5 votes

Meteorites could have brought all five genetic 'letters' of DNA to early Earth

2 comments

  1. CALICO
    Link
    This is more of a tangential thought, (and I may well go off track, sorry) but this topic has brought it back to the front of my brain—and perhaps it'll yield some interesting discussion here: the...

    This is more of a tangential thought, (and I may well go off track, sorry) but this topic has brought it back to the front of my brain—and perhaps it'll yield some interesting discussion here: the focus on panspermia over abiogenesis in some circles always seemed a little odd to me.

    As I understand it, our current understanding of the early ocean, deep sea thermal vents, and chemistry, allow for abiogenesis to work without any major complications. Those same understandings could easily apply to other celestial bodies, given similar conditions, which allows for the possibility of extraterrestrial life to similarly arise from the nonliving-matter of their "host" "body".

    Why is so much intellectual labor being put into panspermia-related research, when (correct me if I'm wrong) there's nothing wrong with our current theories surrounding abiogenesis?

    The concept of life on, Earth, for example, arising from specific molecules or sometimes simple organisms present on a space rock/dust, colliding with the atmosphere and seeding the planet.. that always seemed to me like kicking the can. One would then have to explain where that stuff had come from.

    This article does provide me with a satisfying explanation for that, however. So now I can see some more merit.

    But, now I have more thoughts. If life were seeded on Earth from space, then for it to be a successful seeding the environment the compounds arrive at would have to have the appropriate prebiotic conditions & raw materials available to allow for the chemical reproduction of these compounds to occur, and thus allow for our understanding of early evolution to then take place. Does this now over-complicate things in contrast to our current theories regarding abiogenesis? Deep sea thermal vents are already heated chemical factories in an aquatic environment.

    My understanding is that we currently believe that life only began once on Earth (or at least, any other potential life seems to have died out & we haven't found evidence to suggest its existence). Is it not more likely it began around a thermal vent in the ocean, or some similar environment of early Earth, than it is to suggest meteorites or their debris ended up in a part of the Earth with the appropriate chemicals and conditions to then self replicate?

    It would also seem to make the successful seeding of other celestial bodies similarly more problematic, if they then as well must have these same prebiotic conditions and the statistical chance of the appropriate space debris making it to the appropriate location. Wouldn't that lower the overall probability of life (as we understand it) on other worlds, compared to if these worlds were "permitted" to have their own abiogenesis in their own thermal vents (or whatever)?

    I suppose there's validity in putting energy into this if we're thinking about the forms life can take, and if life NEEDS to be built from A/T/C/G/U, or if a hypothetical extraterrestrial life-form could use different chemicals, arranged in something unlike the DNA or RNA molecules. I understand that carbon based life is the only form of complex life that is theoretically stable, or likely. So I guess it would be natural to then ask if the form that carbon based life has taken on Earth, is the only way life can work.

    Finding all the nucleotides in space is interesting, but doesn't seem to answer anything on its own, right? Not for my questions anyway.

    I guess then abiogenesis and panspermia are both firmly on the table, but the body of evidence & the logic behind abiogenesis still far outweighs panspermia to me. Absent of any examples of extraterrestrial life that we could examine on a molecule level, we can't know for sure if life needs to be DNA & RNA made of A/T/C/G/U or not.

    Personally, I take the fringe position that life must be carbon-based; use DNA/RNA; be built on nucleotides generally, if not A/T/C/G/U specifically; that life might have originated on Earth multiple times & we would be hard-pressed to tell through genetic analysis, because life can only be built this way, the conditions of Earth are the conditions of Earth, and the results between an evolutionary tree with one trunk, or several, would appear (and may actually be) nearly identical; and that we can use life on Earth as an excellent model of what to both look for and expect in any potential extraterrestrial life. That is, not that aliens would be like Star Trek—basically human with latex forehead prosthetics. (although I can make an argument for the selective pressures for intelligent bipedal "humanoids"), but that extraterrestrial life would be identifiable to us as life. We would recognize it for life, and unless it evolved in an environment very different from conditions we find on Earth (from the mundane, to the extreme), then it would appear no stranger than a virus, a unicellular organism, or a fungi, mammal, reptile, etc. and no more bizarre than what we see in the midnight zone of our oceans, or anywhere throughout the evolutionary record.
    There's an asterisk in here somewhere, regarding mitochondria, and the probability of that happening *at all *, here, regardless of the potential for something similar to happen elsewhere, but I'm already brain-dumping a wall of text, so.

    So from that standpoint, this article is interesting to me because it shows some level of prevalence towards nucleotides existing outside of the Earth. Specifically having a celestial origin implies some lack of rarity in the nucleotides existing, just generally. That raises the likelihood of them existing on say, a stable enough body, for long enough, to be allowed the potential to undergo evolution in some form. I find it suggestive (w/r/t my above position) that we're finding these bases, but not much more there.

    I don't really know where to go from here, this was entirely stream of consciousness.

    Thoughts?

    4 votes