Grand Canyon as old as the dinosaurs

One of the Seven Wonders of the World is older and with a more interesting history than was previously assumed. Mineral grains from the bottom of the western Grand Canyon have indicated it was formed around 70 million years ago, according to a study led by the University of Colorado Boulder.

This new research pushes back the conventionally accepted date for the Grand Canyon’s formation by more than 60 million years. The team used a novel dating method that exploits the radioactive decay of uranium and thorium atoms to helium atoms in a phosphate mineral known as apatite.

“Our research indicates that the Grand Canyon was directly carved to within a few hundred meters of its modern depth by about 70 million years ago,” said CU-Boulder Assistant Professor Rebecca Flowers.

There is significant controversy among scientists over the age and evolution of the Grand Canyon. The most popular theory places the age of the Grand Canyon at 5 million to 6 million years based on the age of gravel washed downstream by the ancestral Colorado River. In 2008, a study published in Science estimated the age of the Grand Canyon to be around 17 million years old after scientists date mineral deposits from the canyon walls.

“The variety of conflicting information has caused scientists to argue about the age of the Grand Canyon for more than 150 years,” added Flowers.

Helium atoms were locked in the mineral grains as they cooled and moved nearer to the surface during the carving of the Grand Canyon. Whether helium is retained or lost from the individual apatite crystals is a function of temperature in the rocks of the Earth’s crust. If the temperatures of the apatite grains are greater than 70°C helium is lost, but at 30°C, all of the helium is retained.

The team also analysed the spatial distribution of helium atoms near the margin of individual apatite crystals to determine whether the rocks had a rapid cooling or slow cooling history.

“The main thing this technique allows us to do is detect variations in the thermal structure at shallow levels of the Earth’s crust. Since these variations are in part induced by the topography of the region, we obtained dates that allowed us to constrain the timeframe when the Grand Canyon was missed,” Flowers added.

Apatite ⁴He/³He and (U-Th)/He Evidence for an Ancient Grand Canyon