CSI alum, Susmita Garai (PhD 2026), publishes Nature Geoscience paper: Experimental simulation of water formation on Earth from dry pebble rain

Experimental simulation of water formation on Earth from dry pebble rain. Susmita Garai, Zachary D. Sharp, Peter L. Olson & Anthony M. Gargano  Abstract. Water is vital to planet habitability. However, the sources of water for terrestrial planets and timing of delivery remain controversial. Here we show experimentally how oceans of water can be produced within the high-temperature H₂-rich atmosphere above a terrestrial planet growing by capture of millimetre-to-centimetre-size silicate pebbles. We simulate this process by melting anhydrous mafic lithologies in H₂ streams. Measurements show large amounts of water generated by hydrogen reduction of iron oxide to iron metal within several hours. We also find that the produced metal strongly sequesters phosphorus, stripping it from the silicate. Our experimental results imply that silicate pebbles settling through a hot H₂-rich atmosphere experience volatile loss, iron reduction to iron metal and H₂O vapour production. Transfer of this metal to the core offers an explanation of the low phosphorus content of Earth’s mantle relative to Mars as well as the low Fe/Mg ratio of Earth’s primitive mantle. Atmospheric reduction of iron oxide under pebble accretion represents an endogenous source of water, and Earth-sized exoplanets built from pebbles may inherit oceans of water this way, representing a step towards habitability.