In a groundbreaking new study, researchers have made significant strides in unraveling one of Earth’s most enduring geological mysteries: the origin of its hydrogen and carbon. These elements, fundamental to life and planetary evolution, have long intrigued scientists seeking to understand how Earth acquired them during its formative years. By meticulously analyzing the partitioning behavior of hydrogen and carbon between Earth’s core and mantle, the team has provided fresh insights into the distribution and abundance of these critical volatiles within the planet.
The enduring question of Earth’s hydrogen and carbon origin connects directly to the planet’s deepest interior, a region largely hidden from direct observation. The core and mantle, constituting the bulk of Earth’s volume, control much of the planet’s chemical and physical properties. Understanding how hydrogen and carbon partitioned between these layers during Earth’s early differentiation not only reveals where these elements reside today but also helps reconstruct the volatile inventory available to the surface environment, ultimately affecting habitability and geological processes.
Hydrogen and carbon are essential for life as we know it, and their presence on Earth has profound implications for the planet’s atmosphere, oceans, and biosphere. These elements’ origin narratives are complex, shaped by various processes ranging from primordial accretion of planetary building blocks to late veneer additions after core formation. This study brings clarity by integrating experimental petrology, geochemical modeling, and bulk Earth abundance data to constrain how these volatile components behaved during core-mantle segregation.
Central to the researchers’ approach was high-pressure, high-temperature experimentation replicating the conditions present during Earth’s early differentiation. By simulating core formation under these extreme conditions, they measured how hydrogen and carbon distribute themselves between metal phases, representing the core, and silicate melts, symbolizing the mantle. This approach allows for a more accurate estimation of the partition coefficients that govern element migration during planet formation.
The results highlight a nuanced behavior of hydrogen and carbon in early Earth materials. Contrary to previous assumptions that most hydrogen would readily migrate into the core, the data suggest that a significant fraction of hydrogen remained associated with the silicate mantle due to its moderate partitioning characteristics. Carbon demonstrated similarly complex behavior, with its affinity depending heavily on the redox state and pressure conditions prevailing during core-mantle differentiation.
By combining these partitioning results with current knowledge of Earth’s bulk composition, the authors inferred the total inventory of hydrogen and carbon in the Earth system. Their models suggest that Earth’s mantle retains a surprisingly large amount of these volatiles, contradicting some earlier models that postulated extensive loss or sequestration into the core. This finding has profound implications for understanding how Earth maintained sufficient volatile content to develop and sustain its oceans and atmosphere.
Moreover, the study establishes critical constraints on the timing and processes of volatile acquisition. The relative proportions of hydrogen and carbon in the mantle versus the core imply that Earth’s early accretion incorporated volatile-rich materials that underwent incomplete metal-silicate separation. This incomplete separation allowed these life-essential volatiles to remain accessible in the mantle, setting the stage for the development of a habitable planet.
The findings also shed light on the redox evolution of Earth’s interior. Since carbon’s partitioning behavior is sensitive to oxygen fugacity, the observed distribution implies that Earth’s mantle maintained certain oxidation states conducive to retaining carbon in silicate materials. This redox state would also influence early mantle melting, volatile outgassing, and the composition of early Earth’s atmosphere.
Importantly, this research bridges geochemical data with planetary dynamics, offering new perspectives on how Earth compares to other terrestrial planets. The retention of hydrogen and carbon in Earth’s mantle might explain why Earth emerged as a uniquely habitable world compared to Mars or Venus, where volatile inventories and redox conditions differ markedly. This insight could guide future space missions aimed at understanding planetary habitability beyond our solar system.
Another remarkable aspect of the study is the precision achieved in quantifying bulk Earth volatile contents. By integrating their experimental data with seismic models and geochemical estimates, the authors provide robust predictions for how much hydrogen and carbon reside at different Earth depths. These benchmarks establish a new foundation for interpreting geophysical and geochemical observations related to volatile cycling within the deep Earth.
The implications extend to the long-term cycling of volatiles between Earth’s interior and surface environments. Knowing the deep reservoirs’ size and composition informs models of mantle convection, volcanic degassing, and the gradual replenishing of surface volatiles over geological timescales. Understanding these cycles is vital to piecing together Earth’s climatic history and the evolution of its biosphere.
This research embodies a multidisciplinary synthesis of mineral physics, geochemistry, and planetary science, showing how experimental constraints can profoundly enhance our understanding of planetary formation. It highlights the value of replicating planetary interior conditions to unlock secrets concealed beneath kilometers of Earth’s surface, unreachable by direct sampling.
Future investigations may build on these findings by probing the behavior of other volatile elements such as nitrogen and sulfur, further refining our picture of Earth’s volatile inventory and its implications for habitability. Additionally, extending these studies to exoplanetary contexts could illuminate the likelihood of volatile retention and habitability beyond our solar system.
In summary, the study offers a transformative perspective on Earth’s volatile origin story, demonstrating that hydrogen and carbon’s fate during core-mantle differentiation played a pivotal role in shaping the Earth we inhabit today. By tightly constraining the partitioning and abundance of these elements, the authors unravel how early Earth managed to retain life-essential volatiles, setting the stage for the emergence of the biosphere and shaping planetary habitability in the process.
Subject of Research: The origin and distribution of hydrogen and carbon in Earth’s interior, focusing on their partitioning between core and mantle during planetary differentiation.
Article Title: Origin of Earth’s hydrogen and carbon constrained by their core-mantle partitioning and bulk Earth abundance.
Article References:
Tsutsumi, Y., Sakamoto, N., Hirose, K. et al. Origin of Earth’s hydrogen and carbon constrained by their core-mantle partitioning and bulk Earth abundance. Nat Commun 16, 10038 (2025). https://doi.org/10.1038/s41467-025-65729-5
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41467-025-65729-5
