Hari Mix, a doctoral candidate in Environmental Earth System Science, analyzed samples taken from dozens of basins around the western United States.
Analyzing the isotope ratios of ancient raindrops preserved in soils and lake sediments, Stanford researchers have shown that a wave of mountain building began in British Columbia, Canada, about 49 million years ago and rolled south to Mexico. The finding helps put to rest the idea that there was once a Tibet-like plateau across the western United States that collapsed and eroded into the mountains we see today. 50 million years ago, mountains began popping up in southern British Columbia. Over the next 22 million years, a wave of mountain building swept (geologically speaking) down western North America as far south as Mexico and as far east as Nebraska, according to Stanford geochemists. Their findings help put to rest the idea that the mountains mostly developed from a vast, Tibet-like plateau that rose up across most of the western U.S. roughly simultaneously and then subsequently collapsed and eroded into what we see today. The data providing the insight into the mountains - so popularly renowned for durability - came from one of the most ephemeral of sources: raindrops. Or more specifically, the isotopic residue - fingerprints, effectively - of ancient precipitation that rained down upon the American west between 65 and 28 million years ago.
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