The terrestrial abundance anomalies of helium and xenon suggest the presence of deep-Earth reservoirs of these elements, which has led to great interest in searching for materials that can host these usually unreactive elements. Here, using an advanced crystal structure search approach in conjunction with first-principles calculations, we show that several Xe/He-bearing iron halides are thermodynamically stable in a broad region of P–T phase space below 60 GPa. Our results present a compelling case for sequestration of He and Xe in the early Earth and may suggest their much wider distribution in the present Earth than previously believed. These findings offer insights into key material-based and physical mechanisms for elucidating major geological phenomena.
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