Perseverance has found shallow preserved organic carbon on Mars, raising new questions about ancient Martian environments. Organic carbon is one of the chemical building blocks associated with life, although it can also form through nonbiological processes. The analysis revealed macromolecular carbon (MMC), a form of organic carbon made of large, tangled networks of carbon atoms. The result is notable because the Martian surface is hostile to organic molecules. Still, the next step requires more sensitive instruments on Earth, where scientists could test whether the organic carbon came from biology or geology.