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Earth is Missing a Huge Part of Its Crust. Now We May Know Why. (nationalgeographic.com)
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.
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.
> because glaciers don't "move"
They certainly do. Or at least they can...
https://en.wikipedia.org/wiki/...
And they're pretty effective at scrubbing the underlying terrain.
=Smidge=
you exactly where the crust went, and when, and why.
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.
I live in Finland and the movement of the glaciers is clearly visible on rocks here.
> 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=
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.
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.
Look back up at my post, now look back down, you're on the Internet. Now look back up. I'm a signature.
The poor sods who wrote this paper will be crushed by the Global Warming maniacs.
Not at all. This aligns perfectly with our existing understanding of Earth. Climate changes slowly over periods hundreds of thousands and millions of years.
The problem with global warming is that the climate is changing in a periods of decades. This is a problem because this does not provide the time required for fauna/flora to evolve. As a result of this decreased period, many species are facing extinction.
Anons need not reply. Questions end with a question mark.
You must have head of the Roman Optimum and the Medieval Warm Period - and the many other examples of this. Even the Little Ice Age.
1. The Medieval Warm Period was localized to the north Atlantic region, with the pacific region getting colder. Current warming is increasing average temperatures across the globe.
2. The cause of the Medieval Warm Period (as per the link) is believed to have been solved.
3. Atmospheric CO2 has increased from ~300 to ~400 PPM since the 60s, in line with increased fossil fuel emissions.
4. The cause of the current warming is believed (by 90+% of the scientists investigating it) to have been solved. Spoiler alert it's the increasing atmospheric CO2.
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=