The tree of life might be rooted in the branch leading to Nanoarchaeota.

It is suggested that the tree of life might be rooted in the domain of the Archaea, in the branch leading to the phylum of Nanoarchaeota. This hypothesis seems to be corroborated by the uniqueness and ancestrality of some traits possessed by Nanoarchaeum equitans, such as split genes separately codifying for the 5' and 3' halves of the tRNA molecule. These half genes are the oldest ancestral form of gene we have ever seen. This, along with the absence of operons from the genome of N. equitans, would seem to indicate that this genome is a molecular fossil of the evolutionary stage which the ancestral genomes had reached when the first lines of divergence were established. Moreover, the late appearance of DNA coinciding with the rooting of the universal phylogenetic tree would make the genome of N. equitans a witness to this fundamental event.