Petrified Forest National Park, Arizona, USA

© Ian Shive/Tandem Stills + Motio

A petrified forest. Petrified Forest National Park, USA

Welcome to Petrified Forest National Park in the US state of Arizona, where these fallen trees are made of stone, not wood. They look similar on the outside but contain a core of colourful quartz crystals. More than 200 million years ago, trees and vegetation covered much of this area. Logs washed into an ancient river system and were quickly buried by massive amounts of sediment and debris, slowing their decay. Minerals, including silica from volcanic ash, was absorbed into the wood over hundreds of thousands of years, replacing the organic material and turning the logs to stone. Millions of years later the rivers in the area dried up, revealing the fossilised wood.