The Grand Canyon is missing over a billion years of rocks. Now scientists know why.
More than a billion years of geological history is missing from the walls of the Grand Canyon, and now, scientists may know why.
Key points
- Importantly, the model also shows that in the past 540 million years, these same areas started sinking instead of rising, creating areas for sediments to get caught and then keep piling up in neat layers on the continents — marking the point where the Great Unconformity ends.
- For example, the ancient Paleo-Tethys ocean, which lapped off the shores of the supercontinent Pangaea until it closed about 200 million years ago, was rich in carbon-bearing sediments that eroded from the continents, Peters said.
- In the canyon's sides, ancient metamorphic and igneous rocks that formed 1.7 billion years ago sit directly under younger sedimentary rocks laid down 500 million years ago.
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Additional details
- What's getting pushed into the mantle now is therefore a different chemical composition than what existed 200 million years ago.
- "We looked at, where are the best places that the mantle would help create a Great Unconformity?" study co-author Nicolas Flament, a geoscientist at the University of Wollongong in Australia, told Live Science.
- "And these three places turned out to be three places where it's known to be quite extensive." Erosion during Neoproterozoic times, followed by sedimentation during early Phanerozoic times, formed the Great Unconformity.
- (Image credit: Author provided, CC BY-ND) The cause of the Great Unconformity is hotly debated, with some arguing that a global deep freeze known as Snowball Earth could have shoveled sediment off the continents in this period.
- Nicolas Flament, geoscientist at the University of Wollongong in Australia Today, in contrast, most of Earth's subduction is around the Pacific Rim, and much of the Pacific seafloor is remote from continents, so the seafloor is relatively starved of carbon.
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