A granite outcrop at the base of Pikes Peak in Colorado reveals a geological feature called the "Great Unconformity," in which young rocks sit on top of much older stone. (Credit: Rebecca Flowers)
A team of geologists led by the University of Colorado Boulder is digging into what may be Earth's most famous case of geologic amnesia.
Researchers have spotted that phenomenon, called the "Great Unconformity," at locations around North America, including in the Grand Canyon and at the base of Pikes Peak in Colorado. There lie sites of missing time, where relatively young rocks dating back about 550 million years sit right on top of much more ancient stone-in some cases more than 3 billion years old.
In other words, a huge chunk of geologic history has vanished from in between.
"Researchers have long seen this as a fundamental boundary in geologic history," said Rebecca Flowers, an associate professor in the Department of Geological Sciences.
Top: Rebecca Flowers stands near exposed rock on Pikes Peak; bottom: A hiker walks past one site of the Great Unconformity near the town of Manitou Springs, Colorado. (Credits: Rebecca Flowers)
For a study published today in the Proceedings of the National Academy of Sciences, she and her colleagues drew on a technique known as "thermochronology" to take a fresh look at that fundamental boundary. They found that the Great Unconformity might not be the result of a single, catastrophic event in the planet's past like many scientists thought. Instead, a series of smaller calamities may have triggered many different unconformities around the world.
The results could help scientists better understand the flourishing of complex life that occurred not long after that tumult settled down, about 540 million years ago in an era called the "Cambrian Explosion."
"There is a lot of the geological record that is missing," Flowers said. "But just because it's missing doesn't mean that this history is simple."
Pike's Peak
To study that less-than-simple history, Flowers and her colleagues turned to Pikes Peak. In a granite outcrop near the mountain town of Manitou Springs, geologists can find one of the clearest cases of the Great Unconformity.
