Earth's Building Blocks: New Data Challenges Outer Solar System Origin

Determining the origin of Earth's building materials is crucial for understanding its formation.

Revisiting Earth's Formation: The Pebble Accretion Theory

A prior study suggested that Earth formed from pebbles drifting inward from the outer Solar System. This theory was based on the similar iron (Fe) isotopic composition found in Earth's mantle and Ivuna-type (CI) chondrites.

Distinct Iron Isotope Signatures Emerge

However, new high-precision Fe isotopic data now challenges this view. Researchers found that CI chondrites and Earth's mantle possess distinct Fe isotopic compositions, especially when considering the neutron-rich 58Fe isotope.

This finding contradicts the idea that the iron in Earth's mantle originated from CI chondrite-like material or from the accretion of sunward-drifting pebbles.

Inner Solar System: A New Source for Earth's Iron

The current study proposes an alternative. It suggests that the iron in Earth's mantle instead originated within the inner Solar System. This iron was partly or entirely delivered by bodies from the innermost disk, which are not represented among current meteorite samples.

This new understanding aligns with the classical model of Earth's formation, which describes a hierarchical growth process among planetesimals and planetary embryos within the inner Solar System.