A new study conducted by the University of Colorado Boulder, reveals the complex history behind one of the Grand Canyon’s best-known geological features: a mysterious and missing time interval in the canyon’s rocks information, covering hundreds of millions of years. The research comes close to solving a puzzle, called the “Great Discord,” which has puzzled geologists since it was first described nearly 150 years ago.
Think of the Grand Canyon’s red cliffs and cliffs as Earth’s history textbook, explained Barra Peak, lead author of the new study and graduate student of geology at CU Boulder. If you go down the cliff walls of the canyon, you can go back almost 2 billion years into the past of the planet. But that textbook is also missing pages: in some areas, more than 1 billion years 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 geological features in North America,” Peak said. “But until recently, we didn’t have a lot of constraints on when or how it happened.”
Now, she and her colleagues think they’re shrinking on an answer in an article published this month in the journal Geology. The team reports that a series of small but violent fault events may have rocked the region during the rupture of an ancient supercontinent called Rodinia. The resulting chaos likely ripped up the earth around the canyon, causing rocks and sediments to wash away into the ocean.
The team’s findings could help scientists fill in the missing pieces of what happened during this critical period for the Grand Canyon, now one of North America’s most important natural wonders.
“We have new analytical methods in our lab that allow us to decipher history in the missing time window across the Great Disconformity,” said Rebecca Flowers, co-author of the new study and professor of geology. “We’re doing this in the Grand Canyon and other Great Disconform locations across North America.”
It’s a mystery that goes back a long time. John Wesley Powell, the namesake of today’s Lake Powell, he first saw the Great Discordance during his famous 1869 expedition by boat along the rapids of the Colorado River.
Peak, who completed a similar rafting research trip through the Grand Canyon in the spring of 2021, said the feature is stark enough to see from the river.
“There are nice lines,” Peak said. “Deep down, you can see very clearly that there are rocks that have been pushed together. Their layers are vertical. Then there’s a cut, and above are these beautiful horizontal layers that form the spikes and peaks you associate the Grand Canyon with. “
The difference between these two types of rocks is significant. In the western part of the canyon towards Lake Mead, the basement stone is 1.4 to 1.8 billion years old. The rocks at the top, however, are only 520 million years old. Since Powell’s trip, scientists have seen evidence of similar periods of lost time at North American sites.
“There’s more than a billion years that have gone by,” Peak said. “It is also a billion years during an interesting part of Earth’s history where the planet was transitioning from an older environment to the modern Earth we know today.”