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2w ago

Simulations Point to Carbon as Trigger for Earth’s Inner-Core Formation

Atomic-scale modeling indicates roughly 3.8% carbon by mass would allow crystallization under limited supercooling.

Drawing of Earth with cutaway showing the mantle and inner and outer core. Magnetic field lines produced by the geodynamo extend into space and interact with the solar wind. The iron-rich core at Earth's center is slowly freezing from the inside out. This growth of the solid inner core powers the magnetic field that shields our planet from harmful space weather. How and when the inner core first began to freeze remains a mystery but new research shows that solving it could reveal the core's composition, giving us a clearer picture of Earth's deep interior. Credit: Dr. Alfred Wilson
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Artist's concept of Earth's core (Credit: NASA/JPL)
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Overview

  • A peer-reviewed study published September 4 in Nature Communications by teams at Oxford, Leeds, and UCL identifies carbon as a key light element in the core.
  • Large atomic-scale simulations (~100,000 atoms) under core-like pressures and temperatures tracked nucleation, the first step in freezing, without requiring external seeds.
  • Carbon accelerated iron crystallization while silicon and sulfur slowed it, reshaping which light elements are plausible major core constituents.
  • Extrapolating the results shows about 3.8% carbon lowers the required supercooling to roughly 266°C, consistent with geophysical limits and far below the 800–1,000°C expected for pure iron.
  • The finding offers a concrete chemical constraint that helps explain the core’s lower-than-iron density and informs models of inner-core age, thermal history, and the geodynamo, with further experimental and modeling tests expected.