Analysis of the small subunit rrnas from all organisms in the three current domains suggests that

Cellular life forms have been divided into a three domain system. This system divides cellular life forms in archaea, bacteria and eukaryote domains. While studying the r RNAs of the organisms from these 3 domains, scientists came to the conclusion that all the organisms have a common ancestor due to the many similarities found. This common ancestor is not the first living organism in the Earth. This common ancestor is referred to as Last Universal Common Ancestor.