The mystery of where Earth’s essential elements came from—and why some of them are missing—has intrigued scientists for centuries. Elements like copper, zinc, and others in the class known as moderately volatile elements (MVEs) are crucial for life and planetary chemistry. These elements tend to appear alongside other life-essential substances, such as water, carbon, and nitrogen, which are abundant on Earth. Yet, both Earth and its planetary neighbor, Mars, contain fewer MVEs than primitive meteorites, known as chondrites, that are thought to represent the raw material from which the planets formed.
To answer these questions, a groundbreaking study led by Assistant Professor Damanveer Grewal from Arizona State University’s School of Molecular Sciences and the School of Earth and Space Exploration, in collaboration with researchers from Caltech, Rice University, and MIT, challenges long-standing theories and proposes a new understanding of why Earth and Mars are depleted in these essential elements.
Traditional Theories: A Mystery of Loss
For years, scientists have debated why Earth and Mars, two planets formed from the same early solar system material, are so deficient in MVEs. One widely accepted theory held that these elements were either not abundant in the early solar system or that they evaporated into space during the planetesimal differentiation process. Planetary differentiation is a key phase in the formation of planets when materials within a planetary body separate based on their density, with heavier elements sinking to the center and lighter ones rising to the surface. Under this theory, MVEs, due to their volatility, were thought to escape or not condense in sufficient quantities to be present on these planets.
However, the new research by Grewal and his team uncovers a surprising twist in this narrative, challenging the notion that Earth and Mars were never rich in MVEs in the first place.
A Fresh Approach: The Role of Iron Meteorites
In a novel approach, the study turned to iron meteorites, which are remnants of the metallic cores of early planetesimals—the small building blocks that collided and merged to form larger planets. Iron meteorites are thought to have formed from the cores of planetesimals that underwent differentiation in the early solar system, making them an ideal source of information on the processes that shaped planetary bodies.
“We found conclusive evidence that first-generation planetesimals in the inner solar system were unexpectedly rich in these elements,” said Grewal. This discovery is monumental because it directly contradicts previous assumptions that MVEs were either too volatile to condense or were lost during the differentiation of planetesimals.
The study found that many of these early planetesimals, particularly those in the inner solar system, retained chondrite-like abundances of MVEs. These planetesimals had accreted and preserved MVEs despite undergoing differentiation, meaning they had managed to retain these important elements throughout their early development.
The Shift in Understanding: Collisions and Chemical Evolution
The findings of the study suggest a new narrative for the chemical evolution of planets. Instead of Earth and Mars being formed from already depleted planetesimals, the new data indicates that the building blocks of these planets were initially rich in MVEs. It was only later, during the violent cosmic collisions that played a central role in the formation of these planets, that these elements were lost.
This shift in thinking suggests that the depletion of MVEs was not a result of incomplete condensation in the early solar system or a natural consequence of planetesimal differentiation, as previously believed. Instead, the loss of these elements occurred over an extended period during the collisional growth of the planets, a process that involved repeated impacts and the gradual accumulation of material. During these intense collisions, the outer layers of these planets were subjected to heat and pressure that could have caused the volatility of the MVEs, leading to their eventual depletion.
“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.”
Implications for the Origin of Life on Earth
The results of this study hold significant implications for our understanding of the origin of life on Earth. MVEs, such as copper and zinc, are essential not only for the chemistry of life but also for many of the biochemical processes that sustain life today. If Earth’s early planetesimals had retained their MVEs, it would suggest that the planet’s formation may have included these critical elements from the start, providing a potential foundation for the development of life.
Understanding how and why these elements became depleted over time also offers a more nuanced view of the environmental conditions on early Earth and Mars. These insights could help scientists better understand how planets evolve chemically and why Earth, in particular, became a habitable world, capable of supporting life, while Mars—a planet with similar building blocks—became inhospitable.
The Next Steps: Exploring the Chemical Evolution of Other Planets
This new study opens up exciting possibilities for future research. The discovery that early planetesimals were rich in MVEs may change the way scientists view the formation and chemical evolution of planets beyond our own. It also raises important questions about the conditions that led to the depletion of these elements in Earth and Mars—and whether similar processes could have occurred on other planets in the solar system or on exoplanets in distant star systems.
In particular, researchers will likely focus on examining meteorites from other parts of the solar system to see whether the patterns observed in the inner solar system also hold true for planets further from the Sun, like Jupiter and Saturn, or for planets in other solar systems. By continuing to study the remnants of early planetesimals, scientists could uncover more details about the chemical evolution of planets and the conditions that lead to habitable environments.
Conclusion: A New Perspective on Planetary Formation
In conclusion, the findings of this groundbreaking study not only reshape our understanding of planetary formation but also challenge long-held assumptions about the origin of life-essential elements on Earth. By revealing that the first planetesimals in the inner solar system were unexpectedly rich in moderately volatile elements, the research highlights a new chapter in the history of the solar system’s evolution.
This discovery emphasizes the importance of collisions and chemical evolution in shaping the planets we know today and underscores the dynamic processes that played out over billions of years in the formation of Earth and Mars. As scientists continue to investigate the mysteries of planetary chemistry, they move ever closer to unraveling the complex and fascinating story of how the essential ingredients for life came to be on our planet.
In the end, this study not only reshapes our understanding of Earth’s formation but also brings us closer to understanding the fundamental processes that make our world—and others—suitable for life.
Reference: Damanveer Grewal, Enrichment of Moderately Volatile Elements in First-Generation Planetesimals of the Inner Solar System, Science Advances (2025). DOI: 10.1126/sciadv.adq7848. www.science.org/doi/10.1126/sciadv.adq7848