Rocks Tell the Earth Story

Rocks look still and silent, but they are pages in the longest book ever written - the story of our planet. Geologists read that story in layers: older rocks usually lie deeper, newer rocks on top, so a canyon wall is a timeline you can walk along.

Rocks come in three families, and each forms in its own way. Igneous rocks are born from cooled melted rock - lava that hardened. Sedimentary rocks build up in layers as sand, mud, and shells settle and get squeezed together over enormous stretches of time. Metamorphic rocks are changed rocks: heat and pressure deep underground transform one kind of rock into another.

The rock cycle means no rock stays the same forever. Mountains wear down into sand, sand squeezes into stone, stone melts and hardens again - the same atoms, endlessly recycled. Fossils, the traces of ancient life preserved in sedimentary rock, are the illustrations in this book: footprints, shells, and bones from a world millions of years older than us.