The Grand Canyon: Majestic, beautiful, and... a Frankenstein Monster?
How can a canyon be a Frankenstein Monster? A new theory claims that it is one large canyon formed by pieces of smaller, older canyons. A team of researchers, including three New Mexico EPSCoR participants, developed this new theory regarding the formation of the modern Grand Canyon. Their research states it was carved starting about 5-6 million years ago by the Colorado River through older "paleocanyons." Dr. Karl Karlstrom, Dr. Laura Crossey, and Dr. Shari Kelley of the Geothermal Energy team worked with researchers from California, New York, and Arizona to develop this theory and reconcile several different theories for how long ago the Grand Canyon formed. Their findings were published in Nature Geoscience on Janurary 26, 2014, followed by a storm of articles across scientific and media outlets due to the controversy of their claim, including NPR's Morning Edition, Nature News, BBC, Washington Post, National Geographic, and Science AAAS News.
In order to date the Canyon, Karlstrom and his team used a helium dating technique, paired with other techniques, to determine when certain segments of the canyon were exposed by erosion. The researchers measured temperature constraints to determined when rocks beneath the surface (always at warmer temperatures) were exposed by erosion (effectively cooling the rocks). They discovered that rocks from two of three middle segments, the Hurricane fault segment and the Eastern Grand Canyon segment, were dated at 55-70 million years old and 15-25 million years old respectively. However, rocks from the end segments, the Westernmost Grand Canyon and Marble Canyon are much younger, exposed by erosion between 5-6 million years ago. These dates oddly inconsistent, and inspired Karlstrom and his team to develop the paleocanyon theory. They state that the Hurricane and Eastern segments formed long ago from now non-existent river systems, and the Westernmost and Marble segments were exposed and connected to the other segments by the Colorado River 5-6 million years ago. So while parts of the modern Grand Canyon are certainly old, the Canyon we know today was formed by the Colorado River exposing new rock and flowing into the paleocanyon systems on its way to the Gulf of California.
Geochemical methods for dating are sometimes inconsistent, however, so it is likely the debate over the Grand Canyon's age and formation will continue. Still, many researchers and scientists agree this is the best theory to date. The full article can be read online on the Nature Geoscience website. Congrats to Karl, Laura, and Shari and their team!