Sean McMahon

How does planet Earth interact with its living biosphere over billions of years? My research explores how geological materials (rocks, minerals and sediments) select, shape and sustain communities of organisms, and how organisms in turn produce, degrade and modify rocky substrates to leave lasting traces in the geological record. The study of these interactions (geobiology) deepens our understanding of where we come from and enhances our ability to search for life elsewhere in the universe. My recent and current work falls under three themes: 1. The deep biosphere: one of Earth's largest microbial biomes, which encompasses subseafloor and subterranean rocks and sediments. Here, my work aims to understand: (1) the geological history of the deep biosphere in relation to the rest of the Earth–Life system; (2) the fossil and geochemical record of deep life; (3) controls on the habitability of subsurface environments and their potential to preserve fossils; (4) whether these habitats and fossils tell us anything useful in the search for life on Mars. 2. Experimental taphonomy: the attempt to understand the processes that allow fossils to form by replicating them under controlled conditions in the laboratory. These processes intimately involve microbes, which can help explain how soft-bodied animal tissues and plants are able to be preserved. Similarly, experiments can be used to understand how microorganisms themselves become fossilized on Earth and (potentially) Mars. 3. Pseudofossils: structures formed by abiotic processes that resemble fossil organisms, and so can mislead researchers looking for evidence of life on Mars or the early Earth.

[2026] Self-organized pattern formation in geological soft matter, Physics Reports, 1183, p. 1-98 [2026] Can Pareto Optimality Be Evidence of Life?, Astrobiology, 26(6), p. 492-499 [2026] Experimental Evidence for a Microbial Origin of Reduction Spots in Red Beds on Earth—and Mars?, Astrobiology, 26(6), p. 485-491 [2026] False negatives in the search for extraterrestrial life, Nature Astronomy, 10(5), p. 624-629 [2026] Tricks of Nature From the Ancient Earth and Early Mars: Chemical Gardens Generate Biomorphs With High Preservation Potential, Geobiology, 24(2), p. 1-12