While Olduvai Gorge, Tanzania, is most famous for its impressive and formative record of early human technology, Pleistocene fauna and hominin fossils, its geological record is equally important. At Olduvai, palaeoanthropologically significant sites are often preserved in primary context (not redeposited), and they can be contextualized within the palaeoenvironments in which the hominins lived. This has provided an exceptional opportunity to assess not only hominin evolutionary changes over time, but also to understand their adaptive behaviour including toolmaking, foraging and sociality. Abundant volcanic material from the nearby Ngorongoro Volcanic Highlands, interspersed within and between archaeology-bearing deposits, made Olduvai a target for some of the earliest applications of radiometric dating using the K/Ar system. Ultimately, the ⁴⁰Ar/³⁹Ar dating system has produced ages with exceptional precision. Early radiometric dating at Olduvai helped establish the antiquity of the hominin lineage, and early palaeomagnetic studies (and the ‘Olduvai event,’ the longest normal subchron within the reversed Matuyama Chron) were critical in establishing the importance of Olduvai in the field of geochronology. More recently, high-resolution palaeoclimate studies of the palaeolake that once occupied the Olduvai Basin have helped to reconstruct the palaeoenvironments encountered by hominin species. Over a century of geological research has secured Olduvai's status as an important site for geoheritage.