a complex geological sequence in northeastern Canada – harbors surviving fragments of Earth's oldest crust, dating back to ~4.16 billion years old, according to a new study. The preservation of Hadean rocks on Earth's surface could provide valuable insights into the planet's earliest times. Much about Earth's earliest geologic history remains poorly understood due to the rarity of Hadean-age (>4.03 billion-year-old) rocks and minerals. These ancient materials are typically altered or destroyed as the planet's crust is recycled through ongoing tectonic processes. One candidate for surviving Hadean-age crustal rock is the NGB, which contains rock argued to be as old as 4.3 billion years. However, this claim is controversial; some argue that the isotopic data underpinning these estimates may instead reflect later geological mixing processes rather than the true age of the formation. If shown to be Hadean in origin, the NGB would represent the oldest preserved rock sequence on Earth. It would offer critical insights into early Earth geology, including the potential setting for the emergence of life.
To constrain the age of the NGB, Christian Sole and colleagues focused on a specific type of ancient rocks – metagabbroic intrusions – within the belt. According to the authors, these intrusions intersect older basaltic rocks, and this feature allowed the authors to use combined uranium-lead (U-Pb) dating with both short- and long-lived neodymium (Sm-Nd) isotopic analyses to determine a lower age limit on the more ancient formations (the older basaltic rocks). Sole et al. report that the Sm-Nd data yielded consistent isochron ages around 4.16 billion years, regardless of sample location or mineral composition. The fact that both isotopic systems yield the same age in rocks linked by clear evidence of magmatic differentiation strongly supports their Hadean-age crystallization. This, in turn, supports the idea that fragments of mafic crust from the Hadean Eon have survived in the NGB.
