Great Unconformity

FILE PHOTO: The Great Unconformity exposed in Grand Canyon separates the Tapeats Sandstone from ancient Proterozoic rocks. The Great Unconformity represents ~1.2 billion years of missing rock record, either due to erosion or non-deposition.
New research provides further evidence that rocks representing up to a billion years of geological time were carved away by ancient glaciers during the planet's "Snowball Earth" period, according to a study published in Proceedings of the National Academy of Sciences.

The research presents the latest findings in a debate over what caused the Earth's "Great Unconformity" -- a time gap in the geological record associated with the erosion of rock up to 3 miles thick in areas across the globe.

"The fact that so many places are missing the sedimentary rocks from this time period has been one of the most puzzling features of the rock record," said C. Brenhin Keller, an assistant professor of earth sciences and senior researcher on the study. "With these results, the pattern is starting to make a lot more sense."

The massive amount of missing rock that has come to be known as the Great Unconformity was first named in the Grand Canyon in the late 1800s. The conspicuous geological feature is visible where rock layers from distant time periods are sandwiched together, and it is often identified where rocks with fossils sit directly above those that do not contain fossils.

"This was a fascinating time in Earth's history," said Kalin McDannell, a postdoctoral researcher at Dartmouth and the lead author of the paper. "The Great Unconformity sets the stage for the Cambrian explosion of life, which has always been puzzling since it is so abrupt in the fossil record -- geological and evolutionary processes are usually gradual."

For over a century, researchers have sought to explain the cause of the missing geological time.

In the last five years, two opposing theories have come into focus: One explains that the rock was carved away by ancient glaciers during the Snowball Earth period about 700 to 635 million years ago. The other focuses on a series of plate tectonic events over a much longer period during the assembly and breakup of the supercontinent Rodinia from about 1 billion to 550 million years ago.

Research led by Keller in 2019 first proposed that widespread erosion by continental ice sheets during the Cryogenian glacial interval caused the loss of rock. This was based on geochemical proxies that suggested that large amounts of mass erosion matched with the Snowball Earth period.

"The new research verifies and advances the findings in the earlier study," said Keller. "Here we are providing independent evidence of rock cooling and miles of exhumation in the Cryogenian period across a large area of North America."

The study relies on a detailed interpretation of thermochronology to make the assessment.

Thermochronology allows researchers to estimate the temperature that mineral crystals experience over time as well as their position in the continental crust given a particular thermal structure. Those histories can provide evidence of when missing rock was removed and when rocks currently exposed at the surface may have been exhumed.

The researchers used multiple measurements from previously published thermochronometric data taken across four North American locations. The areas, known as cratons, are parts of the continent that are chemically and physically stable, and where plate tectonic activity would not have been common during that time.

By running simulations that searched for the time-temperature path the rocks experienced, the research recorded a widespread signal of rapid, high magnitude cooling that is consistent with about 2-3 miles of erosion during Snowball Earth glaciations across the interior of North America.

"While other studies have used thermochronology to question the glacial origin, a global phenomenon like the Great Unconformity requires a global assessment," said McDannell. "Glaciation is the simplest explanation for erosion across a vast area during the Snowball Earth period since ice sheets were believed to cover most of North America at that time and can be efficient excavators of rock."

Comment: Glaciers are not the only 'efficient excavators of rock', electrical scarring due to plasma discharge events is just as 'simple' and even more efficient, and there is evidence of its occurance on Mars. The problem here is that mainstream science, for the most part, has yet to incorporate principles proposed by Electric Universe theory and catastrophism into its uniformitarian model.

As Pierre Lescaudron notes in Did Earth 'Steal' Martian Water?:
There are several canyons on Earth, including the Grand Canyon, which hold features of electric scarring.

Does the bedrock of Antarctica show any sign of positive electric scarring, i.e. a massive canyon-like geological feature? Indeed it does. As shown in the satellite picture above, Antarctica is considered to host the largest canyon on Earth, according to a 2016 geological survey:
[...] the largest unsurveyed region on the icy continent is a region called Princess Elizabeth Land. Now a team of geologists has scoured that area to reveal a massive subglacial lake and a series of canyons, one of which — more than twice as long as the Grand Canyon — could rank as Earth's largest.

One of the main geological features of Mars is Valles Marineris. At more than 4,000 km (2,500 mi) long, 200 km (120 mi) wide and up to 7 km (4.5 mi) deep, it is the second largest canyon in the entire Solar system, and stretches for nearly a quarter of the planet's circumference. Mainstream science theorizes that Valles Marineris formed as a result of water erosion billions of years ago. However, this explanation doesn't seem to match some of the characteristics of Valles Marineris:

According to the research team, the competing theory that tectonic activity carved out the missing rock was put forth in 2020 when a separate research group questioned whether ancient glaciers were erosive enough to cause the massive loss of rock. While that research also used thermochronology, it applied an alternate technique at only a single tectonically active location and suggested that the erosion occurred prior to Snowball Earth.

"The underlying concept is pretty simple: Something removed a whole lot of rock, resulting in a whole lot of missing time," said Keller. "Our research demonstrates that only glacial erosion could be responsible at this scale."

According to the researchers, the new findings also help explain links between the erosion of rock and the emergence of complex organisms about 530 million years ago during the Cambrian explosion. It is believed that erosion during the Snowball Earth period deposited nutrient-rich sediment in the ocean that could have provided a fertile environment for the building blocks of complex life.

Comment: The sudden deposition of nutrients does not equal an explosion of life nor does it explain the sudden increase in complexity. However, it may actually support the possibility of electrical scarring, because there have been other cataclysmic and extinction level events that appear in the geological record that were also then followed by the sudden appearance of more complex life: Another hit for Intelligent Design: Scientific paper reaffirms that new genes were required for Cambrian Explosion

The study notes that the two hypotheses of how the rock eroded are not mutually exclusive -- it is possible that both tectonics and glaciation contributed to global Earth system disruption during the formation of the Great Unconformity. It appears, however, that only glaciation can explain erosion in the center of the continent, far from the tectonic margins.

"Ultimately with respect to the Great Unconformity, it may be that the generally accepted reconstruction(s) of more concentrated equatorial packing of the Rodinian continents along with the unique environmental conditions of the Neoproterozoic, proved to be a time of geologic serendipity unlike most any other in Earth history," the research paper says.

According to the team, this is the first research that uses their thermochronology modeling approach to study a period that extends well beyond a billion years. In the future, the team will repeat their work on other continents, where they hope to further test these hypotheses about how the Great Unconformity was created and preserved.

According to the team, resolving differences in the research is critical to understanding early Earth history and the interconnection of climatic, tectonic and biogeochemical processes.

"The fact that there may have been tectonic erosion along the craton margins does not rule out glaciation," said McDannell. "Unconformities are composite features, and our work suggests Cryogenian erosion was a key contributor, but it is possible that both earlier and later erosion were involved in forming the unconformity surface in different places. A global examination will tell us more."

William Guenthner, from the University of Illinois at Urbana-Champaign; Peter Zeitler from Lehigh University; and David Shuster from the University of California, Berkeley and the Berkeley Geochronology Center served as co-authors of the paper.
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Materials provided by Dartmouth College. Original written by David Hirsch. Note: Content may be edited for style and length.

Related Multimedia: The Great Unconformity, massive rock loss

Journal Reference: Kalin T. McDannell, C. Brenhin Keller, William R. Guenthner, Peter K. Zeitler, David L. Shuster. Thermochronologic constraints on the origin of the Great Unconformity. Proceedings of the National Academy of Sciences, 2022; 119 (5): e2118682119 DOI: 10.1073/pnas.2118682119