Life as we know it is primarily composed of the elements carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur—collectively known as CHNOPS.
These elements form the foundation of biomolecules like proteins, nucleic acids, lipids, and carbohydrates. In biological systems, CHNOPS elements are enriched and maintained in relatively stable ratios, such as the well-known Redfield Ratio in marine ecosystems. While these elements can be found in abiotic materials, their relative abundances and co-occurrence in specific proportions may indicate biological processing and help differentiate between living and non-living sources.
Argumentation that supports the use of this feature as a biosignature based on biological prevalence.
PRO arguments and evidence highlight the presence of the feature in and/or due to life. CON arguments and evidence highlight how biological prevalence cannot justify the use of this feature as a biosignature.
CHNOPS elements are abundant across life as we know it. Prevalence arguments deal with the known abundances of these specific elements in biomolecules.
Biological Signal Strength - Background
Argumentation that supports the use of this feature as a biosignature based on signal strength.
PRO arguments and evidence highlight the strength of signals such abundance, rate, structure, patterns, and intensity to be indicative of life. CON arguments and evidence highlight how the strength of specific signals are not justifications to support a biological origin.
Abiotic Prevalence - Background
Argumentation that refutes the use of this feature as a biosignature due to abiotic prevalence.
PRO arguments and evidence highlight the presence of the feature due to abiotic processes. CON arguments and evidence highlight how abiotic prevalence cannot refute the use of this feature as a biosignature.
Abiotic Signal Strength - Background
Argumentation that refutes the use of this feature as a biosignature based on signal strength of abiotic processes.
PRO arguments and evidence highlight the strength of signals such abundance, rate, structure, patterns, and intensity to be caused by abiotic processes. CON arguments and evidence highlight how the strength of specific signals from abiotic processes do not refute a potential biological origin.
CHNOPS form >95 % of biomass and are present in all known biopolymers.
Comprehensive review shows CHNOPS are foundational to terrestrial life’s molecular architecture and elemental cycles.
Evidence is Sourced from:
Title
The Astrobiology Primer v2.0
Authors
Domagal-Goldman,Shawn D. and Wright, Katherine E. and Adamala, Katarzyna and Arina de laRubia, Leigh and Bond, Jade and Dartnell, Lewis R. and Goldman, Aaron D.and Lynch, Kennda and Naud, Marie-Eve and Paulino-Lima, Ivan G. andSinger, Kelsi and Walther-Antonio, Marina and Abrevaya, Ximena C. andAnderson, Rika and Arney, Giada and Atri, Dimitra and Azúa-Bustos,Armando and Bowman, Jeff S. and Brazelton, William J. and Brennecka,Gregory A. and Carns, Regina and Chopra, Aditya and Colangelo-Lillis,Jesse and Crockett, Christopher J. and DeMarines, Julia and Frank,Elizabeth A. and Frantz, Carie and de la Fuente, Eduardo and Galante,Douglas and Glass, Jennifer and Gleeson, Damhnait and Glein, ChristopherR. and Goldblatt, Colin and Horak, Rachel and Horodyskyj, Lev and Kaçar,Betül and Kereszturi, Akos and Knowles, Emily and Mayeur, Paul andMcGlynn, Shawn and Miguel, Yamila and Montgomery, Michelle and Neish,Catherine and Noack, Lena and Petryshyn, Victoria and Rugheimer, Sarahand Stüeken, Eva E. and Tamez-Hidalgo, Paulina and Walker, Sara Imariand Wong, Teresa
Redfield’s original data and modern global compilations support consistent ratios.
Redfield (1934) and Martiny et al. (2014) show strong global consistency in marine C:N:P ratios.
Evidence is Sourced from:
Title
Concentrations and ratios of particulate organic carbon, nitrogen, and phosphorus in the global ocean
Authors
Martiny, Adam C and Vrugt, Jasper A and Lomas, Michael W
Abstract
Knowledge of concentrations and elemental ratios of suspended particles are important for understanding many biogeochemical processes in the ocean. These include patterns of phytoplankton nutrient limitation as well as linkages between the cycles of carbon and nitrogen or phosphorus. To further enable studies of ocean biogeochemistry, we here present a global dataset consisting of 100,605 total measurements of particulate organic carbon, nitrogen, or phosphorus analyzed as part of 70 cruises or time-series. The data are globally distributed and represent all major ocean regions as well as different depths in the water column. The global median C:P, N:P, and C:N ratios are 163, 22, and 6.6, respectively, but the data also includes extensive variation between samples from different regions. Thus, this compilation will hopefully assist in a wide range of future studies of ocean elemental ratios.
Introduction The elemental composition of life as we know it is dominated by six key elements—carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S)—collectively known as CHNOPS. These elements are essential to the structure and function of all known biological molecules, including amino acids, nucleotides, lipids, and carbohydrates. Their relative abundances and patterned ratios in living systems distinguish them from most abiotic materials and provide a valuable lens for life detection.
Mechanisms and Formation CHNOPS elements are chemically versatile and abundant in Earth’s biosphere and many extraterrestrial environments. In abiotic contexts, they may arise from processes like volcanic outgassing, atmospheric photochemistry, or delivery via meteoritic material. However, these processes often yield heterogeneous distributions and lack stoichiometric coherence. In contrast, biological [read more]Introduction The elemental composition of life as we know it is dominated by six key elements—carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S)—collectively known as CHNOPS. These elements are essential to the structure and function of all known biological molecules, including amino acids, nucleotides, lipids, and carbohydrates. Their relative abundances and patterned ratios in living systems distinguish them from most abiotic materials and provide a valuable lens for life detection.
Mechanisms and Formation CHNOPS elements are chemically versatile and abundant in Earth’s biosphere and many extraterrestrial environments. In abiotic contexts, they may arise from processes like volcanic outgassing, atmospheric photochemistry, or delivery via meteoritic material. However, these processes often yield heterogeneous distributions and lack stoichiometric coherence. In contrast, biological systems actively acquire and recycle CHNOPS elements to support metabolism, structural integrity, and genetic information. Organisms integrate these elements into complex macromolecules through enzyme-mediated pathways, resulting in internally regulated and consistent elemental compositions.
Biogenic Signals A hallmark of biological systems is the patterned use of CHNOPS in defined proportions. One well-known example is the Redfield Ratio (C:N:P ≈ 106:16:1), which describes the average elemental composition of marine phytoplankton and reflects ecological and evolutionary pressures. Biological material often exhibits enrichments in these elements relative to surrounding non-biological matrices. Additionally, sulfur and phosphorus are incorporated into specialized structures—such as iron-sulfur clusters and phosphate backbones in DNA and ATP—demonstrating a preference for functional integration. When CHNOPS elements co-occur in consistent ratios or concentrations, especially in conjunction with molecular complexity, they may serve as strong indicators of life.
Abiotic Influences and Ambiguity CHNOPS elements are certainly not exclusive to life. They are present in most non-biological environments across the cosmos. Their mere detection does not confirm life, as they may exist in planetary atmospheres and surfaces (e.g., Titan, Mars), meteorites, or hydrothermal systems. Abiotic processes often produce variable or environment-specific elemental signatures, and lack the uniformity seen in biology. For example, abiotic C:N:P ratios typically deviate from biological norms, and the spatial or temporal distribution of these elements in non-living systems tends to be irregular. Thus, interpreting CHNOPS ratios as biosignatures requires caution and environmental context.
Why This Matters CHNOPS ratios offer a powerful yet non-definitive biosignature. They are relatively easy to measure and can serve as a first-line indication of potential biological activity. When specific CHNOPS elements are found in patterned ratios or enriched in particular locales—especially if paired with organic molecules, isotopic signals, or structural biomarkers—they strengthen the case for life detection. The diagnostic value of CHNOPS comes not from their presence alone, but from their organization, proportionality, and congruence with environments where life might plausibly operate. Their study remains central to astrobiological missions seeking to evaluate chemical evidence for life on other worlds.
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