Spearheading: scanning electron microscopy reveals a large magnetofossil from an unknown organism surrounded by smaller magnetofossils from bacteria. Scientists have unearthed giant magnetic fossils, the remnants of microbes buried in 55-million-year-old sediment. The growth of these unusual structures during a period of massive global warming provides clues about how climate change might alter the behaviour of organisms. Some bacteria, both living and fossilized, contain magnetite — magnetic iron oxide crystals — that the organisms are thought to use to navigate, orienting themselves along the magnetic field lines of the Earth. But the new fossils are "unlike any magnetite crystal...