"Long before it's in the papers"
January 28, 2015


Dinosaurs along the Grand Canyon?

April 10, 2008
Courtesy University of Colorado at Boulder
and World Science staff

The Grand Can­yon may be so old that di­no­saurs once lum­bered along its rim, new re­search sug­gests. This comes shortly af­ter an­oth­er study that al­ready seemed to raise the can­yon’s es­ti­mat­ed age, though not nearly as much.

The Grand Can­yon may be as old as the dino­saurs, ac­cord­ing to a new study. (Im­age cour­tesy Re­bec­ca Flow­ers, CU-Boul­der)

“The Grand Can­yon has an old­er pre­his­to­ry than many had thought,” said Re­bec­ca Flow­ers, a ge­olo­g­ist at the Uni­ver­s­ity of Col­o­rad­o at Boul­der. Flow­ers is lead au­thor of the stu­dy, to ap­pear in the May is­sue of the Ge­o­log­i­cal So­ci­e­ty of Amer­i­ca Bul­le­tin.

Flow­ers and col­leagues used a tech­nique called ra­dio­met­ric dat­ing to con­clude that the Grand Can­yon may have formed more than 55 mil­lion years ago. That pushes back by 40 mil­lion to 50 mil­lion years the as­sumed ori­gins of the enor­mous gorge, in north­ern Ar­i­zo­na.

The re­search­ers gath­ered ev­i­dence from rocks in the can­yon and on sur­round­ing plat­eaus thought to have been de­posited near sea lev­el sev­er­al hun­dred mil­lion years ago. Lat­er, the Earth’s crust pushed up­wards and erod­ed in the ar­ea to form the can­yon. 

“As rocks moved to the sur­face in the Grand Can­yon re­gion, they cooled of­f,” said Flow­ers, adding that her team re­con­struct­ed the an­cient lay­out by de­ter­min­ing the cool­ing his­to­ry. The team be­lieves an an­ces­tral can­yon de­vel­oped along the east­ern sec­tion of the cur­rent one some 55 mil­lion years ago, only lat­er link­ing with oth­er parts that de­vel­oped sep­a­rate­ly.

The an­cient sand­stone in the can­yon walls con­tains a min­er­al called ap­a­tite, host­ing min­ute amounts of the ra­dio­ac­t­ive el­e­ments ura­ni­um and tho­ri­um. These slowly de­cay, or dis­in­te­grate, Flow­ers said. An abun­dance of the el­e­ments, paired with tem­per­a­ture in­forma­t­ion from Earth’s in­te­ri­or, of­fered a sort of clock to cal­cu­late when the ap­a­tite grains were em­bed­ded in rock a mile deep­—the can­yon’s ap­prox­i­mate depth to­day—and when they cooled as they neared the sur­face as a re­sult of ero­sion.

Ap­a­tite from the bot­tom of the can­yon’s Up­per Gran­ite Gorge re­gion yields si­m­i­lar dates as sam­ples col­lect­ed on the near­by plat­eau, said ge­olo­g­ist Bri­an Wer­nicke of the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy, a col­la­bo­ra­tor in the re­search. 

“Be­cause both can­yon and plat­eau sam­ples re­sid­ed at nearly the same depth be­neath the Earth’s sur­face 55 mil­lion years ago, a can­yon of about the same di­men­sions of to­day may have ex­isted at least that far back,” he said, “pos­sibly as far back as the time of di­no­saurs at the end of the Cre­ta­ceous per­i­od 65 mil­lion years ago.” That’s when the di­no­saurs died off.

One of the most sur­pris­ing find­ings was that plat­eaus sur­round­ing the can­yon may have erod­ed as swiftly as the gorge it­self, each drop­ping a mile or more, said Flow­ers: small streams on the plat­eaus seem to have stripped rock just as ef­fec­tively as the an­cient Col­o­rad­o Riv­er carved the can­yon. 

If you stand on its rim now, “the bot­tom of the an­ces­tral can­yon would have sat over your head, in­cised in­to rocks that have since been erod­ed away,” said Flow­ers. The Col­o­rad­o Riv­er was likely run­ning in the op­po­site di­rec­tion as now, she added.

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The Grand Canyon may be so old that dinosaurs once lumbered along its rim, new research suggests. This comes shortly after another study that already seemed to raise the canyon’s estimated age, though not nearly as high as the new work. “The Grand Canyon has an older prehistory than many had thought,” said Rebecca Flowers, a geologist at the University of Colorado at Boulder. Flowers is lead author of the study, to appear in the May issue of the Geological Society of America Bulletin. Flowers and colleagues used a technique called radiometric dating to conclude that the Grand Canyon may have formed more than 55 million years ago. That pushes back by 40 million to 50 million years the assumed origins of the enormous gorge, in northern Arizona. The researchers gathered evidence from rocks in the canyon and on surrounding plateaus thought to have been deposited near sea level several hundred million years ago. Later, the Earth’s crust pushed upwards and eroded in the area to form the canyon. “As rocks moved to the surface in the Grand Canyon region, they cooled off,” said Flowers, adding that her team reconstructed the ancient layout by determining the cooling history. The team believes an ancestral canyon developed the eastern section of the current one some 55 million years ago, only later linking with other parts that developed separately. The ancient sandstone in the canyon walls contains a mineral called apatite, hosting minute amounts of the radioactive elements uranium and thorium. These expel helium atoms as they decay or slowly disintegrate, Flowers said. An abundance of the three elements, paired with temperature information from Earth’s interior, offered a sort of clock to calculate when the apatite grains were embedded in rock a mile deep—the canyon’s approximate depth today—and when they cooled as they neared Earth’s surface as a result of erosion. Apatite from the bottom of the canyon’s Upper Granite Gorge region yields similar dates as samples collected on the nearby plateau, said geologist Brian Wernicke of the California Institute of Technology, a collaborator in the research. “Because both canyon and plateau samples resided at nearly the same depth beneath the Earth’s surface 55 million years ago, a canyon of about the same dimensions of today may have existed at least that far back,” he said, “possibly as far back as the time of dinosaurs at the end of the Cretaceous period 65 million years ago.” That’s when the dinosaurs died off. One of the most surprising findings was that plateaus surrounding the Grand Canyon may have eroded as swiftly as the gorge itself, each dropping a mile or more, said Flowers: small streams on the plateaus seem to have stripped rock just as effectively as the ancient Colorado River was at carving the canyon. “If you stand on the rim of the Grand Canyon today, the bottom of the ancestral canyon would have sat over your head, incised into rocks that have since been eroded away,” said Flowers. The ancestral Colorado River was likely running in the opposite direction millions of years ago, she added.