Coming upon the Grand Canyon long ago, an old prospector is supposed to have said in amazement, “Something awful happened here.”
The something appears to have started happening some 17 million years ago, geologists concluded in a study reported in Friday’s issue of the journal Science. If correct, that is at least 11 million years earlier than previous estimates.
By dating mineral deposits inside caves up and down the canyon walls, the geologists said they determined the water levels over time, as erosion carved out the mile-deep canyon as it is known today. They concluded that the canyon started from the west, then another formed from the east, and the two broke through and met as a single majestic rent in the earth some six million years ago.
Previous theories had posited six million years as the earliest age for the beginning of the entire Grand Canyon of the Colorado River.
The new research was conducted by geologists at the University of New Mexico, led by Victor Polyak. The researchers, supported by the National Science Foundation, used an improved uranium-lead dating technique, which yields ages of mineral back tens to hundreds of million years.
Tests at nine sites established the ages of thick white and yellowish-orange calcite deposits lining walls of cave interiors, as a measure of lowering water levels as the canyon deepened. The results indicated that the erosion rate was much slower in the western canyon than in the eastern section, the geologists reported.
“We were surprised by our results,” Dr. Polyak said in a telephone interview. “There have been a lot of theories over the last 100 years, and we didn’t expect the canyon history to go back so far.”
In an accompanying commentary, two British geologists who were not involved in the research wrote that some scientists had suspected the greater time-scale for the canyon’s formation, but the new study “demonstrates it firmly for the first time.” – nytimes