- The paper demonstrates that similar morphological structures can arise from abiotic self-assembly and biological processes, challenging traditional biosignature identification.
- It applies detailed laboratory models and geochemical analyses to reveal overlapping morphospaces in tubular, dendritic, and spheroidal structures.
- The review advocates integrated, multidimensional assessment methods combining isotopic, mineralogical, and machine learning techniques for robust biosignature detection.
Introduction
The formation mechanisms of patterns in geological materials remain a central controversy in geobiology and astrobiology. "Self-assembled versus biological pattern formation in geology" (2601.00323) provides an exhaustive examination of the overlapping morphospaces between abiotic self-organization and biological processes, advancing our understanding of how apparent biogenic structures may arise in purely physicochemical environments, and vice versa. This comprehensive synthesis offers a framework crucial both for interpreting the terrestrial rock record and in the context of astrobiological exploration.
Concepts and Definitions
The paper clarifies several terminologies fundamental to cross-disciplinary dialogue. It distinguishes between "patterns," as perceived regularities or morphological motifs, and "biomorphs," which refer to life-resembling structures—whether generated by biological or physicochemical processes. The review emphasizes the ambiguity inherent in defining biosignatures based exclusively on morphology, given the convergence of forms arising from disparate mechanisms.
Examples of Shared Morphologies
Tubular and Filamentous Structures
Tubular and filamentous forms constitute some of the oldest putative microfossils and pseudofossils. Extensive documentation is provided for morphological convergence between abiotic processes (e.g., chemobrionic structures, zeolite tubes, chemical gardens) and biological architectures (e.g., remains of cyanobacteria, agglutinated and biomineralized tubes from proto-metazoans and extant microbiota). The review highlights that even well-accepted biosignatures, such as ancient filamentous fossils from the Apex Chert or the Strelley Pool Chert, require careful interrogation through geochemical, contextual, and textural criteria, as abiotic analogs are now recognized [barge2016self, podbielski2025troubles].
Branching and Dendritic Patterns
Branching morphologies, ranging from river drainage networks to mineral dendrites, can be generated through both deterministic biological mechanisms and physical processes such as diffusion-limited aggregation, viscous fingering, or electrical discharge. Of particular note, the review systematically evaluates manganese- and iron-rich dendrites, detailing mounting evidence for microbially mediated mineralization (especially in structures such as Frutexites), but also emphasizing the persistence of plausible abiotic models [Hou2023, Neubeck2025Mixed]. The paper presents isotopic, mineralogical, and textural data supporting biological mediation, but does not discount chemically self-organized dendrites, advocating a continuum model.
Structures such as vesicles, ooids, spherulites, and polymetallic nodules have long been contentious, given their simple geometry and the ubiquity of physico-chemical routes to their formation. The paper details several formation scenarios for polymetallic nodules, acknowledging both hydrogenetic/diagenetic abiotic mechanisms and active microbial roles in metal cycling [blothe_manganese-cycling_2015, wang_biogenic_2009]. It also emphasizes the ambiguity surrounding cave pearls, automicrite, and carbonate spherulites, where abiogenic precipitation and microbially mediated mineralization can often be intimately intertwined.
Banded and Laminated Structures
Periodic banding in rocks presents frequently ambiguous origins. Banded iron formations, stromatolites, and Liesegang banding are considered in detail. The authors dissect the range of intrinsic (reaction–diffusion–transport feedbacks, self-oscillatory precipitation) and extrinsic (environmental cycles, biotic productivity) processes implicated. Notably, the review does not restrict banding as a biosignature to external drivers, underscoring the requirement of integrative geological, chemical, and isotopic analysis for robust inference [Wang2009BIFInternalDynamics].
The review rigorously evaluates self-organized chemical systems as analogs for geological patterning—highlighting chemical gardens, silica-carbonate/–sulfur biomorphs, and organic vesicle self-assembly. These systems recapitulate a range of biogenic morphologies (e.g., filaments, spheroids, helices) under strictly abiotic conditions, further challenging efforts to employ morphology as a unique biosignature. Mechanistic discussion of pattern selection, non-equilibrium effects, and the role of environmental controls in both laboratory settings and natural analogs is thorough and technically detailed.
Criteria and Limitations for Assessing Biogenicity
The review articulates the fundamental limitation of morphologically driven biosignature interpretation. It calls for multidimensional assessment protocols integrating textural, mineralogical, isotopic, and molecular evidence, referencing frameworks like NASA's Ladder of Life Detection. The paper also advances the notion that, in an Earth context, the possibility for microbe-mediated "overprinting" of purely abiotic patterns is nearly ubiquitous, making experimental laboratory validation of abiotic pathways even more essential.
Machine Learning and Biosignature Identification
The prospect of employing machine learning for biosignature interpretation is addressed, with reference to recent successes in classification based on pyrolysis–GC–MS datasets [wong2025organic]. However, the authors note limitations concerning training data, interpretability, and the ever-present risk of overfitting in high-dimensional domains.
Implications, Open Problems, and Future Directions
The implications of this review are broad. Practically, the need for integrating laboratory abiotic self-organization models with in situ geochemical and isotopic data is emphasized, particularly for both paleobiological assessments and planetary exploration. Theoretically, the review advocates for a continuum framework—recognizing that biological and abiotic influences almost always act in concert, with temporal and spatial superposition.
The robust critique of prevailing biogenicity criteria strengthens the call for improved abiotic baseline characterization. This entails systematic study of self-organized inorganic patterning in plausible prebiotic and extraterrestrial analog environments.
In astrobiology, the review issues a caution that reliance on morphology alone for life detection is fraught with risks of both false positives and false negatives. The authors posit that future developments should focus on devising highly multiplexed, context-rich detection protocols—potentially incorporating mechanistic and AI-guided pattern comparison but always grounded in geochemical plausibility.
Conclusion
"Self-assembled versus biological pattern formation in geology" provides a comprehensive, technically rigorous taxonomic and mechanistic synthesis of geological patterns at the interface of abiotic and biological processes. By meticulously cataloging case studies, experimental analogs, and theoretical criteria, the paper redefines the landscape of biosignature interpretation and highlights essential knowledge gaps in abiotic pattern formation. The review's insights will inform both future biosignature assessment frameworks and research into the origins and early evolution of life on Earth and beyond.
