Francevillian Basin, Gabon

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A Palaeoproterozoic sedimentary basin in southeastern Gabon containing black shales about 2.1 billion years old, in which a 2010 paper reported centimetre-scale pyritised structures with regular, lobed outlines and radial fabric, interpreted as colonial organisms showing coordinated growth. If the interpretation holds, it pushes macroscopic, possibly multicellular life back by more than a billion years relative to the next accepted examples, and places it immediately after the Great Oxidation Event and the Lomagundi carbon-isotope excursion — an oxygen pulse that would plausibly permit larger bodies. The interpretation is genuinely contested. Sceptics argue the structures are abiotic pyrite growths or sedimentary concretions, and note that nothing comparable appears anywhere in the following billion years, which would require a very long ghost lineage or an origin that failed. The Francevillian is the clearest case in this Journey of a claim whose significance depends entirely on whether a shape is biological.