January 27, 2014
Modern Grand Canyon May Actually Be Fairly New
[ Watch the Video: How Old Is The Grand Canyon? ]
Brett Smith for redOrbit.com - Your Universe Online
Since the deeper a stone sits, the warmer it is – scientists can date the Grand Canyon’s creation with geochemical techniques that measure the temperature of rocks over time. When erosion takes away a layer of rocks, the exposed layer of stone moves closer to the surface and cools down – meaning a rock has been on the surface from the time that it cooled.
The mineral apatite contains several stripes of evidence that can be used to trace a rock’s temperature history. For instance, the breakdown of radioactive uranium within the apatite generates helium atoms, which distribute from the mineral based on the stone’s temperature.
The study team used the helium technique and other methods to study rocks along the length of the Grand Canyon. They found two segments near the canyon's middle are older, as expected: the eastern Grand Canyon is 15 to 25 million years old and another expanse downriver is 50 to 70 million years old. However, the researchers also discovered two other segments were eroded far more recently.
“Different segments of the canyon have different histories and different ages, but they didn’t get linked together to form the Grand Canyon with the Colorado River running through it until 5 to 6 million years ago,” Karlstrom said.
Previous studies have found similar helium dates for these parts of the canyon, and yet reach diverse outcomes about what the dating information means.
“It will take a bit more time to understand fully why their interpretations are so different from ours,” said Rebecca Flowers, a geologist from the University of Colorado Boulder who published a similar study on the canyon in 2012.
Small changes in suppositions can mean big changes in interpretation, the study team said. For instance, some previous research studies presupposed that the ground temperature at the surface is 77 degrees F, unlike Karlstrom’s team, which used a range of 50 to 77 degrees. These differences in calculations can translate into big differences for interpreting how long a sample has been buried.
“That just hit me like a ton of bricks,” said Brian Wernicke, a Caltech geologist who has argued for an ancient canyon, of choices made by Karlstrom’s team. “They’re not thinking this through.”
Karlstrom has argued for using a range of surface temperatures, unlike other studies, as the temperatures most likely swayed over millions of years.
In Flowers’ 2012 study, the researchers used radioactive decay in apatite to conclude that rocks now sitting exposed in parts of the canyon must have been on or close to the surface for 70 million years.