Jonathan O’Neil

Assistant professor, Department of Earth and Environmental Sciences, University of Ottawa


My research interests are focused on the early Earth and its evolution through time. Topics of interest include: the formation and evolution of Earth’s primitive crust; the early differentiation of the silicate portion of the Earth; the evolution and interactions of the early formed geochemical reservoirs.

My research projects combine fieldwork, petrology, geochemistry and isotope geochemistry in order to understand the different geological processes that shaped our planet in the Hadean and Archean. Our ability to investigate early Earth history is compromised by the rarity of ancient terranes limiting our understanding of the geological processes shaping the early Earth shortly after its formation. However because of the increasing precision of analytical techniques, we can use new geochemical tools to better extract information from the small remnants of ancient Earth’s crust. Rare occurrences of ancient crust (older than 3.6 billion years) provide the only compositional constraints on the nature of Earth’s early crust. Despite their scarcity, these ancient terrains can provide invaluable information about the processes that were shaping the Earth shortly after its formation.

The primary tools I use are extinct isotopic systems which are powerful tracers to study early silicate differentiation and primitive crust formation. The main short-lived isotopic system I use is the 146Sm-142Nd. The daughter isotope, 142Nd, is produced from the decay of 146Sm having a short half-life of 68 Myr. Therefore, variations in the relative abundance of 142Nd can only be generated while 146Sm was still extant, basically prior to 4.0 Ga.