Meet the mysterious electrides

For nearly a century, scientists have grappled with a perplexing question: What happened to Earth's lighter elements? When comparing Earth to the Sun and various meteorites, it's evident that our planet has significantly lower amounts of hydrogen, carbon, nitrogen, sulfur, and noble gases like helium—sometimes more than 99% less. While some of this discrepancy can be attributed to losses during Earth's formation, researchers have long suspected an additional mystery. A recent study led by a team of scientists has proposed a compelling explanation: these elusive elements may be residing deep within Earth's solid inner core. Under extreme pressures of 360 gigapascals—equivalent to 3.6 million times the pressure we experience at sea level—the behavior of iron alters dramatically, transforming it into a little-known variant known as an electride. This unique form of metal has the capacity to absorb lighter elements, potentially accounting for the observed differences in seismic wave movements that suggest the inner core's density is 5% to 8% lower than expected if it were solely composed of metal. Electrides are experiencing a resurgence in scientific interest. They not only offer solutions to longstanding planetary enigmas, but they can also be synthesized at room temperature and pressure from various elements. The unique properties of electrides, particularly their ability to provide reactive electrons, make them exceptional candidates for catalysts and other agents that facilitate complex chemical reactions. One such electride is already making waves in the production of ammonia, a crucial ingredient in fertilizers. Japanese developers of this electride claim that their method uses 20% less energy compared to conventional ammonia manufacturing processes. Moreover, chemists are continually identifying new electrides that hold the promise of enabling more cost-effective and environmentally friendly approaches to pharmaceutical production.