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Small Microbes, Big Questions: How Were Two-Billion-Year-Old Microbial Buildups Organized?

Session: New Voices in Geobiology

Presenting Author:

Jade Wells

Authors:

Wells, Jade¹, Larson Tevis, A. Anders², Mehra, Akshay³

(1) Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA, (2) Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA, (3) Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA,

Abstract:

Polygonal patterns are widespread in nature. These patterns emerge through a variety of physical and biological processes, including contraction and strain (e.g., mud cracks and basalt columns) and organismal activity (e.g., the hexagonal honeycombs of honeybees and microbial mats). In deep time, some aggregations of microbial mats and stromatolites, the latter being centimeter- to meter-scale laminated buildups, exhibit polygonal organization at the outcrop scale. Understanding the mechanisms that drive the formal organization of such sedimentary structures can provide us with insights into the behavior of early life on Earth and potentially inform the search for biology elsewhere in our solar system. Here, we examine and describe the morphology of 1.9 billion-year-old stromatolite outcrops from the Pethei Group in the Northwest Territories, Canada in an effort to constrain their morphogenesis and test whether their spatial patterns reflect self-organization. Using structure from motion (SfM) photogrammetry, we generate centimeter-resolution three-dimensional (3D) reconstructions of four field sites and digitally trace more than 3,000 individual fossilized microbial aggregations. From these tracings, we quantify spatial organization using metrics such as area, width, length, aspect ratio, circularity, and nearest neighbor distance. We then compute scale-invariant metrics such as polygonality, a measure of how closely an arrangement of shapes resembles an ideal polygonal pattern, to compare the geometry of the studied stromatolites to both abiotic (e.g., mud cracks, basalt columns) and biotic (e.g., extant microbial mats) polygonal systems. Our approach enables us to test various extant hypotheses for stromatolite morphogenesis, including whether the observed polygonal morphologies reflect growth on antecedent topography (e.g., mud cracks) or arise through microbial self-organization. We aim to extend our analyses to additional stromatolites preserved within the rock record to further investigate the relative contributions of environmental and biological factors in the morphogenesis of ancient microbial buildups.