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Thread: Is there any debate on emergence of prokaryotes?

  1. #1 Is there any debate on emergence of prokaryotes? 
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    http://www.sciencedaily.com/releases...0819162641.htm

    The oxygen killed off anerobes that didn't find refuge in sediments, the deep ocean and other airless environments and led to the evolution of aerobes that could use oxygen to spark their metabolism.
    That's quite a leap that anerobes suddenly evolved into aerobes just because? Don't we have any better theory?


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  3. #2 Re: Is there any debate on emergence of prokaryotes? 
    Veracity Vigilante inow's Avatar
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    Quote Originally Posted by ArrowSmith
    That's quite a leap that anerobes suddenly evolved into aerobes just because?
    That's not a valid representation of their argument, though. The point is that those who could use oxygen were able to be more successful than those who could not. They were selected for.



    It makes all the difference: the bacterium that causes botulism, and the methanogens that make swamp gas are anaerobes, and thrive in reducing conditions. Badgers and butterflies, on the other hand, are aerobes, and require oxygen to keep going.

    <...>

    Fike, assistant professor of earth and planetary sciences in Arts & Sciences, focuses on the dramatic change from anoxic to oxygenated conditions in the world's oceans that preceded the Ediacaran period (from 635 to 542 million years ago) when the first multicellular animals appeared.

    If you look in a textbook, you'll find a story that goes something like this: Four billion years ago the earth's atmosphere was a deadly mixture of gases spewed forth by volcanoes, such as nitrogen and its oxides, carbon dioxide, methane, ammonia, sulfur dioxide and hydrogen sulfide.

    The oceans that formed from condensing water vapor (or incoming comets) were reservoirs of dissolved iron, pumped through hydrothermal vents on the ocean floor.

    Then about 2.7 billion years ago, cyanobacteria, which have been called the most self-sufficient organisms on the planet because they can both photosynthesize and fix nitrogen, began bubbling oxygen into the atmosphere and shallow waters.

    At first oxygen built up gradually in the atmosphere, but about 2.5 billion years ago there was a sudden spike upward, traditionally called the Great Oxygenation Event.

    The oxygen killed off anerobes that didn't find refuge in sediments, the deep ocean and other airless environments and led to the evolution of aerobes that could use oxygen to spark their metabolism.


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  4. #3 Re: Is there any debate on emergence of prokaryotes? 
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    Quote Originally Posted by inow
    That's not a valid representation of their argument, though. The point is that those who could use oxygen were able to be more successful than those who could not. They were selected for.
    That implies there were aerobic creatures already existing at the time of the GOE and natural selection suddenly favored them.

    Note: for some reason quote tag doesn't work for me.
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  5. #4 Re: Is there any debate on emergence of prokaryotes? 
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    Quote Originally Posted by ArrowSmith

    That implies there were aerobic creatures already existing at the time of the GOE and natural selection suddenly favored them.
    Uh, and there's a problem with that why?

    Several species of bacteria tolerate the presence of oxygen without being aerobes, and there certainly would have been environments where oxygen would have been in high enough concentrations to select for such organisms prior to the extinction event.

    I would suspect organisms that tolerated the presence of oxygen, such as several species of cyanobacteria, would have appeared before the development of organisms that use oxygen as an electron donor.
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  6. #5  
    Universal Mind John Galt's Avatar
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    And it is not as if one day there was no oxygen and the next the concentration was 20%. The increase took place over millions of years - there was plenty of time for valuable mutations to occur.
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  7. #6  
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    Quote Originally Posted by Ophiolite
    And it is not as if one day there was no oxygen and the next the concentration was 20%. The increase took place over millions of years - there was plenty of time for valuable mutations to occur.
    That's a valid way of looking at it.
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  8. #7  
    WYSIWYG Moderator marnixR's Avatar
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    implying that the others aren't valid ?

    think exaptation - where a trait originates for no strict adaptationist reason, then later gets co-opted when a change in the environment makes that trait advantageous

    this type of scenario is rather more believable than the one often caricatured as organisms realising that the environment has changed and then thinking "crap, i'd better evolve otherwise i'll die"
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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