| Title | Earth is Missing a Huge Part of its Crust. Now We May Know Why. | |
| Date | Wednesday January 02 2019, @05:25PM | |
| Author | Fnord666 | |
| Topic | ||
| 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).
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