This striped rock is a piece of banded iron formation and evidence of Earth’s oxygenation. Billions of years ago, the oceans contained high amounts of dissolved iron. When cyanobacteria released oxygen into the water, it sparked a major chemical reaction. The iron rusted and settled to the seafloor, forming massive deposits of these red rocks. It took almost a billion years, but eventually the iron was used up, and the oxygen spread throughout the water and into the atmosphere.