Organic molecules found in a 500-million-year

Scientists have discovered remnants of a strong material that previously made up the outer shells of ancient sea creatures known as trilobites, preserved within fossils dating back over 500 million years.

This finding indicates that parts of living organisms can endure much longer in rock than previously thought, altering scientists’ understanding of how carbon is stored deep within the Earth over extended periods of time.

In shale rock layers near Death Valley in eastern California, researchers unearthed a trilobite fossil belonging to the species Olenellus, an extinct marine creature that inhabited the ocean floor over half a billion years ago. Remarkably, a small fragment of its original shell was still intact.

Through laboratory analysis at the University of Texas at San Antonio (UTSA), a distinct chemical signature was extracted from this shell fragment. Earth and planetary scientist Elizabeth Bailey at UTSA identified this signal as a shell polymer that had been overlooked in earlier investigations.

The presence of chitin in the fossils suggests that certain carbon-rich compounds can remain preserved even under typical burial conditions. Chitin, a robust sugar-based substance found in the outer coverings of modern crab shells and insect skins, is essential for maintaining stiffness and lightness.

Researchers pointed out that chitin, following cellulose, ranks as the second most prevalent naturally occurring polymer on Earth due to its widespread presence in various life forms. The rate at which chitin decays plays a key role in determining whether organic carbon cycles swiftly or remains buried for extended periods.

To prevent any modern contamination, the UTSA team conducted chemical analyses to identify specific fingerprints associated only with the ancient polymer. These tests confirmed the presence of chitin in the fossil material through fluorescent staining, infrared light, and mass testing.

The process of mineral seepage into the shell’s minuscule cavities, followed by solidification, created a barrier that hindered water and microbes from reaching the chitin. This preservation effect, known as mineral sealing, helped reduce decay by limiting the oxygen supply necessary for microbial breakdown.

The study suggests that chitin can endure much longer in the geological record than previously assumed, offering insights into carbon sequestration and long-term storage of carbon away from the atmosphere.

The research, published in Palaios, emphasizes the importance of understanding how chitin persists in ancient shells to refine carbon-cycle estimates and guide future fossil investigations.