Evidence for abiogenesis

Discussion in 'Biology & Genetics' started by SetiAlpha6, Oct 25, 2018.

  1. Michael 345 Home just over a week still jet lag sleepy Valued Senior Member

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    I would think that finding complex molecules in space, where no life exist, would be a good pointer indicating, at the very least, a ability for complex molecules surviving under extreme conditions

    It could be they were bounced off planets but again they can survive harse conditions

    No real stretch complex molecules can become more complex in a softer environment until they become self replicating

    I would contend self replicating molecules have more ability to react to external conditions

    The pathway to life has begun

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  3. sideshowbob Sorry, wrong number. Valued Senior Member

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    No, the focus of the thread is not on ingredients. The focus is on what happened to the ingredients.
     
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  5. Write4U Valued Senior Member

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    Easy, Robert Hazen (Carnegie Institute for Science) demonstrates the chemical processes which may lead to life, from radiation bombardments in cosmic clouds long ago, to a near infinite number of chemical reactions in the universe, and continuing today on earth. Numbers which are impossible to duplicate in a laboratory.

    Hazen estimates that the earth alone has performed about 2 trillion, quadrillion, quadrillion, quadrillion, chemical reactions during its lifetime.

    Start at 25:15 (to avoid lengthy introduction) This is a really good presentation, without being overly technical.
     
    Last edited: Oct 27, 2018
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  7. Dinosaur Rational Skeptic Valued Senior Member

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    We know (or have excellent reasons to believe) that there was a time when there was no life on Earth.

    Ergo: Life some how originated from some non-living chemicals or came from outer space.

    The "came from space explanation" merely pushes the problem of its origin to some place other than Earth & is not really an explanation.

    All we really know is that in the distant past there was no life on Earth & now there is life.

    While we might never know how it occurred, we do know that some how life originated from non-life.
     
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  8. Write4U Valued Senior Member

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    Hazen explains how this might occur, possibly by several different chemical processes and interactions, both on earth and in space, wherever there is a chemical rich and hospitable environment.
    https://en.wikipedia.org/wiki/Biochemistry

    Cyano bacteria evolved via "endosymbiosis".

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    ......................

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    A representation of the endosymbiotic theory......Diagram of a typical prokaryotic cell.

    A prokaryote is usually a unicellular organism, sometimes a multi cellular organism, that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle

    Prokaryotes reproduce without fusion of gametes. The first living organisms are thought to have been prokaryotes.

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    Phylogenetic tree showing the diversity of prokaryote

    https://en.wikipedia.org/wiki/Prokaryote
     
  9. Yazata Valued Senior Member

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    Yes, I agree with that.

    Or it was created by some sort of divine being. That's the theory being promoted by some of the theists (many theists have no problem with abiogenesis) so we shouldn't ignore it.

    What panspermia (the extraterrestrial origin of life) seeks to explain isn't how life originated, but rather how something as incredibly complex as life could have appeared on Earth so early in Earth's history. People have been trying to push back the first appearance of life on Earth to a point right after (or even before) Earth became habitable for life. But life doesn't appear to be the kind of thing that would just pop into existence overnight. (It's also possible that life didn't appear on Earth nearly so early.)

    If life came from outer space, we've given ourselves more time, but we still need to account for how life appeared wherever it originated in outer space. If the universe terminates with the big bang in the pastward temporal direction, we seemingly can't say that life has always existed.

    So even if we embrace panspermia, we still have to ultimately decide between a natural and a supernatural origin.

    I opt very strongly for some kind of natural account. That's because it makes the origin of life comprehensible, instead of just further mystifying it by introducing entirely hypothetical divine beings about which we know nothing.

    The whole point of an explanation (especially in science) is to reduce the unknown to the known. Explanations don't succeed when they merely attribute unknowns to even bigger unknowns.

    The advantage of naturalistic accounts of life's origins is that these accounts make use of known chemistry. They propose possible mechanisms for how this or that might have happened, that can be tested and assessed.
     
    Last edited: Dec 9, 2018 at 6:20 PM
  10. Yazata Valued Senior Member

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    I don't think that anyone at this point really knows how life originated. There's an entire industry of biologists speculating about it. (Just do a web search for "origin of life".) It's a fascinating question.

    I don't think that's true. The idea seems to be that photosynthetic eukaryotes like plant cells and some protists like Euglena evolved by absorbing something like cyanobacteria as endosymbionts. These gradually became the chlorophyll-bearing chloroplasts found in plant cells today.
     
  11. DaveC426913 Valued Senior Member

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    Well put.
     
  12. Write4U Valued Senior Member

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    Robert Hazen proposes that life was an invitable and deterministic evolutionary result of chemical interactions.
    If you haven't watched his presentation at Carnegie Institute, I can highly recommend it.
    He shares you fascination...........

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    Does this explain?

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    http://www.fossilmuseum.net/Evolution/Endosymbiosis.htm
     
  13. Michael 345 Home just over a week still jet lag sleepy Valued Senior Member

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    I understand that abiogenesis stood for the NATRAL spontaneous origin of life

    Which would rule out the supernatural, god, being the cause

    So yes we should ignore it

    Testing what we have is available

    Not a single lab that I know of has a bottle with a 'god' label on it which could be used to test how the god factor might work

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  14. Write4U Valued Senior Member

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    In one of the links it is mentioned that the first forms of life may have been extremophiles due to the extreme conditions on earth at that time. This special adaptation was beneficial to survival but also placed restrictive evolutionary barriers on the organism. The Prokaryotes.
    They are still around in several places such as around deep sea "black smokers".

    Only when the earth cooled and cyanobacteria began to build the oxygen levels in the earth's atmosphere, did evolution take off in an exponential manner generation by generation.
    An evolutionary explosion, starting with the evolution of Eukaryotic organisms.
     
  15. exchemist Valued Senior Member

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    Prokaryotes are not just "still around in several places". We are surrounded by prokaryotes everywhere and they even live inside us.
     
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  16. Write4U Valued Senior Member

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    Thank you for that clarification.
    The mention of "several places" was in reference to extremophiles. I should have been clearer..

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  17. Write4U Valued Senior Member

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    Unexpected chemicals detected in interstellar clouds

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    View inside the Lagoon Nebula.
    https://en.wikipedia.org/wiki/Interstellar_cloud
     
  18. Write4U Valued Senior Member

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    Robert Hazen mentioned Louis Allamandola.
    http://www.astrochem.org/bios/allamandola.php
     
  19. Write4U Valued Senior Member

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    I believe cyanobacteria are older and existed before eukaryotes evolved (emerged)

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    http://hoopermuseum.earthsci.carleton.ca/stromatolites/CYANOB.htm
     
  20. Yazata Valued Senior Member

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    I think that most biologists believe that. What I was suggesting in post #87 was that cyanobacteria didn't appear as the result of endosymbiosis. (One organism taking up residence inside another, to both organisms' benefit.) Rather, already existing cyanobacteria took up residence inside another prokaryote (an archaean probably) as part of the process in which eukaryotes emerged, in so doing the cyanobacteria became the ancestors of the photosynthetic chloroplasts that are found within plant cells today. (Or at least that's the current theory.) Plant cells are eukaryotic, as are animal and fungal cells. The prokaryotes are bacteria and archaea. (And as Exchemist points out, bacteria are ubiquitous, they are everywhere.)

    I'm not sure that I'd agree that prokaryotes were the earliest form of life. That idea seems to assume that LUCA (the last universal common ancestor, from which all life today is thought to be descended) was a prokaryote. But given the complexity of the known prokaryotes, they seem to many biologists to be the result of a prior process that led up to them. So there may be even simpler sorts of cells back in that earlier history, sorts of cells too simple to compete with later models and didn't survive down to today. LUCA may not have been a bacterium or an archaean at all, but something simpler that is ancestral to them (and to us).

    I'm reasonably confident that cyanobacteria weren't the earliest prokaryotes. The ability to photosynthesize seems to have been a later development. It was probably the massive bloom of photosynthetic bacteria in the early oceans that led to the so-called "oxygen holocaust". Oxygen is very destructive to biochemistry since it tends to oxidize everything in sight. So as the oxygen in the Earth's atmosphere rose, the atmosphere became more poisonous to life. But the rise in the amount of oxygen in the Earth's atmosphere happened gradually (at first there was very little and the Earth's atmosphere was very unlike today's) and cells evolved to tolerate oxygen. Not only tolerate it, but make use of it in more efficient respiration.

    This may or may not have also been associated with the appearance of the eukaryotes, since they don't appear until afterwards. There are a group of biologists who seem to want to associate evolutionary developments with the amount of oxygen in the atmosphere and the efficiency of different respiration schemes.

    https://www.amazon.com/dp/0393088812

    https://www.amazon.com/Oxygen-molecule-Oxford-Landmark-Science/dp/0198784937

    https://www.amazon.com/dp/160819907X

    Here's a (very speculative) timeline:

    https://www.newscientist.com/article/dn17453-timeline-the-evolution-of-life/
     
    Last edited: Dec 10, 2018 at 10:03 PM
  21. Write4U Valued Senior Member

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    Thanks for the links, very informative.

    I do have a question regarding this statement;
    https://www.newscientist.com/article/dn17453-timeline-the-evolution-of-life/
    Google. That is a difference of 1.35 billion years earlier than 2.15 billion years. Can the fossil records show dates that far apart?

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    At right is a layered stromatolite, produced by the activity of ancient cyanobacteria. The layers were produced as calcium carbonate precipitated over the growing mat of bacterial filaments; photosynthesis in the bacteria depleted carbon dioxide in the surrounding water, initiating the precipitation.

    http://www.ucmp.berkeley.edu/bacteria/cyanofr.html
     
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  22. Yazata Valued Senior Member

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    Because the earlier date for the appearance of cyanobacteria is controversial. There's a whole literature on it in the journals.

    The earlier date seems to be based on fossil evidence that looks to the eye like modern day stromatolites, which are associated with cyanobacteria today so many assume they must have involved cyanobacteria then too. There are additional supporting strands of evidence for early photosynthesis such as early traces that might be indicative of carbon-fixation. In other words, the whole thing is kind of speculative, it's inferences from evidence.

    On the other hand, the so-called "Great Oxygenation Event" seems to have happened about 2.4 billion years ago. That's more than a billion years after the hypothesized first appearance of photosynthetic life according to the scheme above. (Despite being more than a billion years later, life on Earth still probably only consisted of prokaryotes at that time, bacteria and archaea.) This event involved a dramatic rise in the amount of oxygen in the Earth's atmosphere (hence its name). Evidence for this is abundant, since the oxygen caused widespread oxidation resulting in a distinct worldwide rust-layer in the geological record. But inevitably, there are controversies about what actually caused it. The leading hypothesis is that it was biogenic and associated with the appearance of oxygenic photosynthesis.

    So how can the early-photosynthesis and the late-photosynthesis views be reconciled? If photosynthesis was as early as the early-photosynthesis advocates want it to be, why didn't it alter the atmosphere much earlier?

    The mainstream view today seems to be that the first photosynthesizers did appear early but possessed relatively crude and inefficient photosynthetic systems. We still see these earlier systems today in some bacteria. The important thing to note is that these earlier versions of photosynthesis didn't break down water releasing O2. There are basically two of these earlier systems, distinguished by the molecules that serve as electron-receptors, sometimes called 'Photosystem I' and 'Photosystem II'.

    The modern efficient oxygenic photosynthesis consists of both Photosystem I and Photosystem II combined and working in concert. The appearance of this 'new and improved' version of photosynthesis seems to have been later than the appearance of either of its precursors and is likely what is associated with the Great Oxygenation Event. Here's a diagram:

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    The difficulty in identifying cyanobacteria as the earliest photosynthesizers is that cyanobacteria practice the newfangled oxygenic photosynthesis. (They would have to if they are the ancestors of today's plant chloroplasts, since all the higher plants practice the more advanced photosynthesis.)

    So my (layman's) opinion is it's possible that the very early fossil things being interpreted as stromatolites are indeed biogenic. If so, it's possible that they are associated with photosynthesizers. But... I'm skeptical that these organisms were cyanobacteria. Whatever early prokaryotes produced these mats were probably some of the earlier photosynthesizers ancestral to the cyanobacteria.

    Here's a very good short survey article written for botanists that explains all of this in relatively easy to understand non-technical language.

    http://www.plantphysiol.org/content/plantphysiol/154/2/434.full.pdf

    The author writes: "The accumulated evidence suggests that photosynthesis began early in Earth's history, but was probably not one of the earliest metabolisms and that the earliest forms of photosynthesis were anoxygenic, with oxygenic forms arising significantly later."

    Which returns us to the topic of abiogenesis, LUCA and the first forms of life. As fascinating as all of this stuff about photosynthesis and cyanobacteria is, and the evolutionary history of microorganisms is fascinating (more than 80% of the history of life on Earth was before multicellular organisms appeared, it's when much of the essential biochemistry was hammered out), it's all subsequent to hypothetical abiogenesis and its initial products.

    There are probably good reasons to think that photosynthesis appeared subsequent to the appearance of earliest life. The author writes: "Chlorophylls are essential pigments for all phototrophic organisms. Chlorophylls are themselves the product of a long evolutionary development, and can possibly be used to help understand the evolution of other aspects of photosynthesis. Chlorophyll biosynthesis is a complex pathway with 17 or more steps. The early part of the pathway is identical to heme biosynthesis in almost all steps and has clearly been recruited from that older pathway."

    So even if we accept the early photosynthesis view, it's still exceedingly unlikely in my opinion that the earliest cells were photosynthesizers. If the earliest lifeforms on Earth were photosynthesizers, it would perhaps be an argument for an extraterrestrial origin of life and for panspermia
     
    Last edited: Dec 12, 2018 at 4:51 PM
  23. Write4U Valued Senior Member

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    A billion years? That's a longgg time.....

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    But then, that was a longgg time ago.....

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    And evolution itself would suggest an earlier version of phototropic biology.....

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    Last edited: Dec 12, 2018 at 5:35 PM

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