Plate tectonics not needed to sustain life | Hacker News Reader

Plate tectonics not needed to sustain life

phys.org

50 pointsdnetesn17 comments

Based on some unverifiable computer models.

I think I'm just going to start flagging all the science stories that are press releases about someone's unverifiable computer models.

You're demanding more proof about the claim (based on unverified models) that there's reason to believe that a previous (and equally unverified) claim may not be true.

That's a bizarre burden of proof, there.

It is indeed a press release so that's not great, but why wouldn't their model be verifiable? We know the applicable laws of physics, someone else can code up a simulation and verify the results.

A simulation is a prediction, not a verification. Verification would be going out to a load of planets and seeing if they look the way the simulations say.

In fact there's been several news stories about extraterrestrial planets over the past few years, since we're finding more of them now. But the ones we hear about focus on things like "can they support life". There is nothing per se wrong with playing with the math and playing with models and trying to get a sense of the space of possibilities.

Where I get crabby is when the whole process is condensed down to the level the title is at: "Plate tectonics not needed to sustain life". No. The level of confidence expressed in those words is utterly unjustified. We have perhaps a trace more than absolutely no idea. That trace is scientifically valid and I do not begrudge some planetary scientists fiddling around. But we must not place excessive confidence in the results.

The inability to practically proof the correctness of a computer model does not mean it is scientifically valid to then just assume they are correct!

To put it in local terms, that's exactly as valid as expecting a programmer to just type a few thousand lines of code into an editor, compile, and deploy to production with no further testing required. Because, in a fairly real way, this isn't even a metaphor, this is precisely what making such concrete predictions off of an unproofed computer model is doing. Being unable to test the correctness of the code does not therefore render it correct. I am reminded of the classic quote "On two occasions I have been asked, — "Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" In one case a member of the Upper, and in the other a member of the Lower, House put this question. I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question." by Babbage. I am not able to apprehend the confusion of ideas that produces this concept that if we can't test the model, we are justified in assuming it is correct. To my understanding of science, exactly and precisely the opposite is true.

(Incidentally, I also consider the phrase "Plate tectonics are necessary to support life" to be completely unjustified! Our one sample of life-supporting planet has plate tectonics. Our own solar system is at least suggestive of the possibility that plate tectonics across a long time period may be rare, but no more than "suggestive" without a lot more data. Given the very-slowly-increasing evidence that life may be rare in the cosmos, it is suggestive that rare characteristics of our planet and the rare characteristic of "life" may be connected. We have some plausible-sounding theories as to why plate tectonics may be helpful. But we can not say absolutely "they are necessary for life" by any means.)

We can't even verify, say, dark matter and dark energy, no matter how much we look for it, and we handed out Nobels for them.

Just because we have "laws of physics" and "computer modules based on simulations of said laws of physics" doesn't mean it's real.

I was not aware that Earth was the only planet to have confirmed tectonics. That seems really weird. I wonder what the percentage winds up being between planets with and without tectonics.

If you have a rotating spherical body with a (sufficiently) heterogeneous fluid composition, it seems like you'll get plate tectonics. When you realize it's just a fluid with convection currents and the surface of the fluid "freezing", you realize it should be relatively common for across planets for a portion of their existence.

ps - if any actual physicists out there are reading, I've been curious about the case of Mars and if tectonics there could have been halted by whatever caused the hemispheric dichotomony for a long time, in case there's any good reading/research on that out there to pass along...

"Plate tectonics" means something a bit more specific than "convection currents with the surface of the fluid freezing". In particular, it implies 1) relatively large stable plates, 2) organized regions where crust is created/destroyed, and 3) large horizontal movement of those plates relative to each other.

Prior to ~2 billion years ago, Earth didn't have plate tectonics. You had large vertical motion (not horizontal), and creation+destruction of crust, but no organized centers where this was occurring. In other words, you didn't have large plates and what plates there were did not move long distances horizontally.

As another example, Venus has tectonic activity (it's periodically resurfaced and has volcanoes), but it doesn't have plate tectonics. You see regions of compression and extension, but no subduction zones and spreading ridges.

It's likely that what we call plate tectonics requires abundant water, at least on "rocky" planets. Hydrous phases of silicate minerals are required for the very weak faults and localized weak mantle required to have subduction. Without subduction, you don't have plate tectonics.

> Prior to ~2 billion years ago, Earth didn't have plate tectonics. You had large vertical motion, and creation+destruction of crust, but no organized centers where this was occurring. In other words, you didn't have plates.

Well that would be great evidence that you don't need plate tectonics to sustain life. ;-)

Yeah, the exact start of plate tectonics on Earth is very hard to pin down, but it's almost definitely after the start of life.

On the other hand, even when Earth didn't have plate tectonics, it probably never had a stagnant lid, which is what this article is modeling.

This is only tangentially-relevant, but I recently read that the earth's mantle is mostly solid! (It does still flow, but as a solid.)

The state of the rock beneath the crust is subject to two competing influences:

* High temperature [promotes liquid state]

* High pressure [promotes solid state]

and apparently the latter influence (mostly) wins.

Of course, when such rock reaches the surface, number 1 wins so we see liquid rock.

Also, the deep earth is filled with lots of water, well mixed that is. Evidently this lowers the melting point and promotes plasticity, from what I've read.

Water may be one of the bigger requirements.

Not exactly water, hydrated minerals. So stuff (mostly olivine) with OH groups stuck to them.

But yeah the factoid is 7x the water of the oceans.

Also Europa. But it's just a moon of Jupiter. And there's tidal heating.

This is 1:1 identical with the press release from the Penn State University. Maybe link to the original?

https://news.psu.edu/story/529527/2018/07/30/research/plate-...

Revolving around a sun and rotating at the same time needed?

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