October 21, 2022 | David F. Coppedge

Yosemite Just Got a Lot Younger

This is why you should never trust national park displays.
Yosemite Valley could be less than 4% previous age estimates.

 

For decades, tourists reading the scientific explanations for Yosemite Valley have been taught that the iconic glaciated valley formed 40 million years ago or more. But did geologists know that? Here is what five geologists with a new estimate just revealed:

“Yosemite Valley is one of the most famous topographic features on the planet,” said glaciologist Kurt Cuffey, UC Berkeley professor of geography and of earth and planetary science. “And of course, if you go to Yosemite Park and read the signage, they will give you numbers for when it became a deep canyon. But up until this project, every single claim about how old this valley is, when it formed a deep canyon, was just based on assumptions and speculation.”

They just made it up!

A little artwork and some authoritative pronouncements tell the public, “Scientists say” and it becomes gospel truth. Unlike some gospels, certain geological and biological gospels have ways of evolving.

How old is Yosemite Valley? (UC Berkeley News, 20 Oct 2022). Take your pick. Yosemite Valley could be anywhere from 3 to 50 million years old.

First-time visitors to Yosemite Valley gape in awe at the sheer granite wall of El Capitan and the neatly sliced face of Half Dome, aware, perhaps vaguely, that rain and glaciers must have taken a long time to cut and sculpt that landscape. But how long?

Did it all start 50 million years ago, when the granite through which the valley cuts was first exposed to the elements? Was it 30 million years ago, when data suggest canyons in the southern Sierra Nevada began to form? Did the valley only begin to form after the Sierra tilted toward the west some 5 million years ago, or was it mostly due to glaciers that formed in a cooling climate 2 to 3 million years ago?

The new gospel truth has arrived: less than 5 million Darwin Years.

Geologists from the University of California, Berkeley, employed a novel technique of rock analysis to get a more precise answer, and concluded that much of Yosemite Valley’s impressive depth was carved since 10 million years ago, and most likely even more recently — over the past 5 million years.

The press release quips, “This shaves about 40 million years off the oldest estimates.” If we take the extremes of the estimates, this means that previous “expert” opinions could have been up to 96% wrong. The consensus is dead. Long live the [new] consensus!

Assuming Based on Assumptions

The new estimate is based on several assumptions. They admit they cannot be precise.

Rivers performed the initial carving in a preexisting shallow valley, they determined, and then both rivers and ice contributed recently.

While the scientists are unable to be more precise, the new estimate is the first to be based on an experimental study of the granite rocks in and near Yosemite, rather than on inferences based on what was going on elsewhere in the Sierra Nevada.

They used a dating divination method called thermochronometry. It’s based on assumptions about how rapidly granite should cool after it is buried. Supposedly granite deep underground is cold, and warms up faster as it gets closer to the surface. But is that always the case?

The geologists took readings from various places around the park to put together a new model of the valley’s exhumation by glaciers. They couldn’t get to important data under the valley, though, because it’s buried under 1/3 mile of sediments. They assumed that nearby exposures formed at the same time.

Park geologist Greg Stock is eager to preach the new gospel truth at the displays in Yosemite.

Stock, who has held the position of park geologist for 17 years and is the park’s first geologist, said the new study will revise how the park tells the geological history of Yosemite Valley.

“The timing of this new study is perfect in the sense that, over the next several years, we’re hoping to completely redo the Geology Hut displays at Glacier Point. I’m very excited to include these new results in those displays,” he said. “It’s a perfect place to tell that story, because there’s a view straight up Tenaya Canyon.”

And a story it will be, adorned with artistic flair. By the time the displays fade for this generation, a new story will likely evolve.

Yosemite Valley from the top of Half Dome (DFC)

Yosemite Valley Age Determined by Radiogenic Helium (Geological Society of America, 20 Oct 2022). Notice the assumptions this press release from GSA admits went into previous estimates. Notice also the wide range of guesses.

Despite such broad interest, more than a century of geological investigation has failed to provide direct constraints on when Yosemite Valley formed. Previous studies exploring when it might have become a deep canyon rest on assumptions—that canyon incision coincided either with tectonics related to mountain building or with valley formation elsewhere in the range. Prior claims about canyon age range from two million to more than 50 million years.

After a century of guesswork, how confident can people be now with the new estimates?

Tenaya Canyon, Yosemite’s deep northeastern branch (named for the last chief of the indigenous inhabitants), most likely deepened by about one kilometer in the last five million years. Accounting for uncertainties, 40% to 90% of the canyon’s current relief probably formed since 10 million years ago. The magnitude of inferred deepening depends on the geothermal gradient, with smaller gradients—such as those currently observed in the western Sierra—implying more deepening. Deepening likely occurred through a combination of fluvial and glacial erosion.

As stated, the new estimates (and the old ones) rest on what experts feel is “likely” at the time. Feelings about likeliness and probability are subject to change without notice. Actually, the new estimate allows the experts to have their cake and eat it, too. The canyon is young, but is also old. We have a word for that: yold.

“The brief history of Yosemite Valley would be that there was some kind of valley in place for tens of millions of years — a river-carved canyon associated with the ancient Sierra Nevada. And then, in the last 5 million years or so, renewed uplift of the range through westward tilting caused rivers to steepen and deepen the canyons that they were in,” Stock said. “So, that probably carved out more of Yosemite Valley and may have started forming Tenaya Canyon. And then in the last 2 to 3 million years, as the climate cooled and glaciers came down through Tenaya Canyon and into Yosemite Valley, they further sculpted the rock, deepening those valleys. And in the case of Yosemite Valley, widening it out considerably. So, there’s some component of an old Yosemite Valley. But I think this recent work shows that much more of that topography is younger, rather than older.”

Meanwhile, you can count on the displays to be convincingly authoritative! Tourists would be very frustrated if the experts said, “We have no idea what we are talking about.”

Remember how wrong the experts were about Yellowstone’s fossil forests and geysers? Remember how wrong they were about Grand Canyon? Remember Death Valley, too? In some cases, “expert” geology has shown extreme time dilation, from one end of the geologic column to the other! We have found cases where millions of years are a hindrance to understanding the Earth, not a help (e.g., 26 Sept 2022).

Geologists don’t know the true ages of things. Their models rest on top of the assumption of Deep Time and Darwinian evolution. They repudiate recent creation from the get-go. And so, flush with millions of Darwin Years to play with, they can move puzzle pieces around at will in their imaginary models, concocting stories about mountains rising and valleys sinking, give or take a few tens of millions of yearssszzzzzz. Now go back to sleep.

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