Today’s Top Science Headline –The Day the Earth Stood Still: “There’s a Missing Chapter in Earth’s History”

 

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“It’s almost like there was a speed limit for 100 million years,” says Ross Mitchell, a geologist at Curtin University in Australia. The planet’s plates slowed to a snail’s pace, its mountains were cut short and its volcanoes fell dormant. The world became quiet and still.


Continents and volcanoes nearly came to a halt billions of years ago, reports today's Scientific American, creating a huge planetary pressure cooker. Our planet is always on the move. Earth’s surface is a jigsaw puzzle of enormous plates of crust that continuously jostle about. They bulldoze into one another, slip under one another and slide apart in mighty processes that build soaring mountain chains, pave new lands with fresh lava and carve colossal oceans. But 2.3 billion years ago that motion slowed to a crawl. That strange hiatus shows up in an uncanny gap in the geologic record, revealed in research published January 29 in Nature Geoscience.

 

“The end result here is that there’s a missing chapter in Earth’s history,” says co-author Mitchell. Because jostling movements leave traces and trails on our planet, including the creation of new rocks, the absence of those rocks indicates a sharp reduction of motion, as if the planet slammed on the brakes roughly 2.3 billion years ago and kept them on for a long time.

Although various data sets have hinted such a gap might exist, many scientists remained skeptical. David Evans, a geologist at Yale University who was not involved in the study, for example, thought those gaps would surely fill in as geologists overturned more and more rocks with time.

To try and settle the issue, Christopher Spencer, a geologist from Curtin, along with Mitchell and other colleagues decided to compile the largest statistical sample yet. They pored through data sets that included over 400,000 minerals and 700,000 rock samples of various types—from those that form from hardened magma to those that form when a continental plate crumples and is pushed upward to create a mountain range. But at the end of the day they simply could not uncover any rocks or minerals that appeared between 2.3 billion to 2.2 billion years ago.

That has convinced Evans. Although he admits he cannot help but worry about the many rocks that lie inaccessible beneath Antarctica’s vast ice sheet, he is more certain the lull will stand the test of time. “This paper undeniably is the most detailed study of this topic,” he says. “In that regard, it is state of the art and should keep us talking about the issue for a long time.”

Spencer and his colleagues think the pause reflects a period in Earth’s history where the continents were welded together into a single supercontinent known as Superia.

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