A groundbreaking study published on September 4, 2025, in Nature Communications proposes a compelling link between the crystallization of Earth's inner core and its substantial carbon content. Researchers from the University of Oxford, University of Leeds, and University College London utilized advanced simulations to suggest that a carbon concentration of approximately 3.8% within the core could have been the catalyst for its solidification. This finding implies that carbon is more abundant in Earth's core than previously estimated and played a pivotal role in the development of the solid inner core.
The formation of the solid inner core is fundamental to sustaining Earth's protective magnetic field, which shields the planet from damaging solar radiation. Grasping the precise chemical composition of Earth's core is crucial for comprehending the planet's thermal evolution and the mechanisms that generate its magnetic field. The study's insights offer a deeper understanding of the intricate processes occurring deep within our planet and hold significant implications for planetary science.
The research employed atomic-scale computer simulations to meticulously model the freezing of molten iron under extreme temperatures and pressures. These simulations indicated that the presence of carbon significantly expedites the nucleation of solid iron, thereby facilitating the formation of the inner core. Conversely, elements such as silicon and sulfur, which were also examined, were observed to impede this crucial freezing process.
Previous scientific understanding suggested that Earth's core might require substantial supercooling, potentially between 800-1000°C below its melting point, to initiate the crystallization process. However, such extreme cooling could have led to an overly large inner core and the collapse of the magnetic field, outcomes not supported by geological evidence. The new findings suggest that a carbon-rich core, specifically around 3.8% carbon, would only require about 266°C of supercooling, aligning more closely with observed planetary conditions.
This concentration of carbon is the only known composition that can explain both the nucleation and the observed size of the inner core. This research builds upon decades of scientific inquiry into the Earth's core, a region that remains largely inaccessible. The collaborative effort by leading UK universities underscores the importance of interdisciplinary approaches in unraveling the planet's deepest mysteries. The findings not only shed light on Earth's formation but also provide a rare glimpse into the deep-seated chemistry that shapes our world. The Natural Environment Research Council (NERC) provided funding for this significant research endeavor.