[HN Gopher] Computer models suggest modern plate tectonics due t...
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Computer models suggest modern plate tectonics due to blobs left by
collision
Author : rbanffy
Score : 58 points
Date : 2024-05-08 16:06 UTC (2 days ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| Aerroon wrote:
| This could be pretty bad news for finding complex life in space.
|
| The stability of Earth's carbon cycle is thought to be (partly) a
| result of plate tectonics. Carbon gets trapped in rocks and
| volcanoes emit carbon again.
|
| Venus doesn't seem to have plate tectonics. One consequence of
| this is thought to be that volcanoes are much more common on
| Venus. It's also thought that 300-700 million years ago Venus
| went through a resurfacing event where basically the surface of
| the planet was replaced (the floor is lava).
|
| If the above is true and plate tectonics is a result of a
| planetary collision then life like ours should be even more rare
| than we thought.
| Pet_Ant wrote:
| What was the surface of Venus like before that?
| Aerroon wrote:
| I don't know. I'm unsure whether scientists do either.
| Chances are that it wasn't really any different than it is
| now. The resurfacing means that the surface is new - many
| fewer impact craters.
| rbanffy wrote:
| Venus' rotation is quite weird, could it be the result of
| an impact?
| duluca wrote:
| That's the fascinating thing about lava/magma's power to
| simply erase what was there before. Plate tectonics does a
| similar thing when continents scrape each other clean. For
| all we know, Earth had an advanced civilization on it way
| before us and we'd have zero ways of knowing about it.
| Evidlo wrote:
| Some bits of landmass have been around for a few billion
| years. From this we have atmospheric records that rule out
| a large industrial civilization.
| tifik wrote:
| Wouldn't large body collisions be a fairly common occurrence in
| young planetary systems though?
|
| Of course any additional condition makes life rarer, I'm just
| thinking this one might not make it rarer by as many orders of
| magnitude as it might look like at first glance.
| jvanderbot wrote:
| And yet - where's all the plate techtonics in our solar
| system? Only 1 of four inner rocky planets seems to
| experience it.
| jajko wrote:
| Out of what, 500-1000 billions of planets just in milky
| way? I dont think folks do realize how big those numbers
| are. And there is no reason to ignore rest of the universe
| if we talk about probabilities and statistics
| dartos wrote:
| Tbh even if the number of life sustaining planets in the
| galaxy goes from 400B to 350B, that's still rarer than we
| thought.
| jvanderbot wrote:
| It's just another fraction to multiply in the drake
| equation. Start with planets, cut down to rocky ones,
| only in habitable zone, only rotating a certain way, only
| with plate techtonics, etc etc.
|
| Or using your numbers, 1/4 factor eliminates 750 million
| possible candidates. That's not a happy thought.
| eep_social wrote:
| Yeah but 25% of a few hundred billion (planets in the milky
| way) is still a fair lot of opportunities.
|
| "Space is big. You just won't believe how vastly, hugely,
| mind-bogglingly big it is."
| jvanderbot wrote:
| Well I suppose it's fair to say that only 1/8 planets has
| plate techtonics, and AFAIK, none of the dozens of moons
| either.
| MPSimmons wrote:
| I thought Titan did (though in that case, I think it's
| more ice quakes)
| eep_social wrote:
| I think the point is that we know the numerator today is
| one, and no matter how much you cut down the denominator,
| increasing the numerator to two would be a huge deal.
| Conversely, given that we think the denominator
| approaches a small infinity, it seems implausible that
| the numerator is actually one.
| jvanderbot wrote:
| Well that's not my point.
|
| Right now the denominator is about 10 trillion.
|
| A single 1/10 factor makes it 1 trillion. 10-ish more
| factors and we're down to a small number of planets
| before we even consider the emergence of life and
| likelihood of propagation.
|
| There are likely many more 1/10 factors: Habitable zone,
| diurnal cycles, billions of years of geological peace,
| sufficient water, a stable moon (maybe only one), a
| particular spectra of the star ...
|
| all those were "well they seem to happen to 1/10 or 1/100
| planets" _individually_. They cut down the space quickly
| when combined.
| irrational wrote:
| But, the 2 may be on the other side of the universe, or
| even past the cosmological horizon. And since FTL speed
| travel is almost certainly impossible, it may very well
| always be 1 to the best of our knowledge.
| eep_social wrote:
| That's what makes this discussion so fun ;)
| TomK32 wrote:
| Even 1 in a million (planets) would allow for 100
| thousand solar systems in the 100 billion stars strong
| galaxy to have at least one tectonic active planet; not
| counting moons.
| jvanderbot wrote:
| As stated in another thread, it's yet another 80%
| reduction in the number of habitable worlds. On top of
| all the factors, the exponential decay is pretty steep.
|
| That's just the nature of the drake equation. It's very
| much a geometric series and if all factors have to line
| up with 1/10 odds, you only need 10-ish "vital things" to
| cancel basically all chance of life except earth.
|
| And here we have a hypothesis which might be about 1/10
| odds and might be vital. 9 left. Water? Diurnal duration?
| Spectrum of star? A billion years of peace? A moon? A
| magnetic field? There's potentially lots of factors.
| eep_social wrote:
| Seems to me like "basically" is doing a lot of work, that
| leaves behind what.. a few billion planets?
| jvanderbot wrote:
| "basically" is doing only what I suggested: a geometric
| series.
|
| Here's exactly what work it's doing:
|
| Pretend there's 10s of trillions of planets. That's 10-13
| zeros depending on whose estimate you trust most.
|
| 1/10 factor cancels one zero.
|
| at _most_ 13 factors accumulated means you have 1
| habitable planet out of all those planets.
|
| We have just hypothesized a 1/10 factor in this thread -
| that leaves 12 more - and I've lised 6 more off the top
| of my head.
|
| It's just a fermi question - ballpark estimates like that
| are a way of thinking of the relative scale. A 1/10
| chance seems like it leaves a lot of planets left (as you
| say - 100s of billions), but there are already many 1/10
| factors floating around.
| delta_p_delta_x wrote:
| The Milky Way alone has about 2.5 x 10^11 stars. The
| Andromeda Galaxy has around 10^12. Let's take 0.5 x 10^12
| stars on average per galaxy.
|
| There are about 2.5 x 10^11 galaxies in the observable
| universe.
|
| This gives us around 10^23 stars in the universe to
| fiddle with. Assume every star has an average of 2
| planets; some have more, some have none.
|
| This is a pretty large number to trim down.
|
| I'd argue the Drake equation is excessively conservative.
| Note that when microbial life first emerged on Earth 4.1
| billion years ago, the Earth's atmosphere was rather
| reducing, and the Sun was around 30% less luminous than
| it is today. There was free water, but no free oxygen,
| and an extremely high-pressure CO2 atmosphere.
|
| The universe is arguably extremely young; the longest-
| lasting stars will only burn out around 10^13 years from
| now, and the universe is barely 10^10 years old. It's
| fair to say that many sun-like stars _haven 't even
| formed yet_.
| jvanderbot wrote:
| You can zoom out arbitrarily far to increase the odds,
| sure. But for discussion purposes i limited to our
| galaxy's 10^10-ish hypothesized planets.
| eep_social wrote:
| Right but the unstated assumption that there is no other
| positive path isn't any more well-supported than the
| converse. For example, observe the variety of life we
| have locally. I'm thinking particularly of the various
| life (or life-like but I digress) that exists in extremes
| like thermal vents or under-explored places like deep
| soil. So maybe it does eliminate 1/10 but maybe we forgot
| to add the other 1/10 for life that wants to live at 100C
| (or whatever) -- I'm pushing back on your assuredness,
| not the math.
| burkaman wrote:
| Only one does at the moment, but others might have in the
| past.
|
| Mars: https://en.wikipedia.org/wiki/Tectonics_of_Mars
|
| Venus: https://www.nature.com/articles/s41550-023-02102-w
| jemmyw wrote:
| Extra conditions like this mean that the path we took would be
| rarer but doesn't necessarily make life any more rare. There
| could be plenty of other pathways to a stable carbon cycle. Or
| it might not even be a prerequisite, you could imagine a
| scenario where life gets a foothold then instigates the cycle
| itself.
|
| We just won't know until we've found something. And for us
| talking now we probably just won't know.
| jvanderbot wrote:
| Especially because they may all just be indicators of
| something else. I've heard magnetic fields, moons, and plate
| techtonics are all important, but that really could just be
| "the right kind of planetary collision not too long ago"
| felsokning wrote:
| > There could be plenty of other pathways to a stable carbon
| cycle.
|
| To be fair, carbon is the only base that we have (first-hand)
| experience with. There _could_ be other bases.
| dexwiz wrote:
| Anything else would be so exotic that it's not worth
| comparing to Earth.
| shagie wrote:
| PBS Space Time: What If Alien Life Were Silicon-
| Based?https://youtu.be/469chceiiUQ
|
| There are very few atoms that allow for the complex
| scaffolding for shapes. Many atoms are too large (and thus
| bond too weakly). Silicon is interesting, but it has some
| difficulties.
|
| https://en.wikipedia.org/wiki/Silicon-oxygen_bond
|
| > Silicon-oxygen single bonds are longer (1.6 vs 1.4 A) but
| stronger (452 vs. about 360 kJ mol-1) than carbon-oxygen
| single bonds.
|
| It is much easier to lock up oxygen and silicon in SiO than
| in CO compounds and in turn makes them less available for
| more complex structures of life.
| opticfluorine wrote:
| My organic chemistry professor always liked to point out
| that while CO2 is a gas that is easily dealt with
| following metabolism, SiO2 - silica/quartz - is most
| decidedly not a gas. Add that to the list of challenges
| for silicon-based lifeforms. Not to say that it isn't
| possible, but it does constrain the solution space
| somewhat.
| api wrote:
| That big thing that whacked us and created the Moon may be
| responsible for our being here. Amazing.
|
| The simplest and most likely explanation for the Fermi paradox
| that does not rely on fanciful future great filters or even
| more fanciful galactic zoo hypotheses is that complex highly
| intelligent life capable of space flight is extraordinarily
| rare in space and time.
|
| When we go out there we might end up finding some bacteria-like
| organisms and simple fossils but nothing close to ourselves.
|
| But ultimately we don't know until we go see.
| dehrmann wrote:
| The sample size is very low, but it's quite the coincidence
| that the only rocky planet in our solar system with life is
| the only one with an oversized moon.
| adriand wrote:
| > complex highly intelligent life capable of space flight is
| extraordinarily rare in space and time
|
| That feels right to me especially given the timescales we are
| dealing with when we consider things even just in a galactic
| context. Heck, even the timescales on this planet alone are
| such that there could be multiple complex intelligent life
| forms on earth separated by sufficient time that they are
| never known to one another! Not to mention the fact that
| there are intelligent life forms on earth right now that we
| barely understand. For all these reasons It seems to me that
| we are far more likely to come across an alien artifact than
| an alien, and we haven't started looking for these.
| kingkongjaffa wrote:
| As the earths core cools, does that mean the tectonic movement
| will slow down and our carbon cycle will become busted?
| jajko wrote:
| By that time we will have completely different issues, like
| enlarged sun burning everything down
| dartos wrote:
| We'd be in the sun
| exe34 wrote:
| Not immediately. We'll see it coming, but quarterly
| corporate plans and 4-5 year election cycles will mean we
| won't do anything until it's too late.
| icehawk wrote:
| The sun will become more luminous to a point it will stop plate
| tectonics by evaporating the oceans far sooner (about a billion
| years from now) than it will take the earth's core to cool.
| idunnoman1222 wrote:
| The answer to fermi paradox isn't about how rare complex life is,
| it's that it's impossible to create self replicating probes that
| can travel interstellar distances
| michaelmrose wrote:
| Are we basing that on the tens of thousands of years between
| stars required for chemical propulsion instead of the tens of
| years feasible with other options?
| lazide wrote:
| It's all based on energy and economy. The amount of energy
| required (even for a relatively slow chemical rocket!) is so
| astronomical, it's apparently not worthwhile to do at scale.
|
| Or there are no actual aliens, except us. For whatever
| reason.
| dboreham wrote:
| Or it is possible but we don't know what they look like.
| digging wrote:
| > it's that it's impossible to create self replicating probes
| that can travel interstellar distance
|
| What makes you say that? I wouldn't actually think that's as
| difficult as many other problems in space exploration. An
| uncrewed probe is free from a lot of really challenging
| constraints.
| lazide wrote:
| Because we haven't seen any - near as we can tell - ever.
|
| If they were possible, we should be having to constantly look
| up to avoid having one land on us.
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