A surprisingly specific genetic portrait of the ancestor of all living things has been generated by scientists who say that the likeness sheds considerable light on the mystery of how life first emerged on Earth. This venerable ancestor was a single-cell, bacterium-like organism. But it has a grand name, or at least an acronym. It is known as Luca, the Last Universal Common Ancestor, and is estimated to have lived some four billion years ago, when Earth was a mere 560 million years old. The new finding sharpens the debate between those who believe life began in some extreme environment, such as in deep sea vents or the flanks of volcanoes, and others who favor more normal settings, such as the “warm little pond” proposed by Darwin. The nature of the earliest ancestor of all living things has long been uncertain because the three great domains of life seemed to have no common point of origin. The domains are those of the bacteria, the archaea and the eukaryotes. Archaea are bacteria-like organisms but with a different metabolism, and the eukaryotes include all plants and animals. Scientists' starting point was the known protein-coding genes of bacteria and archaea. Some six million such genes have accumulated over the last 20 years in DNA databanks as scientists with the new decoding machines have deposited gene sequences from thousands of microbes. Of these, only 355 met their criteria for having probably originated in Luca, the joint ancestor of bacteria and archaea. These 355 genes pointed quite precisely to an organism that lived in the conditions found in deep sea vents, the gassy, metal-laden, intensely hot plumes caused by seawater interacting with magma erupting through the ocean floor. http://www.nytimes.com/2016/07/26/science/last-universal-ancestor.html Study: http://www.nature.com/articles/nmicrobiol2016116
