Evolution is a fundamental, organising concept in biology, yet there is widespread resistance to evolution among US students and there are rising creationist challenges in Europe. Resistance to evolution is linked to lack of understanding of the age of the Earth. An understanding of deep time is thus essential for effective biology education. Landmarks--well-known events of known absolute age--are important in developing a mental framework for deep time. "Collective landmarks" are important events of which a group of students has accurate and precise knowledge. The collective landmarks for time were determined in several semesters of an interdisciplinary undergraduate course at a US public research university. A written survey was employed that asked students to select the appropriate ten-fold time range for ten important cosmological, biological and historical events. The collective landmarks were very similar across classes, including the Big Bang and the Cold War, and there was progress developing additional landmarks. No statistically significant differences in accuracy of estimation were detected across science, technology, engineering and mathematics (STEM) and social sciences majors. The potential utility of collective landmarks within a single biology course, and across a university biology programme, is described.