Martian meteorite, ALH84001. High resolution scanning electron micrograph (SEM) of a cast of a sample from a martian meteorite. The meteorite was found in the Allan Hills area of Antarctica. Some scientists have interpreted the tube-like structures to be fossils of bacteria-like lifeforms. The structures are 20-100 nanometres in diameter, similar in size to theoretical nanobacteria, but smaller than any cellular life known at the time of their discovery.