Production of highly silicic 3.9 to 4.27 Ga crust on the Moon

The preserved remnants of a planetary body’s early crust represent a unique window into chemical and physical processes that shaped its beginning. While iron- and magnesium-rich magmas with low silica (SiO2) are common throughout a rocky body’s active lifetime, the timing of silica-rich crust production during the first 500 Myr of evolution remain uncertain. Silica-rich crust is relatively buoyant, influences the topography of rocky worlds, and concentrates heat-producing radioactive elements. However, identifying early silica-rich crust is challenging due to sample limitation and an inability to directly date silica-rich material like quartz and high-silica glass. Here, we show that the atomic environment around trace amounts of titanium in the mineral zircon is sensitive to the silica content of the magma it crystallised from, providing a new tool to recognise ancient silica-rich crust. By applying this method to 4.27 to 3.93 billion year old lunar zircons, we present evidence for early production of silica-rich crust on the Moon, suggesting this may be a common feature of planetary evolution.