地球の核の炭素は太陽系外縁部からもたらされた可能性（Earth’s ‘core carbon’ may have come from the far reaches of the solar system）

2026-11-09 イェール大学

Photomicrograph of analyzed melt inclusion. Credit: Yves Moussallam

＜関連情報＞

• https://news.yale.edu/2026/11/09/earths-core-carbon-may-have-come-far-reaches-solar-system
• https://www.pnas.org/doi/10.1073/pnas.2610912123

核には同位体的に重い炭素が含まれている Isotopically heavy carbon in the core

Yves Moussallam, Damanveer S. Grewal, Guillaume Georgeais, +7 , and Matthew G. Jackson
Proceedings of the National Academy of Sciences  Published:November 9, 2026
DOI:https://doi.org/10.1073/pnas.2610912123

Abstract

Constraining the origin of Earth’s carbon requires knowing the isotopic composition of the core—a geochemical signature long presumed to be beyond observation for the planet’s largest carbon reservoir. Here, we report high-precision δ¹³C measurements from Hawaiian plume melt inclusions entrapped before significant degassing and sampling distinct mantle sources. Melt inclusions from shield-stage lavas, interpreted to sample the plume’s central axis, inferred to be rooted in the core–mantle boundary thermal boundary layer, converge toward a primary δ¹³C signature of –1 ± 2‰. In contrast, melt inclusions from rejuvenated-stage lavas, derived from entrained mantle at the plume’s periphery, record a normal mantle source signature of –7 ± 2‰. We interpret the uniquely ¹³C-rich shield-stage signature as the isotopic fingerprint of carbon exchanged from the core into the mantle. Our results point to ¹³C-rich carbonaceous chondrites as the primary source of Earth’s carbon.