ETs on Earth?

Discuss

19 Responses to “ETs on Earth?”

  1. querent says:

    i maintain that we must always mistrust rigid classification when dealing with the “biological.” it is mutable. even something as seemingly fundamental as “life” need not be well defined.

    then again, i’m a mathematical biologist (in training…and yeah, i’m being smug…humor me). we (the best among us) long ago abandoned the search for the “true” axiom set. maintain flexibility.

    does seem like a good idea, though. if it started more than once here. never have seen evidence that it had. and if it uses dna, i’m skeptical that it’s different. even within the one big tree, the code isn’t uniform. there exist species where codons code for different amino acids.

  2. benher says:

    I find the concept of exogenesis covered in rich creamery panspermia as fascinating as the next guy, but I’m hoping for at least a side dish of science on this one.

  3. kiint says:

    off your trolley?

    • Anonymous says:

      Jonathon Green, in _Cassell’s Dictionary of Slang_ (1998), writes: “The Manhattan trolley, which were not allowed overhead cbles (as were those in Brooklyn) after so many came down in the hurricane of 1888, picked up their supply from an electrified third rail and so if the car became derailed, its power was lost.” It means nuts.

  4. Anonymous says:

    Any life that evolved here on earth – no matter how weird – is by definition NOT extraterrestrial.

  5. nanuq says:

    Isolated biospheres may not stay isolated long enough to evolve really alien life forms. There are very few places on the planet that haven’t been radically affected by continental drift or other factors.

  6. Derek C. F. Pegritz says:

    ANYwhere you have chemistry, you can have some form of “life”–i.e., some manner of replication of more-or-less stable chemical structures. Carbon chemistry just happens to be the best bet because those elements are so ubiquitous–and carbon chemistry can work in just about any environment from planetary surfaces to the hearts of comets (it just works very *slow* in the latter).

  7. sapere_aude says:

    Any form of life, be it alien or terrestrial, has to find some way to encode information. All of the life forms we have thus far encountered here on Earth use DNA/RNA for this purpose. So, suppose that we someday encounter a previously undiscovered life form here on Earth that is truly unique, and that clearly did not evolve from the same primordial ancestors that produced all of the other life forms we have studied. What do we expect to find when we study its biology? There are two basic possibilities: (A) It, too, will be based on DNA/RNA; or (B) It will encode information using something other than DNA/RNA. The latter would be a huge scientific discovery that would force us to completely rethink our understanding of what life is and under what conditions we are likely to find it. But the former would also have important implications: It would strongly suggest that DNA/RNA is ESSENTIAL for life (at least under earth-like conditions), and that we are unlikely to encounter any alien life forms that are not based on DNA/RNA. So, searching for earth-based life forms that have unique evolutionary origins does seem to be a potentially valuable research agenda.

  8. coop says:

    @sapere_aude

    But how would we know if it’s “life” then.

    “It’s life Jim, but not as we know it.”

    ;-)

  9. SteveNZ says:

    @Sapere_aude: Don’t forget the possibility that life might be based on DNA/RNA, but use the available code strings to produce completely different amino acids from those we’re familiar with. The genetic code we use — where ‘we’ means just about all life on Earth — appears to be arbitrary. An extraterrestrial life form, even if was DNA based, would certainly be very different from us (unless Hoyle/Wickramasinghe notions of panspermia turn out to be correct).

    In practical terms this would mean (among other things) that even DNA-based life forms, if independently evolved, would be mutually poisonous in a big way; I’ve often thought that the first thing you’d notice when being abducted by aliens would be the stench your olfactory organs would detect caused by unexpectedly levo molecules that should be dextro, and vice versa.

    You’ll understand that this gives me a pretty jaded attitude to all UFO stories, and even most science fiction — how those humans, Vulcans and Klingons manage to share the same mess halls, or even pajama-style uniforms, has baffled me for years.

  10. sapere_aude says:

    @ both coop (#5) & phisrow (#6): Those are both excellent questions; and they are closely related to each other. (A happy coincidence that your two posts showed up together.) Could prions be a life form; and how could we tell? Obviously it depends on how we define “life”. (There’s still a lot of debate among biologists as to whether or not viruses qualify as genuine life forms; so “life” is not easy to define.) If we simply assume that life is DNA/RNA based, and that anything that is not based on DNA/RNA cannot be a genuine life form, then we are begging the question. But, if we use the simplest possible definition of “life” — innate capacity for reproduction and evolution — then it would appear that both viruses and prions ought to qualify as life forms. Therefore, prions would indeed be non-DNA/RNA based life forms. (But I don’t think that most biologists currently regard prions as forms of life.)

    • chenille says:

      I don’t think most would regard prions as actually replicating themselves, instead of being passively replicated by their host. There’s of course no definite line, but using their own energy would be a good step.

      • sapere_aude says:

        @chenille: You make a good point. I think that the first step in the search for “alien” forms of life (either here on Earth or in space) has to be to come up with a suitable definition of “life” that is broad enough to include all of the different life forms that we may actually encounter, but is narrow enough to exclude anything that we wouldn’t intuitively regard as being “alive”. Yet that definition has to avoid the danger of “begging the question” by simply assuming that alien life will be similar to the DNA/RNA-based life we are most familiar with. The ability to reproduce may be the first criterion; but it can’t be the only one. (Should we regard computer viruses as forms of life?) Assuming I understand you correctly, then I think I agree with your criterion that life forms must be able to use their own energy — i.e. they must be able to store energy internally, and then run on that stored energy, rather than passively relying on external forces.

    • sapere_aude says:

      Oops, make that coop (#6) and phistow (#7). [Apparently some posts were added above yours after I posted my reply. I still haven't quite got the hang of how BoingBoing manages, arranges, and numbers its comments.]

  11. Anonymous says:

    I, for one, welcome our new off their trolley overlords.

  12. McGrude says:

    I read a fantastic book on the subject called “Life as We Do Not Know It” by Peter Ward. http://www.amazon.com/Life-We-Not-Know-Synthesis/dp/0143038494/ref=sr_1_1?ie=UTF8&s=books&qid=1264449301&sr=8-1

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