The last universal common ancestor (LUCA) of all life is known to have lived about 3.4 billion years ago, yet how and where LUCA lived has remained a mystery. Now, research by William Martin and colleagues of Heinrich Heine University in Düsseldorf, Germany, supports the view that this ancient life form existed in a hydrothermal vent with low oxygen levels. By reconstructing evolutionary trees for more than six million genes from bacteria and single-celled micro-organisms, the team was able to identify 355 protein families that were likely in the LUCA genome and are involved in anaerobic metabolism and the fixing of carbon dioxide and nitrogen. This suggests an environment where lots of those gases were present, in addition to iron, making hydrothermal vents the likely origin of life.