Visitors to Pikes Peak in Colorado may not notice that anything is amiss, but ask a geologist and she'll tell you that something is missing.

At rocky sites across America, including Pikes Peak and the Grand Canyon, 550 million-year-old rock sits on top of rock that has existed as long as 3 billion years. But there's nothing in between. It's as though that time period between 3 billion years ago and 550 million years ago has literally been wiped from Earth.

It's called the Great Unconformity, and some researchers believe it's the result of one massive cataclysmic event in Earth's history.

"Researchers have long seen this as a fundamental boundary in geologic history," said Rebecca Flowers, study author and associate professor in the University of Colorado at Boulder's department of geological sciences, in a statement.

That boundary represents the boundary between rocks that don't contain fossils, and those that do. About 540 million years ago, the so-called Cambrian explosion occurred. This event marks where there is a sudden wealth of a diverse range of animal fossils in Earth's rocks.

Flowers and her colleagues investigated the boundary in a study published Monday in the journal Proceedings of the National Academy of Sciences.