Can we use the fossilized remains of magnetic bacteria to build a new fossil record of life on Earth?

  • Datum:

    26/06/2025

  • Referent:

    Prof. Andrew P. Roberts

  • Zeit:

    16:00 Uhr

  • Abstract 

    Magnetotactic bacteria (MTB) are diverse prokaryotes that biomineralize intracellularly perfect stoichiometric magnetite (Fe3O4), or less perfect greigite (Fe3S4), crystals. MTB are ubiquitous in modern aquatic environments. Their production of magnetically ideal nanomagnets means that their post-mortem remains (magnetofossils) can potentially provide widespread records of ancient planetary magnetic field variations and of life on Earth. MTB live within chemical gradients across the oxic-anoxic interface (OAI) in water columns and sediments. Their strong cellular magnetic moment enables MTB to navigate via magnetotaxis along geomagnetic field lines to reduce their search from three dimensions to one dimension to find ideal niches within chemically stratified aquatic OAI environments. However, sulphidic environments that underlie an OAI will cause magnetite to dissolve. So, I expected for 20 years that, while MTB are interesting organisms, they will not be important in the geological record. About 14 years ago, my views changed when we and other groups started to find widespread magnetofossil preservation in ancient sediments. By avoiding organic-rich sedimentary environments in which their preservation is poor, it should be possible to develop a global magnetofossil record — but how far back could such a fossil record extend? Molecular clock evidence suggests that the genes that enable MTB to navigate along geomagnetic field lines (magnetotaxis) evolved in the Archaean at 3.2-3.4 Ga. The recent explosion of reported magnetofossil occurrences is restricted almost entirely to the Cenozoic (0-66 Ma); there are only a handful of reports from older strata. We are now seeking to develop a global magnetofossil record to answer questions such as: how old are the oldest magnetofossils on Earth, can MTB tell us anything about the early evolution of our planetary magnetic field (which is thought to be an essential ingredient for life to evolve on Earth), and can the hard mineralized remains of MTB, compared to the soft and difficult-to-preserve cells of other bacteria, provide a clearer record of the first three billion years of life on Earth when life was dominantly unicellular? I will explore some of these questions in this talk.
  • Ort:

    Room: -134 in Bldg. 50.41