Ecosystems is one of six units in the Carbon: Transformations in Matter and Energy (Carbon TIME) curriculum, which was developed through an NSF-funded research collaboration focused on learning progressions to support environmental literacy. These units were developed for middle and high school students. The units are designed in three groups, with each group increasing in scale. The Ecosystems unit is one of two units at the large scale of ecosystems and global systems, and it is intended for students to complete one or both of these units. Each large scale unit focuses on three questions: (1) Where are the carbon pools in the environment? (2) How are carbon atoms cycling among pools? and (3) What is happening to energy? In the Ecosystems unit, students investigate a series of phenomena focused on biomass, matter and energy flow, and ecosystem services. The highly guided sequence of five lessons in the unit helps students identify patterns from their observations, develop models for ecosystem functioning, and then apply those models to explain how humans depend on and affect ecosystems. Extensive supporting infomation is provided within each lesson and on the reources page (http://carbontime.bscs.org/resources). The assessment site (http://ibis.colostate.edu/MSP/CTIME/Index.php) includes pre/posttests for each unit and for the overall curriculum. The overview provided here (http://media.bscs.org/carbontime/files/unit_synopses.pdf) provides a helpful orientation to this complex resource.