Description Readers explore various Earth changes while decoding words with the diphthongs /ow/ and /oi/. The ground under our feet is always changing. Natural forces change the Earth. They wear down rocks. They form canyons, volcanoes, and mountains. Beginning readers hone their phonics skills while learning all about different Earth changes. As readers practice decoding words with the diphthongs /ow/ and /oi/, they gain science knowledge. Every Stairway Decodables nonfiction book combines multiple aspects of the Science of Reading to support small group instruction, independent reading, and reading practice at home.