National Geographic News
Sunrise over Mt. Hayden in the Grand Canyon.

Sunrise over Mount Hayden in the Grand Canyon.

PHOTOGRAPH BY ERIK HARRISON, NATIONAL GEOGRAPHIC YOUR SHOT

Sid Perkins

for National Geographic

Published January 26, 2014

To the untrained eye, the Grand Canyon might just look like one big hole in the ground. But to some scientists, the American Southwest's iconic gorge is increasingly looking like several ancient canyons of different ages, stitched together by erosion that occurred about six million years ago, and subsequently sculpted into its modern form.

A new study published in the journal Nature Geoscience, added to more than a century's worth of fieldwork, is helping researchers decipher a geological tale that began unfolding when dinosaurs roamed the landscape.

For nearly 150 years, scientists have been debating how and when the Grand Canyon formed, says Karl Karlstrom, a geologist at the University of New Mexico in Albuquerque. In recent decades they've mostly split into two camps: those proposing a "young canyon" model in which the Colorado River alone carved much of the gorge in the past five million years or so, and those suggesting an "old canyon" model in which a series of ancient rivers carved ancestral canyons along more or less the same route. New research by Karlstrom and his colleagues bolster the notion that what actually happened lies between these two extremes.

To help estimate ancient erosion rates, the team turned to thermochronology—the study of how a rock's temperature has changed through its history. Because temperature rises as depth in the Earth's crust increases, a rock's thermal history provides insight into when, and how quickly, terrain above it eroded away.

Analyzing the Rocks

In the new study, the researchers used a variety of techniques to analyze samples of phosphate-bearing rocks taken from four of the five major sections of the canyon, both from river level and from the canyon rim, which typically lies almost a mile (1.5 kilometers) above the river.

One technique, called apatite fission-track dating, involves counting the number of paths carved through apatite crystals by high-speed alpha particles (helium nuclei) emitted during radioactive decay. Because the atoms in these crystals tend to shift and heal such defects at temperatures above 230°F (110°C), the number of paths remaining in minerals today gives researchers a sense of how long ago the rocks cooled below that threshold.

(Read: "What Created the Rare, Breathtaking Fog Over the Grand Canyon?")

Similarly, by analyzing the amount of radiogenic helium trapped in apatite crystals, the researchers could estimate how long ago the rocks cooled to below 86°F (30°C).

Finally, by measuring the length of fission tracks remaining in apatite crystals, the team got an idea of how long those minerals remained at intermediate temperatures.

So How Old Is It?

Like several previous researchers, Karlstrom and his colleagues found that different parts of the canyon formed at different times. One of the oldest segments, named the Hurricane segment after a famed geological fault, lies in the western portion of the canyon. Data suggest that this stretch of the gorge had been carved to about half its current depth between 70 million and 55 million years ago.

But the researchers posit that erosion hadn't started etching a section that geologists have dubbed "Eastern Grand Canyon," immediately downstream of where the Little Colorado River joins the Colorado, until some 25 million years ago. And the team's analyses suggest that the westernmost and easternmost segments of the canyon were largely carved in the past five million or six million years.

Karlstrom and his colleagues argue that while the Hurricane and Eastern Grand Canyon segments were originally sculpted by different rivers, the Colorado took over the job in the past six million years, joining the disparate canyons and carving them wider and deeper.

"Overall, I think they've done a really good job," says Peter Reiners, a geochemist at the University of Arizona in Tucson. "This new model isn't just a compromise of all previous notions; it's recognition that a big river can have a complicated history."

Not everyone is convinced. Brian Wernicke, a geoscientist at the California Institute of Technology in Pasadena, points out that interpreting thermochronology data, especially fission-track data in terrain where erosion carves downward as well as sideways, is notoriously difficult. "The new model seems to be much too complicated," he says.

21 comments
robert cobb
robert cobb

what was the Grand Canyon like millions years before it was a canyon. is land at the bottom of the canyon millions years older, why cant they drill down inside and see what core drill says. you can tell the different lays of earth would be millions of years old.

Lawrence Gillett
Lawrence Gillett

As a former Earth Science teacher I always thought that if all students had a really good course in historical geology in the early high school years we'd have a population with sufficient reasoning capacity to make good choices in the voting booth thus preventing the  congress of fools we have making a mockery of the USA today.

Geoff Elston
Geoff Elston

The canyon landform is on the order of 50 -100 million years old based on the carving into the sheild /basement rocks. These structures are very long lived.  The theory is that the river flowed north into the Mississippi system and then when the continental divide moved from West of the canyon to east it then emptied into the Snake Columbia system through the green river.  again north.. finally 2.5 million years ago it started to go south to the Gulf where the delat is on the order of 2.5 million years old.

Geoff Elston
Geoff Elston

As river systems lock themselves into "gorge"s these landform structures tend to be very long lived.in geologic time frames 50-100 million years or more especially when carved into the basement or shield portion.  The current delta in the Gulf of California is relatively new with little gas and oil deposits that are indicative of older deltas (try Mississippi and the Orinoco System which was the proto Amazon delta)  The theory is that the River flowed north into the Missouri Mississippi system when the continental divide was West of the current Canyon.  It then migrated to the Snake Columbia River system via north through the  Green River Canyon and finally recently say 2.5 million years ago down into the Gulf.

Christian Probasco
Christian Probasco

Both of the original rivers emptied into deltas. The modern Colorado tries to empty into a delta but usually doesn't quite make it, if I remember right. Anyways, it should be easy to find where these original rivers emptied out of the continent. Just match the sediments from whatever ancient deltas you've got on hand with sediments in the walls of the Grand Canyon and there's your culprits. Then take some core samples of those deltas and you'll know a lot more about the history of the Grand Canyon.

Roy Harper
Roy Harper

This new information will sure come in handy next time I go buy a loaf of bread.

Ted Kay
Ted Kay

I am sure that it is not just American, or liberal, or atheistic scientists who agree with this.  How can we finally put and end to young earth creationisms influence and finally place it along side with Flat Earth theories or geocenterism .   The Grand Canyon is frequently sited by them as an example of  fast erosion and there are even creationist tours there.  Just curious on your thoughts.

Marion Looney
Marion Looney

How youthful I feel after reading this article (88 years).  As an old lady I despair of being knowledgable when it comes to technology...(I read "!984" years ago)...but such technological means of learning more about our past is a real plus.  

Dwayne LaGrou
Dwayne LaGrou

Why don't they simply take a core sample of the entire depth of the canyon and do an erosion test of the layers by measuring the time it takes a water jet set at a precise pressure go through the entire set of layers? It seem to me like a pretty straight forward comparison of time that it takes the water jet to erode through the layers compared to the lesser pressure of the river waters. I mean I 'm no scientist, But I like to think I understand the basic principles of time multiplied by erosion equals a canyon! I would like to hear any real scientists comment on this idea.

Thank You, DL

Bradford Baldwin
Bradford Baldwin

@Lawrence Gillett I couldn't agree more. I just finished two semesters of geology with Historical being the last. It was the most eye opening course I've ever taken. The best class I've ever had. if you want to begin to understand our world, the universe and our significance in it, take geology.


In one exam we covered the particles that make up and atom and the age of the universe!


simply amazing, Geology is the study of Earth using all the sciences. 

David Howard
David Howard

@Roy Harper Do you not feel a sense of awe and wonder when viewing a place of majesty like the Grand Canyon?  Doesn't it make you the least bit curious about how such a phenomenon came to be?  If your answers are "no" to these questions, my last question is why are you reading "National Geographic?"

James Donnaught
James Donnaught

@Ted KayCreationists are at their most creative when coming up with wild explanations for scientific evidence.  They just "know" that God put alpha particle tracks of varying length and density into phosphate crystals, in order to make them LOOK like they aged at different rates over tens of millions of years.  (Their God is really, really into elaborate practical jokes - he also created the universe with light from distant galaxies >already on its way to earth.<)


Point is, there's no point trying to reason with people who simple-mindedly dismiss inconvenient facts and evidence as "tricks".

Dwayne LaGrou
Dwayne LaGrou

Those people are in a serious state do denial. I believe that it is possible to believe in God AND Science. I mean the two things are not mutually exclusive. I believe that our being or soul lives on after we die, And I also believe that science actually has shown proof of that. They say that energy cannot be destroyed, It just changes form. And the fact that our brains are basically electrically powered. So when we die that energy has to continue in some form! It kind of makes you think a little, Doesn't it?

bwana brown
bwana brown

@Dwayne LaGrou but how to decide "a precise pressure"? you oversimplify. erosive action would have been always variable, not "set," and involve many factors from wind to geologic uplifts, &c, as well as water action.  All you would determine from this suggestion is how much theoretical time a constant "water jet" alone might  have taken, all other things being equal, &c, to arrive at the current depth from the current rim . . .

craig hill
craig hill

@Dwayne LaGrou Ancient Buddhism got it right, by denying a "soul" 2500 years ago. In imagining something that can not be physically sensed, because it isn't real, the ego fools himself into thinking his "soul", his identity, continues forever. No soul means the ego is the only part of life which dies, because energy, as quantum physics proves, cannot die, it keeps transforming into new life minus the soul, the old identity. The good news is there is no death, just transformation of life, to new lifeform, forever. Just as the water we drink is the very same water dinosaurs drink, the living form keeps changing but the energy of life remains the same.

Stuart M.
Stuart M.

No, science hasn't shown that our "being" or "soul" "lives on" after we die. So our brain is full of electricity, where does that energy go? You know, a light bulb is full of electricity until you turn it off, then the electricity is gone. You think it went to heaven? Bad news, there is no soul. Even consciousness is material as we see when brains suffer trauma and the victim looses memory. We just have to grow up and accept the fact that we are a freak accident and we are alone. Now let's get down to making this earth a better place for everyone.

reagan hutchinson
reagan hutchinson

@Stuart M. I understand what your saying but it is wrong to tell someone with faith that there faith is wrong because u believe something else. There is no true study to say god isn't real either.  So many scientists said after study the skis or something there belief in god grew. I believe there might be a reason be hide that. I know its the visaversa subject as is most. I wont stand here and tell you your belief is wrong i wont sit here and say what you've been taught isn't correct let alone think i have the right to tell anyone there faith is wrong and useless. A soul is not something to be determined if its real or not but it does stand for your spirit. your hopes believe idea and memories how can you think you know enough to say this isn't real that god isn't real and that human were just some strange accident. I do not believe in god i am not here to say god is right just saying you don't know either yet you feel the need to tell people the faith that keeps them going everyday, that faith that takes away that fear of what next , that faith that make them so happy in this world, is a waste cause hes not there cause science hasn't said so. Faith doesn't mean it has to be proven it doesn't mean there needs to be a research it just is so simple. Its just believing that just maybe there is more to death then death. Only reason this bugs me is i have a friend who not to long after losing her faith cause a group of people on facebook attacked her believe. she went down a rough road soon after she took her own life. I couldn't believe this cause she was so loving and sweet everyone liked her expect ppl who think they know the truth about god. Well lets put it simple who'll regret it later having faith while alive doesnt hurt u but not having it after death and say he is real. How foolish will u be when you dont get to go threw the gates. Dont blacken peoples water on your own hateful believes. Til you have solid concrete to say he isnt real how bout let ppl believe what they believe. cause honestly science isnt always correct as many time other have proven others wrong. science grows and can change with a tiny bit of research you live in a must see to believe world and in that set of mind. you must not believe in air. That under nether the sea theres no fish that out pass the sky there is no universe. If people stopped believing and stop trying we wouldnt know much about this earth the way we move the things who share this place with us. The beauty of the world is why people believe cause. This wasnt an accident gone excaltly right it was a gift that we neglect by calling it a freakish accident.. 

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