Though it looks like a fresco from ancient Greece, this is the fossilized remains of a fern found in Córdoba, Spain. The fossil dates back to the Carboniferous period, roughly 350 million years ago. This is a 'compression fossil'—where a small amount of the original plant material was retained with the mineral deposits that helped form the impression. Why all the paleobotany talk? It's National Fossil Day, and we’re excited! Whether you make a trip to your local natural history museum, trek off to a national park with a fossil exhibit, or just look at fossil photos on the web, we hope you find a fun way to celebrate National Fossil Day.