Understanding where Earth's essential elements came from—and why some are missing—has long puzzled scientists. Now, a new study reveals a surprising twist in the story of our planet's formation.
A new study led by Arizona State University's Assistant Professor Damanveer Grewal from the School of Molecular Sciences and School of Earth and Space Exploration , in collaboration with researchers from Caltech, Rice University, and MIT, challenges traditional theories about why Earth and Mars are depleted in moderately volatile elements (MVEs). MVEs like copper and zinc play a crucial role in planetary chemistry, often accompanying life-essential elements such as water, carbon, and nitrogen. Understanding their origin provides vital clues about why Earth became a habitable world. Earth and Mars contain significantly fewer MVEs than primitive meteorites (chondrites), raising fundamental questions about planetary formation.
Published in Science Advances, the study takes a fresh approach by analyzing iron meteorites—remnants of the metallic cores of the earliest planetary building blocks— to uncover new insights.
"We found conclusive evidence that first-generation planetesimals in the inner solar system were unexpectedly rich in these elements," said Grewal. "This discovery reshapes our understanding of how planets acquired their ingredients."
Until now, scientists believed that MVEs were lost either because they never fully condensed in the early solar system or escaped during planetesimal differentiation. However, this study reveals a different story: many of the first planetesimals held onto their MVEs, suggesting that the building blocks of Earth and Mars lost theirs later—during a period of violent cosmic collisions that shaped their formation.
Surprisingly, the team found that many inner solar system planetesimals retained chondrite-like MVE abundances, showing that they accreted and preserved MVEs despite undergoing differentiation. This suggests that the progenitors of Earth and Mars did not start out depleted in these elements, but instead, their loss occurred over a prolonged history of collisional growth rather than incomplete condensation in the solar nebula or planetesimal differentiation.
"Our work redefines how we understand the chemical evolution of planets," Grewal explained. "It shows that the building blocks of Earth and Mars were originally rich in these life-essential elements, but intense collisions during planetary growth caused their depletion."
