Archaea - The Most Ancient Life


Archaea and Evolution

Page within: Evolution

Halobacteria sp. strain NRC-1. Each cell is some 5 microns in lengthThe Archaea comprise a group of single-celled microorganisms that, like bacteria, are prokaryotes that have no cell nucleus or any other organelles within their cells. Consequently, they were once considered to be an unusual group of bacteria and named archaebacteria. However, it in now known that Archaeans have an independent evolutionary history and have numerous differences in their biochemistry compared to other forms of life. The differences are so great that they are nowPhylogenetic tree showing the relationship between the archaea and other forms of life. Eukaryotes are colored red, archaea green and bacteria blue. classified as a distinctly separate domain in the three-domain system. Carl Woese introduced the three main branches of evolutionary descent as the Archaea, Eukaryota and Bacteria. Classifying Archaea remains difficult, since the vast majority of these organisms have never been studied in the laboratory and have only been detected by analysis of their nucleic acids in environmental samples.

Yellow Stone Hot SpringsArchaeans are an ancient form of life, possibly the most ancient. Putative fossils of archaean cells in stromatolites have been dated to almost 3.5 billion years ago, and the remains of lipids that may be either archaean or eukaryotic have been detected in shales dating from 2.7 billion years ago. Since most prokaryotes do not have distinct morphologies, the shapes of fossils cannot be used to identify them as Archaea. Instead, chemical fossils, in the form of the unique lipids found in archaeans are used, and such lipids have now been detected in rocks dating back to the Archaean. The oldest known traces of these isoprene lipids have been found in Greenland, which include sediments formed 3.8 billion years old and are the oldest on Earth; some scientists, however, dispute this claim.

The Theory of Endosymbiosis proposes that Eukaryotic life evolved from the Archaea. That is, the theory explains that organelles such as mitochondria and chloroplasts in eukaryotic cells evolved from certain types of bacteria that prokaryotic cells engulfed through endophagocytosis. These cells and the bacteria trapped inside subsequently evolved a symbiotic relationship. In this endosymbiotic relationship, the bacteria lived within the other prokaryotic cells.