(AGENPARL) – gio 20 ottobre 2022 Having trouble viewing this press release? [Read it online](https://link.mediaoutreach.meltwater.com/ls/click?upn=uDPfAnrJXoDw8-2BCe3b2e6gTQXqoFtB58fI1KeAEfz1x9zjh6-2BqUOOIUQOVSwqERe2lvViplY71sZP5QTXegqMQ7roBm-2BnMTq0uX0k8XKzp4-3DIQhI_mLoYh0p4AWg4foFr5HgrZ1QioQ33bLwdnQ-2BsYGKFX9mv8wVBOgi5GpVq-2FNhlrfTl-2BTI61oGMQNfTGLPKQc-2F-2BKWIb2uEidh5Cy9Snrxt2Kvdg46NMTv1EBYVNMuj4LXg-2FsAalkqpAcmKsZewjwvvuvqUJFa6Gq11KOwV5N-2FFHXjAb7qfOdBDPiRXEhluPl2bjKjOcUFuOCZuTJBsW0sTw-2F1DA-2F5KGxiKcSYvMmfCgIdIESISI-2By0l1zz4FuZxLnsLNmQiPe5tM9jFLQQngPhVqQ81TF11VlZ-2BPP4STmXlth1tJZYWMQnqYT1DTpKmuH3ZFzbLMak4D-2FhsRvkw-2BVFm2zjeF4DsUZVBoj5slmdikjMIOtTeyfyalv7ltCZESYt-2BPF9kBOCRsYf4Ke8RHJDtlw-3D-3D).
https://link.mediaoutreach.meltwater.com/ls/click?upn=uDPfAnrJXoDw8-2BCe3b2e6gTQXqoFtB58fI1KeAEfz1x9zjh6-2BqUOOIUQOVSwqERe2lvViplY71sZP5QTXegqMQ7roBm-2BnMTq0uX0k8XKzp4-3DGBJI_mLoYh0p4AWg4foFr5HgrZ1QioQ33bLwdnQ-2BsYGKFX9mv8wVBOgi5GpVq-2FNhlrfTl-2BTI61oGMQNfTGLPKQc-2F-2BKWIb2uEidh5Cy9Snrxt2Kvdg46NMTv1EBYVNMuj4LXg-2FsAalkqpAcmKsZewjwvvuvqUJFa6Gq11KOwV5N-2FFHXjAb7qfOdBDPiRXEhluPl2bjKjOcUFuOCZuTJBsW0sTw-2F1shkAWTdeDM2FayxgKjicWsSo0bgIdkewmZKLNrps3e8-2FTnamAedX5in1x2bJlv-2BVqiAA5zQNMYD-2BKKrJvGTtgRkiv6n36rHmpGtCIhwOrpDMD-2FL8-2F-2FQ5OFO-2Fl7xGuFq7PgXcq-2F7Fo9fBorsNMmqwaajYtKln1y6pSpktzKIfNYfGClXD3aCFHdV7x-2BFYZ2nA-3D-3D
For immediate release
[How old is Yosemite Valley?](https://link.mediaoutreach.meltwater.com/ls/click?upn=uDPfAnrJXoDw8-2BCe3b2e6gTQXqoFtB58fI1KeAEfz1x9zjh6-2BqUOOIUQOVSwqERe2lvViplY71sZP5QTXegqMQ7roBm-2BnMTq0uX0k8XKzp4-3DFyit_mLoYh0p4AWg4foFr5HgrZ1QioQ33bLwdnQ-2BsYGKFX9mv8wVBOgi5GpVq-2FNhlrfTl-2BTI61oGMQNfTGLPKQc-2F-2BKWIb2uEidh5Cy9Snrxt2Kvdg46NMTv1EBYVNMuj4LXg-2FsAalkqpAcmKsZewjwvvuvqUJFa6Gq11KOwV5N-2FFHXjAb7qfOdBDPiRXEhluPl2bjKjOcUFuOCZuTJBsW0sTw-2F2CoXbdmWrtwlxAEiR34R1bq622eQRDLAzBycBzThDiZjrsVsLd4-2Fw0WPKERA8ZR2SHBQH7mi-2F-2BwXbF4iaNZHCfH9EbIfZuu1gM-2Bny2-2FSrCVVVz5ssTUpc3eaq5JViUoOhGzVMyieiEy5sM5ONYvm5r-2F9w6it65DuZTMgGpRX0DgP1YgjnoBBCJF5-2BGfCjKSdw-3D-3D)
October 20, 2022
https://link.mediaoutreach.meltwater.com/ls/click?upn=uDPfAnrJXoDw8-2BCe3b2e6gTQXqoFtB58fI1KeAEfz1x9zjh6-2BqUOOIUQOVSwqERe2lvViplY71sZP5QTXegqMQ7roBm-2BnMTq0uX0k8XKzp4-3DI-hU_mLoYh0p4AWg4foFr5HgrZ1QioQ33bLwdnQ-2BsYGKFX9mv8wVBOgi5GpVq-2FNhlrfTl-2BTI61oGMQNfTGLPKQc-2F-2BKWIb2uEidh5Cy9Snrxt2Kvdg46NMTv1EBYVNMuj4LXg-2FsAalkqpAcmKsZewjwvvuvqUJFa6Gq11KOwV5N-2FFHXjAb7qfOdBDPiRXEhluPl2bjKjOcUFuOCZuTJBsW0sTw-2F2Cy9-2FGR17mgtCbcdUbW1zchRUdZ6c-2FfRbT2HT0JpFAJuCRqoE4eP-2FRTnGFRByr4jFTfWxcs-2BXqGfZ9ONsWG381HhQdJ4i2cKDcuorKvvBdP4DYVVxIdUbnCbCnTMotRYrOWnuX3tMo-2FRqQbr8mnAByGD8kGDjZoAn-2BDd9HQjVKneIwi-2F0Una3CykaNQou5OrQ-3D-3DTenaya Canyon (center) and part of Yosemite Valley (foreground) as seen from Glacier Point in Yosemite National Park. Tenaya Creek likely started to scour this granite canyon below Half Dome (center right) about 5 to 10 million years ago, with glaciers arriving about 2.5 million years ago to sculpt the classic glacial valley outlines. (Photo credit: Greg Stock/National Park Service)
Berkeley — 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?
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. This shaves about 40 million years off the oldest estimates.
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.
“Yosemite Valley is one of the most famous topographic features on the planet,” said glaciologist [Kurt Cuffey](https://link.mediaoutreach.meltwater.com/ls/click?upn=uDPfAnrJXoDw8-2BCe3b2e6gpUgvRUPcstsmLmcTIM73vXPUdowEN1URfSbANJW8RbWJQK4lVAILwr-2F7qnk-2FkZnw-3D-3Dqln6_mLoYh0p4AWg4foFr5HgrZ1QioQ33bLwdnQ-2BsYGKFX9mv8wVBOgi5GpVq-2FNhlrfTl-2BTI61oGMQNfTGLPKQc-2F-2BKWIb2uEidh5Cy9Snrxt2Kvdg46NMTv1EBYVNMuj4LXg-2FsAalkqpAcmKsZewjwvvuvqUJFa6Gq11KOwV5N-2FFHXjAb7qfOdBDPiRXEhluPl2bjKjOcUFuOCZuTJBsW0sTw-2F19IQOb4L0u0s2V7-2Fk5Q2rBMqo4D8ftv-2BVsC9UuWB9OEtBPmE8o9lgabdV210u4TcRFbB1CihEfidg-2B00O-2BvPJiVC0fr70oOZFIsnIwCoaOMUw7ayky-2F3oYYJnFBXWwsH48EsC7e1-2BTyBExvnzbEzxjnUxISJjC1tW2dPIrdiq8PIbOLK44TBcoxMxBQ8tD8sw-3D-3D), 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.”
Yosemite National Park geologist Greg Stock admits that the story told about the origin of the park’s iconic granite topography has been a little vague, because geologists still do not agree about what has happened since the Sierra’s signature granite formed underground between about 80 and 100 million years ago, up to 10 kilometers (6 miles) under a mountain range that looked a lot different than it does today.
“We know that the Sierra was a high mountain range 100 million years ago, when the granite was forming at depth. It was a chain of volcanoes that might have looked a bit like the Andes Mountains in South America,” Stock said. “The question really is whether the elevation has just been coming down through erosion since that time or whether it came down some and then was uplifted again more recently. At this point, based on studies I’ve done for most of my career and supported by this study, I see a lot of evidence for recent uplift happening sometime in the last 5 million years.”
That uplift, which happened at the same time that earthquake faulting in the eastern Sierra Nevada created an escarpment several kilometers high, steepened the western slopes and rivers, causing them to incise valleys more quickly.
Cuffey, UC Berkeley geochemist [David Shuster](https://link.mediaoutreach.meltwater.com/ls/click?upn=suPI9oOYRWzT5Ws9fgHvQarC9NFn40dnDvtPDQjP6Fmd4QV0Dyd1klr5D2wh1Jl-2Flp-2BKL-2F3Crfu1uqGyYxsteg-3D-3DVtc8_mLoYh0p4AWg4foFr5HgrZ1QioQ33bLwdnQ-2BsYGKFX9mv8wVBOgi5GpVq-2FNhlrfTl-2BTI61oGMQNfTGLPKQc-2F-2BKWIb2uEidh5Cy9Snrxt2Kvdg46NMTv1EBYVNMuj4LXg-2FsAalkqpAcmKsZewjwvvuvqUJFa6Gq11KOwV5N-2FFHXjAb7qfOdBDPiRXEhluPl2bjKjOcUFuOCZuTJBsW0sTw-2FwR7wcYjyoRirRXbtsaz0gjUT7RmsfEuCeVCWo-2FrlvP8FXvi8skazaUf4twzMXQm-2FB5-2FcdKBX8VO6bP5M-2BeGt3Kv-2B9pQZ3pthyn6vmjEjGQ4U4DGrsQWIoH-2B9w3aegNJxSejhGKSAYxzGX-2FRy1IN6YqYqNnpkAHZjWLT-2BkDOg6ZJkSgBBpsGNwy8CMl5CdFYog-3D-3D) and their colleagues, including Stock, [published the findings](https://link.mediaoutreach.meltwater.com/ls/click?upn=uDPfAnrJXoDw8-2BCe3b2e6mZEgbSlnd1njdoBhC7BghzcZKOrpTRYzBiOGAm2RMJJpZ8qIhN5q0RLiRumizAIANEopPiMET0Hk88erJzqcx3sX8W-2F1WprPEnH8uR52pi8ize-2FyQjLV5qkA7Ihqe6xcguVN-2Fs85GRhhOcuqWSipalM7FukFSUQ-2F4eIiZsn6k0mfcdl_mLoYh0p4AWg4foFr5HgrZ1QioQ33bLwdnQ-2BsYGKFX9mv8wVBOgi5GpVq-2FNhlrfTl-2BTI61oGMQNfTGLPKQc-2F-2BKWIb2uEidh5Cy9Snrxt2Kvdg46NMTv1EBYVNMuj4LXg-2FsAalkqpAcmKsZewjwvvuvqUJFa6Gq11KOwV5N-2FFHXjAb7qfOdBDPiRXEhluPl2bjKjOcUFuOCZuTJBsW0sTw-2FzjAdbXulEcmgNeCe0SzkSpZnplM7pLeKfCHdVI4qVf1sXLRiSOFsZiD6ZE2XfQ2fcJyXY68tMstLXVhDSvRrDfcDHYTx1OkRl5y-2BqLckm0-2FXESOgAKMOfAq8Sk2wHn-2BcYMyiAFKbtBV2vyNhqcOmyA2GcwATXbP4Ym4cNFwpvgkNK1WUmu-2BG6wD-2BDdv36xBZw-3D-3D) this week in the journal Geological Society of America Bulletin.
Rock cooldown
Shuster, a professor of earth and planetary science, [developed a technique 15 years ago](https://link.mediaoutreach.meltwater.com/ls/click?upn=uDPfAnrJXoDw8-2BCe3b2e6gTQXqoFtB58fI1KeAEfz1wJ7MJMe7grCnj9FVY09dR7vWjraD1WRny30AaJQKKRyq0bzrGCeKlIZIVfnsEniBT5qRljxEdiLgfe2XcXFKZsYoNJTcFbdgEU7aoztZNIUA-3D-3DrkPD_mLoYh0p4AWg4foFr5HgrZ1QioQ33bLwdnQ-2BsYGKFX9mv8wVBOgi5GpVq-2FNhlrfTl-2BTI61oGMQNfTGLPKQc-2F-2BKWIb2uEidh5Cy9Snrxt2Kvdg46NMTv1EBYVNMuj4LXg-2FsAalkqpAcmKsZewjwvvuvqUJFa6Gq11KOwV5N-2FFHXjAb7qfOdBDPiRXEhluPl2bjKjOcUFuOCZuTJBsW0sTw-2FxrkpCUC61drC1Zp-2BMRk40W5ApQmwJ9Ioowglw3tlPmVTXzAyPVc8Ekh5zlh70GVwcpotv6v7V7hlkixNju8oigHJIHiBoWwjO4rVEcNAX70FrRfED5QpbTmnUVFRd11K6fCvfaQq6POx8PSMh4x3WmlRWdFTNhpDNB6wpYz6yzhoNPY4F-2F2EpyWw2dInr0kPQ-3D-3D) that he thought at the time might shed light on the origins of the valley, something that has fascinated both him and Cuffey since they first saw Yosemite as kids. Shuster, a California native, has visited it since early childhood. Cuffey, from central Pennsylvania, made his first trip to the park at the age of 15.
Much of what they remember learning is that the valley was carved by glaciers, giving short shrift to what happened before Ice Age glaciers arrived in the Pleistocene some 2.5 million years ago.
“What I learned from the signage in the valley when I was a kid wasn’t quite right, given what the scientific literature said at the time. Nevertheless, the topography has been interpreted to be significantly modified by ice,” Shuster said. “How to quantify that with geochronological tools, rather than just make up a story about it based on geomorphology, is one thing we were trying to do here.”
Shuster’s technique, called helium-4/helium-3 thermochronometry, reconstructs the temperature history of a sample of rock based on the spatial distribution of natural helium-4 in minerals, which is measured by comparison to an artificially-produced uniform distribution of helium-3. Because temperature increases with depth underground, the temperature history can tell when a rock was uncovered as the landscape eroded.
“The temperature of the rock is a function of the surface lowering down into it,” Shuster said. “It’s very analogous to removing a down comforter — the rock beneath it progressively gets colder. This progression through time with the rock cooling is what we get from the geochemistry and thermochronometry.”
The expectation is that granite bedrock exposed on the broad uplands of the Sierra should show a long history of cool surface temperatures, since they’ve been exposed for tens of millions of years longer than bedrock more recently exposed on the floor of Tenaya Canyon, which feeds into Yosemite Valley from the northeast.