The global emission of the greenhouse gas N₂O (nitrous oxide) from soil is an important contributor to global climate. Separating the natural (pre-industrial) rate of these emissions from those presently occuring is important to identify better soil management practices. When N₂O is produced from soil, it leaves the remaining soil enriched in the rare isotope of nitrogen (¹⁵N). Here, we use the ratio of ¹⁵N/N in soil nitrogen as a guide to the fraction of nitrogen lost via gaseous pathways, and use published maps of pre-industrial nitrogen inputs to the global land surface, to estimate pre-industrial nitrous oxide emissions from soils. The results appear to generally match other entirely independent estimates, but provide a novel and independent tool that may offer additional constraints on this important process.