ClimateCooling via Plate Tectonics?

Discussion in 'Earth Science' started by exchemist, Mar 15, 2019 at 8:52 AM.

  1. exchemist Valued Senior Member

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    Interesting article in today's Indie: https://www.independent.co.uk/news/...ty-earth-climate-change-co2-mit-a8822711.html

    MIT seems to have published some research correlating the onset of various ice ages with the upthrust of oceanic crust that often accompanies the closure of oceans. The idea seems to be that the chemical composition of oceanic crust includes rocks that absorb CO2 from the atmosphere.

    I vaguely recall the old distinction between "sial" and "sima", viz. Si/Al vs. Si/Mg that distinguishes the two. However I don't have any detailed information on the mineralogy of these rocks. I can certainly see that Mg has a propensity to form carbonates, but what the thermodynamics is of Mg carbonates vs. various complex Mg silicates I do not know.

    Does anyone have access to the paper? I'd be interested to read it.
     
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  3. sculptor Valued Senior Member

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    Interesting hypothesis.
    Reading more now.
    Thanx
     
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  5. sculptor Valued Senior Member

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    OK from what I've read, I ain't buying it.
     
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  7. James R Just this guy, you know? Staff Member

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    Maybe a link to what you read might help.... (?)
     
  8. exchemist Valued Senior Member

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    What makes you sceptical? As I say, it seems plausible that some lower crustal rocks could have a chemistry that makes them capable of producing carbonates on exposure to CO2. But I would like to see what these minerals are and what chemical reactions they hypothesise.
     
  9. Yazata Valued Senior Member

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    Apparently the paper is published in Science. The latest Mar 15 issue seems to be a special issue on pediatric cancer, so this paper may not be published yet, just submitted and accepted. (Dunno if it will be behind a paywall.)

    http://science.sciencemag.org/

    This isn't the actual paper, but it's an unusually detailed press release from MIT's Earth, Atmosphere and Planetary Science dept. (I think that it's what the news stories are based on):

    https://eapsweb.mit.edu/news/2019/tectonics-tropics-trigger-earths-ice-ages-study-finds

    This isn't the paper that you are referring to either, but it says something similar and seemingly related. It's U. of Texas researchers suggesting that the onset of plate tectonics might have come relatively late in the Earth's history and is what triggered the 'snowball Earth' episodes.

    https://onlinelibrary.wiley.com/doi/full/10.1111/ter.12321
     
    Last edited: Mar 19, 2019 at 2:51 AM
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  10. exchemist Valued Senior Member

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    Thanks for this. These links of yours have led me to two more which I think shed a lot of light on the topic:

    This one: https://www.whoi.edu/fileserver.do?id=142265&pt=2&p=86851 refers to a study of ophiolites in Oman that have been chemically altered to carbonate-rich minerals. The authors are interested in the potential for such rocks to lock up atmospheric carbon in carbon capture processes.

    This one: https://en.wikipedia.org/wiki/Serpentinite. describes the chemical weathering process by which peridotites, and olivine in particular, can be chemically weathered, either by water into serpentinite or by CO2. Reaction 2b is the answer to my original question. So, what I've learned from all this is that indeed anhydrous ultramafic minerals from the mantle, when exposed at the surface, are unstable. They react comparatively readily with both water and CO2, in the latter case forming magnesium and calcium carbonates.

    It seems to me that the MIT study, while suggestive, is far from conclusive that this process could have ushered in the ice ages. For a start, do we have evidence that atmospheric CO2 was lower during the ice ages? And if we do have such evidence, how can we establish the CO2-weathering of these rocks could compete with weathering by water enough to mop up significant amounts of atmospheric CO2? The MIT report does not seem to address these questions, at least, not according to the abstract.
     

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