Its synonym, "TACK"s name an acronym for Thaumarchaeota (now Nitrososphaerota), Aigarchaeota, Crenarchaeota (now Thermoproteota), and Korarchaeota, the first groups discovered.

They are found in different environments ranging from acidophilic thermophiles to mesophiles and psychrophiles and with different types of metabolism, predominantly anaerobic and chemosynthetic.

[4] Thermoproteati is a kingdom that is sister to the Asgard branch that gave rise to the eukaryotes.

[6] The relationships are roughly as follows: "Korarchaeota" "Bathyarchaeota" "Aigarchaeota" Nitrososphaerota "Verstraetearchaeota" Thermoproteota "Geoarchaeota" "Marsarchaeota" Conexivisphaerales Nitrososphaerales Nitrosopumilales Thermoproteales Fervidicoccales Desulfurococcales 2 Desulfurococcales Sulfolobales "Panguiarchaeales" "Korarchaeales" "Bifangarchaeales" [B24] "Hecatellales" [B25] "Xuanwuarculales" [RBG-16-48-13] "Houtuarculales" [40CM-2-53-6] "Wuzhiqiibiales" [TCS64] "Zhuquarculales" [EX4484-135] "Bathyarchaeales" [B26-1] "Caldarchaeales" "Geothermarchaeales" Conexivisphaerales Nitrososphaerales "Nezhaarchaeales" "Culexarchaeles" "Methanomethylicales" "Gearchaeales" Thermofilales Thermoproteales "Marsarchaeales" Sulfolobales The eocyte hypothesis proposed in the 1980s by James Lake suggests that eukaryotes emerged within the prokaryotic eocytes.

[15] One piece of evidence supporting a close relationship between Thermoproteati and eukaryotes is the presence of a homolog of the RNA polymerase subunit Rbp-8 in Thermoproteota but not in Euryarchaea.