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Grand Canyon dates to dinosaur era, study says

Nov. 29, 2012
Courtesy of Uni­vers­ity of Col­o­rad­o Boul­der
and World Science staff

The west­ern Grand Can­yon is so old that di­no­saurs could have seen it, ac­cord­ing to a new anal­y­sis.

The re­search in­di­cates the can­yon in Ar­i­zo­na was largely carved out by about 70 mil­lion years ago, mak­ing it more than sev­en times old­er than widely be­lieved by sci­en­tists.

A view of the west­ern Grand Can­yon and Col­o­rad­o Riv­er from the can­yon bot­tom. (Cour­te­sy R. Flow­ers)


In the stu­dy, geo­sci­en­tist Re­bec­ca Flow­ers of the Uni­vers­ity of Col­o­rad­o Boul­der and col­leagues used a meth­od of dat­ing rocks that ex­ploits the na­tur­al de­cay of ura­ni­um and tho­ri­um atoms in­to he­li­um atoms. 

These atoms were locked in grains of a min­er­al called ap­a­tite as they cooled and wound up clos­er to the sur­face dur­ing the carv­ing of the Grand Can­yon, Flow­ers said. 

Tem­per­a­ture varia­t­ions at shal­low lev­els un­der­ground are in­flu­enced by the Earth’s sur­face shape, she ex­plained. And ap­a­tite pro­vides a tem­per­a­ture his­to­ry that can re­veal how much time has passed since there were ma­jor changes in the can­yon’s depth.

“Our re­search im­plies that the Grand Can­yon was di­rectly carved to with­in a few hun­dred me­ters (yards) of its mod­ern depth by about 70 mil­lion years ago,” said Flow­ers. A pa­per on the sub­ject by Flow­ers and Ken­neth Far­ley of the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy was pub­lished on­line Nov. 29 in the re­search jour­nal Sci­ence.

Sci­en­tists have de­bat­ed the can­yon’s age and ev­o­lu­tion, Flow­ers said. A va­ri­e­ty of da­ta sug­gest that the Grand Can­yon had a com­pli­cat­ed his­to­ry, and the en­tire mod­ern can­yon may not have been carved all at the same time. In 2008, Flow­ers and col­leagues re­ported in a study that parts of the east­ern can­yon likely de­vel­oped some 55 mil­lion years ago, al­though the bot­tom of that an­cient can­yon was above the height of the cur­rent can­yon rim at that time be­fore it sub­se­quently erod­ed to its cur­rent depth.

The di­no­saurs died out about 65 mil­lion years ago.

Over a mile (1.6 km) deep in places, Ar­i­zo­na’s steeply sid­ed Grand Can­yon is about 280 miles long and up to 18 miles wide in places. Vis­ited by more than five mil­lion peo­ple an­nu­al­ly, the icon­ic can­yon was likely carved in large part by an an­ces­tral wa­ter­way of the Col­o­rad­o Riv­er that was flow­ing in the op­po­site di­rection mil­lions of years ago, said Flow­ers.

“An an­cient Grand Can­yon has im­por­tant im­plica­t­ions for un­der­stand­ing the ev­o­lu­tion of land­scapes, to­pog­ra­phy, hy­drol­o­gy and tec­ton­ics in the west­ern U.S. and in moun­tain belts more gen­er­al­ly,” said Flow­ers.

Wheth­er he­li­um is re­tained or lost from the in­di­vid­ual ap­a­tite crys­tals is a func­tion of tem­per­a­tures in the Earth’s crust, she said. When tem­per­a­tures of the ap­a­tite grains are great­er than 158 de­grees Fahr­en­heit, they re­tain no he­li­um, while at tem­per­a­tures be­low 86 de­grees F, they re­tain all the he­li­um.


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The western Grand Canyon is so old that dinosaurs could have seen it, according to a new analysis. The research indicates the canyon in Arizona was largely carved out by about 70 million years ago, making it more than seven times older than widely believed by scientists. In the study, geoscientist Rebecca Flowers of the University of Colorado Boulder and colleagues used a method of dating rocks that exploits the decay of uranium and thorium atoms into helium atoms through radioactive processes. These atoms were locked in grains of a mineral called apatite as they cooled and wound up closer to the surface during the carving of the Grand Canyon, Flowers said. Temperature variations at shallow levels underground are influenced by the Earth’s surface shape, she explained. And apatite provides a temperature history that can reveal how much time has passed since there were major changes in the canyon’s depth. “Our research implies that the Grand Canyon was directly carved to within a few hundred meters (yards) of its modern depth by about 70 million years ago,” said Flowers. A paper on the subject by Flowers and Kenneth Farley of the California Institute of Technology was published online Nov. 29 in the research journal Science. Scientists have debated the canyon’s age and evolution, Flowers said. A variety of data suggest that the Grand Canyon had a complicated history, and the entire modern canyon may not have been carved all at the same time. In 2008, Flowers and colleagues reported in a study that parts of the eastern canyon likely developed some 55 million years ago, although the bottom of that ancient canyon was above the height of the current canyon rim at that time before it subsequently eroded to its current depth. The dinosaurs died out about 65 million years ago. Over a mile (1.6 km) deep in places, Arizona’s steeply sided Grand Canyon is about 280 miles long and up to 18 miles wide in places. Visited by more than five million people annually, the iconic canyon was likely carved in large part by an ancestral waterway of the Colorado River that was flowing in the opposite direction millions of years ago, said Flowers. “An ancient Grand Canyon has important implications for understanding the evolution of landscapes, topography, hydrology and tectonics in the western U.S. and in mountain belts more generally,” said Flowers. Whether helium is retained or lost from the individual apatite crystals is a function of temperatures in the Earth’s crust, she said. When temperatures of the apatite grains are greater than 158 degrees Fahrenheit, they retain no helium, while at temperatures below 86 degrees F, they retain all the helium.