Archaea represent a major prokaryotic domain of life besides Bacteria but were recognized as such only about 40 years ago. Originally, members of the archaea were thought to be confined to extreme environments and of little ecological importance. However, recent advancements in sequencing technologies, which among others allows to sequence DNA directly from environmental samples or single cells using single cell and metagenomics methodologies has revealed the near ubiquitous presence of archaea in all studied environments on Earth. Furthermore, this wealth of sequencing data has unveiled that archaea are much more diverse than anticipated earlier and various novel lineages of high taxonomic rank were recently proposed. Importantly, detailed analyses of genomes of these novel archaea have provided fundamental new insights into the metabolic diversity and potential role of archaea in their natural habitats as well as into evolution of microbial life on Earth and the origin of Eukaryotes.
Here, I will present a historical perspective of the ‘evolution’ of the archaeal tree of life, which will give a synopsis of our current knowledge of archaeal phylogenetic and metabolic diversity today. Subsequently, I will discuss how the discovery of some of these lineages has allowed not only a changed perspective on the early evolution of Archaea but also on the role of archaea in the origin of eukaryotic cells and in the involvement in major biogeochemical nutrient cycles.