A new study led by Yale University reveals that the early solar system favored the formation of heat-forged chondrules over icy, volatile-rich dust when creating its first solid bodies. Published in Nature Astronomy, the research provides the first geochemical evidence that this preference occurred within the first million years of the solar system’s formation—much earlier than previously thought. Earlier studies had only observed this sorting process in objects that formed 2 to 4 million years after the solar system began. Chondrules are small, spherical grains formed by rapid heating and cooling of dust in the early solar system. They are found in chondrites, which are the most primitive meteorites known. The study found that the earliest solid bodies in the outer solar system were made up of 83% to 92% chondrules, with very little of the icy, volatile-rich dust that is more common in later-forming objects. This suggests that the solar system was already sorting materials in favor of chondrules over the icy matrix very early on. Previously, scientists had noticed that older carbonaceous chondrites from the outer solar system contained more chondrules and less matrix, hinting at a preference for chondrules. However, no unaltered bodies from the first million years of the solar system have survived to confirm this. To address this, the researchers turned to iron meteorites from the outer solar system. These meteorites came from parent bodies that had accumulated radioactive aluminum-26, which caused them to melt completely, erasing physical evidence of their original composition. By analyzing chemical tracers like sulfur and the oxidation state of iron, the researchers were able to estimate the original matrix levels in these early bodies. Both tracers indicated that the original planetesimals had only 8% to 17% matrix, much lower than seen in known chondrites. This consistency across different tracers strengthens the conclusion that the early solar system was dominated by chondrule-rich bodies. This finding also explains why older chondrules are rare in the meteorite record—they were incorporated into bodies that later melted, erasing their physical traces. Chondrules, as the basic building blocks of planets, were already being sorted and incorporated into the first solid bodies from the very start of the solar system’s formation.