It has long been suspected that the progenitor of life on planet earth most likely came from the sea. It has been proposed that the possible origins of life could have been in shallow pools or under more extreme conditions such as within deep-sea vents or proximal to active volcanoes.
The current domains of life consist of bacteria –prokaryotes, the archaea -found in deep sea vents and the eukaryotes that comprise all the animal and plant life on the planet. It has also been proposed that the archaea and the bacteria preceded the more complex eukaryotic cell type.
William F. Martin, an evolutionary biologist, from Heinrich Heine University in Düsseldorf, Germany, focused his research efforts on finding the progenitor of archaea and bacteria. To do this, the known genetic structure of members of the archaea and bacteria domains were extensively examined. This involved the examination of some six million genes representing thousands of microbes.
From these data, Martin and his colleagues were able to construct evolutionary family trees and were able to deduce that 355 gene families originated from single cell bacteria-like organism. That organism is referred to as the Last Universal Common Ancestor (LUCA). Furthermore, it is believed that LUCA lived some four billion years ago when the young earth was barely 500 million years old.
If this conclusion is correct, it clearly proposes that life began very early in the evolution of the planet earth and that the evolution of life was a much longer process than previously envisioned.