News item - Grand Canyon began forming about 17M years ago
- UNM Researchers Discover Significantly Older Grand Canyon
Western portion of canyon actually formed 17 million years ago
by Steve Carr
(University of New Mexico press release, 3/13/2008)
Up until recently, it was thought the Grand Canyon was approximately
six million years old. That was until researchers in the Earth and
Planetary Sciences Department in the College of Arts and Sciences at
the University of New Mexico discovered otherwise. Using a technique
called uranium-lead isotope (U-Pb) dating of water table-type
speleothems or cave formations, researchers Victor Polyak, Carol Hill
and Yemane Asmerom, were able to determine the western portion of the
Grand Canyon actually began to form some 17 million years ago.
That revelation, or "Eureka moment" as Asmerom called it, makes the
Grand Canyon almost three times older than originally thought.
The research, which began more than nine years ago, was funded by the
National Science Foundation for $250,000 and published recently in the
journal Science. The discovery was enabled by the realization that
certain cave formations, such as mammillary coatings that form near
groundwater tables, allowed researchers to date both parts of the
canyon radiometrically accurately for the first time.
"The fact that many Grand Canyon caves contain mammillary speleothems
has allowed us to take advantage of advances in U-Pb and U-series
analytical techniques in an effort to make the long sought chronology
possible," said Polyak in the article.
As it turned out, the caves and cave deposits, which are located
throughout the Grand Canyon, were ideal in that the researchers found
both pre-existing and chemical sediments deposited before, during and
after the incision of the canyon.
Naturally, the caves preserved and protected them from weathering.
With sufficient uranium lead ratios and yield U-Pb dates, the
mammillary coatings place the water table within the canyon at a
particular place and at an absolute time. The mammillary coatings
allow for the incision history of the Grand Canyon to be reconstructed.
"We knew if we could successfully determine the age of these coatings,
we could position a pre-existing water table at a certain place in the
canyon at a particular time," said Polyak.
The core data, which included 57 analyses, came from nine mammillary
coatings from throughout the canyon, both east and west. The results
from the eastern Grand Canyon displayed faster water table descent
rates than data from the western Grand Canyon which showed stable,
slow drops in the water table. The data showed a slower incision rate
in the western portion than the eastern.
The resulting data provided a record of water table deposits as the
Colorado River cut through the canyon over millions and millions of
years approximately 17 million for the western portion.
"Based on uranium-lead dates of these deposits and the positions of
these deposits throughout the canyon, that the western Grand Canyon is
much older than what most scientists have thought," said Polyak.
"Normally what you'd expect is for the area around the headwaters to
be older than what they call the 'tail of the river,' said Asmerom.
"Here, essentially, you have a 10 million year old pre-history of the
western Grand Canyon before the Colorado River became a though-flowing
river to the Gulf of California."
The research may provide further clues and could eventually offer the
possibility for a reconstruction of the canyon's history.
"These results were possible by the convergence of new technical
capabilities achieved in our Radiogenic Isotope Laboratory, the
conceptual breakthrough in connecting the mammillary to the water
table and having samples that had sufficient uranium for dating," said
For more information on the Radiogenic Isotope Laboratory at UNM
visit: Radiogenic Isotope Laboratory.