NASA’s Curiosity rover, a robotic explorer on Mars for nearly 12 years, has made recent findings of sedimentary organic material with unique properties have scientists buzzing. These carbon-based materials, particularly their carbon isotope ratios, have led to intriguing questions about their origins.

On Earth, similar organic materials are usually linked to microorganisms, but they can also stem from non-biological chemical processes. This ambiguity left researchers searching for clear answers. However, a new study in Nature Geoscience, conducted by scientists from the University of Copenhagen and the Tokyo Institute of Technology, offers exciting insights.

Professor Matthew Johnson, a co-author of the study, explained that these findings support a decade-old theory about photolysis in Mars’s atmosphere. According to the theory, billions of years ago, solar radiation broke down CO2 in Mars’s atmosphere, producing carbon monoxide. This carbon monoxide then reacted with other atmospheric chemicals to create complex organic molecules, essential for life.

Mount Sharp in the center of the Gale crater, where Curiosity Rover found organic material
Mount Sharp in the center of the Gale crater, where Curiosity Rover found organic material. Credit: NASA / JPL / Caltech / MSSS

Johnson likened this discovery to the classic “chicken or egg” debate. The study suggests that organic material on Mars formed through photochemical reactions, providing the “egg” or prerequisite for life. Whether this material led to life on Mars remains uncertain. This discovery also has significant implications for understanding the origins of life on Earth, given the similar early atmospheres of Earth, Mars, and Venus.

Twelve years ago, Johnson and his colleagues used quantum mechanical simulations to explore the effects of UV light on a CO2-rich atmosphere, a process known as photolysis. They predicted that photolysis would split CO2 into oxygen and carbon monoxide, altering the ratios of carbon-12 and carbon-13 isotopes. These predictions matched findings in a Martian meteorite, Allan Hills 84001, discovered in Antarctica. This meteorite contained carbonate minerals formed from atmospheric CO2, with carbon isotope ratios matching those predicted by the simulations.

However, a key piece of the puzzle was missing—confirmation from organic material on Mars. The new findings by Curiosity provided this crucial evidence. The organic material showed carbon-13 depletion, mirroring the carbon-13 enrichment in the Allan Hills meteorite. These linked data from samples found millions of kilometers apart suggest a shared origin in Mars’s early history.

Researchers believe that the photolysis process, critical for creating life’s building blocks, likely occurred on Earth as well. Finding similar isotopic evidence on Earth has been challenging due to geological changes. Johnson speculates that Earth’s dynamic surface might have altered or buried this evidence. Nonetheless, finding it on Mars, from a time when Mars and Earth were similar, marks a significant step in understanding the origins of life.

Johnson remains hopeful that similar evidence might still be found on Earth, despite the complexities introduced by Earth’s active geology. This discovery on Mars opens new avenues for exploring the beginnings of life both on our planet and beyond.

SOURCES

University of Copenhagen

Ueno, Y., Schmidt, J.A., Johnson, M.S. et al. Synthesis of 13C-depleted organic matter from CO in a reducing early Martian atmosphere. Nat. Geosci. 17, 503–507 (2024). doi.org/10.1038/s41561-024-01443-z

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