This paper presents an instructional strategy for engaging students with the critical exploration of values in introductory geoscience courses. It is argued that the consideration of values (i.e., abstract expressions of desirable qualities such as cooperation, security, curiosity, and honesty) is an integral part of scientific practice and therefore appropriate for a science course. Allowing students to critically reflect on their values has also been shown to increase student engagement and course performance. I have integrated critical thinking about values into an introductory history of life course through a variety of student-centered activities, including class discussions, homework essays, course blog postings, and exam questions. Topics discussed include anthropogenic global warming, evolution versus creationism, federal funding for science, commercial sale of dinosaur fossils, and cloning of extinct species. Portfolio-based assessments and student evaluations indicate that the values-based strategy promotes student engagement and develops students' ability to recognize and use values in analyzing arguments about socioscientific issues. Values-based inquiry increases both students' motivation to learn science and their academic performance in a science course. Because many aspects of geoscience research have social and ethical implications, the values approach can be readily incorporated into any geoscience course. Fostering critical thinking on values-related issues empowers our students to become informed, reflective citizens.