Organic carbon refers to carbon compounds containing C-H bonds or carbon bonded to other heteroatoms (except for CO2), and its abundance and distribution can reflect biological activity.
Biological systems often produce large amounts of organic carbon in recognizable patterns—such as lipids, proteins, and nucleic acids—leading to localized enrichments or specific distributions. While abiotic processes can also generate organic carbon (e.g., through Fischer-Tropsch-type synthesis or photochemistry), these typically result in simpler molecules and broader, less structured distributions. Thus, unusual concentrations or patterns in the abundance of organic carbon may indicate past or present life.
Organic carbon production is a universal feature of all known life.
All living organisms synthesize organic carbon compounds through metabolic processes, often resulting in high local concentrations. These compounds are preserved in sediments, ice cores, and rocks across Earth's geological history, forming a consistent biosignature across time and taxa.
[General]
Biogenic organic carbon can persist in the fossil record for billions of years.
Insoluble organic matter, such as kerogen derived from ancient biological material, resists degradation and can be detected in Archean-aged rocks. This longevity enhances its utility as a biosignature, preserving evidence of life long after its death.
[General]
Organic carbon can be formed abiotically in a variety of planetary environments.
Abiotic synthesis occurs under plausible geochemical conditions, including in hydrothermal systems and through atmospheric or interstellar photochemistry. These processes generate a range of carbon compounds, from methane to more complex organics.
[General]
Insoluble organic carbon of abiotic origin is rare and limited in distribution.
Such material has been primarily found in specific classes of carbonaceous meteorites and is not widespread in most planetary materials. Its limited occurrence reduces the likelihood of false positives in biosignature interpretation.
[General]
Some ancient carbon deposits can be explained by abiotic processes.
Multiple types of carbonaceous material in formations like the Apex chert may result from physical and chemical processes unrelated to biology. These cases demonstrate that abiotic carbon can appear in geologic contexts that resemble biogenic ones.
[Congruence]
Abiotic synthesis typically yields low-complexity organic carbon.
Insoluble organic carbon generated through abiotic processes generally consists of small, simple molecules lacking the structural or functional specificity found in biogenic material. This limits its strength as a misleading signal of life.
[General]