Dr Will MacMahon will deliver the ESE Departmental Seminar on 23rd of February 2023: “The sedimentological impact of evolving land plants, and why it matters when studying sedimentary archives on Earth and beyond”

Join us in room G41 – RSM Building – on Thursday the 23rd of February 2023 at 12h10.

Or on Microsoft Teams: Will MacMahon Seminar


Far too often sedimentary outcrops are dismissed as being imperfect or unreliable. Yet they offer our most accessible record of our planetary history, so it is essential that we continually push to improve understanding of how sediment is generated, deposited, or lost. Recent perceptions of the time-completeness of the sedimentary record have centred on two key points: 1) ancient strata are dominantly a record of commonplace events and therefore provide faithful accounts of ancient processes if properly read; and 2) on Earth, the record of these processes has changed through geological time as the biosphere has evolved. By variously mediating fluid and sediment properties and rates and scales of erosion, weathering, deposition and transport, organisms can induce sedimentary signatures on scales that range from individual grains to the form of entire mountains. This is nowhere more evident than in the ancient record of land plants, with the Paleozoic greening of the continents tied to recognizable shifts in river planform, global changes in the source-to-sink distribution of fine-grained sediment, and even the creation of novel habitats for evolving organisms. Earth’s mudrock record additionally holds clues which suggest expanding vegetation reorganized the carbon cycle by enabling new pathways in hinterland chemical weathering and mud production, although this hypothesis has proved controversial. As we increasingly turn our attention to the sedimentary records now accessible on other barren worlds, determining the extent to which ancient life shaped our own planetary surface has never been more pressing. As depositional models are largely based on sedimentary environments on Earth, where physical form and process is likely influenced by biology in some way, comparisons between terrestrial and extra-terrestrial sedimentary records require careful consideration before application. However, by avoiding idealistic models based on incomplete information, we should be able to work with sedimentary outcrops on Earth and beyond and consider not what is missing, but what is possible.

About the Speaker

William McMahon is a post-doctoral researcher at the University of Cambridge, who uses the sedimentary record to study some of Earth’s most fundamental evolutionary transitions, such as the initial emergence of metazoans and subsequent terrestrialization of the continents. Focused on life’s role in shaping the planetary surface, he also works with the sedimentary record of other rocky planets, considering how terrestrial and extra-terrestrial archives may differ as a consequence of the presence or absence of ancient forms of life.

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