A missing continental impact melt sheet signal in the early Earth detrital zircon record.

Impact-derived melting has been proposed as a significant process in the formation of Earth's early crust which could mean that impact melts are a source for Earth's oldest minerals including ancient zircons. However, the source lithology of many Archean and Hadean zircons is unclear because many grains are detrital. Therefore, in this work, we develop a machine learning model trained on the U/Yb, Th/U, Yb, and Gd/Yb values of zircons from the 1.85 Ga Sudbury impact melt sheet and more typical igneous processes, so that it could distinguish between them. Here, we show that ancient zircons from three >3.2Ga localities did not crystallize from impact melt sheets. Our results support the hypothesis that early earth zircons are not sourced directly from impact melt sheets, especially one produced by impacting continental crust and indicate no evidence for a late heavy bombardment implying a more habitable Hadean.