Did life here begin on Earth, or did it start elsewhere in our solar system, the galaxy, or further? Polymaths like myself love big questions like this, where many disciplines are relevant. This particular question is also a good test case for the "
G, if you look at what organisms do, they take a wide variety of chemicals and find ways to convert them into a much narrower variety of chemicals first. Then they take these building blocks and build all the things they need. It kind of looks like a pair of funnels facing each other.
Simpler, earlier life presumably started with a much narrower set of precursors and built up a narrower set of products. We now have a system to build proteins out of amino acids -- tremendously flexible and efficient for enzymes etc. But strings of nucleic acids can make enzymes too. It would be simpler for life to start out as nucleic acids that didn't yet make proteins but only catalysed chemical reactions that let them reproduce themselves etc.
And we have had laboratory examples of RNA that reproduced itself in a particular environment, one that provides the precursors it needs. I argue that this is life.
Further, some vaguely similar environment is almost certainly where our kind of life started. A place that had lots of nucleic acids freely available and one where they spontaneously linked into chains, and some of those chains had random enzymatic activity, and then some started to reproduce themselves. This environment could have existed on earth -- but it's long gone now, everything that can be used has been re-used many many times since then. Or it could have been somewhere else. But it was probably nucleic acids that did it, and it happened in a place that had most of the building blocks handy and that needed almost no construction work beyond just a rather inefficient replication.
Robin- I'm sorry, I didn't mean to suggest life could not arise.I also recognize that my desire to question certain biases is unusual.I would like to continue with g--as he has been very helpful to me recently, what is the protocol for this? (assuming he wouldn't mind)
Douglas, what result comes from Pasteur and why does it matter that it did? (The synthesis of urea was Woehler, not Pasteur.)
How is the fact that no one has yet synthesized life from non-life evidence that it's impossible? It's evidence that it's not easy, but no one ever expected it to be easy. (Well ... of course it's evidence that it's impossible, just as the fact that I don't have a child called Bartholemew is evidence that it's impossible to have a child called Bartholemew, but it seems to me that it's *extremely weak* evidence. Even the simplest living things are very complicated, and our technology is limited. Why *should* we expect to have been able to synthesize life from non-living ingredients?)
The evidence the other way isn't the mere fact that some guy synthesized urea. It's the fact that scientists looking at the processes of life have consistently failed to find any way in which they are anything other than ordinary physical processes. (The nearest thing to a counterexample is consciousness. I consider most of what's said about the mysteries of consciousness to be mere obfuscation, but even if it were to turn out that consciousness is fundamentally nonphysical that wouldn't indicate that *life* is.)
To put it differently, the evidence that life is a physical phenomenon is rather like the evidence that gravity is: that the planets aren't kept in their courses by angels pushing them in the right directions, etc. And arguing that we should believe life can only come from life because no one has managed to synthesize a living thing from scratch is like arguing that we should believe only angels can keep planets in their orbits because no one has managed to make a solar system and have it work correctly without angels.
Nick-"life is a particular arrangement of matter"This is the assumption that is being questioned.Why should we assume anything other than the evidence in this case?
Life is a particular arrangement of matter. Why should we assume a particular arrangement of matter is impossible to produce naturally, just because we haven't yet been able to reproduce it artificially?
g- that result comes from Pastuer.From TH Huxley (1860)"The proposition that life may, and does, proceed from that which has no life...remained the accepted doctrine of learned and unlearned Europe down to the 17th century."To say the production of urea is the evidence for abiogenesis (which I believe was the chemical used to disprove biogenesis) seems to me an example of the cached thought winning over the evidence. Certainly no one has produced life (or anything like it) from non-life as of today.Steven-Putting the process in space doesn't deal with the main issue.It seems this leads to a paradox-- something that I wish I was better able to deal with. Certainly if life is an irreducible much thinking needs to be re-evaluated-- my attraction to this site in the first place.Is there a contemporary author that deals with this without getting into religious texts?
If we have independent reasons (e.g. Fermi) to believe abiogenesis is improbable, then the fact that life popped up on Earth very soon after conditions allowed is evidence for an extraterrestrial origin:
Douglas, that view used to be universally regarded as true, so just about any author or book before about 1800 would do. It was rejected when scientists started being able to synthesize organic chemicals. I don't understand why the fact that no one has yet made life from scratch should be taken to show that "life can only come from life", and it's hard to see *how* that could be so. Especially as it implies an unattractive infinite regress.
The experimental evidence would indicate that life can only come from life. This seems to be the only valid scientific hypothesis available. (As far as I can tell from my researches the hypothesis of abiogenesis has a mountain of failed experiments as its evidence). I have trouble with this and would like to over come this bias. Where is Kurt Godel when I need him?Does anyone know of an author or a book that accepts this hypothesis as true? (It seems that to make a world view that agrees with the evidence, this is a major stumbling block)
Astronaut[s] ... grew salmonella bacteria, ... Back on Earth, the space-grown bugs were fed to mice. They proved to be nearly three times as likely to cause disease and about twice as deadly as they were before the flight
But that's not evolutionary progress; that's just adaptation to a new set of circumstances: spreading fast and killing hosts is something most diseases evolve to avoid (syphilis used to be a pretty nasty disease that killed all victims within a few years, but benign versions spread farther). I suspect, though, that something adapted to spreading from one planet to the next would be pretty likely to last on any given planet, so a weaker but broader form of the same hypothesis (like "Most planets with life have life that formed on another planet") would be valid.
Expose a microorganism to ionising radiation and its descendents will be more resistant to ionising radiation for some generations with no adaptive mutation involved. They turn on repair mechanisms that are usually turned off. But those repair mechanisms work when the organism is growing, not while it's dormant.
Most of the organisms that are adapted to an evolved planetary system will be unready to deal with a place where there's nothing alive. After a billion or more years adapting the environment to suit themselves, they mostly won't know what to in an abiotic environment. The ones that do best might be things that grow slowly in places that hardly anything lives. If there's a little bit of life growing in comets etc, those might do well colonising comets etc in another system, and expand from there. I don't know how they'd get accelerated to nearly lightspeed so they could get to other systems in a reasonable time, or how they'd survive getting decelerated, etc.
Nick, we can't verify it yet, but presumably we will eventually know if our life started on Earth or elsewhere.
Eliezer, modular unused adaptations will quickly degrade, but unused adaptations that are tied into other used adaptations may last a lot longer.
Martin, the scenario people have in mind is organisms deep inside rocks in space.
Thomas, if the chance is p that life spreads to N planets, and (1-p) that it stays on one planet, then the chance Earth is where our life started is (1-p)/(1+(N-1)p).
Actually, a better example would be spores. Some single-celled eukaryotes in the fungi class can sporulate, withstand dessication, and go dormant for several years. The idea that they could survive a multimillion-year space hike is unlikely, though. My argument stands.
There's also the minuscule probability of spores or anything coming from a solar system light years away. We found a few Martian rocks, but Mars is practically hugging us in terms of space distances. We haven't found any rocks from Pluto. The probability of a rock from another solar system landing here is infinitesimally small.
G, if you look at what organisms do, they take a wide variety of chemicals and find ways to convert them into a much narrower variety of chemicals first. Then they take these building blocks and build all the things they need. It kind of looks like a pair of funnels facing each other.
Simpler, earlier life presumably started with a much narrower set of precursors and built up a narrower set of products. We now have a system to build proteins out of amino acids -- tremendously flexible and efficient for enzymes etc. But strings of nucleic acids can make enzymes too. It would be simpler for life to start out as nucleic acids that didn't yet make proteins but only catalysed chemical reactions that let them reproduce themselves etc.
And we have had laboratory examples of RNA that reproduced itself in a particular environment, one that provides the precursors it needs. I argue that this is life.
Further, some vaguely similar environment is almost certainly where our kind of life started. A place that had lots of nucleic acids freely available and one where they spontaneously linked into chains, and some of those chains had random enzymatic activity, and then some started to reproduce themselves. This environment could have existed on earth -- but it's long gone now, everything that can be used has been re-used many many times since then. Or it could have been somewhere else. But it was probably nucleic acids that did it, and it happened in a place that had most of the building blocks handy and that needed almost no construction work beyond just a rather inefficient replication.
Douglas, g has a website and lists his e-mail address there.
Robin- I'm sorry, I didn't mean to suggest life could not arise.I also recognize that my desire to question certain biases is unusual.I would like to continue with g--as he has been very helpful to me recently, what is the protocol for this? (assuming he wouldn't mind)
douglas and g and Nick, this post is about where life arose, not about whether it is possible for life to arise. You are off topic.
Douglas, what result comes from Pasteur and why does it matter that it did? (The synthesis of urea was Woehler, not Pasteur.)
How is the fact that no one has yet synthesized life from non-life evidence that it's impossible? It's evidence that it's not easy, but no one ever expected it to be easy. (Well ... of course it's evidence that it's impossible, just as the fact that I don't have a child called Bartholemew is evidence that it's impossible to have a child called Bartholemew, but it seems to me that it's *extremely weak* evidence. Even the simplest living things are very complicated, and our technology is limited. Why *should* we expect to have been able to synthesize life from non-living ingredients?)
The evidence the other way isn't the mere fact that some guy synthesized urea. It's the fact that scientists looking at the processes of life have consistently failed to find any way in which they are anything other than ordinary physical processes. (The nearest thing to a counterexample is consciousness. I consider most of what's said about the mysteries of consciousness to be mere obfuscation, but even if it were to turn out that consciousness is fundamentally nonphysical that wouldn't indicate that *life* is.)
To put it differently, the evidence that life is a physical phenomenon is rather like the evidence that gravity is: that the planets aren't kept in their courses by angels pushing them in the right directions, etc. And arguing that we should believe life can only come from life because no one has managed to synthesize a living thing from scratch is like arguing that we should believe only angels can keep planets in their orbits because no one has managed to make a solar system and have it work correctly without angels.
Nick-"life is a particular arrangement of matter"This is the assumption that is being questioned.Why should we assume anything other than the evidence in this case?
Life is a particular arrangement of matter. Why should we assume a particular arrangement of matter is impossible to produce naturally, just because we haven't yet been able to reproduce it artificially?
g- that result comes from Pastuer.From TH Huxley (1860)"The proposition that life may, and does, proceed from that which has no life...remained the accepted doctrine of learned and unlearned Europe down to the 17th century."To say the production of urea is the evidence for abiogenesis (which I believe was the chemical used to disprove biogenesis) seems to me an example of the cached thought winning over the evidence. Certainly no one has produced life (or anything like it) from non-life as of today.Steven-Putting the process in space doesn't deal with the main issue.It seems this leads to a paradox-- something that I wish I was better able to deal with. Certainly if life is an irreducible much thinking needs to be re-evaluated-- my attraction to this site in the first place.Is there a contemporary author that deals with this without getting into religious texts?
If we have independent reasons (e.g. Fermi) to believe abiogenesis is improbable, then the fact that life popped up on Earth very soon after conditions allowed is evidence for an extraterrestrial origin:
http://arxiv.org/abs/astro-...
Douglas, that view used to be universally regarded as true, so just about any author or book before about 1800 would do. It was rejected when scientists started being able to synthesize organic chemicals. I don't understand why the fact that no one has yet made life from scratch should be taken to show that "life can only come from life", and it's hard to see *how* that could be so. Especially as it implies an unattractive infinite regress.
The experimental evidence would indicate that life can only come from life. This seems to be the only valid scientific hypothesis available. (As far as I can tell from my researches the hypothesis of abiogenesis has a mountain of failed experiments as its evidence). I have trouble with this and would like to over come this bias. Where is Kurt Godel when I need him?Does anyone know of an author or a book that accepts this hypothesis as true? (It seems that to make a world view that agrees with the evidence, this is a major stumbling block)
Paul Ewald and Greg Cochran gave a good explanation of how the virulence of germs is determined by how easily they spread here.
Astronaut[s] ... grew salmonella bacteria, ... Back on Earth, the space-grown bugs were fed to mice. They proved to be nearly three times as likely to cause disease and about twice as deadly as they were before the flight
But that's not evolutionary progress; that's just adaptation to a new set of circumstances: spreading fast and killing hosts is something most diseases evolve to avoid (syphilis used to be a pretty nasty disease that killed all victims within a few years, but benign versions spread farther). I suspect, though, that something adapted to spreading from one planet to the next would be pretty likely to last on any given planet, so a weaker but broader form of the same hypothesis (like "Most planets with life have life that formed on another planet") would be valid.
Expose a microorganism to ionising radiation and its descendents will be more resistant to ionising radiation for some generations with no adaptive mutation involved. They turn on repair mechanisms that are usually turned off. But those repair mechanisms work when the organism is growing, not while it's dormant.
Most of the organisms that are adapted to an evolved planetary system will be unready to deal with a place where there's nothing alive. After a billion or more years adapting the environment to suit themselves, they mostly won't know what to in an abiotic environment. The ones that do best might be things that grow slowly in places that hardly anything lives. If there's a little bit of life growing in comets etc, those might do well colonising comets etc in another system, and expand from there. I don't know how they'd get accelerated to nearly lightspeed so they could get to other systems in a reasonable time, or how they'd survive getting decelerated, etc.
Nick, we can't verify it yet, but presumably we will eventually know if our life started on Earth or elsewhere.
Eliezer, modular unused adaptations will quickly degrade, but unused adaptations that are tied into other used adaptations may last a lot longer.
Martin, the scenario people have in mind is organisms deep inside rocks in space.
Thomas, if the chance is p that life spreads to N planets, and (1-p) that it stays on one planet, then the chance Earth is where our life started is (1-p)/(1+(N-1)p).
Actually, a better example would be spores. Some single-celled eukaryotes in the fungi class can sporulate, withstand dessication, and go dormant for several years. The idea that they could survive a multimillion-year space hike is unlikely, though. My argument stands.
There's also the minuscule probability of spores or anything coming from a solar system light years away. We found a few Martian rocks, but Mars is practically hugging us in terms of space distances. We haven't found any rocks from Pluto. The probability of a rock from another solar system landing here is infinitesimally small.