Grand Canyon rocks preserve a 1.2-billion-year record of Earth–Moon interactions, allowing scientists to trace how the Moon’s orbit and Earth’s rotation have evolved over deep time.

-Roughly 1.25 billion years ago, the mudflats bordering an inland sea became the origins of the reddish-orange layers of the Hakatai shale.

This subtropical landscape on the ancient continent of Laurentia periodically became a landscape of evaporating moisture resembling a modern sabkha or playa.

As climate conditions changed, the sediments accumulated in rhythmic patterns.

Today, the same patterns can be traced in outcrops 65 kilometers apart, and preserve a record of a time when an Earth day was radically shorter than the one we all live with.

Back then, a day only lasted about 19 hours.

In a new [study](https://www.nature.com/articles/s41561-026-02100-3), researchers figured this out by examining the colorful repeating patterns of the Hakatai shale that are today exposed in the central-eastern Grand Canyon, which reflect cycles in Earth’s climate driven by its movements through space.