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, a group of evolutionary biologists, led by William F. Martin of Heinrich Heine University in Düsseldorf, Germany, found.
Luca, they said, was 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.
Deep sea vents are surrounded by exotic life-forms and, with their extreme chemistry, have long seemed places where life might have originated. The 355 genes, which were ascribable to Luca, include some that metabolize hydrogen as a source of energy as well as a gene for an enzyme called reverse gyrase, found only in microbes that live at extremely high temperatures, Dr. Martin and colleagues reported Monday in Nature Microbiology.
Dr. Martin argues that Luca is very close to the origin of life itself. The organism is missing so many genes necessary for life that it must still have been relying on chemical components from its environment. Hence it was only “half alive,” he writes.
Others believe that the Luca that Dr. Martin describes was already a highly sophisticated organism that had evolved far beyond the origin of life, meaning the formation of living systems from the chemicals present on the early Earth.