion mechanism. edit - if smashing comets into earth makes amino acids, presumably so might smashing small rocks into comets.
ende 12y ago
Serious question: why is it so necessary for life to have evolved off world? What is the obsession here? Popular science type publications seem single mindedly fixated on the panspmeria hypothesis. What is it about geogenic emergence of life that is so unsatisfying?
- sumitviii 12y ago
  Maybe because we haven't been able to conceive a single how life originated from constituent elements.
- lovemenot 12y ago
  To me, one fact about geogenic emergence of life is very suspicious. The fact that life arose so very quickly here. Certainly within 1 billion of Earth's 4.5 billion years' history. Perhaps sooner. When you consider that in ancient times Earth was molten rock at the surface it seems that, in geological terms, life arose almost as soon as it possibly could. That being the case, we can suppose that getting life going ab initio is trivial in nature (or Earth is a many-sigma anomaly). Life certainly should have arisen many times in this galaxy of 10^11 stars - many of which have planetary systems. So we presumably have life all over this galaxy, let alone the others. Whether life spontaneously arose many times independently or it got spread through panspermia is difficult to get a handle on but, given the age of the Universe (13 billion years), and the fact that distances used to be shorter, the latter hypothesis seems more intuitive to me. Either way, given the precocity of life here on Earth we may reasonably suppose the galaxy to be teeming with the stuff.

This could make more plausible the theory that life on Earth is coming from space and then it evolved from there, rather than being born from scratch on Earth.

by fosk 12y ago

This could make more plausible the theory that life on Earth is coming from space and then it evolved from there, rather than being born from scratch on Earth.

3rd3 12y ago

By Occams Razor, however, it’s probably better to assume that it formed spontaneously on Earth: "Just turning on the spark in a basic pre-biotic experiment will yield 11 out of 20 amino acids." [1] [1]: https://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment https://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment

thret 12y ago
This is conjecture. We don't really know how many billions of years it takes to spontaneously evolve life. Panspermia may well be a much simpler vector.
alanh 12y ago
Hmm, I wonder if Occam's razor is really applicable. Is it simpler for life to form on multiple planets, or one and spread? I would guess your interpretation is more likely, but I suppose we don't know
- 3rd3 12y ago
  It’s applicable if one hypothesis is simpler than the other. Panspermia simply defers the origin of life elsewhere and now you have to explain how seeds survived travelling through the hostile environment of space and impacting on Earth, which complicates it quite a bit.
  - tjradcliffe 12y ago
    Ockham's razor is either useless, or a special case of Bayes' Rule. People argue endlessly about it because they fail to recognize they are assuming different priors. If the Urey experiment is reasonably representative of conditions on primordial Earth, no further work is required to get amino acids. So for some people P(terrestrial primordial amino acids) is ~1 If the Murchison meteor and other evidence is correct, amino acids are common in the universe. Data from the Philae lander may tell us more about this. So for some people P(extra-terrestrial primordial amino acids) is ~1 Nor are these exclusive groups. It appears amino acids aren't all that hard to make, so they may have both fallen from the sky and been created on Earth. But... amino acids are not life. There is a further step that is required for the actual pan-spermia hypothesis: the synthesis of more complex molecules, like RNA and DNA. If you think P(RNA|amino acids) ~ 1 then pan-spermia becomes at best irrelevant: not impossible, but not very interesting. If you think P(R/DNA|amino acids) ~ ε then pan-spermia becomes very important, because it is far more likely than not that life on Earth is due to RNA or DNA that descend from an original synthesis that happened elsewhere. Evidence suggests RNA synthesis given amino acids is not very probable. I don't believe it has ever been observed to happen spontaneously the way amino acids are spontaneously synthesized in the Urey experiment. So pan-spermia cannot be dismissed on the basis that it is uninteresting. DNA propogating itself across the universe is also not very probable, so the two hypotheses remain in competition, and it isn't obvious which is more plausible. Pan-spermia requires things like "DNA can survive re-entry." So the OP is correct: discovering that DNA can survive re-entry makes "Life originated elsewhere" more plausible. You'll notice I never used the word "simplicity" in any of this. There is no simplicity: only probability and plausibility. Evidence is more or less probable. Propositions are more or less plausible. Bayes' rule is the only way to update our beliefs consistently, such that no matter what order we get the evidence we come to the conclusion.
    - deleted 12y ago
      [deleted]
jonahrd 12y ago
From the same article: "The Murchison meteorite that fell near Murchison, Victoria, Australia in 1969 was found to contain over 90 different amino acids, nineteen of which are found in Earth life."
ajcarpy2005 12y ago
There's Occam's Razor but then there's also things like Gravity. Gravity happens on all planets/masses. It could be that life formed on Earth and also forms other places. It could be that the life on Earth has been interbred on a genetic level (think virus insertion of bacteria-based epigenetics) Perhaps for life to really thrive we need very specific planetary conditions (such as Earth-like but for different life with different chemistries they may thrive under different planetary conditions) but the more basic modules of life could be quite plentiful in comparison to what we think of as full-fledged organisms. There is some evidence of bacteria on other planets and in space even. (although scientists are being careful not to rule out contamination from Earth)
duaneb 12y ago
Occam's razor is only useful if it removes complexity. Since amino acids can form just as easily on comets, for instance, how is it any more plausible to form on earth? All our water comes from comets; it would be ludicrous to think it's not also a source of organic material. Indeed, Philae confirmed that organic molecules were abundant on the comet on which it landed. Now whether RNA came from a comet is another story, and one that will probably be very difficult to answer, given the lack of archeological evidence. And finally, what does it matter where our RNA came from? Our roots are in these tiny, self-assembling structures. That's the miracle. It's not like we're surrounded by other solar systems that may be candidates for precursors to our life: either life sat around in a very primitive form for probably billions of years before coming to rest at earth, or it formed somewhere in the vicinity of our solar system.
deleted 12y ago
[deleted]

alevskaya 12y ago

It's still quite unlikely. The original biochemistry needed a liquid aqueous environment to form and replicate, and you won't find that condition outside of a reasonably deep gravity well in a solar habitable zone. Only Venus, Earth, and Mars would be plausible candidates inside the Solar System for an early incubator of life, and relatively speaking, there wasn't all that much matter transferred between these bodies. Early life probably wasn't as tough as modern bacteria, and likely used something less robust than DNA. The problem with the idea that life could have originated from outside the solar system is that Earth has a laughably small "absorption cross-section" with respect to matter ejected from another solar system, plus the fact that it's very unlikely any information-bearing polymer could survive the integrated radiation flux over its long subrelativistic journey between the stars.

DanBC 12y ago

The other interesting theory is smashing comet ice onto a barren Earth gives you amino acids. http://www.bbc.co.uk/programmes/b04pkvpq http://www.bbc.co.uk/programmes/b04pkvpq 28mins30secs http://www.newscientist.com/article/dn24199-crack-a-comet-to-spawn-the-ingredients-of-life.html http://www.newscientist.com/article/dn24199-crack-a-comet-to...

lotsofmangos 12y ago
I have an outside bet with myself that we will find basic life on comets that are using the tail as a dispersion mechanism. edit - if smashing comets into earth makes amino acids, presumably so might smashing small rocks into comets.

ende 12y ago

Serious question: why is it so necessary for life to have evolved off world? What is the obsession here? Popular science type publications seem single mindedly fixated on the panspmeria hypothesis. What is it about geogenic emergence of life that is so unsatisfying?

sumitviii 12y ago
Maybe because we haven't been able to conceive a single how life originated from constituent elements.
lovemenot 12y ago
To me, one fact about geogenic emergence of life is very suspicious. The fact that life arose so very quickly here. Certainly within 1 billion of Earth's 4.5 billion years' history. Perhaps sooner. When you consider that in ancient times Earth was molten rock at the surface it seems that, in geological terms, life arose almost as soon as it possibly could. That being the case, we can suppose that getting life going ab initio is trivial in nature (or Earth is a many-sigma anomaly). Life certainly should have arisen many times in this galaxy of 10^11 stars - many of which have planetary systems. So we presumably have life all over this galaxy, let alone the others. Whether life spontaneously arose many times independently or it got spread through panspermia is difficult to get a handle on but, given the age of the Universe (13 billion years), and the fact that distances used to be shorter, the latter hypothesis seems more intuitive to me. Either way, given the precocity of life here on Earth we may reasonably suppose the galaxy to be teeming with the stuff.