The last universal common ancestor of all life — a microbe dubbed LUCA that existed around 3.5 billion years ago — probably resided in a hydrothermal vent that had low oxygen levels.

To find out how the organism lived, William Martin and his colleagues at Heinrich Heine University Düsseldorf in Germany reconstructed the evolutionary trees of more than 6 million genes from bacteria and archaea. They identified 355 protein families that were probably in LUCA's genome — these are involved in anaerobic metabolism and fixing carbon dioxide and nitrogen. This suggests that LUCA lived in an environment that was rich in hydrogen, CO2 and iron, such as a hydrothermal vent.

LUCA may have depended heavily on the geochemistry of the vent to survive.

Nature Microbiol. (2016)