New evidence suggests Earth didn't actually form from 'space pebbles' like we've all been told.
March 24, 2026
Original Paper
Iron isotope anomalies and the origin of the Earth
arXiv · 2603.21360
The Takeaway
A leading theory of planetary growth suggests Earth was built by sweeping up pebbles drifting from the outer solar system, but new ultra-precise iron measurements show Earth's 'fingerprint' doesn't match those pebbles. Instead, the Earth appears to be made of a unique, hidden reservoir of material from the sun's immediate neighborhood that exists nowhere else in the known meteorite record.
From the abstract
Understanding the origin of the Earth requires determining the original formation location of its building material. Based on the similar Fe isotopic composition of Earth's mantle and Ivuna-type (CI) chondrites, a prior study has argued that Earth formed by accretion of sunward-drifting pebbles from the outer Solar System. Here, using new high-precision Fe isotopic data, we show however that CI chondrites and Earth's mantle have distinct Fe isotopic composition when the neutron-rich 58Fe is also