By the time OH 5 was discovered, the Leakey's had spent 24 years excavating the area for early hominin remains, but had instead recovered mainly other animal remains as well as the Oldowan stone tool industry. Because OH 5 was associated with the tools and processed animal bones, they presumed it to have been the toolmaker. Attribution of the tools was promptly switched to the bigger-brained "H. habilis" upon its description in 1964. In 1965, OH 5 was dated to 1.75 million years ago based on potassium-argon dating of anortoclase crystals from an overlying tuff (volcanic ash) bed.