Stories
Slash Boxes
Comments

SoylentNews is people

posted by Fnord666 on Wednesday January 02 2019, @05:25PM   Printer-friendly
from the someone-removed-the-crust dept.

Submitted via IRC for Bytram

Earth is missing a huge part of its crust. Now we may know why.

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. (Here's what will happen when Earth's tectonic plates grind to a halt.)

AND

What could have wiped 3km of rock off the entire Earth?

Believe it or not, the geology at the bottom of the Grand Canyon is extraordinarily common. There, layers of sedimentary rock lie flat atop angled layers of significantly more ancient metamorphic rock. The gap there is enormous—if Earth's rocks constitute a book of the planet's history, there are about a billion pages missing. The story only picks up again around 540 million years ago in the Cambrian period, with an evolutionary explosion of complex life just as remarkable as the sudden change in the rock.

This gap can be found all around the world, and has picked up the name the Great Unconformity. Cambrian sedimentary rocks rarely rest on anything other than much older metamorphic or igneous rock, implying that whatever rock formed in the intervening time was scrubbed away by something. This erasure of a chunk of geologic history has long been an enticing mystery for geologists.

A period of intensive global erosion doesn't seem sufficient to fully explain the pattern of change in the rock. An alternative, that the formation of new rock suddenly accelerated beginning in the Cambrian, doesn't quite fit the evidence, either. So what gives?

PNAS, 2018. DOI: 10.1073/pnas.180435011  (About DOIs).


Original Submission

 
This discussion has been archived. No new comments can be posted.
Display Options Threshold/Breakthrough Mark All as Read Mark All as Unread
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
  • (Score: 2) by Runaway1956 on Wednesday January 02 2019, @06:47PM (3 children)

    by Runaway1956 (2926) Subscriber Badge on Wednesday January 02 2019, @06:47PM (#781116) Journal

    I'll repeat - it's not "missing". It has merely been made illegible to us, and it's right there beneath our feet. Remember the laws of conservation of energy and matter?

    Starting Score:    1  point
    Karma-Bonus Modifier   +1  

    Total Score:   2  
  • (Score: 0) by Anonymous Coward on Wednesday January 02 2019, @11:18PM

    by Anonymous Coward on Wednesday January 02 2019, @11:18PM (#781234)

    Your expansive definition means nothing material that existed once can ever be "missing."
    It kind of renders the word meaningless.

    Example: Wife leaves behind slice of chocolate cake. Parent poster steps in kitchen and eats it. Wife next morning says cake is missing. Parent poster denies it forcefully, knowing but not revealing that the cake is now in the form of a fecal slurry diluted by a factor of a billion being further destroyed by chorine disinfectant dozens of miles away at the sewage treatment plant.

    Lesson: "missing" has a real meaning that is context dependent.

  • (Score: 0) by Anonymous Coward on Wednesday January 02 2019, @11:48PM (1 child)

    by Anonymous Coward on Wednesday January 02 2019, @11:48PM (#781248)

    But the "history" we're referring to isn't energy or matter, it's information. When you scrub a hard drive, the rust is still there, but the data it previously stored is gone. It's absurd to say the data is still there, and has "merely been made illegible" -- and it's equally absurd to say that when speaking of geological history.

    • (Score: 0) by Anonymous Coward on Wednesday January 02 2019, @11:55PM

      by Anonymous Coward on Wednesday January 02 2019, @11:55PM (#781251)

      More to the point, "missing" means you know something should be there but it is not.
      It doesn't matter if the thing still exists in some form or not. "Missing" describes state of knowledge (a
      consciously incomplete knowledge) on the part of the person who declares something is missing. It declares that there is a mystery to be solved.