The purpose of this assessment probe is to elicit students’ ideas about the cycling of matter. It can be used to determine whether students recognize that once-living matter breaks down and cycles through ecosystems without subtracting or adding mass to the Earth. Elementary students build an understanding of recycling that forms the foundational idea for later understandings about the cycling of living or once-living matter. Middle school students become familiar with ecosystems, including the beneficial role of bacteria in ecosystems. They expand their understanding of decomposers and decay to include microorganisms and recognize the essential role of microorganisms in the decomposition process as matter recyclers. High school students approach decomposition from a molecular view, including the assortment of complex biological processes involved in breaking down once-living material. Teacher notes, standards, assessment, and references are provided. This book selection also includes the Table of Contents, Dedication, Preface, Introduction, and Index.