biosignatureschemical

Biosignatures are indicators that life has influenced a system, past or present. Chemical biosignatures are molecules, isotopic patterns, or chemical imbalances produced or altered by biological activity. They are sought in planetary atmospheres, rocks, and fluids and are interpreted within the context of abiotic chemistry and planetary conditions.

Examples include preserved biomolecules such as lipids, hopanes, steranes, and certain amino acids found in rocks, as well as isotopic patterns that arise from biological fractionation (for example, a preference for carbon-12 in organic matter). In atmospheres, disequilibria like the coexistence of oxygen and methane can indicate metabolism. Some life-related signals are trace gases such as methyl chloride or dimethyl sulfide produced by microbes. Chirality, or an excess of one enantiomer, in biological molecules can also serve as a biosignature.

Detecting chemical biosignatures uses spectroscopy for atmospheres and mass spectrometry or chromatography for solids and fluids. Interpreting them requires ruling out abiotic sources, geological processes, and contamination. Context matters: temperature, pressure, geology, and history shape which signatures are plausible and persistent.

Earth shows strong chemical biosignatures, including the modern oxygen-rich atmosphere and methane that requires replenishment. Ancient rocks preserve fossil lipids and isotopic records. On Mars and icy worlds, detections of methane or organics are debated, and no consensus exists. In exoplanet science, future telescopes seek atmospheric biomarkers, but robust interpretation depends on models and corroborating evidence.

Chemical biosignatures are central to astrobiology, guiding instrumentation and mission design while remaining sensitive to abiotic chemistry and planetary context.