Teaching deep-time concepts, especially geologic time, can help instructors impart an understanding of the big ideas in geology and the biography of the Earth to their students (Dodick, 2003a; Ervin-Blankenheim, 2021; Guffey et al., 2016; Libarkin & Kurziel, 2004; Zen, 2001). The research was conducted through a case study mixed-methods approach (Guetterman & Fetters, 2016; Stake, 2005) and examined instructor practices through a quantitative instructor survey, qualitative semi-structured interviews, and instructors' experiences and reflections on teaching deep-time concepts with three experiential laboratories developed for the study. Situational analysis (Clarke, 2005; Clarke et al., 2018) was then used to examine study results from a broader vantage.

The first research query focused on how instructors teach deep-time concepts. A survey consisting of 34-item multiple-choice, multiple-response, short answer and 5-point Likert scale questions was developed and offered to members of the Geoscience Education Research Division of NAGT through an online Qualtrics instrument. The response rate was approximately 13%, with 60 responses and an average of 38 surveys fully completed.

Based on the results of the survey, most instructors (76.2%) were taught geologic time in their introductory college geology courses, and mainly (62.5%) by analogies or similes; of those surveyed, most (89.5%) teach geologic time in their classes. The most frequently mentioned methods were lectures, analogies, demonstrations, problem sets, think-pair-share, and other active learning approaches. Geologic time as a topic comprised <10% of lectures (47.2%) and between 10-25% of labs (16.7%). When asked how comfortable instructors were in teaching geologic time, most strongly agreed (mean 1.32, std. dev. 0.525), compared to what the instructor thought their students grasped, most somewhat agreed (2.18, std. dev. 0.834).