Breaking Up is Hard to Do and Leads to Missing Rocks

A series of small, violent faulting events caused by the breakup of the supercontinent Rodinia may be responsible for missing Grand Canyon rocks.

IMAGE: The Tonto Group of the Grand Canyon is most easily seen as the broad Tonto Platform just above the Colorado River. CREDIT: Luca Galuzzi via Wikimedia Commons

We can’t see the Colorado River cutting through the Colorado Plateau as it happened, we can see the evidence in the rock records of the Grand Canyon.

Rocks, after all, even cometary ones, record a lot of history.

What do we do when we are literally missing some of that history? Well, if you’re a geologist, you try to solve the why of the missing rock. And in the Grand Canyon, there are areas where more than a billion years’ worth of rock is missing. Of course, we know erosion is a factor, but a billion years is a very long time, even geologically speaking, and we want to know what caused all that rock to disappear.

Let me lay this out for you all, so to speak. The basement rocks of the Grand Canyon, the rocks that are the oldest and sit at the bottom, are between 1.4 and 1.8 billion years old. However, at the western end near Lake Mead, the rocks sitting right on top of that basement rock are only 520 million years old. That’s a significant chunk of the geological record missing.