Dating the grand canyon
Small changes in assumptions can mean big changes in interpretation.
For instance, some studies assume that the ground temperature at the surface is 25 degrees Celsius, whereas Karlstrom’s team used a range of 10‒25 degrees.
The team found that two stretches near the canyon's middle are indeed quite ancient: the eastern Grand Canyon is 15‒25 million years old, and another stretch downriver is 50‒70 million years old.
“It will take a bit more time to understand fully why their interpretations are so different from ours,” she says.Such changes mean big differences for interpreting how long a particular piece of apatite has been buried.“That just hit me like a ton of bricks,” says Brian Wernicke, a Caltech geologist who has argued for an ancient canyon, of Karlstrom's choices.But over the past few years, several studies have marshalled a range of geologic evidence to suggest that the canyon could be tens of millions of years old.Karlstrom and his team find that parts of the canyon could be tens of millions of years old, but that the canyon as a whole is much younger.