Lieutenant Joseph Ives led an army survey team that investigated the area in the mid-nineteenth century. Ives concluded that the region was "completely worthless" and a "profitless location." In 1869, John Wesley Powell was one of the first people to raft the Grand Canyon.
On wooden canoes, he and his group of nine went 1,000 miles through the Grand Canyon. During this perilous journey over rapids and oppressive heat, three men perished. A second trip, in 1871, yielded a lot of knowledge on this little-known area of the United States. Powell is also credited with establishing the United States Geological Society. John Wesley Powell is the namesake of Lake Powell. The Paiutes used the name "The Mountain Lying Down" to characterize the region. In the 1870s, John Wesley Powell started adopting and publicizing the phrase "Grand Canyon," and the name has stayed.
Few geological puzzles are as puzzling as the Grand Canyon's 'Great Unconformity' riddle: more than a billion years of missing rock strata that weren't deposited and piled like the rest of the geological record for some reason. It's as if those years didn't exist.
In 1869, geologist John Wesley Powell was traveling down the Colorado River when he discovered this odd gap. We'd be able to timestamp those layers afterwards. Rocks that are 1.4-1.8 billion years old lie close to rocks that are just 520 million years old in certain locations.
"There are some lovely lines," says University of Colorado Boulder geologist Barra Peak. "There are rocks that have been forced together at the bottom, which can be seen plainly. The layers are stacked vertically. Then there's a cutoff, followed by these lovely horizontal strata that create the buttes and peaks that we identify with the Grand Canyon. "
What happened to the remainder of the rocks?
According to recent research, the Grand Canyon's geological history is more complicated than previously believed, and that various sections of the site may have moved in different ways over millennia, causing some rock and silt to be swept away into the ocean.
"We have new analytical techniques in our lab that enable us to interpret the history in the missing window of time across the Great Unconformity," explains University of Colorado Boulder geologist Rebecca Flowers.
"We're doing it at the Grand Canyon and throughout North America at other Great Unconformity locations."
Thermochronology, which utilizes a series of chemical analysis techniques to determine the heat stored in rock when it was created, is the foundation of these new approaches. The quantity of heat emitted correlates to the amount of pressure exerted on geological formations.
The researchers' findings indicate that the gaps in the geological record were caused by a succession of minor and major faulting episodes. These would have occurred about 633 to 750 million years ago, during the catastrophic breakup of the supercontinent Rodinia, a turbulent period in Earth's tectonics that may have prevented rock strata from settling in a more regular manner.
The western half of the Grand Canyon has undergone quite different geologic contortions than the eastern half, which visitors are most familiar with, according to samples gathered and studied by the researchers.
Peak explains, "It's not a single block with the same temperature history."
Basement rock, for example, seems to have come to the surface in the western half of the canyon 700 million years ago; in the eastern half, the same strata of stone are buried under several kilometers of silt.
The results aren't nearly enough to put an end to the Great Unconformity's mystery, but they're a step in the right direction – and the researchers believe the same methods may be used at other locations in the United States where comparable geologic contortions have been seen.
What is undeniable is that the Grand Canyon continues to inspire awe, not just because of its natural beauty, but also because of the way it depicts our planet's geological history over billions of years.
Peak explains, "There are simply so many things there that aren't present anywhere else." "It's a really incredible natural laboratory."
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