New evidence emerges on the origins of life

Discussion in 'Biology & Genetics' started by paddoboy, Jun 1, 2015.

  1. paddoboy Valued Senior Member

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    http://phys.org/news/2015-06-evidence-emerges-life.html

    New research shows that the close linkage between the physical properties of amino acids, the genetic code, and protein folding was likely the key factor in the evolution from building blocks to organisms in Earth's primordial soup.

    "Our work shows that the close linkage between the physical properties of amino acids, the genetic code, and protein folding was likely essential from the beginning, long before large, sophisticated molecules arrived on the scene," said Carter, professor of biochemistry and biophysics at the UNC School of Medicine. "This close interaction was likely the key factor in the evolution from building blocks to organisms."

    The scientific community recognizes that 3.6 billion years ago there existed the last universal common ancestor, or LUCA, of all living things presently on Earth. It was likely a single-cell organism. It had a few hundred genes. It already had complete blueprints for DNA replication, protein synthesis, and RNA transcription. It had all the basic components - such as lipids - that modern organisms have. From LUCA forward, it's relatively easy to see how life as we know it evolved.

    Read more at: http://phys.org/news/2015-06-evidence-emerges-life.html#jCp
     
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  3. timojin Valued Senior Member

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    I wonder if thy linked the amino acids by condensation or some other way, since there were not enzymes available
     
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  5. cosmictraveler Be kind to yourself always. Valued Senior Member

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    So where did LUCA come from?
     
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  7. exchemist Valued Senior Member

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    Whoever answers that gets a Nobel.
     
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  8. Vegasprof Registered Member

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    LUCA lived on the Earth. The complexity of LUCA was more than half-way to the complexity of modern mammals, according to Sharov and Gordon. "Life Before Earth,"
    Arxiv:1304.3381 Sharov and Gordon claim that the evidence points to the origin of life being 9 or 10 billion years ago. If so, there is life on many planets in our galaxy, all having a common origin with life on the Earth.
     
    Last edited: Jun 12, 2015
  9. paddoboy Valued Senior Member

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    I find Panspermia an attractive and likely proposition.
     
  10. Daecon Kiwi fruit Valued Senior Member

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    Doesn't panspermia simply move the question of the origin of life further back? Where/how did it start before seeding Earth?

    I agree that there's no evidence to discount the idea of panspermia, but it doesn't explain abiogenesis.
     
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  11. Vegasprof Registered Member

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    But it does give a few billion more years. Clearly, the "effort" required to go from dirt to LUCA far exceeds the "effort" required to get from LUCA to us.
     
  12. exchemist Valued Senior Member

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    Fair point certainly, though I do not think I have read anything to suggest LUCA could not have arisen in the time available after conditions became suitable for complex molecules to remain intact. (I rather discount Sharov and Gordon - or at least take them with pinch of salt, having read this unsympathetic review of their work: http://www1.cuny.edu/mu/forum/2013/05/30/moores-law-and-the-origin-of-life-a-study-in-demarcation/ )

    Like Daecon perhaps, I find panspermia rather a cop-out from tackling mechanisms of abiogenesis, though I concede this is an aesthetic feeling rather than a scientific one, since there seems to be no evidence to arbitrate either way at the moment.
     
  13. Yazata Valued Senior Member

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    Yes, and I think that's the point.

    Evidence suggests that procaryotic life appeared at an early point in the earth's history. In the earliest period, the earth would presumably have been hot and under constant bombardment by the kind of asteroid-like bodies that left the moon so pockmarked with craters. And despite its simplicity compared to eucaryotic life, procaryotic life is exceedingly complex, which suggests that it's the result of a long period of development. So that's cutting things a little short, time-wise.

    Addressing the 'how' first, probably by the same processes that are hypothesized to account for the origin of life on earth. As to the 'where', perhaps on some older planet elsewhere in the galaxy.

    The biggest challenge facing panspermia is explaining how bacterial life got from there to here, across many light-years. Have something like bacterial spores escaped from wherever they originated and do they now exist in interstellar space like a fine dust? That would suggest that they have drifted for vast periods of time, perhaps billions of years, in something like a freeze-dried state. So the question is, would bacterial DNA have any chance of surviving intact for that long, given cosmic radiation? I'm a little skeptical about that.

    Another possibility is that life might have originated on another body here in our own solar system. That would render the travel problem less difficult, but it might not provide the additional time that motivated the original panspermia speculation.

    And an old science-fiction nut like me enjoys speculating about interstellar space visitors visiting the early pre-biotic earth with dirty boots. Or perhaps they intentionally seeded the earth with extremophile bacteria capable of surviving in those primitive conditions, in a very long-range (both temporally and spatially) attempt to spread life more widely.

    I don't think that it was ever intended to be an explanation of the origin of life in principle, only the origin of life on earth. The mysterious and difficult problem of the initial origin of life still stands.
     
  14. Yazata Valued Senior Member

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    The age of the earth is commonly given as 4.5 billion years.

    http://pubs.usgs.gov/gip/geotime/age.html

    Apparently (controversial) evidence of large colonies of procaryotes similar to today's stomatolites exists from as early as 3.5 billion years ago.

    http://paleobiology.si.edu/geotime/main/htmlversion/archean3.html

    If that early date for the appearance of life is anything close to accurate, the earth would have had to have cooled, undergone its early asteroid-bombardment phase, and cellular life complete with its genetic code and hugely complicated biochemical processes would have had to have already appeared, in the "short" span of a billion years. That might only give a few hundred million years for chemical evolution with its hypothetical pre-biotic chemical replicators to have taken place.

    (Suggesting another question: where are the prebiotic chemical replicators today?)
     
    Last edited: Jun 13, 2015
  15. exchemist Valued Senior Member

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    Sure. But a billion years is still a very, very long time, even if it is "short" compared to 4.5 bn. We are simply not able to gauge whether this is long enough or not, so far as I can see, which means there is no compelling reason to believe it is too short, at which point Ockham's Razor comes into things a bit.

    As for the question about prebiotic replicators, do we know what to look for? And do we think they would survive in an oxygenated atmosphere?
     
  16. Vegasprof Registered Member

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    Yes, a billion years is a long time. But, there is no getting over the fact that a eucaryotic mat, or even the simplest bacterium, is closer to us than it is to dirt.
    Mars was warm and wet for some time. Rocks were constantly being traded between Earth and Mars, and whatever other bodies in the Solar system that were, at that time, habitable.

    For something like a few hundred million years, the Solar system was part of our birth cluster, an open cluster containing (at least) hundreds of systems. All the planets in those systems were constantly exchanging rocks, according to a paper I have read (I would have to dig it up, but it wasn't on arXiv.) So, contrary to what I said ealier, LUCA might not have lived on the Earth.
     
  17. paddoboy Valued Senior Member

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    Just saw your post Daecon so apologies for the late reply.....Had to take a quick flight to Darwin and back!
    My raising of Panspermia was not to explain Abiogenesis per se,but an explanation of how life on Earth may have arose.
    I havn't looked into it a great deal, but its just I find it an attractive proposition. Of course all it does is push back further the process of Universal Abiogenesis.
     
  18. paddoboy Valued Senior Member

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    Far more certain actually than "according to a paper"....We have found Martial rocks on Earth already...ALH84001 for starters and many others.
    Earth rocks on Mars? Possibly also, particularly if the Moon formation collision theory is valid.
     
  19. Vegasprof Registered Member

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    Extraterrestrial biogenesis doesn't "solve" the problem of abiogenesis. It simply allows more time and space for life to have originated. In principle, life could have arisen on any one of perhaps millions of planets, at any time within the last few billion years, instead of within a narrow time window on just one planet. This makes a very unlikely event more likely, like when you buy a million tickets to the lottery.

    I have read several articles that stress the unlikelihood of life. Serious researchers (i.e., those that agree with me) agree that life doesn't "just happen" even when you have the right ingredients. This means that the origin of life is still a great mystery.
     
  20. Yazata Valued Senior Member

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    My concern is that much of the first billion years of the Earth's history might have been very busy and very unpleasant. The earliest Earth would have still been accreting from planetesimals. Then, so current thinking goes, a Mars sized body struck the Earth, fracturing it, ejecting what was to become the Moon. Presumably the Earth's surface wasn't even solid at this time, and there couldn't have been any oceans or primordial soup. Things didn't calm down a whole lot after that, in the period known as the Late Heavy Bombardment, 4.1 to 3.8 billion years ago, when asteroid-sized bodies were regularly striking the inner planets including the Earth. Apparently the LHB is what pocked craters all over the newly-formed Moon's pristine face.

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

    Assuming that that regular planet-killer asteroid falls would have made the Earth's environment unsuitable for life, and assuming the 3.5 billion year date for the stromatolites holds up, we seem to only have a 300 million year window, from 3.5 to 3.8 billion years ago, for life not only to initially appear, but to produce procaryotic cells, presumably complete with all the bacterial genome and biochemistry stuff.
     
    Last edited: Jun 14, 2015
  21. Yazata Valued Senior Member

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    If the Late Heavy Bombardment ended roughly 3.8 billion years ago, and if we go with 3.6 billion years ago for LUCA, the abiogenesis window-of-opportunity shrinks to maybe 200 million years.

    LUCA was already a very sophisticated thing.

    That's describes the lowest common denominator for cellular life on Earth. But the already amazing complexity of such a thing suggests (to me anyway) that it likely had a long developmental history (somewhere) before it reached that point.

    I guess that one way out of this difficulty is panspermia, which embroils us in the transport problem (especially if life's place of origin was interstellar). Another option might be if life and LUCA made their appearance more recently than the 3.5-3.6 billion year estimates suggest. Perhaps we are putting the origin of life much too early.
     
    Last edited: Jun 14, 2015
  22. exchemist Valued Senior Member

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    Yes that's fair enough.
     
  23. Vegasprof Registered Member

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    We don't actually have to "solve" the transport problem (for transpermia) to strongly suspect that it exists because of the time-line evidence. Fortunately, however, there are a number of people doing research in just that topic. Putting together the results of all the articles I have read, I believe that there is a solution.

    Step 1. An inoculated rock leaves a life-bearing planet. (Big collision.)
    Step 2. The rock escapes its birth system. (Jupiter slingshot, or whatever.)
    Step 3. The rock matches velocity with a GMC (giant molecular cloud). (Takes about a million years, according to one paper.)
    Step 4. The GMC collapses into one or more open clusters. The rock winds up in the "Oort cloud" of one system.
    Step 5. Incorporated into comet, the rock splashes down onto a "nice" planet. Instantly, the entire planet is bursting with life.
    Step 6. Thousands of rocks are exchanged between planets of the cluster. Life spreads through the cluster and evolves.
    Step 7. The cluster dissipates.
    Back to Step 1.

    All these steps are dealt with in peer-reviewed articles I have read. I am satisfied.
     

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