This study presents a STEM activity titled "A Paleontologist's Task: Fossils" designed based on the 5E learning model. The activity was implemented within the unit of "Earth's crust and Earth" in a science lesson with 22 fourth grade students attending a public primary school in Düzce/Turkey in the 2020- 2021 academic year. As part of the activity, the students created fossil models. Later, they uncovered the fossils buried in the schoolyard, working like paleontologists with the help of various tools. They used their knowledge and skills related to STEM disciplines in the role of a paleontologist and using the logic of a scientist. According to the observation notes taken during the lessons, the students had a fun and enjoyable learning experience by engaging in this STEM activity. In addition, it was observed that there was an improvement in students' cooperation skills as well as their interest in the paleontologist profession.