The Grand Canyon presents an unrivaled view into the Earths geologic history. From the canyons Paleozoic-era rims to the bottom of the Precambrian-age inner gorge, nearly 2 billion years of time are represented in the exposed rocks, or about two-fifths of the Earths estimated age of 5 billion years (Hoffman, 1987, p. 11). This quote came from a book that was purchased in 1999 from one of the gift shops at Grand Canyon National Park. The author, John Hoffman goes on to describe how about 40 million years were required for the Grand Canyon to be eroded to its awesome dimensions (p. 12). While that book has truly beautiful pictures, the text inside is in dire need of revision.
An article in the September 30, 2000 issue of Science News has shown that carving this beloved hole in the ground may not have been such a long-term project after all (Perkins, 2000). Prior to the 1930s, geologists proposed that the Grand Canyon was about 40 million years old (p. 218). However, evidence now has come to light that indicates a much younger canyon. Research presented at a June 1999 conference devoted to the origin of the gorge suggests that substantial portions of the eastern Grand Canyon have been eroded only within the past million years. And so, as quickly as ink dries on paper, geologists cut 39 million years off the age of the Grand Canyon, and dropped its age to 1/40 of their previous estimates. This is even 3 million years less than Hoffmans calculation (p. 12).
In justifying their new calculations for the young age of the canyon, geologists suggest a scenario in which the portions of the present-day Colorado River above and below the canyon may not have been connected. They believe that the most likely explanation is that the west flowing tributary of the ancestral lower Colorado River began to carve a small valley eastward into the edge of the Colorado Plateau. The upper portion of the river eventually merged with the ancestral upper Colorado River and its tributaries to form a single river system. The result would have been a strengthened torrent of water that could carve through rock at a faster clip than ever before (p. 219). Faster clip indeed! Thirty-nine million years is a tremendous amount of time to suddenly just vanish! Richard Young, a geologist at the State University of New York, speculated on the swiftness of this erosion: Fifty years ago, geologists didnt realize how fast erosion could occur. When theres a depression in the rock and the river flows through, it can erode incredibly rapidly.
The Science News article listed other studies in which data show how fast rivers can slash through rock. It also listed the erosion rates of several neighboring canyons, and then noted: Downstream in the Grand Canyon, where the Colorado carries much more water and sediment, rates of erosion are likely much higher. This is exactly the point Derek Ager, former president of the British Association for the Advancement of Science (and head of the department of geology and oceanography, University