Envato Elements
The core at the center of the Earth
Recent research suggests that iron in Earth’s solid inner core behaves like an electride, which explains the low amount of light elements on our planet.
For nearly a century, scientists have been puzzling over a fundamental planetary mystery: Why does Earth contain so many fewer light elements, such as hydrogen, carbon, nitrogen, sulfur and noble gases, than expected compared to the Sun or meteorites?
A growing body of research suggests that part of the answer may lie deep within Earth’s inner core and an unusual class of materials known as electrodes.
A recent publication in Communications Materials proposed that, under the extreme pressures of Earth’s solid inner core, iron can behave as an electride, a rare state of matter in which electrons remain trapped in cavities within the atomic structure, rather than orbiting individual atoms or moving freely as in conventional metals.
These trapped electrons could stabilize and absorb light elements over billions of years, potentially explaining why seismic data indicates that the inner core is less dense than pure iron.
Electrodes differ from ordinary solids because their crystal lattices contain “non-nuclear attractors” where electrons accumulate. This gives them unusual physical and chemical properties. High-pressure electrons were first identified in sodium in 2009, when experiments showed that the metal transformed from a shiny conductor to a transparent insulator under extreme compression. Since then, researchers have found evidence of similar behavior in other elements and compounds.
In addition to their possible role in the Earth’s interior, electrides are attracting attention for their practical applications. Because their trapped electrons are highly reactive, electrides can act as powerful catalysts, reducing the energy required for chemical reactions. One of these materials, mayenite, is already being used to produce ammonia more efficiently in a process that consumes around 20% less energy than the traditional Haber-Bosch method, which represents around 2% of global energy consumption.
Despite the hypothesis proposed in the study, some doubts still persist. Scientists debate whether the iron in the Earth’s core actually forms an electron, and there is no reliable theory for predict when materials will adopt this state. Researchers are now turning to advanced simulations and artificial intelligence to identify new electrons and better understand their formation.
