A 3.5-billion-year-old rock formation in eastern India may preserve chemical and layered traces of some of Earth’s earliest microbial communities. Carbon isotope measurements, microscopic layers and the structure of preserved organic material all point toward a biological origin. The claim still needs independent testing, but the rock could give scientists a better-dated record of when early microbial ecosystems were already established. A 3.5 billion-year-old band of black-and-white rock in eastern India may preserve traces of some of Earth’s earliest microbial communities. The key clues are not fossils with recognizable shapes, but thin carbon-rich layers, ancient zircons and chemical signatures locked inside chert. That age matters because evidence for life this far back is difficult to verify. Earth formed about 4.5 billion years ago, but its oldest rocks have endured heat, deformation and chemical alteration. Those changes can create structures or carbon signatures that resemble biological remains. “Preservation of Paleoarchean microbial mats is rare due to subsequent deformation and metamorphism. Thus, careful identification is required as abiotic processes may generate ‘biomarker-like’ signatures,” geologist Trisrota Chaudhuri of …