Devonian and modern relatives of the Precambrian Eosphaera: possible significance for the early eukaryotes

Abstract

The Middle Precambrian problematical microorganism Eosphaera Barghoorn and Eosphaera-like structures known from Early and Middle Precambrian banded iron formations have been compared with the recently discovered Devonian volvocacean alga Eovolvox Kazmierczak and some modern colonial Volvocales. The volvocacean interpretation of Eosphaera implies that algal eukaryotes (green phytoflagellates) were already present in the earth biosphere before at least 1.9 b.y. [billion years] ago (Gunflint Iron Formation, Ontario, Canada), and probably before 2.7 b.y. ago (Soudan Iron Formation, Minnesota, USA). The type of metabolism and the O2 requirements of modern colonial Vovocales indicate that Eosphaera was most probably a photoorganotrophic (mixotrophic) organism able to live in the extremely oxygen-deficient or anoxygenous Early Precambrian environment. As an oxygen-releasing photosynthesizer, Eosphaera could have played a considerable role in the production of free O2 during the Precambrian. The abundance of Eosphaera-like ferriferous structures in the iron microbands of many banded iron formations implies active participation of these organisms in the formation of Precambrian sedimentary iron ores. The exclusively fresh-water habitat of extant volvocacean algae suggests that the Precambrian environments inhabited by Eosphaera were non-marine.