The Tsangpo River is the highest major river in the world, starting at 14,500 feet elevation and plunging to the Bay of Bengal, scouring huge amounts of rock and soil along the way. Yet in its upper reaches, the powerful Tsangpo seems to have had little effect on the elevation of the Tibetan Plateau.

About 15,000 feet up on Tibet's desolate Himalayan-Tibetan Plateau, an international research team led by Florida State University geologist Yang Wang was surprised to find thick layers of ancient lake sediment filled with plant, fish and animal fossils typical of far lower elevations and warmer, wetter climates.

The vast Tibetan Plateau--the world's highest and largest plateau, bordered by the world's highest mountains--has long challenged geologists trying to understand how and when the region rose to such spectacular heights.

Ice cores drilled last year from the summit of a Himalayan ice field lack the distinctive radioactive signals that mark virtually every other ice core retrieved worldwide.

Not all areas of the Tibetan Plateau rose at the same time, according to researchers who are determining the past elevation of plateau locations by studying the remains of terrestrial plants that once grew there.