540-Million-Year-Old Fossils Reveal a Huge Surprise About Early Life on Earth

Scientists have reanalyzed 540-million-year-old microfossils from Brazil’s Mato Grosso do Sul, concluding they represent fossilized communities of bacteria and algae rather than traces of early marine animals. The fossils, previously interpreted as evidence of wormlike or tiny invertebrate organisms, were discovered in the Tamengo geological formation near Corumbá and Bonito. Using microtomography and spectroscopy at CNPEM’s Sirius particle accelerator in Campinas, researchers led by Bruno Becker-Kerber identified cellular structures—including preserved organic material—consistent with microbial life, not animal activity. The findings, published in *Gondwana Research*, suggest Ediacaran oceans may have lacked the oxygen levels necessary to support small invertebrates like meiofauna, which only appear prominently in later Cambrian fossils. Becker-Kerber, now at Harvard University, conducted the work during postdoctoral research at the University of São Paulo (USP) and CNPEM, with funding from FAPESP. The study challenges the idea that complex animals thrived during the Ediacaran period, just before the Cambrian explosion, when rising oxygen levels enabled rapid diversification. The fossils formed in a shallow marine environment along Gondwana’s continental shelf before the supercontinent split into South America and Africa. The research is part of the “Rio de la Plata Craton and Western Gondwana” project, coordinated by Miguel Angelo Stipp Basei of USP, with contributions from Lucas Warren of São Paulo State University (UNESP). Separately, the same team identified a potential 540-million-year-old lichen fossil in the same region, though younger than the microbial samples. Advanced imaging at the MOGNO beamline allowed nanoscale analysis without damaging the fossils, revealing details invisible to earlier studies. Becker-Kerber noted that prior interpretations of animal traces lacked the resolution to detect microbial structures. The discovery reshapes understanding of Earth’s early ecosystems, indicating microbial life dominated oceans long before the rise of complex animals.