What makes a fossil? What are the different types? What makes amber fossils so special... and what causes bone to become rock? Expand your knowledge of these windows into our past world – in four minutes. | National Geographic UK

A fossil is evidence of past life. Paleontologists study fossils to learn about the history of life on Earth. Fossils can be traces, like footprints in stone, or the shells, bones, and teeth of ancient animals. The fossil animals shown here lived in ancient environments from thousands to hundreds of millions of years ago in areas that today are national forests and grasslands of the United States. For information on collecting fossils in National Forest Lands, visit https://www.fs.usda.gov/detai