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Thread: what is ur definition of life

  1. #1 what is ur definition of life 
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    I ask this because I was pondering if we as a species would recognize simple life that might exist elsewhere in the universe?

    my definition includes some of the following features what are ur views:

    1. The ability of a chemical to replicate itself either through pot luck, just happens to be where all the ingredients for the chemical process exist or the chemical has the ability to seek out and find the stuff it needs to replicate

    2. To differentiate it from (so called pure )proper chemical reactions, I would say it has the ability to switch this process on and off, so if the stuff it needs to replicate is in low amounts it has the ability to wait it out.

    3. It can replicate itself many times over, and this is unlike the ordinary chemical reactions where the rate of the reaction gradually declines as a) the output of the reaction increases and b) the stuff used to make the reaction in proportion to the chemicals produced declines.

    and a virus is a good example of some of the above features:

    all it is missing is the rna to replicate itself

    but it does have the ability to seek this stuff out

    if u put a virus into a liquid consisting of rna I am confident it would replicate itself as it has what it needs to do it

    it also had the ability to not chemically reproduce and can sit dormant or still for long periods of time

    I posted this in another thread on the beginnings of evolution but would like to get a feel for other views and definitions and if the above is incorrect

    thanks in advance

    AA


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  3. #2  
    Forum Cosmic Wizard spuriousmonkey's Avatar
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    what is that: we as a species?

    I didn't realize we were united in our thoughts, actions and what not.


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    Quote Originally Posted by spuriousmonkey
    what is that: we as a species?

    I didn't realize we were united in our thoughts, actions and what not.
    I meant if we went to say mars and found life that didn't look like life on earth would we recognize it as life.

    sorry for misunderstanding
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    Forum Cosmic Wizard spuriousmonkey's Avatar
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    We are pretty good at recognizing life. Our brains are hardwired to do so.
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    Quote Originally Posted by spuriousmonkey
    We are pretty good at recognizing life. Our brains are hardwired to do so.
    whats ur definition?
    Just here to Learn =)

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  7. #6  
    Forum Cosmic Wizard spuriousmonkey's Avatar
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    Who are you asking? Me as the human species, or me as the research biologist?
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    Quote Originally Posted by spuriousmonkey
    Who are you asking? Me as the human species, or me as the research biologist?
    research biologist
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  9. #8  
    Forum Cosmic Wizard spuriousmonkey's Avatar
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    The answer would depend on the research question.
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  10. #9  
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by Always.Asking
    I meant if we went to say mars and found life that didn't look like life on earth would we recognize it as life.
    No. We went. We found life. We dismissed it with an elaborate series of excuses and then avoided looking at it again for three decades. Eventually, of course, the truth will out.
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  11. #10  
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    Quote Originally Posted by John Galt
    Quote Originally Posted by Always.Asking
    I meant if we went to say mars and found life that didn't look like life on earth would we recognize it as life.
    No. We went. We found life. We dismissed it with an elaborate series of excuses and then avoided looking at it again for three decades. Eventually, of course, the truth will out.
    I meant by the OP what in whoever replies opinion constitutes life, sometimes its not easy to say if something is alive

    and i am definitely NOT saying we have discovered life

    i am just asking for some broad definitions

    I think if we knew before hand what we were looking for while searching for life elsewhere it will become easier to recognize it once it is found, in whatever form it may appear
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  12. #11  
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    The best definition I came across was in a text book on microbiology. It went something like this.

    Life is a complex organised system of organic molecules that undergoes both reproduction and evolution.

    The exact wording may have been slightly different since I am going by memory.

    Personally, I think the two primary characteristics of life are reproduction and evolution. However, some software systems can undergo both, so the added clause relating to organic molecules is there to exclude that software. The word 'complex' was deliberately added to exclude viruses from the definition, which I do not agree with. I think viruses should be considered to be alive, but I think I am in a minority there.

    It is possible that, in future, alien life may be discovered based on silicon chemistry or something else, forcing us to change the definition. However, there is no requirement to come up with a definition that, ahead of time, caters to all possible hypothetical variations. We only need to define life in a way that covers things we currently know to be alive.

    Just a comment before other people start adding spurious characteristics such as excretion, nutrition, movement etc. A fire exhibits all these. A fire can even be said to reproduce. However, it does not evolve. The definition above, therefore, excludes fire.[/i][/b]
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    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    I would define life as a contained system which actively maintains homeostasis. This would exclude viruses, viroids, plasmids, and prions. Which, some people believe should be considered alive since they are biological.
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  14. #13  
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    To tired and sleepy

    There are software packages that maintain homeostasis and are definitely not life. Even an air conditioning unit maintains homeostasis. Thus, homeostasis is not a life definer.
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  15. #14  
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    An air conditioner is an open system though.

    And I think it's adequate to limit ourself to physical homeostasis, I don't believe a software package could be defined as maintaining homeostasis.

    Although, this definition of life is the basis of Lovelock's gaia hypothesis. So, it certainly can be expanded beyond traditionally defined life.
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    Tired and sleepy

    I have a friend who works in a horticultural research laboratory. His job is to manage and run their environmental facility. This is a set of small rooms which permit specific environmental conditions to be maintained, so that plant growth under these conditions can be measured.

    Those rooms are set for specific conditions of lighting, humidity, gas mixtures, temperature and so on. Each is an enclosed space, and maintains homeostasis. I would not call any of those room 'living'.

    In my own laboratory, I have a modified refrigerator, which I use as a kind of incubator. It is thermostatically controlled to a set temperature (28 C) and has a misting unit to maintain 100% relative humidity. It is kept dark, and I carry out experiments in micro-organism growth within. That cabinet meets your definition for life.
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  17. #16  
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    My own personal definition of life is

    Life is a waste of time. Each of us will one day R.I.P. (or not). If someone say make the best of it, by what? having a good time and then still die at the end? Do something and leave a legacy? As if you'll get to feel that people appreciate what you did. If someone say there is heaven or hell after death, please can you die first get into heaven/hell and then come back and tell me if it is real (although I'll still need to gamble on what you tell me is the truth or not).

    Why the negativity? Because i don't know what life is.
    ~ One’s ultimate perfection depends on the development of all the members of society ~ Kabbalah
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  18. #17  
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by Always.Asking
    and i am definitely NOT saying we have discovered life

    i am just asking for some broad definitions
    I am, saying we discoveed life. And I am stating that, as least as far as NASA is concerned, definitions are far too restrictive.

    What was it about my post that did not make this clear? I felt a set of statements such as "We went (to Mars). We found life. We dismissed it." would be difficult to misunderstand. Help me improve my communication skills by telling me what I did wrong.

    To skeptic: the exclusion of viruses reflects the attempt to deal with life on a digital, rather than an analog basis. Digitally we have binary options - life/not life. It is more probable that there are a spectrum of possibilities and characteristic from the clearly alive to the clearly not alive - an analog perspective. Viruses could sit quite comforably on such a spectrum, away from the not life end.
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  19. #18  
    Forum Radioactive Isotope skeptic's Avatar
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    John

    If we exclude viruses, then we also have to exclude the first life that occurred on Earth. Some 3 to 4 billion years ago, out of the primordial soup, arose a self replicating molecule which evolved over time into complex cells, and ultimately into us. At what stage do you say it has become life?

    My view is that, once it is self replicating and evolving, it is life. By this standard, viruses are also life.

    On your statement
    "We went (to Mars). We found life. We dismissed it."
    I can make a couple of comments.
    First : we do not know that life was found. The researchers of the time concluded it was not life. OK. They could be wrong, but I think their statement is the most probable.
    Second : If life was found, then it fits into the definition I posted. Organic. Self replicating and evolving. Probably somewhat similar to bacteria.

    I have thought for a long time, that if we find life on Mars, it will probably be descended from Earth bacteria. We already know that a massive asteroid impact, such as the dinosaur killer, has the energy to throw debris into space and out to Mars orbit. We know that certain bacteria, especially Bacillus genus, make spores that can survive both the acceleration entailed and the vacuum of space. There is no reason why the dinosaur killer could not have sent Earth bacteria to Mars.

    I do not think we will find truly alien life till we get to explore other star systems, and that will not be for 500 to 1000 years. Even then, I suspect it will be very rare.
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  20. #19  
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by skeptic
    John
    If we exclude viruses, then we also have to exclude the first life that occurred on Earth. .
    I'm sorry if my meaning was obscure. I am speaking in favour of an analog view of life, a continuous range (not necessarily, and possibly not ever, all present in the same biosphere) in which viruses can sit comfortably. It is a binary approach that favours definitions that exclude viruses.

    Quote Originally Posted by skeptic
    On your statement
    "We went (to Mars). We found life. We dismissed it."
    I can make a couple of comments.
    First : we do not know that life was found. The researchers of the time concluded it was not life. OK. They could be wrong, but I think their statement is the most probable...
    I just felt like going out on a limb. I think NASA bottled it (is this an expression outside the UK?) I don't mean they put some life in a bottle. I think they panicked at the possibility they'd all been looking for actually being real. That's just an opinion, because if they did find life the other explanations for nay-saying it fit right into conspiracy theory and I detest those kind of nutters.

    The researcher whose experiment showed the strongest indications for life, Gary Levin (IIRC), has never doubted that his experiment found life. The indications from two of the three experiments were such that they would have been considered positive indicators before the mission began. Their rejection was a post hoc decision. Levin and others claim the mass spectrometer was not sufficiently sensitive to detect low levels of organics, such as are found in the Antartic for example. I've never been able to find any reliable refutation of this claim.

    Quote Originally Posted by skeptic
    Second : If life was found, then it fits into the definition I posted. Organic. Self replicating and evolving. Probably somewhat similar to bacteria.
    I was at pains to point out that it was the NASA definition of life that was questionable. In my view they rigged their definition to exclude exotic chemistry that could have explained the experimental observations.
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  21. #20  
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    Quote Originally Posted by skeptic
    I have thought for a long time, that if we find life on Mars, it will probably be descended from Earth bacteria. We already know that a massive asteroid impact, such as the dinosaur killer, has the energy to throw debris into space and out to Mars orbit. We know that certain bacteria, especially Bacillus genus, make spores that can survive both the acceleration entailed and the vacuum of space. There is no reason why the dinosaur killer could not have sent Earth bacteria to Mars.
    Meteors tend to fall towards the sun, not away. We are more likely to have seeded Venus.
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  22. #21  
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    free radical

    You are correct, except that a really massive impact like the dinosaur killer will send fragments in all directions, and it has been calculated (from an article I read a while back. Sorry - lost the reference) that an appreciable number of items would have made it to Mars.

    I am skeptical of the possibility of seeding life on Venus due to its extreme heat. It is possible something might have stayed in the high atmosphere, in cooler regions, but seems a little unlikely to me. I would love to be proved wrong.
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  23. #22  
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    Quote Originally Posted by skeptic
    free radical

    You are correct, except that a really massive impact like the dinosaur killer will send fragments in all directions, and it has been calculated (from an article I read a while back. Sorry - lost the reference) that an appreciable number of items would have made it to Mars.
    And yet, there was no organic material found on Mars' surface.

    Although, recent developments suggest that a chemical in the soil may have interfered with the identification of organic compounds, so it is still theoretically possible that there are minute amounts of bacterial life present.
    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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  24. #23  
    Forum Radioactive Isotope skeptic's Avatar
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    Yeah.
    Perchlorates in the Martian soil under high temperatures would have broken it down to CO2 and water. However, even if those results were valid, the number of bacteria would be likely to be minute. Thus hard to detect. Future studies may reveal more.
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