[HN Gopher] A Wrinkle in Nature Could Lead to Alien Life
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A Wrinkle in Nature Could Lead to Alien Life
Author : rbanffy
Score : 47 points
Date : 2021-04-26 16:46 UTC (6 hours ago)
(HTM) web link (nautil.us)
(TXT) w3m dump (nautil.us)
| unnouinceput wrote:
| Quote: "Even after millions of years of evolution, that continent
| has less genetic diversity in its flora because of its single
| common ancestor"
|
| I disagree with this. After each extinction event, even after the
| one who vanished 80% of existing species, geological studies
| showed that evolution only need ~10 million years to have the
| same diversity as before (https://en.wikipedia.org/wiki/Permian%E
| 2%80%93Triassic_extin...).
| piyh wrote:
| 80% of the species was gone, but that's doesn't mean 80% of the
| genetic distance from species to species was wiped out.
|
| You could cull from all the branches of the tree of life evenly
| and keep wild genetic diversity vs killing off everything
| except for certain plants and bacteria.
|
| The genetic diversity of a new continent would be highly
| dependent on the founder. If the founder has near perfect
| genetic replication and long lifespans measured by the century,
| the genetic diversity will be less than if you drop something
| that divides every half hour into a virgin pond.
|
| You're also using extinction events on earth as a anchor point
| for the discussion where the entire point of the article is
| that our starting conditions as a civilization are not directly
| transferrable to considering other alien life.
| ajuc wrote:
| to be fair any advanced life will probably carry simpler,
| quickly replicating life with it
| joshuahedlund wrote:
| > For one thing, if you were an advancing species some 12 billion
| years ago (an era where there's reason to think that biological
| life as we know it might have already been possible)
|
| This was eyebrow-raising for me, as I thought the consensus was
| advanced civilization was only "recently" possible due to the
| lack of heavy elements in the first generations of stars. The
| article fleshes out this claim a bit at the end...
|
| > During the period when biochemistry could have first got
| underway--some 100 million years after the Big Bang--the heaviest
| elements were woefully scarce as the first generations of stars
| forged new atomic nuclei.
|
| > Bereft of those atoms, terrestrial-sized planets might have
| wound up as "carbon worlds,"4 chemically rich in some ways, but
| with a severe shortage of some of the heavier elements that
| today's life fully relies on. Life could have gotten going, but
| with different restrictions and imperatives.
|
| ...but still seems to be making a giant unsupported leap from
| "life may have been possible without heavy elements" to "advanced
| civilization may have been possible without heavy elements"
| bena wrote:
| A large problem with any of this is that we have a very, very,
| very limited dataset with regards to life.
|
| We know of one planet, in one solar system, in one galaxy that
| supports life. And it is incredibly hard to collect data from
| other planets in our own solar system much less data from other
| solar systems and other galaxies may be impossible to get any
| meaningful information with regards to the existence of life.
|
| But it's also the only data we have to go off of.
|
| So the best we can say is that _this_ couldn 't have happened
| in those conditions.
| dheera wrote:
| Agreed. I would think that silicon-based life is possible and
| would require an entirely different set of elements to
| sustain.
|
| I would argue that a better definition of life should be
| based on (a) entropy and (b) propagation. Living systems (a)
| actively counteract entropy-increasing forces within their
| system as long as they are alive, and (b) are able to
| propagate indefinitely given the necessary energy inputs.
|
| I've heard other definitions of life including dependence on
| water and I think those aspects should not be part of such a
| definition.
| dotancohen wrote:
| I agree with you, but the counterpoint is that anything other
| that _this_ might not fit any defensible definition of life.
| adrian_b wrote:
| Life as we know it cannot start without at least iron, cobalt
| and nickel, besides the 5 lighter elements H, C, N, O and S.
|
| Iron, cobalt and nickel are the minimum set of elements
| required as catalysts and, as far as we know at this time, life
| cannot appear without them.
|
| Actually life can appear using Fe, Co & Ni, when both
| dihydrogen and carbon monoxide are available in the
| environment. When only carbon dioxide is available instead of
| carbon monoxide, molybdenum or tungsten becomes also necessary.
|
| So at least the elements around the iron peak are needed, which
| are produced in supernovas. Realistically, for the evolution of
| more complex life forms, also a few of the heavier elements
| that are produced in intense neutron fluxes are also required.
|
| So no, according to current knowledge life was impossible 12
| billion years ago and I cannot see any workaround, because the
| catalysts are at least as essential for life as the light
| elements that compose the bulk of the living matter.
| 1_person wrote:
| My understanding is that the earliest stars would have begun
| to form only a few hundred thousand years after the event and
| begun to explode not terribly long after that on account of
| their mass and rapid reaction rate, seeding the early
| universe with some amount of nucleosynthesis product almost
| from the outset.
|
| Of course, I think it was rather a while longer before it
| cooled down enough for things other than raging thermonuclear
| fireballs to find hospitable.
| Gatsky wrote:
| The workaround is that we are totally wrong about theoretical
| predictions stretching back billions of years.
| rbanffy wrote:
| > according to current knowledge life was impossible 12
| billion years ago
|
| At what point in time we can expect the first supernovas to
| seed planets with heavy elements?
| mrfusion wrote:
| How does all life use tungsten? I've never heard of that.
| adrian_b wrote:
| I have said "molybdenum or tungsten".
|
| Most living beings use molybdenum, but tungsten can replace
| molybdenum and it is used for this purpose by some living
| beings (mostly by Archaea).
|
| It is pretty certain that the common ancestor of all
| existing living beings already had molybdenum enzymes,
| while tungsten began to be used later, as an adaptation to
| higher temperatures.
|
| Nevertheless, there was a hypothesis that maybe before the
| oxygenation of the oceans tungsten was used in preference
| to molybdenum, because oxygenated molybdenum compounds are
| more soluble than oxygenated tungsten compounds while in
| reduced environments their solubility properties are
| reversed.
|
| However this hypothesis is most likely wrong, because it is
| contradicted by the distribution and phylogeny of the
| molybdenum enzymes and tungsten enzymes, which are
| consistent with the universal use of molybdenum already
| much earlier than the evolution of the ability for water
| photolysis and with the gain of the ability to use tungsten
| as an alternative only in certain archaea and bacteria.
|
| The earliest life forms were probably dependent on having
| ammonia and carbon monoxide in their environment, as
| sources of carbon and nitrogen, in which case molybdenum is
| not strictly needed.
|
| The use of molybdenum enzymes enabled the use of the more
| abundant carbon dioxide and dinitrogen as sources of carbon
| and nitrogen. This achievement must have happened some time
| before LUCA (last universal common ancestor), which already
| had these enzymes.
| joshuahedlund wrote:
| Thank for those details.
|
| (And yes I get the arguments that "things could happen that
| are outside of our capacity to imagine" but while true at
| some levels it can only take you so far with fundamental
| finite properties like the number of elements in the periodic
| table and the compounds you can make with them)
| karmakaze wrote:
| The post is presenting scientific ideas to fuel a hypothetical
| Hollywood plot.
|
| > Our fairytale concepts of "galactic empires" could be woefully
| too conservative.
|
| > theoretical possibilities for the fundamental parameters of
| nature to vary
|
| > Room exists for future surprise.
|
| > Even without these exotic possibilities, we know for sure that
| the environmental properties of the universe have changed since
| those same early times.
|
| Right. The consequence is present without the premises. Any
| discovered alien life would likely be vastly different or at
| least vastly technologically progressed.
| Semiapies wrote:
| The idea of any system, much less a society and state, lasting
| for hundreds of billions of years in any recognizable version of
| itself is dubious. The idea of any relativistic society
| functioning as a thing over vast stretches of the observable
| universe is also dubious. The variations time and space would
| bring would make worrying about alien competitors beside the
| point.
|
| But even granting those premises, any early-universe super-
| civilization would eventually be cut off from its own distant
| reaches by expansion. This would be true of any civilization that
| expanded to its observable limits.
| rbanffy wrote:
| A relativistic society can't function as a cohesive whole with
| humans when the round-trip time exceeds a human life. Other
| lifeforms would be different, as their timescales would not be
| the same as ours.
|
| > This would be true of any civilization that expanded to its
| observable limits.
|
| If stable traversable wormholes are at all possible, I'd expect
| one such civilization to be able to use networks of those to
| remain connected. Even if matter couldn't traverse them,
| information could.
|
| But, then, if they resemble us in this sense, isolation will
| probably make them diverge.
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