Relics of the paleosol of Mesoarchean age (3000–2930 Ma) developed on tuffs and lavas of komatiites from Koikary Area (Central Karelia) were studied. Microscopic tubular and spherical structures morphologically similar to fossilized remnants of microorganisms were found in the preserved part of the crust profile, represented by a layer of chloritite. The nature of these micro structures and the possibility of their interpretation as acidophilic bacteria inhabiting the land in the zone of chemical weathering of volcanic rocks are discussed.