Ultrathin sectioning and cryofracture of fibrous kerite, sampled from 1.8-1
.75 billion year old Volyn sediments (Ukraine), revealed in bacteria-like b
odies the presence of structures similar to sheath, cell wall, periplasm, c
ytoplasm, septum, membranes, intramembrane particles, poly-beta -hydroxybut
yrate inclusions. On the strength of these data and also the fatty acid pro
files of these microfossils, we concluded that fibrous kerites are biogenic
formations, namely fossilized bacterial mats.