Wood Cell-like Microstructures in Martian Meteorite NWA 16788: A Compelling Biosignature

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The structures in question, highlighted in SEM images and annotated with red arrows (Fig. 1), include:

- Tubular elements approximately 20–80 microns across.

- Cell wall-like margins that suggest permineralized or infilled features.

- Organized, quasi-regular alignment, evoking the modular arrangement of xylem tissue. 

These features differ markedly from:

- Pipe vesicles seen in basalts, which are irregular in size and lack cell walls.

- Crystallographic cleavage or shock-induced fractures, which tend to be planar or polygonal.

- Fibrous minerals like asbestos, which do not form closed lumens with layered wall boundaries.

Abiotic vs. Biotemplated Interpretations

Abiotic Hypotheses (Rejected):

1. Pipe vesicles – Lack internal organization or structural walls.

2. Saponite/serpentine fibrils – Too fine, lacks lumen/wall geometry and repetitive architecture.

3. Crystal cleavage/faults – Structurally dissimilar; lacks modular segmentation and directional growth. 

Biotemplated Hypotheses:

Given the rejection of plausible abiotic analogs, these structures are best interpreted as biomineralized remains:

- Fossilized microbial mats or vascular plant-like tissues replaced by secondary minerals.

- Multicellular filaments mineralized under low-temperature hydrothermal conditions.

- Analogous to terrestrial petrified wood where silica or carbonate preserves lumen-wall anatomy.

Such fidelity in cellular architecture is unknown in purely abiotic systems and strongly supports a once-living template.

Suggested Analytical Criteria

To assess these structures further, we propose the following differentiation framework: 

Criterion | Abiotic Origin | Biotemplated Origin

——— | ————– | ——————-

Wall-lumen architecture | Absent | Present

Regular spacing and modularity | Irregular | Hierarchical

Secondary mineral overgrowth | Uniform coating | Confined to organic template

Elemental/isotopic biosignatures | None expected | Possible δ13C, δ15N anomalies, trace organics

Chirality/symmetry | Crystallographic | Biological axes and polarity

Conclusion and Implications

The morphological evidence from NWA 16788—particularly the arrowed microstructures—cannot be satisfactorily explained by any known abiotic mechanism. Instead, the anatomical resemblance to terrestrial fossil wood cells, including the preservation of walls and lumens at micron scale, constitutes compelling evidence of biological templating in a Martian context. This interpretation moves beyond speculation and into the domain of testable, falsifiable biosignatures. The structures in NWA 16788 may represent the first hard physical evidence of fossilized Martian life. 

Further analyses using high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, stable isotope geochemistry, and focused ion beam (FIB) cross-sections are urgently needed to validate this hypothesis.