Our study explores how students apply geoscientific knowledge learned in the classroom to phenomena in a field setting. This was investigated by collecting video data from an ordinary high school context in Norway involving one teacher and a class of 17 high school students. We analyzed how the students learned rock identification and relative dating, first during the classroom preparation and then in the field. Supplementary data were collected 1 y after the fieldwork, when six of the students solved two posttasks of rock identification and relative dating. The video analyses of the students' talk and behavior while doing rock identification and relative dating focused on the level of student engagement, their thinking moves, and the extent of their understanding. The findings reveal that students who were able to apply their knowledge of relative dating were not able to do so for rock identification. One reason for this, we suggest, is that the nature of the geoscientific content influenced the students' ability to apply their knowledge in a field environment. Therefore, we identify qualities of relative dating and translate them to what we call "tools for observation and interpretation." The article closes by suggesting how the qualities of relative dating can inform the development of tools for observation and interpretation for rock identification.