For more than 20 years, a simple white slab sat in the main office of Biloela State High School, blending into the background. It was a relic of the nearby Callide Mine, a gift to the school by a geologist.

"It's incredible to think that a piece of history this rich was resting in a schoolyard all this time." In 2002, coal miners in Queensland, Australia, uncovered a rock slab with several three-toed footprints preserved in it.