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Earth Science

Earth is Missing a Huge Part of Its Crust. Now We May Know Why. (nationalgeographic.com) 163

A fifth of Earth's geologic history might have vanished because planet-wide glaciers buried the evidence. From a report: The Grand Canyon is a gigantic geological library, with rocky layers that tell much of the story of Earth's history. Curiously though, a sizeable layer representing anywhere from 250 million years to 1.2 billion years is missing. Known as the Great Unconformity, this massive temporal gap can be found not just in this famous crevasse, but in places all over the world. In one layer, you have the Cambrian period, which started roughly 540 million years ago and left behind sedimentary rocks packed with the fossils of complex, multicellular life. Directly below, you have fossil-free crystalline basement rock, which formed about a billion or more years ago.

So where did all the rock that belongs in between these time periods go? Using multiple lines of evidence, an international team of geoscientists reckons that the thief was Snowball Earth, a hypothesized time when much, if not all, of the planet was covered in ice. According to the team, at intervals within those billion or so years, up to a third of Earth's crust was sawn off by Snowball Earth's roaming glaciers and their erosive capabilities. The resulting sediment was dumped into the slush-covered oceans, where it was then sucked into the mantle by subducting tectonic plates.

Effectively, in many locations, Earth buried the evidence of about a fifth of its geological history, the team argued this week in the Proceedings of the National Academy of Sciences. The notion is elegant but provocative, and the authors themselves predict that some geoscientists will express skepticism. "I think, though, we have extraordinary evidence to support that extraordinary claim," says study leader C. Brenhin Keller, a postdoctoral fellow at the Berkeley Geochronology Center.

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Earth is Missing a Huge Part of Its Crust. Now We May Know Why.

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  • by Anonymous Coward
    It's called the moon.
  • Except the glaciers didn't "saw" off the crust (because glaciers don't "move") but pulverized it under their weight as the ice and snow built up and with annual run-off draining the sediment away.

    Certainly that's what I was taught in my midwest high school surrounded by lots of plains and "flatland", made so by the glaciers that came before us.
    • by Smidge204 ( 605297 ) on Wednesday January 02, 2019 @02:34PM (#57893042) Journal

      > because glaciers don't "move"

      They certainly do. Or at least they can...

      https://en.wikipedia.org/wiki/... [wikipedia.org]

      And they're pretty effective at scrubbing the underlying terrain.
      =Smidge=

      • They can SHIFT just like anything else sitting on this planet - they don't act like bulldozers.
        • by Smidge204 ( 605297 ) on Wednesday January 02, 2019 @02:46PM (#57893130) Journal

          > they don't act like bulldozers.

          Yes they do. Glaciers can slide for miles, picking up chunks of rock and dragging them along the underlying surface literally scouring the underlying earth like a river of sandpaper. They can dig out valleys, transport the material miles away and dump it. A few million tons of ice sliding around will easily act like a bulldozer. Glacially formed striation and moraines are all over the place.

          They are literal rivers of ice; they flow, not just shift.
          =Smidge=

          • a river of sandpaper

            I like that.

            Also, GP is an imbecile.

          • Jakobshavn Glacier is the world's fastest glacier and moves 66-150 feet per DAY! Glaciers typically only move about 3 feet per day.

            https://en.wikipedia.org/wiki/... [wikipedia.org]

            Crazy.

          • by Toad-san ( 64810 )

            But but but ... if you want a flow, you need a downhill. Surely not EVERYPLACE a glacier existed was downhill! Where's the bottom?

            Oh ... yeah ... those subducting tectonic plates :-(

            • You don't need a downhill necessarily. A glass of water poured onto a flat and level surface will still flow and spread out.

              =Smidge=

    • I live in Finland and the movement of the glaciers is clearly visible on rocks here.
    • by dissy ( 172727 )

      I thought this was already known ... Except the glaciers didn't "saw" off the crust (because glaciers don't "move") but pulverized it under their weight as the ice and snow built up and with annual run-off draining the sediment away.

      It was previously suspected, not known, that the basement rock was crystallized under the weight of the 2 kilometer thick ice sheets, but there was little evidence this part of the hypothesis was correct, it was just the best fitting piece of the puzzle so far.

      The authors of this new puzzle piece both claim it's a better fitting piece and that they have evidence.

      If that evidence turns out to be true that would give this explanation a pretty huge leg up over the old guess.

      • It was previously suspected, not known, that the basement rock was crystallized under the weight of the 2 kilometer thick ice sheets

        When was that? 1750?

  • up to a third of Earth's crust was sawn off by Snowball Earth's roaming glaciers and their erosive capabilities.

    Let's see, we could worry about the Earth maybe getting a few degrees warmer and having to back away from the ocean a bit.

    Or we could worry about ENTIRE CONTINENTS being "sawed off the earth" by glaciers as the rest of us starved because there was nowhere on earth you could grown more than a handful of crops in the icy cold.

    Way better in my mind to engineer how to deal with warming - and keep it p

    • Christ. How dumb. The problem is that the few degrees warmer is going to kill you first because it is happening in decadal time. You have a couple of thousand years to worry about how to handle an ice age.
    • by Terwin ( 412356 )

      Glacial period, not Ice Age.
      The current age is an ice age(The entire Quaternary period is an ice age, as can be seen by year-round polar ice-caps, those ice-caps did not exist for a majority of the history of life on earth).

      It would be great for biodiversity if we moved away from being too cold for plants for much of the year for large parts of the planet. A warmer climate leads to more prolific and productive plants which in turn lead to more energy available for other forms of life.

      Sure change sucks for

      • by Tablizer ( 95088 )

        But there's no evidence an ice-age is coming. The big problem with man-made global warming is that it's happening relatively fast, not giving Earth life nor human populations enough time to adapt. IF a natural ice-age were coming up, most likely it would occur rather gradual.

        A warmer climate leads to more prolific and productive plants

        As far as what is the "ideal" temperature for the Earth is per farming etc., that's certainly an interesting question. I suspect too much heat will lead to too many deserts, r

      • by rtb61 ( 674572 )

        We are a technological society, what ever the climate our cities were estblished in, is the climate we want to maintain. Only a idiot could accept the majority of the worlds coastal cities wiped out by widespread flooding. You do have some understanding that sea levels were a couple of hundred metres lower in the last ice age, only a psychopath would accept that chaos as reasonable or claim some idiots benefit.

    • by hey! ( 33014 )

      An Earth 2C or even 4C warmer or cooler isn't inherently more or less hospitable to humans. What is inhospitable to our economy and the vulnerable people in it is any kind of change that is too fast for them to cope with. If over the course of a thousand years the southern Great Plains becomes a desert, nobody would even notice. If it happens in a hundred years, you will be looking at a series of refugee crises.

      Insofar as any disruptive change is the result of our actions, we should worry about it. Rap

    • by balbeir ( 557475 )
      I for one welcome our new Penguin overlords
    • by AC-x ( 735297 )

      and having to back away from the ocean a bit.

      Yeah it's so easy we can just just just move 10%+ of the world's population and flood 2/3rds of the worlds largest (+5 million people) cities [npr.org] it'll be fine!

      • You act like that is hard but over a hundred years, that is not hard. Nor is it even a lot of people affected compared to the bitter reality of a colder climate truly getting a grip on the world.

        • You act like it's easier than just *burning less of our finite supply of fossil fuel*.

          Plus if the earth starts to cool like that we will have centuries to come up with a solution, perhaps burning that fossil fuel we kept in reserve..?

          • Plus if the earth starts to cool like that we will have centuries to come up with a solution, perhaps burning that fossil fuel we kept in reserve..?

            You are not thinking about all this in terms of momentum - way easier to keep the Earth from sinking into a decline, than it is to stop a decline in progress (especially given how long it would take us all to agree the danger is real).

            We have lucked out into warming the climate by about the right amount before we switch to mostly alternative energy sources.

            • Even if we switch to 100% carbon-neutral energy overnight (and fix all the other sources like construction and agriculture) - what makes you think the warming we've started will stop at "the right amount"? The carbon we've already released will continue warming us for decades and centuries to come, the seas will keep rising, and the ocean will keep acidifying. We'll be lucky if glaciers exist anywhere by the time it eventually stabilises.

              It's ridiculous to worry about potential future glaciation when we've

              • Even if we switch to 100% carbon-neutral energy overnight (and fix all the other sources like construction and agriculture) - what makes you think the warming we've started will stop at "the right amount"?

                Because even the IPCC thinks we are hitting the 2C or so mark, and between 2C-4C is fine. Basically anything that is not runaway warming (remember, the thing that was supposed to scare us originally, now not in the cards in any forecast) can be dealt with.

                The carbon we've already released will continue w

                • between 2C-4C is fine

                  Lol, if you say so. Yes we can "deal with it" - at the cost of hundreds of billions [wri.org] annually in adaption costs, not to mention [www.ipcc.ch] displacing billions from coastal areas, threatened sea ecologies from CO2 acidification, famines from shifting agriculture in undeveloped nations, etc etc. Better to avoid those costs wherever possible, don't you think?

                  If you want to believe that fine

                  I believe the research [uliege.be]. Linear kinetics models suggest an atmospheric lifetime of 30-95 years. Equilibrium models tell us that even after equilibrium is reached once

  • by mark_reh ( 2015546 ) on Wednesday January 02, 2019 @02:37PM (#57893058) Journal

    you exactly where the crust went, and when, and why.

    • Re: (Score:3, Informative)

      by Anonymous Coward

      That's an old meme and its a very very small minority of kooky off shoot heretic protestants that believe that. The mainstream christian rites like Catholicism don't believe that at all.

      • but it checks out [google.com].

        Jokes aside, approx 38 % of Americans [wikipedia.org] believe in "Young Earth" creationism and 24% believe everything in the bible is the literal word of God ("literal" here means that nothing is a parable).
    • Oh that's easy. I've seen enough Young Earth Creationist mumbojumbo that even I can explain that.

      The gap is where the water was hidden before the great flood. There's no rock layer because that layer was water, not rock! During the great flood, the water rose up and the crust sank, becoming temporarily submerged. As the waters receded and flowed into what is today's oceans, finding its new level, it carved the Grand Canyon and other geological features that "scientists" insist are the result of millions of

    • If you believe the Earth is only 6000 years old, you'd argue there is no missing crust.

    • you exactly where the crust went, and when, and why.

      Well, it's perfectly obvious to me . . . someone ate the crust . . . just like that last piece of pizza in the box that mysteriously disappears.

      Keep your eyes out for folks with Earth Crust Crumbs on their chins!

    • This is very true.
    • you exactly where the crust went, and when, and why.

      Because "Snowball Earth" is a better explanation? It sounds like an L. Ron Hubbard novel.

      You (collectively) are literally just making stuff up because your version of how things came to be must (in your mind) be true. You are doing that every bit as much as your targets of derision (in your estimation) are doing so.

      Since your version of things must be true, therefore, er, something or other must have happened to that whole missing geological layer ...

      In other words, you're hardly in any position to snark

      • An explanation based on stitching together related, objectively verifiable facts, and a willingness to change the explanation when new objectively verifiable facts come to light is completely different from the other type of explanation.

      • by dryeo ( 100693 )

        You do know that without any greenhouse gases, the average temperature of the Earth would be about -20C currently and in the past the Sun was cooler?

    • you exactly where the crust went, and when, and why.

      Damn cat! I told it not to stand on top of the earth and push that crust onto the turtles. The little bastard likes to watch the look on my face as it slowly pushes the crust off the edge of the earth.

  • Awfully uniform (Score:5, Interesting)

    by cyberchondriac ( 456626 ) on Wednesday January 02, 2019 @03:11PM (#57893338) Journal

    The problem they might encounter with the skeptics is explaining why the missing rock seems to be so uniform all over the globe. Surely the glaciers would be thinner at the equator? The missing rock should not go as far back at the equator as the topical zones, I would think.

    • You seem to be a little unclear on the scale of this whole thing.

      * Are you aware what "snowball earth" means? Do you have an understanding of how much glaciation there was?
      * Do you understand that a half billion years is a very, very long time, even in geologic terms?
      * Do you have a concept for what plate tectonics might look like on the scale of a half billion years?
      * Do you know where the continents were during this period? Or even what they were? Or if they were?

      Seriously, your comment reads like a 12 ye

      • Seriously, your comment reads like a 12 year old trying to sound smart, and failing really, really badly.

        It's funny that you say that, since it appears the OP may be correct about thinner glaciers at the equator. From the Snowball Earth Wikipedia page [wikipedia.org]:

        A number of unanswered questions remain, including whether the Earth was a full snowball, or a "slushball" with a thin equatorial band of open (or seasonally open) water.

        at the temperatures predicted by models equatorial sublimation would prevent equatorial ice thickness from exceeding 10 m

        Given those statements, it would be reasonable to posit that the glacial

        • by geggam ( 777689 )

          Thing is... the earth might have not always rotated the same way ?

        • No, you've got the same problem OP has. Thanks for trying to shame me, however. Feel free to read through what I wrote and answer those questions for yourself. You've got the aptitude for learning if you took the baby step of looking up the Snowball Earth, so I have hope for you.

      • WOW... Seriously, fuck you. You have just invalidated everything you ever say.
        I didn't come across as more knowledgeable than anyone else, I merely posited a thought that was reasonable.
        It's still reasonable, because you haven't said anything to actually counter it, you just came across as a pompous dickwad with rude assumptions that didn't negate a thing I said.
        Regardless of how continents and plates move or how long the period was, the equator is always subjected to more sunlight. Glaciation will never b

        • Still wrong, and entirely missing the big picture.

          I've been coming to /. for a long time for intelligent discussion, and I get a little irritated when stupid, ignorant shit gets modded up. Not knowing the first thing you're talking about doesn't entitle you to a polite education from me or anyone else.

          You've thrown a little temper-tantrum because I didn't treat your ignorance with respect. Sorry kid, but it doesn't deserve respect. I gave you some really good starting points for you to correct your deep cha

          • "..kid" Oh, That's funny. You pull assumptions out of your behind like there's no tomorrow.
            If you check my id, you'll see I've been coming to slashdot for a long time too, and I started when I was older, and I get irritated when some pompous, supercilious blowhard feels they have the right to belittle another user for unmaliciously positing an assumption or question on a subject they find interesting. I never passed myself off as a geologist. It's also not my fault that my post got modded up, so sorry

            • where is the proof that each and every landmass during the precambrian/cyrogenian period moved and distributed themselves equally between temperate and tropical zones, ensuring the same degree of solar exposure?

              The good news is that you're at least getting closer to understanding why your question about about glaciation all the way to the equator is a stupid question. The bad news is that this is a dumber question, and shows a remarkable lack of understanding of the topic at hand. One step forward and two back, it seems.

              But you're welcome to continue on with your little rant about how arrogant and dumb I am rather than reading and learning enough to understand.

    • Surely the glaciers would be thinner at the equator?

      The distribution of land was very different then - what's at the equator now wasn't at the equator then. So, first, locate the landmass that was under the equator then and check it's layers - assuming they survived.

  • https://www.livescience.com/62... [livescience.com]
    Artifacts of human or other industrial civilizations are unlikely to be found on a planet's surface after about 4 million years, said Frank and study co-author Gavin Schmidt, director of NASA's Goddard Institute for Space Studies in New York. For instance, they noted that urban areas currently take up less than 1 percent of Earth's surface, and that complex items, even from early human technology, are very rarely found. A machine as complex as the Antikythera mechanism
    • there is zero reason to believe any advanced ancient civilizations exist, especially since there are nonliving artifacts not needing any fossilization that *would* endure.

      Would you care to hazard a guess how long these things would last:

      a silicon based integrated circuit in a ceramic package

      a fiber optic cable

      a gold tooth or a porcelain crown

      The windshield of a car

      titanium alloy aircraft and rocket bodies

      aluminum engine blocks

      corpses preserved with formaldehyde

      this stuff is all o

  • We should have a reward here for the most misleading topic.

    The very linked article itself, and further research about "Great Unconformity" clearly state that this particular unconformity is limited to the Great Canyon GRAND CANYON - THE GREAT UNCONFORMITY [usra.edu] and from wikipedia Great Unconformity [wikipedia.org] one can further learn about this "annomaly" together with it's explanation:

    Unconformities in general tend to reflect long-term changes in the pattern of the accumulation of sedimentary or igneous strata in low-lying areas (often ocean basins, such as the Gulf of Mexico or the North Sea, but also Bangladesh and much of Brazil), then being uplifted and eroded (such as the ongoing Himalayan orogeny, the older Laramide orogeny of the Rocky Mountains, or much older Appalachian (Alleghanian) and Ouachita orogenies), then subsequently subsiding, eventually to be buried under younger sediments.

    We could've avoid all the wide speculations if only the topic was reflecting the content, as "Hi, look what interesting about geology I found -

  • I watched this video on YouTube just a little while ago. I've not really looked into the science of it nor modeled the impacts he's talking about but it might be possible that our earth is a remnant from a not-that-long-ago clash with an itinerant planet's moon. We live on the half of a then larger planet that was smashed by that moon, the rest became an asteroid belt and probably our moon. I think this is a more likely explanation for why a huge part of the crust might be missing than it having been scr

  • Aliens had a quarry here for a billion years or so before moving operations elsewhere...

    Anyway what would really blow some people's minds and start some speculation would be if in exploring other planets such as mars, we find the same discrepancy during the same time period... Some destructive stellar event perhaps?

    Also one of the big detractors of a past advanced civilization is the lack of any evidence surviving at all. However if about a billion years of geological data is missing, that's a pretty big ga

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