Concept

Biosignature

Summary
A biosignature (sometimes called chemical fossil or molecular fossil) is any substance – such as an element, isotope, or molecule – or phenomenon that provides scientific evidence of past or present life. Measurable attributes of life include its complex physical or chemical structures and its use of free energy and the production of biomass and wastes. A biosignature can provide evidence for living organisms outside the Earth and can be directly or indirectly detected by searching for their unique byproducts. In general, biosignatures can be grouped into ten broad categories: Isotope patterns: Isotopic evidence or patterns that require biological processes. Chemistry: Chemical features that require biological activity. Organic matter: Organics formed by biological processes. Minerals: Minerals or biomineral-phases whose composition and/or morphology indicate biological activity (e.g., biomagnetite). Microscopic structures and textures: Biologically formed cements, microtextures, microfossils, and films. Macroscopic physical structures and textures: Structures that indicate microbial ecosystems, biofilms (e.g., stromatolites), or fossils of larger organisms. Temporal variability: Variations in time of atmospheric gases, reflectivity, or macroscopic appearance that indicate the presence of life. Surface reflectance features: Large-scale reflectance features due to biological pigments, which could be detected remotely. Atmospheric gases: Gases formed by metabolic and/or aqueous processes, which may be present on a planet-wide scale. Technosignatures: Signatures that indicate a technologically advanced civilization. Determining if a potential biosignature is worth being investigated is a fundamentally complicated process. Scientists must consider any and every possible alternate explanation before concluding that something is a true biosignature. This includes investigating the minute details that make other planets unique and being able to understand when there is a deviation from the expected non-biological processes present on a planet.
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