Short answers, pulled from the story.
Carl Woese and George E. Fox discovered the Archaea domain in 1977 when they analyzed ribosomal RNA sequences. Their analysis revealed that methanogens possessed genetic machinery distinct from bacteria, constituting a completely new domain of life. This discovery fundamentally rewrote the tree of life and is known as the Woesian Revolution.
Archaea cell membranes utilize ether-linked lipids constructed from isoprenoid chains rather than the ester-linked lipids found in bacteria or eukaryotes. These isoprenoid chains often feature multiple side branches and sometimes form cyclopropane or cyclohexane rings to prevent leakage at extreme temperatures. In some species like Ferroplasma, the standard lipid bilayer is replaced by a monolayer where the tails of two phospholipid molecules are fused into a single molecule.
The Lokiarchaeum lineage was discovered in 2015 in hydrothermal vents off the coast of Antarctica and identified as the closest known relative to eukaryotes. Subsequent discoveries of sister phyla such as Thorarchaeota, Odinarchaeota, and Heimdallarchaeota formed a new supergroup called Asgard. These organisms appear to be the missing link between simple prokaryotes and complex eukaryotes.
Archaea in the plankton community may represent up to 40% of the total microbial biomass in the oceans. They are particularly numerous in the sediments covering the sea floor, making up the majority of living cells at depths over one meter below the ocean bottom. These organisms play a critical role in global biogeochemical cycles by recycling carbon, nitrogen, and sulfur.
The methanogen Methanobrevibacter smithii is the most common archaeon in the human gut, making up about one in ten of the prokaryotes found there. This organism consumes hydrogen produced by protozoa in the anaerobic environments of ruminants and termites to facilitate digestion. While most archaeal interactions are mutual or commensal, some species like Nanoarchaeum equitans exhibit parasitic behavior.