How Old Is The Grand Canyon? Younger Than We Thought, New Research Suggests
In a study published journal Nature Geoscience, a team led by Karl Karlstrom of the University of New Mexico says that the Grand Canyon is both very old and a little less old. They suggest that about six million years ago, the Colorado River began flowing through the two-billion-year-old rocks that make up the canyon walls. The team does believe that sections of the Grand Canyon may be tens of millions years old, but not the entire thing, as those in the "old canyon" camp believe.
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"I think we've resolved the 140-year-long debate about the age of the Grand Canyon," Karlstrom told Nature. "We're making a major leap from thinking of a canyon that has a simple history...to a more sophisticated understanding of how landscapes actually evolve through time," he told NPR.
The difficulty in determining the Grand Canyon's age stems from the fact that rivers, by their very nature, carry evidence away from geologists. Erosion makes the rock record disappear, so geologists are left looking at a lack of something--not exactly ideal when you're trying to gather evidence, says Karlstrom.
Karlstrom and his team used thermochronology to analyze how the canyon walls' temperature varies layer by layer. The temperature of rocks increases the further down into the earth's crust it goes, so determining the temperature of each rock layer over time of rock can tell scientists when the layers were formed and when they eroded.
Karlstrom and co. took samples of rocks from four of the Grand Canyon's major sections, both at river level and at the mile-high canyon rim, and looked at apatite in the samples. In this mineral, the radioactive breakdown of uranium creates helium, which arrays itself in a specific way according to the temperature of the rock. By looking at this helium distribution in various sections of the Grand Canyon, the team could determine the rocks' ages. They found that two segments in the middle of the canyon were 15 to 25 million years old, while a section further downriver was 50 to 70 million years old.
"Different segments of the canyon have different histories and different ages, but they didn't get linked together to form the Grand Canyon with the Colorado River running through it until five to six million years ago," said Karlstrom.
The study won't be settling the old canyon vs. young debate anytime soon, though. Rebecca Flowers, author a 2012 study estimating that the Grand Canyon is 70 million years old, said: "It will take a bit more time to understand fully why their interpretations are so different from ours." Brian Wernicke, a Caltetch geologist and member of the old canyon camp, was more blunt: "That just hit me like a ton of bricks," he said of Karlstrom's conclusions. "They're not thinking this through."
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