Evolution photos
Evolution photos
A petrified tree trunk in Arizona (cross section)
A petrified tree trunk in Arizona (cross section) 
 
A forest of Araucarioxylon conifers died over 250 million years ago in what is now Arizona. The wood mineralized, and today you can see the layers of wood and the xylem rays, highlighted by metal atoms in the minerals. Petrified Forest National Park. Photograph by Stanley A. Rice.