Microbial life from Mars and Earth. Illustration comparing the sizes of microscopic Earth life and a Martian micro-organism (blue, lower right). Part of a eukaryotic cell (one that contains a nucleus) is seen across top. A smaller prokaryotic cell (one that does not contain a nucleus) is at lower left. The Martian micro-organism is based on the fossil ovoids found in asteroid ALH84001. This asteroid, found in Antarctica in 1984, is believed to have originated from Mars, where it may have been ejected by an asteroid impact.