Researchers from Yale University and the Berkeley Museum of Paleontology argue the mountains were at their current height 50 million years ago, the Los Angeles Times reports. Previously, the Sierras had been believed to be about 20 million years old.
Michael Hren, who led the study while he was at Yale, said the scientists were able to analyze the chemistry of the surface of leaves that grew on the mountainsides 50 million years ago. They found some leaves had a higher proportion of deuterium, a heavy isotope of hydrogen, on their surface and assumed those grew at lower elevations because water drops containing deuterium would tend to fall first as clouds moved up.
Hren said the mountains then overlooked a warmer, lusher world.
"This is a time period where there would have been crocodiles in Wyoming," Hren said.
Diane Erwin, another author of the study, said the research also provides new tools for working out the shape of ancient landscapes.
The study was published in the journal Geology.