The outer shell of the Earth is broken into about a dozen plates that are in constant motion. Plates move slowly, about as fast as fingernails grow. But over tens of millions of years, plates move apart to form new oceans or crash together and push up mountains.

Plate motions have caused changes in global climate, ocean chemistry and the distribution of natural resources and hazards.

Together with 16 other University of Arizona geosciences faculty and students, I document what happened to Earth's interior, surface and climate as oceans disappeared and mountains rose between colliding plates. Our laboratory includes two of the highest and most impressive topographic features on Earth: the Himalaya mountain range and the Tibetan Plateau.

We seek to understand when and how the Himalayas and Tibet reached their present heights and what happened to the Indian and Asian plates deep beneath those mountains. The Himalayas began rising about 50 million years ago when the Indian and Asian continents began colliding. Since then, India has penetrated about 2,000 miles into Asia - and continues northward today.

Today, the region's high topography keeps Central Asia's deserts dry, drives the monsoon that floods India and Bangladesh, and changes atmospheric circulation patterns from Indonesia to Africa. The emergence of these mountains likely influenced global climate in the past also, but when and how remain mysteries.

To unravel Tibet's history, we need to study the rocks. We hike hundreds of miles at elevations higher than the highest peaks in the continental U.S. to examine Tibetan rocks in detail and to collect samples for analysis.

Our ability to decipher mountain building, geography, climate and elevation back through time is advancing at a revolutionary rate. Using cutting-edge techniques pioneered at the UA geosciences department, we determine precisely when rocks formed and how much and how quickly they were buried and brought back to the surface. We can reconstruct the composition of ancient rain and snow from rocks, which tells us about the region's past elevation.

We are just starting to tap the secrets encoded in Himalayan and Tibetan rocks. Already we see that the region behaved in unexpected ways.

We have found that central Tibet was uplifted and became arid tens of millions of years earlier than previously thought. Even more shocking is evidence that along the boundary between the Indian and Asian continental plates, the region lost elevation and had a tropical climate at one time during the collision process.

Although scientists once thought continental plates are too buoyant to plunge deep into the Earth, geophysical images of the deep Earth suggest the Indian plate has descended about 600 miles below the surface, one-third of the way down to the Earth's core. An episode of rapid descent of the Indian plate may have triggered the enigmatic phase of elevation loss along the India-Asia collision zone, while the rest of Tibet remained high and dry.

Indeed, I'm eager to discover what other surprises Tibet - and our planet -will reveal as we continue to investigate it from the core to the clouds.

About the scientist

Paul Kapp is an associate professor of geosciences. His research seeks to understand the history and mechanisms of mountain building on Earth. One of his recent projects has shown that wind can be a much more powerful force in wearing down mountains than previously thought. He received the Donath medal, an award given by the Geological Society of America to outstanding young scientists, in 2008. He earned his B.S. in geosciences from the UA.

Experience Science

• Paul Kapp's website:

• More photos from the Tibet expedition: /arizonatectonics/

• Kapp's "Young Scientist'' award:

• Decelles receives lifetime achievement award:

• Wind can keep mountains from growing: