Earth's 'core carbon' may have come from the far reaches of the solar system

A new study published in the Proceedings of the National Academy of Sciences suggests that the majority of Earth's carbon came from the outer solar system rather than the inner solar system where most of the planet formed. Researchers from Yale and Columbia University analyzed magma droplets called melt inclusions from historic volcano eruptions in Hawaii to determine the isotopic composition of carbon in Earth's core.

These melt inclusions, captured within crystals during the cooling of magma deep within the Earth, provided the first observational estimate of the core's carbon signature. The study's lead author, Damanveer Grewal, found a heavy carbon-13 signature in magma believed to originate from a boundary area between the Earth's core and mantle, suggesting that some carbon escaped into the core from this region.

Grewal argues that Earth's core carbon is too heavy to have originated from the rocky, carbon-poor material of the inner solar system, but matches the composition of carbonaceous chondrites, carbon-rich meteorites from the outer solar system. This discovery implies that the carbon in Earth's core likely arrived during the final stages of the planet's formation, as earlier arrival would have been lost during subsequent collisions, and later arrival would have been trapped within the core, as it couldn't escape as Earth's core became more compact.