Author: Carolyn Gramling / Source: Science News
Plant fossils discovered in rocks from the Tibetan Plateau and a new analysis of the area’s geochemistry are rewriting the uplift history of the region dubbed the “roof of the world.” This new research suggests that the story of the rise to its current dizzying height is far more complicated than just raising the roof.
Previous research has suggested that the plateau reached its current height — about 4.5 kilometers above sea level, on average — by at least 40 million years ago. But chemical evidence left in the region’s rocks suggest that couldn’t have happened before about 40 million years ago, researchers report in the March 1 Science.
Meanwhile, another team of researchers suggests that, as recently as 25 million years ago, the region wasn’t yet a flat, windswept plateau. Instead, it was a diverse landscape of steep mountains surrounding a deep valley where palm trees grew, the team reports online March 6 in Science Advances.
The uplift of the Tibetan Plateau altered atmospheric patterns in the region, causing the onset of monsoons in South Asia as well as the drying out of Asia’s interior, says Svetlana Botsyun, a paleoclimatologist at the University of Tübingen in Germany. In fact, the plateau is so tall that it also affects the atmosphere around the globe, altering temperature, precipitation, humidity and cloud cover, Botsyun says.
Yet when exactly that all began to happen isn’t clear.
Traces of rain hold clues to elevation
About 55 million years ago, the Indian subcontinent rammed northward into the Asia plate, and the land between them buckled. The Himalaya mountain range was born, and the Tibetan Plateau north of the mountains was pushed upward.
Previous techniques to estimate changes in the region’s elevation over time have given varying answers on how long this took. One, called paleoaltimetry, uses oxygen isotopes, forms of the element with the same number of protons but different masses. At higher elevations, the ratio of oxygen-16 to oxygen-18 in rainfall is higher than it is at lower elevations. Previous analyses of the ratio of those isotopes preserved in the minerals of carbonate rocks, along with the dates of those rocks, have suggested the plateau must have been more than 4 kilometers high by at least 40 million years ago.
Another way to figure out the timeline is to use plant fossils from species with a limited range of temperature or altitude tolerance. That fossil evidence has tended to suggest the plateau was much lower 40 million years ago, Botsyun says.
The discovery of this fossilized palm frond in what’s…
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