Scientists are able to reconstruct in detail the Earth’s past history only with fossils, rocks and other objects they find in the wild. However, there are times when the geological record is lost, leaving scientists confused about where it all went.
This phenomenon, better known as The Great Unconformity, is a time gap that appears in rocks around the world. As a result, Earth’s history is lost for billions of years. 550 million year old stone formed on top of ancient layers 1.7 billion years old with no trace of any history.
The discrepancy of time, which erased much of the Neoproterozoic era, has been a hot topic among geologists for centuries. Some scientists hypothesize “Unconformity” is caused by tectonic activity associated with the formation and breakup of the supercontinent Rodinia, while others see the cause as widespread glacier erosion during the “Snowball Earth” phase about 700 million years ago.
The team led by Kalin McDannell, a postdoctoral researcher studying earth sciences at Dartmouth College, United States, has found new evidence that believes glaciers are the main cause of the time gap.
The researchers found strong “cooling signals,” or cooling signals, at four geological locations across North America, suggesting continental-scale glaciation is “the only process that can explain the creation of The Great Unconformity”. They describe their views on this phenomenon in Education which is published in The Proceedings of the National Academy of Sciences.
“I think it’s interesting because there’s something unique about global geodynamics and the surface processes that drive the creation of The Great Unconformity and its preservation,” said McDannell when contacted with C. Brenhin Keller, assistant professor of earth sciences at Dartmouth College who also wrote. this research.
Previous research has found evidence of tectonic erosion at several locations, such as Pikes Peak in Colorado and the Ozark Plateau in Missouri, which were near the active fault lines of Rodinia 700 million years ago. Meanwhile, McDannell and colleagues expanded the area and studied rocks found in East Lake Athabasca, Canada and the Minnesota River Valley. Both locations are very far from areas affected by tectonic activity in this era.
Researchers studied the causes of The Great Unconformity using thermochronometric data from four locations in North America. Image by Kalin McDannell.
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When analyzing available thermochronological data from these regions, the research team found signs of synchronous rock cooling associated with glacier erosion. While tectonic activity can cause The Great Unconformity in certain areas, they conclude that only the process of glaciation can knock down strata for kilometers in various regions.
“There are signals of tremendous cooling in the interior of the continent. It’s hard to imagine any other way that could have done this other than glaciation,” said Keller, who chaired the 2019 research which also supports the theory of glaciation processes as a cause.
While the new study supports the glaciation hypothesis, McDannell’s team plans to analyze samples from other locations around the world to gain a broader understanding of this time gap. In addition to solving intriguing geological mysteries, further study could have implications for understanding the emergence of complex life on Earth.
The lost geological record is estimated to be around 550 million years, just before the appearance of complex life on Earth. While there is no definite link between the causes of The Great Unconformity and the emergence of modern species, the close proximity of time has caught the attention of scientists.
“At least we can imagine, without being too speculative, that a period of extended glacier erosion could create a lot of igneous rock that was pulverized, and crustal rock that was reworked more broadly. These rocks contain a lot of nutrients, which wouldn’t hurt the organisms that were trying to diversify and reproduce during that period,” Keller said.
“There was an explosion of life after the boulder disappeared massively,” McDannell added. “So you can make this causal conclusion, both cautiously and tentatively. This field may not be well known, but it can be learned.”
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