Scientists approximate that parts of the Grand Canyon was formed between five and six million years ago, much younger than initially suspected. However, other segments of the natural wonder are conjectured to be as old as 70 million years.
The latest research study was published in the Jan. 26 issue of the journal Nature Geoscience. Snaking through the American state of Arizona, the researchers insist the full system of the canyon is relatively young. Professor Karl Karlstrom from the University of New Mexico, Albuquerque, explains that his research team is refuting both “young” and “old” canyon models; the young model argues the canyon was cut entirely within the last six million years, while the old model claims it was cut 70 million years ago.
Instead, Karlstrom explains that the Colorado River found “low places and paleocanyons and ancient topographies,” which ultimately led to the Grand Canyon’s formation. The Colorado River sprang from the Rocky Mountains around 11 million years back. Karlstrom suggests, about six million years ago, the Colorado river headed southwest and caused two of the older segments of the grand canyon to integrate with two remarkably young segments, before it began flowing into the Gulf of California.
Research teams have harnessed thermochronology to determine previous temperatures of the rocks along the wall of the Grand Canyon. As parent isotopes in the apatite crystals of the rock decay, helium is liberated and accumulates within the rocks. When the apatite is hotter than around 50 degrees Celsius, the helium is lost. However – looking specifically at the Grand Canyon – when the canyon-carving river removes the rock’s cover, the rock becomes cooler and allows the helium to remain trapped within the crystals. Measuring the amount of helium present can provide an indication of how long the rock has been exposed to the surface and, therefore, its age.
Karlstrom’s group looked at different segments of the Grand Canyon and determined how old each part was. According to the researchers, five segments of the canyon were carved at varying times, while two of the segments were less than six million years old, including the Marble Canyon and the Westernmost Grand Canyon. Meanwhile, the 1,500 meter deep Eastern Grand Canyon was carved 25 million years ago, whereas the Hurricane Canyon was estimated to have been carved, to around half of its present-day depth, 70 million years ago.
Karlstrom recently explained that the canyon is split up into regions of varying age, and continues to deepen, to this day. Over the past 500,000 years, he claims the Grand Canyon continues to deepen by the thickness of a piece of paper, each year. Karlstrom spoke to BBC News about the canyon’s age range:
“If you were to add up the 280-mile length and ask, ‘how much is young?’ More than half of it is young; a quarter of it is middle-aged – 15-25 million years old; and the rest of it is 70 million years old.”
University of Colorado geologist Rebecca Flowers was lead author on a 2012 paper, published in Science, that proclaimed the old canyon model to be true. In responding to the latest study, Flowers informed Live Science that it would take time before her group fully understood why the two studies’ conclusions were so different, and whether it is possible for the erosion history to vary “… so dramatically within this short reach of the canyon.” Meanwhile, California Institute of Technology geologist Brian Wernicke, who co-authored the 2012 paper, continues to support the old canyon theory and believes the westernmost stretch of the canyon to be 70 million years of age.
Most concede that Karlstrom’s research will not end the debate over the Grand Canyon’s age. The main source of contention typically lies in interpretation of the cooling ages of sampled rock by geochemists, who are often found to derive different conclusions.
By James Fenner