The article was published Thursday in the online version of Science, and concludes "[Rebecca] Flowers and [Kenneth] Farley analyzed four rock samples from the western portions of the Grand Canyon and four from the eastern reaches of the gorge. The pattern of helium concentrations in the samples suggests that substantial parts of the western portion of the Grand Canyon were already carved to within a few hundred meters of their current depth by about 70 million years ago and that erosion hasn't increased dramatically in recent eras, the researchers report. That's a far cry from the 5-million-to 6-million-year-old age suggested by previous research, and is about quadruple the oldest previous estimate from other teams for the canyon's age."
Meanwhile, the Geological Society of America published a new book, "Grand Canyon Geology: Two Billion Years of Earth’s History," edited by Michael Timmons and Karl E. Karlstrom. The summary notes "Carved in the last 6 million years by the Colorado River and its tributaries, Grand Canyon is one of the premier geologic landscapes in the world."
Karl and UA geologist Bill Dickinson are quoted in Science expressing some skepticism over the new 'old' results. Previous work by AZGS geologists supports the younger age for the canyon. We need to take a hard look at these new dates.