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As you read this story, you will learn the following:
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About a billion years of rock is missing from geological formations around the world, especially in the American Southwest—a mystery known as the “Great Unconformity.”
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Scientists speculate that the Great Unconformity was caused by Earth’s “Snowball Earth” phase or the formation of the supercontinent Rodinia, but a new study suggests that a major erosional event occurred both epochs before.
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By analyzing ancient rocks in China, new research finds that the formation of Columbia, Earth’s first supercontinent, may be the culprit behind this rock conundrum.
Our planet’s 4.6 billion-year history can be explained in large part by the vast story of the geological layers that fold beneath the Earth’s surface. But sometimes the story reads more like mystery Than a piece of history. One of the greatest examples of this geological mystery is known as the “Great Unconformity.” While its name seems more appropriate for awkward teenage years than geology class, this rock puzzle is found around the world, especially in the American Southwest, including the Grand Canyon, and involves missing geological layers between Cambrian and Precambrian rocks that represent about a billion years of missing Earth history.
Since the discovery of unconformities in the mid-1800s, geologists have come up with some interesting speculations about their origins. One is called “Snowball Earth,” a period in Earth’s history about 700 million years ago that essentially carved these formations through geological forces unleashed by a long period of severe global cold. Another possible suspect is the supercontinent Rodinia, which formed about a billion years ago, uplifting older rocks and exposing them to weathering. Now, an international team of scientists says they’ve made a startling discovery by analyzing five locations where the Great Unconformity is exposed in North China. Their results suggest that rock formation failure actually precedes Both these events. Research results published in journal Proceedings of the National Academy of Sciences (Proceedings of the National Academy of Sciences).
“The Great Unconformity… represents a globally important period of continental exposure and erosion, which is also notable for the first appearance of all major animal phyla on Earth,” the authors write. “The most obvious erosional indications in the thermochronological record of continental weathering and geochemical indicators correspond to the development of Earth’s first true supercontinent.”
Although the supercontinent Pangea is quite famous, it was far from the first continental collapse on Earth. In fact, there are already At least Four true supercontinents, the oldest of which is Colombia, which formed about 2 billion years ago and began the Great Breakup about 400 million years later. By looking at rocks on the older side of the Great Unconformity Divide, scientists analyzed radioactive elements and were able to determine how much time had passed since the rocks cooled to a certain point. science.
This timeline shows that much of the erosion occurred long before “Snowball Earth” or Rodinia formed. Liang Duan of Northwestern University, lead author of the study, told us science The geological forces at work in these other events may have played a role in the Great Unconformity, but they are not the primary cause of the billion-year-old rock disappearing.
If this conclusion stands up to scrutiny, it is puzzling in many ways. Previous theories suggested that the Great Uniformity was a major erosional event that flooded the oceans with nutrients and minerals, potentially triggering the Cambrian Explosion, a rapid evolutionary event about 540 million years ago. The new timeline certainly complicates that narrative. The data indicate that major erosion events must occur in return Known as the “Boring Billion” – a period of Earth’s history approximately 1.8 to 800,000 years ago that is considered geologically boring.
Of course, what’s the use of a suspense novel without some plot twists?
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