Researchers Dig Into Case of Geologic Amnesia – In Search of a Billion Years Missing From the Geologic Record

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Great Unconformity

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A hiker strolls along a roadway near Manitou Springs, Colorado, where an exposed outcrop reveals a function called the “Great Unconformity.”Credit: Rebecca Flowers

A group of geologists led by CU Boulder is digging into what might be Earth’s most well-known case of geologic amnesia.

Researchers have actually identified that phenomenon, called the “Great Unconformity,” at areas around North America, consisting of in the Grand Canyon and at the base of Pikes Peak in Colorado. There lie websites of missing out on time, where fairly young rocks going back about 550 million years sit right on top of far more ancient stone—in many cases more than 3 billion years of ages. 

In other words, a big piece of geologic history has actually disappeared from in between. 

“Researchers have long seen this as a fundamental boundary in geologic history,” stated Rebecca Flowers, an associate teacher in the Department of Geological Sciences.

Rebecca Flowers

Rebecca Flowers stands near an outcrop on Pikes Peak in Colorado. Credit: Rebecca Flowers

For a research study released on April 27, 2020, in the Proceedings of the National Academy of Sciences, she and her associates made use of a strategy called “thermochronology” to take a fresh appearance at that basic limit. They discovered that the Great Unconformity may not be the outcome of a single, devastating occasion in the world’s past like numerous researchers believed. Instead, a series of smaller sized disasters might have set off various unconformities around the globe. 

The results might assist researchers much better comprehend the thriving of intricate life that took place not long after that tumult settled, about 540 million years earlier in an age called the “Cambrian Explosion.”

“There is a lot of the geological record that is missing,” Flowers stated. “But just because it’s missing doesn’t mean that this history is simple.”

Pikes Peak

To research study that less-than-simple history, Flowers and her associates relied on Pikes Peak. In a granite outcrop near the mountain town of Manitou Springs, geologists can discover among the clearest cases of the Great Unconformity. 

Follow the strata down, and you will see young rocks—less than 510 million years of ages—and older “basement” rocks—going back about 1 billion years. But you won’t discover anything in between.

Geologists understand that something should have occurred in the past to eliminate all that history, Flowers stated. What that was and when precisely it took place, nevertheless, are still a secret.

“Only recently have we had the ability to reach far enough back in time to start filling in that gap,” she stated.

Rocks, Flowers stated, bring a sort of memory. By penetrating the specific atoms that have actually been secured inside geologic samples, smart researchers can produce a heat-based history of those rocks—basically, how hot or cold the sample was at numerous points in its life time.

Using that technique, the scientists found that the Pikes Peak basement rocks were given the surface area of the world about 700 million years earlier. For Flowers’ group, that finding was essential.   

When all that rock increased to the surface area, she described, it would have all of a sudden been at the grace of wind, snow and other extremes. And those aspects might have caused disintegration—a great deal of disintegration—basically cleaning the geologic history of the area tidy. Imagine shaking an Etch-a-Sketch however on a huge level. 

“Earth is an active place,” Flowers stated. “There used to be a lot more rocks sitting on top of Mount Everest, for example. But they’ve been eroded away and transported elsewhere by streams.”

Blame Rodinia

But what raised those rocks up in the very first location? Flowers and her associates believe it has something to do with Rodinia. That’s the name of a huge supercontinent—believe Pangea, just much older—that formed at Earth’s surface area approximately 1 billion years earlier. 

“At the edges of Rodinia, where you have continents colliding, you’d see these mountain belts like the Himalayas begin to form,” Flowers stated. “That could have caused large amounts of erosion.”

The scientists likewise recognized something else: The Great Unconformity may not have actually been so excellent in the very first location. As Rodinia crashed together then pulled apart over numerous countless years, all that geologic activity might have triggered numerous different cases of amnesia around the globe—not simply one. 

“We’re left with a feature that looks similar across the world when, in fact, there may have been multiple great unconformities, plural,” Flowers stated. “We may need to change our language if we want to think about the Great Unconformity as being more complicated, forming at different times in different locations and for different reasons.”

It’s something to consider the next time you opt for a walking on Pikes Peak. 

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Reference: “Diachronous development of Great Unconformities before Neoproterozoic Snowball Earth” by Rebecca M. Flowers, Francis A. Macdonald, Christine S. Siddoway and Rachel Havranek, 27 April 2020, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.1913131117

Coauthors on the brand-new research study consist of Rachel Havranek, a college student in Geological Sciences at CU Boulder; Francis Macdonald of the University of California, Santa Barbara; and Christine Siddoway of The Colorado College.



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