Continuing past the concrete ruins, my friend and I followed the scar of the old road to the top of a cliff. Smooth, dark rock peeked out from beneath dry leaves and grass. Kneeling for a better look, we found stripes of red, black, and gray with smooth, waxy, and sparkling surfaces. Crustose lichens had found toeholds in each tiny crack, so the surface was also decorated with little blobs in shades of brown, white, and yellow. These lichens may be much younger than the outcrop, but the rock itself is no stranger to photosynthesizing friends. In fact, iron formations like this one record a major milestone in the history of life on Earth.