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Parts of Sierra Nevada much older than previously thought

A view from the summit of Brokeoff Mountain in the Lassen National Forest.
Miguel Vieira via Creative Commons
A view from the summit of Brokeoff Mountain in the Lassen National Forest.

The Sierra Nevada mountains are famous for their jagged peaks and high elevation — features typically associated with young ranges.

While the Sierras are relative new-comers, geologically speaking, a recent study suggests the northern end of the range might be tens of millions of years older than previously thought.

Rather than forming a mere 3 to 5 million years ago, it now appears these northern peaks hit their current height 40 million years back.

“We’re starting to get a better picture of how old they are,” explained Hari Mix, an assistant professor at Santa Clara University and an author on the new study.

Mix and a team from Stanford University figured this out by analyzing traces of ancient rainwater trapped in mountain clay.

Water with heavier isotopes tends to fall at lower elevations, leaving a tell tale sign of the mountain’s height when the water merged with the clay.

Mix says this provided evidence that the range sprung up during a period called the Eocene, though the granite in the mountains formed in the earth much earlier.

During this period, the Earth was a very different place with no ice caps to speak of, crocodiles and palm trees in the Arctic and lots of ocean water. 

“Such a crazy time,” Hari noted.

Much of California's Central Valley was under a shallow sea, and the Sierra Nevadas were born as volcanos formed from a subduction zone as one tectonic plate was pushed underneath another.

There was also much more carbon dioxide in the atmosphere. Mix says the data show this was a much warmer period.

"A lot warmer, maybe say 10 or 15 degrees [Celsius] warmer than say the modern day temperatures in that area," he said.

Interestingly, other studies have shown that the southern Sierras, areas like areas like Yosemite and Kings Canyon, seem to have kept uplifting until just a few million years ago, making them much younger.

Mix said this type of information helps climate scientists piece together what the ancient Earth looked like and gives clues to how our planet might change in the future.