The ancient kingdom of Thermoproteati holds the secret to our own evolutionary origins

Gardening · Published 3 October 2026 Swipe more like this →

In short: Deep within the Earth's most extreme environments, from boiling hydrothermal vents to subterranean gold mines, lives a mysterious group of organisms called Thermoproteati. As a sister branch to the lineage that eventually birthed all eukaryotes, these resilient archaea offer a profound glimpse into the fundamental mechanisms of life on Earth.

Thermoproteati represents a kingdom of archaea that has historically been grouped under the acronym TACK, standing for Thaumarchaeota, Aigarchaeota, Crenarchaeota, and Korarchaeota. Recent taxonomic revisions, specifically by Guy and Ettema in 2024, have established Thermoproteati as the only validly published name for this group within the International Code of Nomenclature of Prokaryotes. This classification is significant because the kingdom is considered a sister group to the Asgard archaea, which are widely believed to be the ancestors of eukaryotes.

The diversity within this kingdom is vast, spanning organisms that thrive in acidic, high-temperature environments to those that prefer moderate or even cold conditions. Many are anaerobic and chemosynthetic, meaning they generate energy through chemical reactions rather than sunlight. For instance, the phylum Thermoproteota—formerly known as Crenarchaeota—includes hyperthermophiles found in hydrothermal vents, yet other members of this group are the most abundant archaea in marine ecosystems at depths shallower than 100 meters. These organisms are vital to global carbon fixation, a role that earned them the historical nickname of sulfobacteria due to their heavy reliance on sulfur.

The evolutionary connection between Thermoproteati and eukaryotes is a subject of intense scientific interest, rooted in the eocyte hypothesis first proposed by James Lake in the 1980s. This hypothesis suggests that eukaryotes emerged from within the prokaryotic eocytes. Supporting this link is the discovery of specific genetic markers, such as the homolog of the RNA polymerase subunit Rbp-8, which is present in Thermoproteota but notably absent in Euryarchaea. While research continues into phyla like Aigarchaeota—originally identified from the genome of a species found in a Japanese gold mine—and the recently discovered Nezhaarchaeota from hot springs in Yunnan, China, the study of these organisms remains central to understanding the transition from simple prokaryotic life to the complex eukaryotic cells that define modern biology.

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