Tracking organics in (bio)carbonates – A step forward in the search for biosignatures
An innovative analytical method conducted by researchers from IPGP, in collaboration with Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA, UMR 7583, Université Paris Cité / Université Paris-Est Créteil) and the Institut des Sciences de la Terre de Paris (ISTeP , UMR 7193, Sorbonne Université) has been applied recently to (bio)carbonates with the aim to detect and characterize organic compounds preserved within carbonate minerals — a crucial step toward identifying biosignatures of past or present life.
Carbonates, whether abiotic or influenced by biological processes or the presence of organics (a process known as organomineralization), can trap organic molecules during their formation. These minerals thus represent potential records of biological activity. However, distinguishing between biogenic and abiotic origins remains challenging, particularly when using instruments designed for space missions.
In this study, the team developed a modified Rock-Eval thermal analysis protocol, inspired by the instruments on planetary missions such as NASA’s Mars Science Laboratory (SAM) and ESA’s ExoMars (MOMA). By combining sequential air and nitrogen heating cycles, this approach distinguishes between organic compounds on mineral surfaces and those trapped within the crystal lattice.
Analyses of more than sixty natural and synthetic carbonate samples revealed distinct CO, CO₂, and SO₂ gas profiles, characteristic of different formation mechanisms. This new method enables the rapid identification of potential biosignatures under analytical conditions similar to those of in situ planetary instruments, contributing to future astrobiological explorations on Mars, Enceladus, and Europa.
False-colored scanning electron microscopy images showing, at the top left, an organo-carbonate formed in the presence of abiotic amino acids; at the bottom left, an abiotic carbonate formed without any biological influence and in the absence of organic compounds; and on the right, two views of a biologically induced carbonate (in blue) formed through the activity of bacterial cells (in yellow and orange), which became trapped within the growing crystals.
These carbonates display different degrees of crystallinity, with more structural defects and organic residues in the biologically influenced samples, affecting both the gases released during pyrolysis and the temperature of their thermal decomposition.
Reference article : Perron, A., Ménez, B., Baudin, F. & Stalport, F. A modified Rock-Eval approach to track organics in (bio)carbonates. Chemical Geology 690, 122815 (2025) – doi : 10.1016/j.chemgeo.2025.122815
