Ifyou become conversant with Geology, you soon learn to treat all agesuggestions as tentative at best. You have to be always readyfor outright reconsideration. This is particularly true when itcomes to understanding physically reshaped rock. There is a reasonthat you can artificially age an artifact by treating it toaccelerated weathering.
Letme give you a great example. The Sphinx experienced intenseweathering. It has been suggested that this means we have to go backseveral thousands of years. Let me propose something else. It wasbuilt inside a thousand years of the Great Pyramid or during thethousand year run up to the beginning of the fully mature EuropeanBronze Age that culminated in the actual building of the GreatPyramid.
Whythen? Because that period is the period in which agriculturedeforested the Sahara. A forested Sahara would have brought humidconditions and ample rainfall more that sufficient to give us ourweathering history. We have simply forgotten to connect the dots andhave possibly misdated the desiccation of the Sahara likely becausesomeone made the assumption that it was driven by a slow naturalchange that needed centuries of desiccation.
Withan already established population, the advent of the goat would havedone its work inside of a century.
Physicalgeology is profoundly altered by storm surges, freshets, and floods,all of which do all the work and then go away. Left to its devices,Hurricane Sandy has left a new sedimentary layer that is feet thickin places. Prior to that the underlying ground went untouched fordecades.
Inthe end it requires the type of detailed sleuthing as shown here tobegin to approach a correct answer. It usually does not happen andall such claims are always tentative. An outsider does not reallyknow that.
Grand Canyon 70million years old, formed during era of dinosaurs, new study claims
The canyon isn’t6 million years old, some scientists say, but more like 70 millionyears old. If this order-of-magnitude challenge to the othodoxy holdsup, it would mean the Grand Canyon has been around since the days ofT. rex.By Joel Achenbach, Published: November 29
http://www.washingtonpost.com/national/health-science/grand-canyon-70-million-years-old-formed-during-era-of-dinosaurs-new-study-claims/2012/11/29/5788b9d0-3a45-11e2-b01f-5f55b193f58f_story.html
To stand on the SouthRim and gaze into the Grand Canyon is to behold an awesome immensityof time. The serpentine Colorado River has relentlessly incised a280-mile-long chasm that in some places stretches 18 miles wide andmore than a mile deep. Visitors to Grand Canyon National Park willencounter an exhibit titled the Trail of Time, and learn thatscientists believe the canyon is about 6 million years old —relatively young by geological standards.
Now a few contrarianscientists want to call time out. The canyon isn’t 6 million yearsold, they say, but more like 70 million years old. If thisorder-of-magnitude challenge to the orthodoxy holds up, it would meanthe Grand Canyon has been around since the days of T. rex.
“Our data detects amajor canyon sitting there about 70 million years ago,” saidRebecca Flowers, 36, a geologist at the University of Colorado andthe lead author of a paper published online Thursday by the journalScience. “We know it’s going to be controversial.”
About that she isquite correct. Her research, which reconstructs the ancient landscapeusing a technique called thermochronology, is being met with a coolreception from veteran geologists who study the Colorado Plateau.
“It is simplyludicrous,” said Karl Karlstrom, 61, a professor of geology at theUniversity of New Mexico who has made more than 50 river tripsthrough the canyon — one with Flowers, when she chipped her samplesoff the canyon walls — and helped create the Trail of Time exhibitfor the National Park Service.
“We can’t put acanyon where they want to put it at the time they want to put it,”said Richard Young, a geologist at SUNY Geneseo who has been studyingthe Grand Canyon for four decades.
Wondrous though it is,Grand Canyon doesn’t seem terribly mysterious at first glance. It’sa gash in the landscape with a river at the bottom. The causalityseems obvious. But Flowers and her fellow Old Canyon theorists saythat what we see today in northern Arizona was originally carved, inlarge degree, by two rivers — neither of which was the ColoradoRiver.
The western part ofthe canyon, they say, was largely incised about 70 million years agoby what has been dubbed the California River, which drained amountain range to the west and flowed to the east, in the oppositedirection from today’s Colorado River. The eastern part of thecanyon, they say, was created later, around 55 million years ago, bya different river.
Under the Old Canyonscenario, the Colorado River, which originates in the RockyMountains, is a bit of an opportunist, and about 6 million years agotook advantage of the pre-existing canyons and linked them in afashion that creates the sinuous canyon of today.
The debate to someextent hinges on the semantic question of whether “an Ancient GrandCanyon” (as the Science paper calls it) is the same thing as theGrand Canyon of today. The Flowers paper says the depth of theancient canyon was within a “few hundred” meters — roughly athousand feet — of today’s canyon.
Karlstrom warns thatthe Old Canyon theory threatens to confuse the park’s 5 millionannual visitors: “To them, it seems like dinosaurs might have livedwith humans (like the Flintstones) and that geologists do not know ifGrand Canyon was carved by the Colorado River or not (it was),” hewrote in an informal note crafted in response to the new paper.
Flowers beganadvancing the Old Canyon scenario in 2008, and the idea has beenchampioned by Brian Wernicke, a geologist at Caltech.
“I see all the dataas aligning very nicely for an Old Canyon model,” Wernicke said.
Thermochronologystudies the interiors of tiny crystals of phosphate minerals known asapatite. The crystals contain a record of uranium and thoriumdecaying into helium. If the temperature of the crystals is above 158degrees, as would be expected in rock buried deep in the warm crustof the Earth, they retain no hint of helium. But if the rock has beencooler, below 86 degrees — as you’d expect if it was relativelyclose to the surface — the helium is abundant.
Scientists interviewedfor this article believe the technique is a robust method forreconstructing ancient landscapes. But there are multi-foldobjections to the interpretation advanced by Flowers and Wernicke.
The consensus estimatefor the age of the Grand Canyon is based on multiple factors,including well-dated gravel deposits on the western mouth of thecanyon where the river exits the Colorado Plateau and river sedimentsdeposited into the Gulf of California.
The river incises thecanyon at a known rate — about 150 meters per million years, orabout the thickness of a piece of paper annually, Karlstrom said. TheOld Canyon scenario doesn’t claim that the Colorado has beengrinding away in the canyon bottom for 70 million years, but it doesrequire that ancient, abandoned canyons remain dry for long periodsof time, Karlstrom said.
“Rugged topographylike that fills in with erosion in way less than a million years,”he said.
Professor Young,meanwhile, has an objection based on boulders and gravel that arefound on the south side of today’s canyon. They come from the cliffface of the Shivwits Plateau at the canyon’s north rim. Thematerial eroded from that cliff face at least 24 million years ago,Young said; in the years since, the cliff has receded to the north,and the Grand Canyon formed as the river ran along the bottom of thecliff.
In that scenario,there can’t have been a canyon in that spot 70 million years ago;the boulder and gravel from the Shivwits cliff would have had to jumpthe canyon like Evel Knievel.
Young — who hasspent more than 40 years studying another paleocanyon, the HinduCanyon, which runs parallel to the Grand Canyon and is now filledwith sediment — believes the new Flowers research is recording thegradual recession of the cliff, not the carving of a deep canyon.
“I think what’shappened is the recession of the cliff is what’s caused the cooling[of the minerals] to occur,” Young said. “Their calculation isreally measuring the fact that the surface was being erodedbackward.”
Joel Pederson, anassociate professor of geology at Utah State, applauds the new paper,though he makes a semantic distinction when discussing the age of theGrand Canyon.
“They are looking ata really awesome precursor canyon that the Colorado River later intime took advantage of,” Pederson said. “This new study reallyadds teeth to the realization that those paleocanyons, they werebigger and they were older than we thought they were.”
But as for the age ofGrand Canyon proper, Pederson is emphatic: “It is 6 million yearsold.”
The Grand Canyoncontroversy is in many respects a case of science at its mostvigorous, notwithstanding the grousing. Geologists have to find thenarrative in landscapes that do not always speak clearly. The GrandCanyon provides a wonderful stratigraphic record, revealingsedimentary rock that formed hundreds of millions of years ago, butgeologists struggle to discern the timing of the erosion that exposedthe formations.
“Erosion’s alwaysbeen the toughest problem in geology,” Wernicke said, “becausewhat you’re trying to study is all gone now.”
As for why it mattersat all — why we should care about when, and how, the canyon formed— Wernicke has a ready answer: “It’s a fundamental question ofhuman curiosity. It’s about as basic a scientific thing as one canimagine.”
Flowers will give atalk next Wednesday in San Francisco at the big fall meeting of theAmerican Geophysical Union, as will her ally, Wernicke — and theircritic, Karlstrom. Back to back to back.
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