Our planet is under intense observation—by satellites, seismometers, buoys, radar, and more. These instruments generate authentic data sets that are freely accessible online, and thus available for K-12 students and teachers to use in STEM classrooms. This chapter examines how teachers engaged in the NASA Endeavor program, a STEM teacher professional development initiative, use authentic online data in their classrooms and the effects of these activities on teaching and learning. Endeavor teachers use data in many ways, including through curriculum programs developed to scaffold earth data sets for use by students. Through qualitative analysis of teacher interviews, teacher course work, student work, and other relevant data, the researchers discovered that employing authentic online data in Endeavor teachers' classrooms helped students to construct explanations based on evidence and make real world connections to science content.