Grand Canyon time gap is about to be explained

Over a billion years of geological history is lacking in parts of the Grand Canyon and, according to some geologists, much of the rest of the world. A new investigation into this mysterious time shift, which has puzzled geologists for 152 years, attributes it to the collapse of the supercontinent Rodinia, 700 million years ago.

Rocks in northern Arizona have been deposited over the past two billion years. The Colorado River exposed these layers as it made its way downward, and therefore through time. However, for much of the length of the canyon is a huge strip missing, with rocks from one era stacked directly on top of those deposited much earlier, a feature known as ‘unconformity’.

Mismatches are common, but the one the Grand Canyon exhibits is so immense that it was named the “Great Mismatch” after it was discovered in 1869, and has left geologists baffled ever since. New evidence presented in Geology offers an explanation using differences along the Canyon.

“The great unconformity is one of the first well-documented geological features in North America,” aptly named Barra Peak, a student at the University of Colorado, Boulder, said in a statement. “But until recently, we didn’t have a lot of constraints on when or how it happened.

The mystery deepened with the discovery of other discrepancies elsewhere in the world around the same time. Some geologists believe they are related, attributing them to the massive glaciation known as Snowball Earth scraping the underlying rocks bare. Others think that these are just random events, some of which inevitably coincide in time.

Rodinia included most of the world’s continents, but the separation began around 800 million years ago and then accelerated. Peak argues that Rodinia’s great divorce produced a series of violent fault events in the region around what is now the Canyon. The rocks were dragged upward and exposed to the elements, eventually swept into the ocean.

With so many geologists studying the unconformity without coming to a conclusion, Peak had to do something different. She and her co-authors considered that the pressure from the overlying layers heats up the rocks, inducing chemical reactions that create a record of past temperatures, a process known as thermochronology.

By measuring the diffusion of helium from ancient rocks, the authors concluded that the eastern and western parts of the canyon have quite different temperature histories. Some 700 million years ago, as Rodinia disintegrated, the rock from the western basement was brought to the surface where it was weathered, but the eastern half remained buried 12-15 kilometers (8-10 miles) away. ) depth.

The time taken for the unconformity varies, but near Lake Mead rock 520 million years old sits directly on a stone 1.4 billion to 1.8 billion years old. “Over a billion years have passed,” said Peak. “It’s also a billion years during an interesting part of Earth’s history where the planet transitions from an older setting to the modern Earth we know today.”

Peak and his colleagues are now broadening their attention to other North American sites where the great discordance can be observed. While the geological opportunity offered by the Grand Canyon is hard to match, other places can indicate if what Peak observed was part of a widespread phenomenon.