Jonathan O'Neil

Ancient terrains provide the only constraints on the nature and evolution of Earth’s earliest crust. Only few terrains older than 3.5 billion years old (Ga) are preserved, limiting our understanding of the processes that formed our first continents. Moreover, with its active tectonics, the Earth is very efficient at reworking and recycling its own crust. The primitive crust, formed shortly after Earth’s formation, has therefore mostly been destroyed and re-melted to form younger rocks. My research aims at better understand the geological processes that formed the first terrestrial crust, the impact on the early chemical evolution of Earth’s mantle and how this primitive crust was reworked to form the oldest continental crust. 

Archean cratons are the most ancient cores of our continents. They are mostly composed of rocks formed between 2.5 to 3 Ga, leaving more than the first billion years of Earth’s crustal history difficult to study. This Archean crust can, however, contain the isotopic signature of its older precursor. With the increasing precision of analytical techniques, we can use novel isotopic tools to better extract information from ancient terranes. This helps us to build an improved picture of how and when our first continents formed and to investigate the nature of Earth’s primitive crust forming shortly after its accretion. 

A better understanding of the formation of the early crust can help us unravel fundamental broader questions such as: When and how did the primitive crust formed? Were the differentiation processes forming the early crust local or global? What processes contributed to the formation and stabilization of the Archean cratons? How much of our oldest continents were formed by reworking older crustal sources?