^1,2William F. McDonough
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.12.060]
¹Advanced Institute for Marine Ecosystem Change (WPI-AIMEC), Department of Earth Sciences and Research Center for Neutrino Science, Tohoku University, Sendai, Miyagi 980-8578, Japan
²Department of Geology, University of Maryland, College Park, MD 20742, USA
Copyright Elsevier

One in every two atoms in the Earth, Mars, and the Moon is oxygen; it is the third most abundant element in the solar system. The oxygen isotopic compositions of the terrestrial planets are different from those of the Sun and demonstrate that these planets are not direct compositional analogs of the solar photosphere. Likewise, the Sun’s O/Fe, Fe/Mg and Mg/Si values are distinct from those of inner solar system chondrites and terrestrial planets. These four elements (O, Fe, Mg, Si) make up 90% to 94% by mass (and atomic %) of the rocky planets, and their abundances are determined uniquely using geophysical, geochemical, and cosmochemical constraints.

The rocky planets likely grew rapidly (with    10 million years) from large populations of planetesimals, most of which were differentiated, having a core and a mantle, before being accreted. Planetary growth in the early stages of protoplanetary disk evolution was rapid and was only partially recorded by the meteoritic record. The noncarbonaceous meteorites (NC) provide insights into the early history of the inner solar system and are used to construct a framework for how the rocky planets were assembled. NC chondrites have chondrule ages that are two to three million years younger than  (the age of calcium–aluminum inclusions, CAI), documenting that NC chondrites are middle- to late-stage products of solar system evolution.

The composition of the Earth, its current form of mantle convection, and the amount of radiogenic power that drives its engine remain controversial topics. Earth’s dynamics are driven by primordial and radiogenic heat sources. Measurement of the Earth’s geoneutrino flux defines its radiogenic power and restricts its bulk composition. Using the latest data from the KamLAND and Borexino geoneutrino experiments affirms that the Earth has   20 TW of radiogenic power and sets the proportions of refractory lithophile elements in the bulk silicate Earth at   2.7 times that in CI chondrites. The bulk Earth and the bulk Mars are enriched in refractory elements about 1.9 times that of the CI chondrites. Earth is more volatile-depleted and less oxidized than Mars.

¹Eleanor C. McIntosh, ¹James M.D. Day
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.12.059]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
Copyright Eslevier

The Apollo 17 high-Ti orange (74220) and Apollo 15 low-Ti green (15426) lunar pyroclastic glasses are some of the most primitive igneous samples from the Moon and are considered critical for understanding the volatile content of the lunar interior. The orange and green glass deposits are petrologically distinct, containing both holohyaline (glassy) and crystallized beads. In this study, edge and center analyses on holohyaline beads representative of the deposits were conducted by laser ablation inductively coupled plasma mass spectrometry to constrain the distribution of moderately volatile elements (MVE: K, Cu, Zn, Cs, Ga, Ge, Rb, Cd, and Pb), and trace element images were produced of the beads in 74220. Bead edges have elevated MVE abundances compared to centers in the larger (107 µm average diameter) low-Ti Apollo 15 green glasses, likely resulting from syn-eruptive processes. Leaching experiments of 15,426 bulk beads support a large fraction of Na, K, Zn, Cd, Cd and Pb on their outer surfaces. The smaller (42 µm average diameter) high-Ti Apollo 17 orange glasses have a greater extent of overlap in MVE contents between bead edges and centers. Orange and green glass bead centers offer approximations of melt MVE abundances, indicating ∼500 µg/g K, ≤20 µg/g Zn, ∼6 µg/g Cu, <4 µg/g Ga and ≤ 1 µg/g Rb and <0.1 µg/g Pb and ≤ 100 µg/g K, ≤1 µg/g Zn, ≤2.5 µg/g Cu, <2 µg/g Ga and ≤ 0.5 µg/g Rb and Pb, respectively. These estimates are as much as ten times lower than bulk bead abundances for these and other MVE within the pyroclastic glass deposits, are depleted compared to terrestrial mid-ocean ridge basalts, and are similar, or lower than, bulk silicate Earth (BSE) concentration estimates. Partial melting estimates for the source of the pyroclastic glass beads indicate similarities with tholeiitic and komatiite lavas on Earth and between ∼10 and 30 % melting of their mantle source, consistent with high mantle potential temperatures at ∼3.5 billion years ago in the Moon. The estimated MVE composition of the orange glass bead mantle source is marginally higher than the green glass mantle source, and both are within or lower than bulk silicate Moon estimates. More shallowly derived mare basalts have been shown to be yet more MVE depleted, indicating that the lunar interior had a heterogeneous distribution of volatile elements, with a deep interior with volatile abundances ∼10 times lower than BSE, volatile-poor upper magma ocean cumulates, and an incompatible volatile-enriched KREEP reservoir.