Geologists dig into Grand Canyon's mysterious gap in time

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A new study led by the University of Colorado Boulder reveals the complex history behind one of the Grand Canyon's most well-known geologic features: A mysterious and missing gap of time in the canyon's rock record that covers hundreds of millions of years.

The research comes closer to solving a puzzle, called the "Great Unconformity," that has perplexed geologists since it was first described nearly 150 years ago.

Think of the red bluffs and cliffs of the Grand Canyon as Earth's history textbook, explained Barra Peak, lead author of the new study and a graduate student in geological sciences at CU Boulder. If you scale down the canyon's rock faces, you can jump back almost 2 billion years into the planet's past. But that textbook is also missing pages: In some areas, more than 1 billion years' worth of rocks have disappeared from the Grand Canyon without a trace.

Geologists want to know why. "The Great Unconformity is one of the first well-documented geologic features in North America," Peak said. "But until recently, we didn't have a lot of constraints on when or how it occurred."

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