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Earth Space Science

Venus' Crust Heals Too Fast For Plate Tectonics 135

Posted by samzenpus from the too-hot-to-crack dept.
An anonymous reader writes in with an interesting look at how important plate tectonics may be to life and why the crust on Venus works differently than it does on Earth. "Without plate tectonics, carbon would build up in the atmosphere. Venus, which does not have tectonics, shows the results: an atmosphere that is 96 percent carbon dioxide. It's toxic. Yet Venus is about the same size and composition as our planet, so why doesn't it have plate tectonics? Some researchers made a model to explore how Earth initiated plate movements, and these same researchers made one model of its neighbor for comparison. A 1.5-billion-year-old Earth and a similarly aged Venus were modeled as a hot, mushy material made of tiny particles of rock. The model uses physics at the one-millimeter rock grain scale to explain how the whole planet behaves. According to David Bercovici, a geophysicist at Yale who was an author on the paper, the model also shows how plate tectonics emerged on Earth but not on her twin."
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Venus' Crust Heals Too Fast For Plate Tectonics More

Venus' Crust Heals Too Fast For Plate Tectonics

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  • Venus isn't Earth's "twin" really at all. (Score:1, Insightful)

    by Anonymous Coward

    Is it very surprising that a completely different orbit around the sun and different composition result in different crust phenomena?

    • Re: (Score:1)

      by Anonymous Coward

      Is it very surprising that a completely different orbit around the sun and different composition result in different crust phenomena?

      No, but that's not what the article is about either. The article is saying that they've found a causal mechanism linking the known differences in venus's orbit/formation to the observed lack of tectonic plates. And more importantly they have a model that may allow them to predict what planets would/would not have tectonic plates based on their temperature.

    • you are mistaken, the composition of Venus rock from surface on down is nearly identical to Earth.

      • Re: (Score:3, Insightful)

        by darthlurker ( 663459 )

        There's a big difference between Earth and Venus.

        Later doesn't have an over-sized moon.

        • Re: (Score:2)

          by mmell ( 832646 )
          Currently theorized to have resulted from an impact so severe that it nearly shattered the planet, an impact so severe that the entire surface of the planet was blasted loose and redeposited on the surface.

          • blasted loose, cooled, and redeposited on the surface.

            Hmmm. that might make some nice big rocky plates.

            • I think the authors of the paper have overlooked something. It has been discovered that if we pump water into the ground along a fault line, we can literally lubricate the fault and help the plates slide past each other. (Side note: sounds like a good way to prevent major earthquakes, but nobody wants to be responsible for causing the initial quakes associated with unlocking long-locked plates. The problem with that attitude is, those quakes are eventually going to happen anyway, except they will be bigg
              • The amount of water injected into the mantle by subduction is sufficient to have a major effect on the mantle's stiffness. Without that water, plate tectonics is likely to stop considerably sooner than otherwise as the Earth cools.

        • There's a big difference between Earth and Venus.

          Later doesn't have an over-sized moon.

          That adds a lot of stress. Then pile on 1.3 billion cubic kilometres of water that tends to try to follow the moon around...
          1,400,000,000,000,000,000 metric tons sloshing around would put cracks in pretty much anything.

        • Good point. Tidal forces pull the crust up and down. On the other hand, this might be construed as heating it, which would be anti-tectonic.

    • Is it surprising that there is a difference in the behavioral history of a single planet and a similar planet that happens to be part of a binary planet system?

      Hint: Venus does not have tides; has never had tides. Earth tides were a lot larger when Earth was young and the Moon was closer. They are still large enough to put a significant do-si-do waggle in the Earth's orbit about the Sun. Despite what dumb-ass astronomer conventions might say, when a satellite is so large that it deflects its primary from

      • which "dumb-ass" scientists that do not influence the impact of the moon on the earth are you talking about?

        The Moon is considered a moon as the barycentre is within the Earth. Pluto on the other hand has its barycentre outside of it, though in its case we usually refer to it as a Dwarf planet rather than Dward binary. ...or am i missing something?

        • No, you have not missed anything. You are parroting the "logic" of the Committee for Small Body Nomenclature of the International Astronomical Union. This is a true committee of fifteen members whose job it has been to decide on definitions of words. There was and is no science here. Nor was there any logic based on science; the logic was that of taxonomy: making pigeonholes to classify stuff. Nor was logic used in making the final determinations; what the pigeonholes were to be called was decided by vote.

          • Well you do need a naming system and Planet is a useful naming system. What is evil about that? There are only 8 planets so you don't really need to subdivide them more. And if the earth-moon is a binary then what are Mars, Jupiter, Saturn, Uranus and Neptune? Pluto on the hand was relabelled by that evil committee not because it is also a binary, quaternary or whatever, simply because there are potentially thousands of dwarf planets, so calling them planets was not useful. That is usually the big complain

      • But the pot which is NOT stirred is the one that will build up layers of floating junk on top, earthstyle.
        • To segregate low-density material to the surface you need to have mass movement. Without external stirring, then you'll need to have internal stirring, which seems to be achieved with convection as a result of self-heating by radioactive decay in the mantle. The resulting movement results in the accumulation of low-density material at the surface and high density material at the core-mantle boundary.
    • But.... isn't Venus warmer because of the excess CO2, which is the result of lack of plate tectonics, which these guys say is the result of Venus being warmer? Who lit the fuse?

  • Rare Earth? (Score:5, Informative)

    by K. S. Kyosuke ( 729550 ) on Monday April 21, 2014 @11:51AM (#46806209)
    I believe I've read similar arguments some time ago in a book titled Rare Earth: Why Complex Life is Uncommon in the Universe [amazon.com]. It was published a decade ago. So it's a slow news day again, I guess. ;-)
    • (Just to be a little bit more specific, this was about the "how important plate tectonics may be to life" part, not about new findings in the area of plate tectonics mechanisms which I'm sure are new.)

      • the "how important plate tectonics may be to life"

        To complicate matters (and yes, I read Ward & Brownlee's book when it came out too. It was an interesting read, but not 100% convincing. But then I am a geologist, not an OOL researcher.), when life started around 3800 million years ago (possibly as early as 4300 million years ago) the tectonic regime was decidedly different to today. This was probably driven by the higher heat flow of the early Earth, as there were more radioactive materials around th

    • Re: (Score:2)

      by radtea ( 464814 )

      You added your own addendum, but it's worth repeating: the idea that plate tectonics is important to life is not new.

      The detailed model as to how and why plate tectonics got going on Earth and that also explains why it didn't get going on Venus is both new and interesting, which is pretty much the definition of "news for nerds, stuff that matters", eh?

    • Re: (Score:1)

      by Tablizer ( 95088 )

      But we don't know if Earth's path to complex life is the only viable path. There may be "other angles" to get to complex life. We only have one sample to judge on.

  • Without plate tectonics, carbon would build up in the atmosphere

    Why is that?

    • Re:Why? (Score:5, Informative)

      by K. S. Kyosuke ( 729550 ) on Monday April 21, 2014 @12:03PM (#46806349)
      If you bothered to read the article (or the book I linked), you'd find out that plate tectonics is crucial in the long-term carbon cycle that snatches carbon-containing minerals and, passing through subduction zones, deposits them in the depths of the Earth. (I'm not a geologist but I also vaguely recall that the hydration of these minerals contributes to the increased levels volcanic activity near the subduction zones, by means of lowering the melting point of rocks - which is how the cycle gets closed, since this volcanic activity releases the carbon back.)

      • Re: (Score:2)

        by tomhath ( 637240 )

        which is how the cycle gets closed, since this volcanic activity releases the carbon back

        That's kind of the question though. A huge amount of carbon is tied up in the Earth's crust. Some gets pulled down into the mantle, some gets released. From what I've read that cycle is in balance. So why wouldn't the carbon in the limestone stay there without tectonics?

        • I'm not sure it's about the limestone "not staying there", I always understood it as a matter of increasing the crust's overall absorbing capability, by circulating it over greater thickness of rock layers. If you absorb as much CO2 in a comparatively thin (but static) layer of rocks near the surface as you can (with the absorption speed steadily decreasing), what happens then to the rest of atmospheric CO2? That might just be the thing that happened to Venus. Or not. I'm not the expert, I'm afraid.

          • So basically you're just making shit up as you go? Somehow you think that the crust wouldn't be layered without plate tectonics even though that isn't the reason the crust is layered in the first place ...

            In that situation, when you can just make up silly answers to the holes in your theory, any theory can look sound.

            • If by "making shit up as I go", you mean "recalling interesting stuff from books I've read years ago", then yes. Otherwise you're not making too much sense.

  • Wow. Talk about ignorance. (Score:5, Insightful)

    by mmell ( 832646 ) on Monday April 21, 2014 @12:59PM (#46806847)
    I mean here, not from the article's author.

    If instead of yelling about how Mr. Bercovici's theory doesn't explain life, the Universe and everything we accept that he has provided a reasonable theory explaining one of the factors which led to the current difference between Earth and Venus, the conversation here might be more productive.

    Yes, Venus gets considerably more energy from the Sun than Earth does. Yes, this alone could reasonably be expected to make it very different from Earth. Is that the only thing which caused Venus to be different from the Earth? If not, it might be interesting to know what other factors resulted in the differences we see - hence, the article exploring how plate tectonics may have contributed to the differences we see.

    Oh, one last observation - Mr Bercovici has postulated a theory. I'm sure he started with a hypothesis for which he then sought supporting evidence, which he has provided. So far, sounds like good science to me.

    • Re: (Score:1)

      by Anonymous Coward

      I think most people here are taking issue with the journalist and not the researcher. She should read more Feynman if she really believes the tautological narrative presented in paragraph 3 and that simulation=reality as implied by the headline.

  • Venus assumed to be 200 degrees hotter? (Score:5, Interesting)

    by erice ( 13380 ) on Monday April 21, 2014 @01:45PM (#46807303) Homepage

    From TFA:

    the Venus model, which was a couple hundred Kelvin hotter,

    So, how does it get so much hotter than Earth? It is certainly that much hotter now but that is attributed almost entirely to the greenhouse effect. However, the article earlier states:

    Without plate tectonics, carbon would build up in the atmosphere. Venus, which does not have tectonics, shows the results: an atmosphere that is 96 percent carbon dioxide.

    So, because plates did not form, Venus experienced a runaway greenhouse effect and high temperatures. But high temperatures are supposed to prevent plates from forming. A little circular, no?

    Don't get me wrong: this is interesting work but it doesn't really answer the question of how Venus became the way it is . To close the gap, you need to assume that:
    a) Venus started out 200K hotter though some other means (Proximity to the Sun is not generally considered sufficient for that)
    -or-
    b) Venus plate tectonics stalled early on for some other reason, allowing the greenhouse effect to take over.

    • Re: (Score:1)

      by Anonymous Coward

      From the paper:

      A similar exercise using hotter Venusian surface conditions permits
      a comparison to Earth’s putative twin25–27.Using the same material properties
      but a lithosphere temperature elevated by 200–400K above the
      Earth-like case, the damage number D is reduced by a factor of about
      10, and the healing numbers Ci and CI are increased by a factor of up to
      10 (see Methods). In this case, as a downwelling migrates to various
      positions (see Fig. 2), only very faint weak zones accumulate becau

  • "The model uses physics at the one-millimeter rock grain scale to explain how the whole planet behaves."

    A 3,000 x 3,000 x 3,000 grid is considered very large for modern scientific models. Assuming they are working on a cartesian grid, and an earth diameter of 12,000 km, their model would be 12,000,000 x 12,000,000 x 12,000,000; twelve orders of magnitude larger than the biggest physical model I've ever heard of.

    This cannot be the case.

    • "The model uses physics at the one-millimeter rock grain scale to explain how the whole planet behaves."

      A 3,000 x 3,000 x 3,000 grid is considered very large for modern scientific models. Assuming they are working on a cartesian grid, and an earth diameter of 12,000 km, their model would be 12,000,000 x 12,000,000 x 12,000,000; twelve orders of magnitude larger than the biggest physical model I've ever heard of.

      This cannot be the case.

      Whew! Its a good thing they never claimed they were doing any such thing.

      "physics at the one-millimeter rock grain scale" does not mean that they were using a model grid of that same scale.

      To show that the assumption that it must, or even should, is incorrect consider any engineering model that involves the effects of static friction.

      The phenomena that cause static friction exist on the molecular and atomic level, and theoretical predictions of friction under arbitrary conditions need to be analyzed and cal

      • Re: (Score:2)

        by cusco ( 717999 )

        Thanks, that makes more sense. I also was wondering how the hell they managed to crunch the numbers for a grid that size, which from TFS sounds like what they were doing.

  • Since nobody was around billions of years ago, many assumptions have to be made about conditions on earth at that time. This is true even more so about Venus. About the only thing these “scientists” can say for sure is that the mathematics and programming of their computer models are likely correct. That is certainly not true about the original assumptions used as a starting point. As the saying goes: “garbage in, garbage out”.

    • Since nobody was around billions of years ago, many assumptions have to be made about conditions on earth at that time.

      So you look at proxies. For example, you might ask how we know that there was liquid water on the Earth's surface 3.5 billion years ago, as there were no people to witness it. But there WERE rocks to witness it. In particular, there were pebbles and sand grains that were being transported by the water, and their shape and grain size distributions match the shapes of modern water-transported

  • Just another example on how many factors affect a planet’s ability to support life not to mention sentient species and civilizations. The more we learn, the longer the list becomes (e.g. the right kind of star system with the right kind of star, the right planetary materials in the right zone, the right kind of magnetosphere, the right kind of moon, shepherd planets, the right kind of galaxy/cluster, the right place in place in the galaxy/cluster, the right kind of geological tectonics, the right kin

    • Re: (Score:2)

      by cusco ( 717999 )

      The Drake Equation didn't come with any numbers pre-decided. Some of the numbers, such as rate of star formation, were known. Some, such as percentage of stars with planets and percentage of planets in the 'Goldilocks Zone', are only becoming known now. Others, such as the percentage of planets that give rise to life, are still unknown. You can plug any numbers you want into any of the variables.

      • Indeed, but I wasn't commenting on the equation as much as the tendency to plug in optimistic numbers yielding estimates of tens of thousands of advanced civilizations in the Milky Way alone. I don't have the numbers handy (so my memory may be betraying me), but I believe that somewhere around 90% of stars, in our galaxy, reside in areas too violent to support life for the requisite periods of time regardless of all other factors. I'm not qualified in the least to say whether you facter that into R itself

    • the right kind of moon

      That's a very popular claim - that the presence of a large Moon was necessary to the origin of life/ complex life/ civilisation - but I've only heard it made by popular science journalists. I've not heard a serious scientist make that assertion and then defend it.

      It may be true, but I wouldn't make that claim, because I wouldn't like to try to defend it.

      • Fair enough; of course I would be hard pressed to defend any of this in a rigorous manner as I am neither a trained scientist nor in the habit of reading scholarly papers, journals, etc. The 'scientific' facets of my worldview are largely informed via popular scientific outlets, some more rigorous than others. I certainly haven't scoured the scientific papers on the subject.

        On the other hand, I wonder what you mean by 'very popular claim?' Do you mean a claim made often by non-scientist? Perhaps, but the

        • On the other hand, I wonder what you mean by 'very popular claim?' Do you mean a claim made often by non-scientist?

          It's something that I hear a lot on things like Discovery channel. I do spend quite a lot of time and effort trying to keep up with the literature, and I don't see such claims being made or repeated there.

          Moon's theorized role in Earth's evolutionary process

          1. from the stabilization of the axis,
          2. to the early tilde affects on Earth's magma (when the Moon was much closer)
          3. decreasing the amount of as

          • You said:

            Given all of these issues, I wouldn't attempt to defend the proposition that "a large moon is necessary for the origin of life". It may be a true proposition, but I don't think that the state of knowledge at the moment allows one to claim it as a fact.

            Over to you.

            Consider these statements from my last reply:

            ...I wouldn't argue that a moon like the Moon is necessary for life, nor could I...

            and

            Is a Moon like moon a necessary condition for advanced sentient species? Probably not...

            As such, I'm not sure we disagree significantly on that specific point.

            My point is that I once held an fairly optimistic stance regarding the possible numbers of alien civilizations 'out there.' That stance has been tempered and refined as we discover just how many things Earth has going for it. Are all of them strictly necessary? By no means, but there is probably a critical mass in the matrix of variables needed to foster not only life, but an on

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