In a groundbreaking scientific revelation that is reshaping our understanding of Earth’s deep interior, researchers have unveiled evidence that the ratio of ferric iron (Fe³⁺) to total iron (ΣFe) in the Earth’s mantle has doubled since the Early Archean eon. This discovery, which appears poised to revolutionize geological and geochemical paradigms, offers unparalleled insights into the dynamic oxidation state evolution of Earth’s mantle over billions of years. The finding is detailed in a comprehensive study published recently in Nature Communications by Zhu, Duan, Gerya, and their colleagues.
The Earth’s mantle, the vast layer of rock sandwiched between the crust and the core, plays a pivotal role in controlling the planet’s thermal and chemical evolution. Iron, one of the most abundant elements in the mantle, exists mainly in two oxidation states: ferrous (Fe²⁺) and ferric (Fe³⁺). The ratio between these states influences mantle properties, including its viscosity, melting behavior, and ability to store volatiles such as oxygen. Until now, however, the long-term historical trend of this redox ratio was poorly constrained. This study breakthrough not only quantifies the increase in Fe³⁺/ΣFe ratio but also links it to fundamental geodynamic processes that have operated over Earth’s 4.5 billion-year history.
Using advanced petrological modeling combined with a complex suite of geochemical proxies, the researchers reconstructed the oxidation state trends of the mantle with remarkable precision. Their multi-disciplinary approach incorporated the latest experimental data on iron’s behavior under extreme mantle conditions, integrating findings from high-pressure and high-temperature laboratory experiments. This enabled the team to model how the Fe³⁺/ΣFe ratio has evolved, revealing the unanticipated doubling since the dawn of terrestrial life in the Archean eon, roughly 4 billion years ago.
One of the marvels of this new research is its ability to connect subtle geochemical signals preserved in ancient mantle-derived rocks—such as mantle xenoliths and komatiites—to broader planetary chemical cycles. Komatiites, ultra-mafic volcanic rocks that erupted predominantly during the Archean, served as a critical archive for the team’s hypotheses. The researchers demonstrated that the increasing Fe³⁺ content likely reflects an escalating oxidation state of the mantle, linked intimately to processes such as subduction-driven plate tectonics and deep Earth volatile cycling.
The oxidation state of Fe in the mantle impacts not only its physical characteristics but also has profound implications for the nature of magmatism and mantle convection. A more oxidized mantle favors the stabilization of certain mineral phases and affects the solubility and partitioning of elements critical for sustaining life on the surface. The study’s findings imply a fundamental shift in the mantle’s redox budget that accompanied Earth’s escalating tectonic activity and biological oxygen production, representing a coupling between deep Earth and surface processes. This strikingly connects mantle evolution to biospheric development indirectly influencing atmospheric composition over geological timescales.
The gradual increase in Fe³⁺/ΣFe ratio further suggests a feedback mechanism through which the mantle’s redox state could have influenced volcanic gas emissions, shaping the chemistry of the early atmosphere and hydrosphere. Volcanic emissions, dominated by iron and sulfur-bearing species, would be modulated by the mantle’s oxidation state, thereby controlling surface conditions conducive to life. Such intricate coupling between mantle geochemistry and surface environments underscores the importance of these findings for understanding Earth’s habitability through deep time.
Moreover, the mantle’s oxidation state capped by Fe³⁺/ΣFe serves as a sensitive proxy for global geodynamic processes. The team’s integrated models reveal that the mantle redox evolution stretches beyond just chemical changes in contained iron; it also provides insight into the history of mantle melting regimes and the nature of mantle convection currents. These motions dictate the transfer of heat and materials from deep Earth to the surface and are intimately tied with the tectonic cycles that define Earth’s geological landscape.
Importantly, the doubling of the Fe³⁺/ΣFe ratio since the Early Archean helps explain previously puzzling disparities in ancient rock geochemistry. Many Archean rocks showed evidence for a more reduced mantle source than modern rocks, consistent with lower ferric iron content in the past. This study offers a quantitative framework tying together these petrological and geochemical observations with large-scale planetary processes, clarifying the contrasting characteristics of modern versus early Earth mantle chemistry.
This advancement also opens the door to envisioning how Earth compares to other terrestrial planets like Mars and Venus. While Earth’s mantle oxidation state has evolved to favor a more oxidized environment, contributing to the sustaining of life and plate tectonics, the static or differently evolving redox states of neighboring planets might help explain their divergent tectonic and atmospheric outcomes. Thus, the mantle’s Fe³⁺/ΣFe ratio doesn’t just inform Earth’s internal chemistry but also planetary evolution in a broader cosmic context.
The researchers utilized cutting-edge computational techniques to simulate mantle convection, oxidation-reduction reactions, and iron speciation at a spatial scale previously unattainable, enabling realistic temporal reconstruction from Archean conditions to the present day. These simulations corroborate observational data from isotope geochemistry and mineral physics, providing a holistic picture that interlinks iron’s oxidation changes to mantle dynamic processes. Their robust multi-method approach validates the conclusion that oxide iron increased by a factor of two, a result with far-reaching implications for geoscience.
Another fascinating aspect emerging from this study is the potential linkage to the Great Oxidation Event (GOE) that fundamentally transformed Earth’s atmosphere around 2.4 billion years ago. While the GOE is often discussed in terms of atmospheric oxygen rise driven by biological activity, this mantle redox shift highlights a previously underappreciated internal Earth contribution. The interplay between mantle oxidation state and surface oxidation might have been symbiotic, with mantle changes potentially priming the conditions for atmospheric oxygenation.
The increase in Fe³⁺/ΣFe ratio may also impact the deep carbon cycle, as iron redox speciation governs the stability of carbon-bearing phases like carbonates and diamond in the mantle. A more oxidized mantle favors carbonate stability, influencing the deep storage of carbon and thus modulating the long-term planetary climate. This could have played a role in the relative stability of Earth’s climate over geological timescales, supporting the emergence and persistence of complex life.
Their work additionally sheds light on the interactions between mantle redox evolution and the generation of metallic cores during Earth’s early accretion. The Earth’s core formation would have sequestered much of the iron in its metallic state, initially leaving the mantle relatively reduced. The doubling of Fe³⁺ in the mantle implies gradual reoxidation through processes such as subduction of oxidized material and recycling of surface oxidants—a remarkable testament to Earth’s active and evolving interior.
In terms of broader scientific implications, this revelation challenges some existing models of mantle dynamics and mantle source compositions, calling for updates to geochemical cycle models and mantle convection paradigms. Future research will need to further explore how the mantle Fe³⁺/ΣFe ratio parameters influence mantle phase transitions, partial melting processes, and the mantle’s electrical conductivity, all of which bear on geophysical observations.
This discovery also presses forward the importance of acquiring high-resolution, deeply penetrating geochemical and geophysical datasets, encouraging the scientific community to refine tools and techniques for probing the Earth’s interior. It inspires cross-disciplinary collaboration between mineral physicists, geochemists, geodynamic modelers, and planetary scientists to knit together Earth’s oxidation narrative with wider planetary evolution themes.
In sum, the doubling of Earth’s mantle Fe³⁺/ΣFe ratio since the Early Archean casts light on one of our planet’s most fundamental chemical evolutions. As we deepen our understanding of Earth’s inner workings, we unlock secrets that link deep mantle chemistry to surface environments, tectonic activity, atmospheric evolution, and life itself. This work not only redefines the primordial conditions of our planet but also proposes a new framework for interpreting the interconnected processes that have shaped Earth’s redox history over eons.
The uncovering of such a monumental shift in mantle chemistry comes at a timely moment, promising to invigorate future geoscience research and offering tantalizing clues on how oxidation states govern planetary habitability on Earth and beyond.
Subject of Research: The evolution of the mantle Fe³⁺ to total Fe ratio and its implications for Earth’s oxidation state since the Early Archean.
Article Title: The Mantle Fe³⁺/ΣFe Ratio Has Doubled Since the Early Archean
Article References:
Zhu, XX., Duan, WY., Gerya, T. et al. The Mantle Fe³⁺/ΣFe Ratio Has Doubled Since the Early Archean. Nat Commun 17, 429 (2026). https://doi.org/10.1038/s41467-025-66969-1
Image Credits: AI Generated
