The whole world is made of rocks! The Earth's rocky crust was formed millions years ago, and its rocks are always changing. It is full of fascinating minerals, and we use its treasures in hundreds of ways. Did you know that toothpaste contains finely ground rock dust, that the stripes in the Grand Canyon's rocks were once layers of sand at the bottom of the sea, and that robots are examining the rocks on Mars? This Level 2 Reader teaches readers all about the different kind