Ancient iron meteorites have provided new insights into the early days of our Solar System, revealing that the first solid bodies formed mostly from tiny, heat-forged rock beads called chondrules, while water-rich dust was largely excluded. This discovery pushes back the timeline for this selective planet-building process to within the first million years of the Solar System's formation. Scientists had previously thought that such a selective process began much later, but this research suggests it started almost immediately. During the early stages of planet formation, two main types of material were available in the young Solar System. One was chondrules—millimeter-sized pieces of rock formed at high temperatures. The other was matrix, a cold, fine-grained dust rich in water ice and organic material. New research led by Yale University has found geochemical evidence showing that chondrules were already being preferentially incorporated into solid bodies during the Solar System’s first million years. This finding challenges previous assumptions and suggests that the earliest planetesimals were highly selective in their composition. Scientists had long observed that carbonaceous chondrites—primitive meteorites from the outer Solar System—show a pattern linked to their age. Older chondrites tend to have more chondrules and less matrix, while younger ones contain more of the icy, volatile-rich material. This pattern suggested that the regions where the first solid objects, called planetesimals, were forming favored chondrules while excluding much of the icy dust. However, confirming this during the Solar System's first million years was difficult, as no undifferentiated bodies from that time remain. To overcome this challenge, researchers examined chemical clues in iron meteorites from the outer Solar System. These meteorites came from parent bodies that contained so much radioactive aluminum-26 that they eventually melted completely, erasing physical structures. However, their chemistry still preserved useful information. By identifying two chemical tracers—sulfur, which is highly concentrated in matrix, and the oxidation state of iron, which can indicate the amount of water ice and oxidized dust—the team reconstructed the compositions of these ancient bodies. They found that matrix made up only 8% to 17% of the original material, meaning chondrules dominated. This convergence of evidence strengthens the conclusion that the earliest planetesimals were remarkably matrix-poor. The findings also help explain why very old chondrules are uncommon today. Many of these ancient chondrules were likely incorporated into the first generation of planetesimals, which later melted, destroying the physical evidence. This research shows that the process of selecting and sorting planetary ingredients began almost as soon as solid bodies started forming. Chondrules, the basic building blocks of planets, were already being sorted and incorporated into the first solid bodies from the very start.