Though the presence of water was primordial for the origin of life, the origin of Earth’s water remains an open question. Since our planet accreted in the dry inner Solar System, ice-rich outer Solar System materials have been held responsible for providing the Earth with volatiles. However, due to their isotopic similarities with the Earth and despite their reduced nature, enstatite meteorites have been proposed to constitute an important source of inner Solar System water following measurements of substantial amounts of water in these meteorites. To better constrain the history of water in the inner Solar System and the contribution of enstatite meteorites to the water budget of the Earth, seven enstatite chondrites (ECs) and one aubrite were investigated in this work. Chondrule phases from unequilibrated samples were targeted to constrain the pre-accretionary origin of primordial water in chondritic components, and Nominally Anhydrous Minerals (NAMs) from equilibrated samples were investigated to constrain the influence of parent body processes on the water budget of EC parent bodies. Finally, the aubrite Mayo Belwa was investigated to understand the water budget of enstatite achondrites following the later stage of planetary differentiation. The water content and H isotopic compositions of samples were investigated using in-situ nanoscale secondary ion mass spectrometry (NanoSIMS), which revealed that chondrule phases of the primitive type 3 samples of the low-iron group (“EL3”) contain low water content, two orders of magnitude below those reported for chondrule phases of the primitive type 3 samples of the high-iron group (“EH3”). Preservation of both protosolar and interstellar pre-accretionary signatures in EL3 chondrule NAMs suggests that although the accretion region of ECs was likely a dry and reducing environment, transport mechanisms within a turbulent inner protoplanetary disk could have provided this region with chondrule precursors containing water of diverse origins. Equilibrated, type 4 ECs yielded low water contents with no pre-accretionary H isotopic signatures, and no detectable water contents for samples of higher metamorphic grade, attesting that parent body processes cause efficient water loss and erasure of primordial H isotopic signatures. High water contents measured in the impact melt of Mayo Belwa are not representative of the bulk aubrite parent body, likely sampling localised re mobilisation of volatiles in this highly-shocked sample. Modelling of the water budget of EC parent bodies and their contribution to the terrestrial water budget showed that EC material alone could have provided enough water to account for the lowest ii estimates of the total water content of our planet, and provide a good match to the H isotopic composition of terrestrial water. To fit the highest estimates of Earth’s water content, established assuming that the core is an important reservoir of H, mixing of a majority of EC material with addition of some carbonaceous-chondrite material provides enough water to account for the entire water budget of the Earth and produces H isotopic compositions within the range of terrestrial values. In both cases, contribution of a majority of EC material can explain the origin of Earth’s water.
Chloé Cécile Sonia Gruyer (Thu,) studied this question.