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Can life begin today as it did 4billion years ago

  1. Jul 30, 2009 #1
    Hello I am new to the field.

    Can someon answere, i cannot find the answere in books.

    if life 3.8 billion years ago could form in very harsh conditions. then whay cannot it happen again today. whay cannot it have been happening all the time for almost 4 billion years.

    i have read that all animals have a cummon ancestor and all plants have a cummon ancestor too, and there also is a cummon ancestor for both plants and animals, and it all leads back to single cell organism.

    now if we can trace back a cummon ancestor for all living or growing things on earth, then where are the living things that came later.

    Does this mean that in 4 billion years there have been only one spark of life that led to complete diversity of life... and guess what, it happened right next day after earth stopped being bombarded by asteroids. hmm what a coincidence.

    1. WHERE ARE ANIMALS (OR SOMETHING ELSE ALIVE) THAT APEARED AFTER THE EARTH WAS ALLREADY INHABITED???

    2. have this aspect been discussed in science world?

    3. If we want to know so bad how life on earth got started, cannot we just observ it starting today?
     
    Last edited: Jul 30, 2009
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  3. Jul 30, 2009 #2

    mgb_phys

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    The same type of life can't start again, we have been filling the atmosphere with a highly toxic gas called Oxygen for the last 3Bn years.

    Correct. But it even goes further than that, there are common ancestors for plants+animals and fungi and all complex celled organisms and for simple celled organisms.

    Like us ?

    Generally the problem for entirely new forms of life to appear now is that there is a lot of competition. Anything with any chemical energy (which is pretty much the definition of life in these terms) would instantly be food for some other existing form of life.
     
    Last edited: Jul 30, 2009
  4. Jul 30, 2009 #3
    Ok but it is not said that new life forms necesserily have to be food for someone else.

    well it started first time when there was no oxigen. life can get through hardship.

    I mean advanced life on earth have been for something like 500 million years. is it really so that for all this time it have been desperatelly trieing to begin everywhere on planet, and consitantly failed for 500 million years by becoming food to existing species?
    life can form in a way that it is not eatable (rock-like life for example), or in places or time where are no predators (after great extinction 250 million years ago (siberian traps))
     
  5. Jul 30, 2009 #4
    Life will almost certainly "begin" de novo in our time. It will happen in a laboratory somewhere. Life is chemistry and we understand a lot of that chemistry now. We can synthesize proteins and nucleic acids. Getting them to work together in a test tube or Petri dish is the current challenge. To say this is artificially created life is missing the point. Life on earth (us) will create new life forms from non-living molecules.
     
    Last edited: Jul 30, 2009
  6. Jul 30, 2009 #5
    the question of curse is not about artificial life creation
     
  7. Jul 30, 2009 #6
    As you said, and have been told by others, the conditions for spontaneous development of life do not appear to exist on earth today. Moreover, any near-life would almost certainly be eaten before it got very far. However, there's nothing artificial about the kind of life that might come out of a laboratory. It will chemically be life, with self replicating DNA or RNA coding for proteins within a primarily lipid membrane. It will have metabolism and replicate (the basic defining features of life). The only thing that's different is that the first generation will be not be spontaneously generated.
     
    Last edited: Jul 30, 2009
  8. Jul 30, 2009 #7

    russ_watters

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    Why not? Or more to the point: how can the new life defend itself from being eaten?
    You missed the point: when there was no oxygen, the earth was more hospitible to the original life. Then that original life polluted the atmosphere and essentially caused its own demise.
    There is good reason to believe that life must be chemically/biolgically compatible with what we have now. Things like the chemical properties of carbon and water appear to be unique and important (and are features of our planet). Rock like life? I saw that on a movie once - it's just fantasy. And there is no such thing as a place with no predators - everywhere on earth hospitable to life is already covered with it.
     
  9. Jul 31, 2009 #8
    Ok OK.

    Even if I think that entirly new life forms that began life after world was inhabited does not neceserally have to be eaten stright away.

    (I mean there are so many speceis in world that should not exist because someone should have eaten them well before it even got started ( for example slowmoving, week, small and yet rather dumb, ground animals in sabretooth cat world - austrolapitecs))

    but even if all newly appearing life forms are being eaten by existing ones, at least for some time this strange, alien like weird DNA or no DNA life can be found here or there, at least the remains of such life. or other signs that it has existed.

    cummon there have been billions of years of time for alternative life to evolve, that does not use our DNA alfabet, but stors information elsehow.

    you are saying atmosphere is polluted with deadly poison - oxigen. Is it proved somewhere that new life forms can appear only in oxigenfree world?
     
  10. Jul 31, 2009 #9

    russ_watters

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    Note that "newly formed life" means something no more complicated than a bacterium. And for the first couple of billion years, it was all bacterium and similar organisms. A small land animal (like a mouse) represents billions of years of evolution. So it wouldn't make sense to think there would be fossils or other remnants of completely different life.
    No, we don't know that - we only know that there was never the option for life to begin in an oxygen rich world on earth as the earth was covered with life before oxygen filled the atmosphere.
     
  11. Jul 31, 2009 #10

    mgb_phys

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    No I was saying that the same chemical path way use by the earliest life on earth couldn't be used now. Some relatives of the early anaerobic bacteria do still survive, anywhere that smells bad.
    It doesn't mean that life can't begin using oxygen, we have recently found life in ocean vents and in deep oil wells that lives on sulphur. Pretty much anywhere there is available chemical energy then something will appear/adapt to use it.

    It is easy to imagine alien life that didn't use RNA/DNA (that's one reason to laugh at people that use DNA as the definition of life) what would be interesting is alien life that didn't use some discrete gene-like mechanism for inheritance - that would be interesting.
     
  12. Jul 31, 2009 #11

    DavidSnider

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    Funny. Now that we know about genes a non-gene like mechanism would be interesting. For the whole of human history before that everybody pretty much assumed it was like mixing chemicals =)
     
  13. Jul 31, 2009 #12
    There are autonomous proteins called prions which can infect animals and humans (Mad Cow disease). As infectious agents, they can be considered quasi-life forms, but they have no nucleic acids. They invade nerve cells and convert normal proteins to abnormal ones. They are unlike viruses in that viruses do have DNA or RNA.

    http://www.cdc.gov/od/ohs/biosfty/bmbl4/bmbl4s7d.htm
     
  14. Jul 31, 2009 #13
    Ok but I know that there is no mouse size organism.

    I am saying that leftovers from alienlike single cell organisms are not even found. every single cell organism that has EVER lived have ONLY one tipe of DNA. We have found a LOT of extinct single cell organisms but they all use DNA.

    Could it be that life that starts olways start with our good old DNA structure.

    What if our way of life is the only way of life - that would mean that wherever we go on what ever planet we find life it will look very much like earth life?
     
  15. Jul 31, 2009 #14

    mgb_phys

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    Anything that didn't use DNA was probably 2nd place in the eat or be-eaten competition. The palealogy evidence for simple cell's chemistry isn't that good, there could easily be none-DNA early life that we haven't found evidence of, or has left no evidence.
    Remember we are talking about <3Bn year old life that was little more than a few associated chemicals - we aren't going to find fossils in the normal sense.
     
  16. Jul 31, 2009 #15
    As infectious agents, prions probably need to be considered life forms (if it's strict dichotomy between life and non-life). They are certainly around NOW and they're very hard to kill. They are the most primitive life forms known.

     
    Last edited: Jul 31, 2009
  17. Jul 31, 2009 #16

    mgb_phys

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    They are the simplest structure that could be called life (or pseudo life).
    I'm not sure that they are necessarily ancient or that that more complex life evolved from them - prions seem to have formed from animal proteins and are found in only a few species which suggests modern,
     
  18. Jul 31, 2009 #17
    You're most likely correct. Nevertheless, they manage to replicate without nucleic acids. It's still not known for certain, but they probably use the host DNA or mRNA in some way which would explain why they are so species specific.
     
  19. Jul 31, 2009 #18

    CRGreathouse

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    We don't know. Current evidence points strongly toward that sort of monogenesis. If there were several they would have happened around the same time -- otherwise the ones that were earlier would have a strong enough competitive advantage to simply wipe out the others (as food sources or competitors).

    What day was that? As far as I know we're still being bombarded regularly.

    Don't be silly. Animals are far too complex to develop independently. Even modern bacteria with their many organelles are much more complicated than any spontaneous creation would be.

    The trouble is that even if there was an abiogenesis event now (conditions are very different now, but I see no reason this wouldn't happen) the resultant life-form wouldn't be able to survive amongst the broad variety of existing life, which would have billions of years of evolutionary advantage over the new creation.

    Now if we could carefully eradicate all life on earth (including viruses, for those who may not otherwise consider these living) without altering other conditions overly then I'd put my money on seeing abiogenesis -- heck, I think it would be pretty fast, too, maybe less than a million years. But it would probably take hundreds of millions of years before they were even close to modern one-celled organisms in terms of complexity.

    (Anyone wishing to pick this apart, feel free!)
     
  20. Aug 1, 2009 #19
    ^ Totally agreed. Well said.
     
  21. Aug 1, 2009 #20
    I agree with you generally except for this last part quoted above. Why do you think life would begin now, given current conditions are so different now than 3.5-4.0 billion years ago? You are aware that early life was anaerobic and existed under reducing conditions. Oxygen was a product of their metabolism which accumulated in the atmosphere and eventually poisoned most, but not all anaerobic species. It's true that anaerobes survive today, in such environments as the human mouth (under the gum line) and colon. But if you eradicate all the mouths and colons (and biology in general), its not clear where anaerobes might get started today. Either you need to outline a new mechanism for abiogenesis under oxidizing conditions or indicate where and how life might begin on present day earth in reducing conditions (absent mouths and colons).

    http://nitro.biosci.arizona.edu/courses/EEB105/lectures/Origins_of_Life/origins.html

    There's also a good article in the source that can't be mentioned.
     
    Last edited: Aug 1, 2009
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