Sean McMahon

Research group website: astrobiology.ac.uk/mcmahon-group

ResearchGate      Google Scholar      Edinburgh Research Explorer

My research at the University of Edinburgh’s UK Centre for Astrobiology explores how rocks, minerals and sediments on Earth and Mars can select, shape and sustain communities of organisms, and how organisms in turn produce, degrade and modify rocks and minerals to leave lasting traces. I use experimental, analytical and field-based techniques, and publish in a wide range of journals.

Active research questions:

1. How do fossils from Earth — particularly from microbial and subsurface ecosystems — inform the search for past or present life on Mars?
2. How do fossils form, and how much palaeobiologically valuable information is preserved at the molecular level?
3. How can we optimise the search for extraterrestrial life in such a way that the risks of “false positives” and “false negatives” are both minimised?

Career highlights

2023– Reader in Astrobiology, University of Edinburgh
2019–2023 Chancellor’s Fellow in Astrobiology (tenure track),
University of Edinburgh
2019 (Michaelmas) Institute of Advanced Study Fellow, Durham University
2017–2019 Marie Skłodowska-Curie Fellow, University of Edinburgh
2014–2017 Postdoctoral Associate, Briggs lab, Yale University
2011–2019 BA (Philosophy), Birkbeck College, University of London
2010–2014 PhD (Geology), University of Aberdeen
2013 (Summer) Planetary Biology Intern, NASA Ames Research Center
2006–2010 MEarthSci (Earth Sciences) St. Edmund Hall, Oxford

Publications

2024

62. Astrobiology: life detection and the abiotic baseline. McMahon, S. and Cockell, C.S. Astronomy and Geophysics.

61. Entophysalis in the Rhynie chert: Implications for cyanobacterial evolution. McMahon, S., Loron, C.C. Cooper, L.M., Hetherington, A.J. and Krings, M. Geological Magazine [in [press].

60. Taphonomic experiments fixed and conserved with Paraloid B72 resin via solvent replacement. Lethaia [in press].

59. Breakthrough results in astrobiology: is ‘high risk’ research needed? Jeancolas, C. Gillen, C., McMahon, S., Ward, M. and Vickers, P.J. International Journal of Astrobiology

2023

58. Is astrobiology serious science? Jeancolas, C., Gillen, C., McMahon, S., Vickers, P. Nature Astronomy.

57. The call for a new definition of a biosignature. Gillen, C., Jeancolas, C., McMahon, S., Vickers, P. Astrobiology 23, 1228-1237.

56. Is there such a thing as a biosignature? Astrobiology. Malaterre, M., Ten Kate, I.L., Baqué, M., Debaille, V., Grenfell, J.L., Javaux, E.J. , Khawaja, N., Klenner, F., Lara, Y.J., McMahon, S., Moore, K. Noack, L., Lucas Patty, C.H., Postberg, F. Astrobiology 23, 1213-1227.

55. Confidence of Life Detection: The Problem of Unconceived Alternatives. Vickers, P., Cowie, C., Dick, S.J., Gillen, C., Jeancolas, C., Rothschild, Lynn J. and McMahon, S., Astrobiology 23, 1203-1212.

54. Toward sustainable space exploration: a roadmap for harnessing the power of microorganisms. Santomartino, R., Averesch, N.J., Bhuiyan, M., Cockell, C.S., Colangelo, J., Gumulya, Y., Lehner, B., Lopez-Ayala, I., McMahon, S., Mohanty, A. and Santa Maria, S.R., Nature Communications 14, 1391.

53. Molecular fingerprints resolve affinities of Rhynie chert organic fossils. Loron, C.C., Rodriguez Dzul, E., Orr, P.J., Gromov, A.V., Fraser, N.C., McMahon, S. Nature Communications 14, 1387

52. Chemical gardens mimic electron paramagnetic resonance (EPR) spectra and morphology of biogenic Mn oxides. Huld, S., McMahon, S., Sjoberg, S., Huang, P. & Neubeck, A. Astrobiology.

2022

51. Petrified chemical gardens. Knoll, P., Batista, B. C., McMahon, S., and Steinbock, O. ACS Earth and Space Chemistry 6, 2644-2650.

50. A fundamental limit to the search for the oldest fossils. McMahon, S. & Jordan, S. Nature Ecology and Evolution 6, 832–834.

49. Prebiotic Chemistry and the Origin of Life. Neubeck, A., & McMahon, S. (Editors). Springer.

48. The Effect of Grain Size on Porewater Radiolysis. deWitt, J., McMahon, S. & Parnell, J. Earth and Space Science e2021EA002024.

2021

47. False biosignatures on Mars: anticipating ambiguity. McMahon, S. & Cosmidis, J. Journal of the Geological Society (available online).

46. Late Ediacaran life on land: desiccated microbial mats and large biofilm streamers. McMahon, S. Matthews, J.J., Brasier, A., Still, J. Proceedings of the Royal Society B 288, 20211875.

45. Estimating microbial growth and hydrogen consumption in hydrogen storage in porous media. Thaysen, E.M., Strobel, G., McMahon, S., Heinemann, N., Wilkinson, M., Butler, I., Ngwenya, B., Hassanpouryouzband, A., McDermott, C., & Edlmann, K. Renewable and Sustainable Energy Reviews, 151111481.

44. Astrobiology (Overview). McMahon, S. Oxford Research Encyclopedia of Planetary Sciences. Oxford University Press, New York (available online).

43. Dubiofossils from a Mars-analogue subsurface palaeoenvironment: the limits of biogenicity criteria. McMahon, S., Ivarsson, M., Wacey, D., Saunders, M., Belivanova, V., Muirhead, D., Knoll, P., Steinbock, O., & Frost, D.A. Geobiology 19, 473–488.

42. Ediacaran metazoan reveals lophotrochozoan affinity and deepens root of Cambrian Explosion. Shore, A. J., Wood, R. A., Butler, I. B., Zhuravlev, A. Yu., McMahon, S., Curtis, A., & Bowyer, F. T. Science Advances (available online).

41. When is Life a Viable Hypothesis?:The Case of Venusian Phosphine. Cockell, C. S., McMahon, S., & Biddle, J. F. Astrobiology (available online).

40. Determination of the microscopic mineralogy of inclusion in an amygdaloidal pillow basalt by fs-LIMS. Tulej, M., Lukmanov, R., Grimaudo, V., Riedo, A., Koning, C., Ligterink, N. F. W., Neubeck, A., Ivarsson, M., McMahon, S. & Wurz, P. Journal of Analytical Atomic Spectroscopy (available online).

2020 (annus horribilis)

39. Mars-Analog Calcium Sulfate Veins Record Evidence of Ancient Subsurface Life. McMahon, S., Parnell, J. & Reekie, P. B. R. Astrobiology 20 (available online).

38. 0.25 Ga salt deposits preserve signatures of habitable conditions and ancient lipids. Cockell, C. S., Wilhelm, M. B. Scott, P., Wadsworth, K., Payler, S., McMahon, S., Paling, S., & Edwards, T.  Astrobiology 20, 864–877.

37. Do Extraordinary Claims Require Extraordinary Evidence? The Proper Role of Sagan’s Dictum in Astrobiology. McMahon, S. In: Smith, K.C., & Mariscal, C. (Eds.), Social and Conceptual Issues in Astrobiology. Oxford University Press, New York.

2019

36. Earth’s earliest and deepest purported fossils may be iron-mineralized chemical gardens. McMahon, S. Proceedings of the Royal Society B: Biological Sciences 286, 20192410.

35. A laboratory for multi-century science. Cockell, C.S., Santomartino, R., McMahon, S., Reekie, P., Alberti, S.J.M.M., Phillipson, T., Russell, S. In: Astronomy & Geophysics 60, 6.26–6.28

34. Sample Collection and Return from Mars: Optimising Sample Collection Based on the Microbial Ecology of Terrestrial Volcanic Environments. Cockell, C.S., McMahon, S., Lim., D.S.S., Rummel, J., Stevens, A.H., et al. Space Science Reviews 215: 44.

33. Forum Reply: Petrological evidence in support of the death mask model for Ediacaran soft-bodied preservation in South Australia. Liu, A.G., McMahon, S., Matthews, J.J., Still, J., Brasier, A.T., & Marosi, D.M. Geology 47, e474.

32. Lifeless Martian samples and their significance.Cockell, C.S., McMahon, S. Nature Astronomy 3, 468-470.

31. A new frontier for palaeobiology: Earth’s vast deep biosphere.McMahon, S., & Ivarsson, M. BioEssays 41, 1900052.

30. Petrological evidence in support of the death mask model for Ediacaran soft-bodied preservation in South Australia Liu, A.G., McMahon, S., Matthews, J.J., Still, J., & Brasier, A.T. Geology 47, 215-218.

2018

29. Reduction spheroids preserve a uranium isotope record of the ancient deep continental biosphere McMahon, S., Hood, A. vS., Parnell, J., & Bowden, S. Nature Communications 9, 4505.

28. The deep history of Earth’s biomass McMahon, S., & Parnell, J. Journal of the Geological Society 175, 716–720.

27. Exogeoconservation: Protecting geological heritage on celestial bodies Matthews, J. J., & McMahon, S. Acta Astronautica 149, 55–60.

26. A field guide to finding fossils on Mars McMahon, S., Bosak, T., Grotzinger, J.P., Milliken, R. E., Summons, R. E., Daye, M., Newman, S. A., Fraeman, A., Williford, K.H ., & Briggs, D. E. G.  Journal of Geophysical Research: Planets 123, 1012–1040. Top 20 most downloaded article in JGR: Planets, 2017–2018

25. Palaeobiology of latest Ediacaran phosphorites from the upper Khesen Fm., Khuvsgul Gp., northern Mongolia Anderson, R. P., McMahon, S., Macdonald, F. A., Jones, D. S., & Briggs, D. E. G. Journal of Systematic Palaeontology.

24. Demonstrating deep biosphere activity in the geological record of lake sediments, on Earth and Mars Parnell, J., McMahon, S., & Boyce, A. International Journal of Astrobiology 17, 380–385.

2017

23. Doushantuo-type microfossils from latest Ediacaran phosphorites of northern Mongolia Anderson, R. P., Macdonald, F. A., Jones, D. S., McMahon, S., & Briggs, D. E. G. Geology 45, 1079–1082.

22. Biofilms mediate the preservation of leaf adpression fossils by clays Locatelli, E., McMahon, S., & Bilger, H. Palaios 32, 708–724. Palaios Outstanding Paper of 2017.

21. Decay of the sea anemone Metridium (Actiniaria): Implications for the preservation of soft-bodied diploblast-grade animals. McMahon, S., Tarhan, L. G., & Briggs, D. E. G. Palaios 32, 388–395.

20. Palaeobiology of the early Ediacaran Shuurgat Formation, Zavkhan Terrane, southwestern Mongolia Anderson, R. P., McMahon, S., Bold, U., Macdonald, F. A., & Briggs, D. E. G. Journal of Systematic Palaeontology 15, 947–968.

19. The Origin and Occurrence of Subaqueous Sedimentary Cracks McMahon, S., Hood, A. v S., & McIlroy, D. Geological Society of London, Special Publications 448, 285–309.

2016

18. The aesthetic objection to terraforming Mars McMahon, S. In: Schwartz, J.S.J., & Milligan, T. (Eds.), The Ethics of Space Exploration. Springer, London.

17. Evidence for seismogenic hydrogen gas, a potential microbial energy source on Earth and Mars McMahon, S., Parnell, J., & Blamey, N. J. Astrobiology 16, 690–702.

16. Experimental evidence for inhibition of bacterial growth by clay minerals and its implications for fossil preservation McMahon, S., Anderson, R. P., Saupe, E. E., & Briggs, D. E. G. Geology 44, 867–870.

15. The Tully Monster is a Vertebrate McCoy, V. E., Saupe, E. E., Lamsdell, J. C., Tarhan, L. G., McMahon, S., Lidgard, S., Mayer, P., Whalen, C. D., Soriano, C., Finney, L., Vogt, S., Clark, E. G., Anderson, R. O., Petermann, H., Locatelli, E. R., & Briggs, D. E. G. Nature 532, 496–499.

14. Mineralogical determination in situ of a highly heterogeneous material using a miniaturized laser ablation mass spectrometer with high spatial resolution Neubeck, A., Tulej, M., Ivarsson, M., Broman, C., Riedo, A., McMahon, S., Wurz, P., & Bengston, S. (2016) . International Journal of Astrobiology 15, 133–146.

13. The role of experiments in investigating the taphonomy of exceptional preservation Briggs, D.E.G., & McMahon, S. Palaeontology 59, 1–11.

12. Physical and Chemical Controls on Habitats for Life in the Deep Subsurface Beneath Continents and Ice Parnell, J., McMahon, S. Transactions of the Royal Society of London A 374, 20140293.

2015

11. Martin Brasier (1947-2014): Astrobiologist McMahon, S., Cockell, C. S. International Journal of Astrobiology 14, 527–531.

10. Evidence for methane in martian meteorites Blamey, N., Parnell, J., McMahon, S., Mark, D., Tomksinson, T., Lee, M., Shivak, J., Izawa, M., Banerjee, N., & Flemming, R. Nature Communications 6: 7399.

2014

9. Parnell, J., McMahon, S., Blamey, N. J. F., Hutchinson, I. B., Harris, L. V., Ingley, R., Edwards, H. G. M., Lynch, E. & Feely, M. Detection of reduced carbon in a basalt analogue for martian nakhlite: a signpost to a habitat on Mars. International Journal of Astrobiology 13: 124-131.

8. Price, M., Ramkissoon, N., McMahon, S., Miljkovic, K., Parnell, J., Wozniakiewicz, P., Kearsley, A., Blamey, N., Cole, M., & Burchell, M. Limits on methane release and generation via hypervelocity impact of Martian analog materials. International Journal of Astrobiology 13: 132-140.

7. McMahon, S., Parnell, J. Weighing the deep continental biosphere. FEMS Microbiology Ecology 87: 113-120. Chief Editor’s Choice, January 2014.

2013

6. McMahon, S., O’Malley-James, J., & Parnell, J. Circumstellar habitable zones for terrestrial deep biospheres. Planetary and Space Science 85, 312–318.

5. McMahon, S., Parnell, J., Ponicka, J., Hole, M., & Boyce, A. The habitability of vesicles in martian basalt. Astronomy & Geophysics 54, 1.17–1.21.

4. Brasier, M., Matthewman, R., McMahon, S., Kilburn, M., & Wacey, D. Pumice from the ~3,460 Ma Apex Basalt, Western Australia: a natural laboratory for the early biosphere. Precambrian Research 224, 1–10.

3.Sampling methane in basalt on Earth and Mars. McMahon, S., Parnell, J., & Blamey, N. J. F.  International Journal of Astrobiology  12, 113-122.

2012

2. McMahon, S., Parnell, J., & Blamey, N. J. F. Sampling methane in hydrothermal minerals on Earth and Mars. International Journal of Astrobiology 11, 163-167.

2011

1. Brasier, M.D.,  Matthewman, R., McMahon, S., & Wacey, D. Pumice as a Remarkable Substrate for the Origin of Life. Astrobiology 11, 725-735.