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Origins of Life

  1. Feb 7, 2004 #1
    I was thinking about the idea that we originated from a basal group of animals and plants. I saw a program that traced the DNA from a sea sponge, showing it to be an ancestor to a large diversity of life including us.
    My question is, sea sponges are rather complex life forms, so where do we look for cells or molecules, which are evolving from the first processes? Water seems to be where life originates, so does new life appear continuously? I think if we look around we may see the first formations of life.

    After reading some threads, some people think life may have come to earth from space, which is something I don’t want to go into here. Our planet for starters has all the right conditions for life to start.
  2. jcsd
  3. Feb 7, 2004 #2
    Life originated in very different condition and has survived through very different conditions. Life is over 3.5 billion years old, so no we will not find evidence of the original life form.

    There are, however, many different theories. All the way from the primordial soup to life arriving from other plants to the theory of creation.

    But, at this point in time, theories will be all you get.

  4. Feb 8, 2004 #3

    Sounds pretty close minded to me. Why should life only originate around that period, 3.5 billion years ago? There are plenty of species alive today such as sea sponges which preserve their basal DNA record.
  5. Feb 8, 2004 #4


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    But sea sponges are already highly developed organisms: they symbolize the switching point from unicellular to multicellular organisms.

    Cyanobacteria or certain types of algae are more primitive, but still complex. What you won't find today is how the first cell evolved or how the first biosynthetic reactions evolved.. only in the lab can this be reproduced, the problem there is: how do you reproduce million years of evolution in a decade?
  6. Feb 8, 2004 #5
    So there must be some process towards the beginning of the earth’s formation which causes life to evolve? I don’t understand how, unless the different composition of elements on earth made it more likely for those first cells to evolve.
    What I can understand is that the period of evolution from that first cell, to self-replicating cells, is probably the slowest in the evolutionary process.

    Why should we assume the reactions that occurred to form the first cells, aren’t still happening? What do they actually do in the lab that causes those reactions to evolve into cells?

    Depends where you look I think, some places might still have the right conditions.
  7. Feb 8, 2004 #6


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    If I remember it correctly, all of earth's oxygen was bonded to iron. There was no free oxygen: a very toxic molecule to cells. Even today, if you prevent oxidative metabolism (reduced caloric intake) you'll live longer.

    So that is one main factor very different now from then. Also, think about the temperature. Or the fact that all basic materials are now being used by countless organisms, there is high competition. Back then there was no competition for nutrients thus lots of space to experiment.
  8. Feb 8, 2004 #7


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    According to my textbook:

    Major events that are believed to have occurred during the evolution of living organisms on earth.

    4.6 BYA formation of Earth
    4.4 BYA formation of oceans and continents
    3.7 BYA first living cells
    3.6 BYA first photosynthetic cells
    3.4 BYA first water-splitting photosynthesis releases O2
    1.8 BYA aerobic respiration becomes widespread
    ..at the same time start of rapid O2 accumulation (Fe2+ in oceans used up)
    1.6 BYA origin of eucaryotic photosynthetic cells
    0.7 BYA first multicellular plants and animals
    0.5 BYA first vertebrates

    During the first 2 billion years after which life appeared, all oxygen was thus dissolved with abundant ferrous iron. Now 20% of the atmosphere is composed of O2.
  9. Feb 8, 2004 #8


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    Also an interesting note, it took 3 billion years to go from unicellular to multicellular organism.. but it took only 0.2 billion years to go from multicellular to vertebrate
  10. Feb 9, 2004 #9
    Alternate physical substrates for life

    In our case, it appears that life as we know it may have emerged via auto-catalytic loops of molecular interactions in a chemical soup.

    If true, this is surely one of the most fundamental realizations of out time!

    Complexity/Emergence concepts suggest that life could theoretically arise on alternate substrates, providing that the required elements of positive feedback and constraint are present.

    Interestingly, there is another physical system that also provides an environment capable of supporting auto-catalytic loops. That system is less complex and more fundamental than chemistry, not dissimilar it, and also a pre-requisite for it.

    That system is the one which governs the evolution of chemical elements, via nuclear reactions, occuring inside stars.

    The system is discussed in http://www.europhysicsnews.com/full/14/article1/article1.html by M.G. Edmund . To me, the paper is very clear and interesting, do not be put off by a couple of typograpical malfunctions.

    It is natural to ask whether the auto-catalytic loops that arise on this alternate substrate could support any form of evolution/life? (Echoing Science Fiction concepts of “intelligent suns”, or at least a stellar environment capable of supporting competing life-forms)

    Given the high energy densities present, any such substrate might support a very complex (rapid, high-resolution) environment.

    Is there some form of factal relationship between the auto-catalytic loops in the nuclear environment and those of our own environment based on chemistry and molecular biology?

    Can we recognize a single system, an unpwards-growing pyramid, the lowest levels including:

    Nuclear Physics
    Molecular biology

    Higher levels seem to involve more complex organisational entities and systems, i.e. Cells, Multi-celled organisms, Families, Groups, Species, Ecosystems, etc.

    Can we detect systematic recursive (fractal-like) relationships across some or all of these levels?
  11. Feb 9, 2004 #10
    It's believed that the early atmosphere of the earth was reductive in nature. Lots of ammonia, no oxygen. If you remember your sort of broad biochemistry if you want biosynthesis to take place, you need reductive power. That's "reductive" in the chemical oxidative/reductive sense. It was these conditions that Urey and Miller used to show amino acids could be synthesized abiotically, and subsequent experimenters used to make even more impressive biomolecules. Obviously the atmosphere is not like that anymore, although there's much speculation about whether or not deep sea vents could still be doing the job.
  12. Feb 9, 2004 #11


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    As suggested above, the theories about the formation of first life on Earth (abiogenesis) are still in the works...evidence is being gathered, but there is no single, strongly-supported theory to explain it yet.

    As far as new life forming, there's one big problem...the niche is filled. New life from non-life would start at the very simplest form. Modern day bacteria, with 4 billion years of fine tuning from evolution in their DNA, would make a quick breakfast of any newcomer.

    In order for a newcomer to succeed at any level (self replicating molecule, bacteria, plant, animal, fungi, etc.) it would either need to find a new niche with no competition or outcompete whatever organism is already in that niche. With abiogenesis, the latter is unlikely. The former is also unlikely on the microbial scale given that bacteria are everywhere.
  13. Feb 9, 2004 #12
    Reply to Vast

    If the auto-catalytic loop based theory is right, then there is a continuum between ordinary chemical reactions and life, and life is constantly evolving all the time de-novo, in every area where chemical reactions occur, but it will almost always fail due to a paucity of complexity in the environment, and ultimately from competion with more sophiphisticated (already evolved) organisms as discussed above.

    Brief explanation of my version of the auto-catalytic loop theory:

    Imagine a chemical soup in a fixed size container with many different compounds in it (ideally including carbon, hydrogen, oxygen, nitrogen).

    Map the chemicals in the soup into a conceptual 3-d array, so each unique element or compound has a spot in the array.

    Within the soup, each chemical has electric fields around it, and these fields influence the probability of chemical reactions taking place in it's vicinity, usually by a very small amount, but in a few case (as in a catalytic reaction between nearby molecules) by a lot.

    Thus every chemical in the soup influences the rate of formation of every other chemical in the soup, although usually by a very very small amount. The influence may be positive or negative, and varies dramatically by distance.

    We can represent the influence of one chemical on the rate of formation of another by a line on the map. If the influence is negative, we can color the line red, and if it is positive we can colour the line green. We can make the thickness of the line represent the strength of the influence. Most lines will be almost infinitely faint, but a small proportion will be clearer.

    Now the key part: some green lines will form loops. For example where chemical (A) increases the rate of formation of chemical (B) which influences the formation of chemical (C) which increases the formation of chemical (A) again, in a closed loop.

    Each loop is a positive feebback loop, only limited by the resources available and competition for those resources from other green loops.
    (Red loops also form, but these are negative feedback loops, and not so interesting).

    So as time progresses in the soup, molecules which co-operate by assisting each others formation via green loops will tend to become dominant in the soup, because they will "out-compete" other molecules that are not components of green loops. Molecules in red loops will become less common. Simpler elements and chemicals will tend to disappear (get used up).

    Thus the soup provides reproduction (of specific molecules) and competition (for raw materials).

    One more key item: often green loops will have alternate pathways, in other words they will not be simple loops, but will have branches via other compouns that mean the loop is actually a set of branching loops which overlap and rejoin in complex ways. As one specific chemical resource is depleted, loops will tend to operate via alternate pathways that use different resources. So the loops almost have an existence of their own.

    Also, different loops can form cooperative loops with one another, in super-loops.

    Since a molecule's effect on other molecules in the soup is much greater when they are closer together, there is an incentive to evolves so different molecules are somehow held together in a more concentrated soups, so some sort of 'bag' to keep sets of co-operating molecules together would be a very effective way to beat the competition. Thus single celled organisms evolve, but clearly a lot needs to happen before that can take place.

    The beauty of this understanding is that is automatically creates life as a co-operative set of intereacting molecules of different types right from the start. There is no need to worry about whether the first life bas RNA-based, Sugar based or Lipid-based. By this theory it _starts_ as a co-operating mixture and carries on from there.

    Another deduction that can be made form this theory is that this simplest of all life is happening all the time whenever chemicals can interact.

    You could argue that it is not life, but you can't really argue that it does not lead smoothly and continuously to life, so where is the dividing line? - we have reproduction, competition and variation, essential ingredients, we even have an ecosystem.

    Another important deduction, life will eveolve automatically and naturally whenever an appropriate environment is present, and it starts immediately. Thus we would expect to find life in every feasible environment in the universe. It is simply a question of how sophisticated and complex it has become in that environment.
  14. Feb 9, 2004 #13
    Slight refinements to auto-catalytic post

    1. The green and red lines should ahve arrows associated with them, showing the direction of influence, then loops have all their arrows head to tail.

    2. There are more complex intereaction where combinations of different or similar molecules affect the rate of formation of another molecule. This is difficult to map, but does not invalidate the basic concept, although it does complicate it.
  15. Feb 10, 2004 #14
    Thanks for the replies everyone.

    After giving it some thought, I can see how the explosion of life may leave little room for any new cells to form, although I think it is presumptuous to say that it cannot still occur, After all many volcanic regions may provide the right conditions?
    In any case, it seems consistent that any planet given the right conditions, will automatically trigger life to begin.
  16. Feb 11, 2004 #15
    Yes, it has been known for a while that there are certain organisms that "begin" life after the destruction of a volcanoe.

  17. Feb 11, 2004 #16


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    Presumptuous perhaps to say it's impossible. But life on Earth seems to bear this out as all species seem to share a common ancestry (same type of genetic material).

    Let's hope we can test his hypothesis (sure, we're trying to on Mars, but NASA is looking at cutbacks for missions to Jupiter's moons and for more powerful telescopes to see into other star systems).
  18. Feb 11, 2004 #17


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    You answered your question before you asked it! It took a long time. So even if it is still happening today, the chances of us observing anything useful in our human timescale are small.
    Grrr. We really can test these things if NASA (Bush) gets its priorities straight.
  19. Feb 13, 2004 #18


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    Exactly. I don't think he wants to know the answer.
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