New research strengthens the link between glaciers and Earth’s ‘Great Unconformity’
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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…