Self-assembled versus biological pattern formation in geology

TL;DR

The paper examines whether geological patterns arise from abiotic self-organization or biotic processes, and emphasizes the difficulty of distinguishing true biosignatures from mimics. It surveys a wide array of morphologies—filaments, tubes, branching, globular forms, banded textures, stromatolites, nodules, veils such as varnish, and more—highlighting cases where abiotic and biotic formation pathways can produce indistinguishable patterns. It then discusses chemical biomimetism (chemical gardens, silica-carbonate biomorphs, carbon-sulfur and organic biomorphs) as purely abiotic lifelike forms and constructs a framework for evaluating biogenicity across fossils, trace fossils, and microbe-mediated structures, including mineral evolution and the role of isotopic signals. The authors argue for an abiotic baseline and for recognizing the continuum and cooperation between abiotic and biological processes in pattern formation, with implications for life-detection strategies and for understanding life's origins on Earth and other worlds. They also suggest leveraging advances in isotopic analysis and machine learning to improve biosignature discrimination, while cautioning about overinterpretation of morphology alone in complex geological records.

Abstract

Both abiotic self-organization and biological mechanisms have been put forward as the origin of a number of geological patterns. It is important to comprehend the formation mechanisms of such structures both to understand geological self-organization and in order to differentiate them from biological patterns -- fossils and bio-influenced structures -- seen in geological systems. Being able to distinguish the traces of biological activity from geological self-organization is fundamental both for understanding the origin of life on Earth and for the search for life beyond Earth.

Figures (34)

• Figure 1: Biological and abiotic tubes. SEM images of tubular colonies of a) Aspergillus niger feeding on straw (image: Anna Neubeck) and b) manganese oxide chemical gardens (image: Huld2023Chemical, Huld2023Chemical). The A. niger tubes ranged in size between 2-5 $\mu$m in diameter, and the manganese oxides were found in ranges between 1--20 $\mu$m in size. SEM images of c) A. niger (image: Anna Neubeck), d) manganese oxide chemical gardens (image: Anna Neubeck), and e) A. niger closeup (image: D. Gregory & D. Marshall, CC BY 4.0).
• Figure 2: Etching features within basaltic glass A) Etching features observed by secondary Scanning Electron Microscopy (SEM) in basalt glasses observed by cockell2009alterationcockell2009bacteria (scale bar 15 $\mu$m), B) Back-scattered SEM images of pitted features and tubule-like etchings around the rim of a vesicle in weathered basalt glass sliced and polished through a vesicle (scale bar 15 $\mu$m). The material within the vesicle is palagonite.
• Figure 3: Biomorphic features in basalt glass and its palagonite weathering products observed in secondary SEM. A) Hemispherical structures on palagonite rinds in terrestrial weathered basalt glass, Iceland (from cockell2009bacteria) (scale bar 20 $\mu$m), B) Manganese-rich biomorphs in the same weathered glass as (a) (scale bar 20 $\mu$m), C) Biofilm-like spherical assemblages in weathered basaltic glass from the mid-Atlantic Rift (from cockell2010microbial) (scale bar 5 $\mu$m).
• Figure 4: SEM images of a) hollow tubular halloysite (Turplu Mine, Balikesir, Turkey); b) prismatic halloysite (Hospital Quarry, Elgin, Scotland); c) spherical halloysite (Pama Mine, Province of Rio Negro, Argentina); d) spherical kaolinite on gel grains, formed in hydrothermal experiments HUERTAS1993Hydrothermal. Images a, b, c reproduced from the ‘Images of Clay Archive’ of the Mineralogical Society of Great Britain & Ireland and The Clay Minerals Society (https://www.minersoc.org/images-of-clay.html)
• Figure 5: SEM images of fibres of a) imogolite (Kyushu, Japan; Eswaran_1972) and b) chrysotile (Macizo de Ojén, Málaga, Spain); TEM image of the cross-section of chrysotile tubules (Tasmania; Yada1971Study).