Could bacteria have formed the Precambrian banded iron formations?

Abstract

Banded iron formations (BIFs) are prominent sedimentary deposits of the Precambrian, but despite a century of endeavor, the mechanisms of their deposition are still unresolved. Interactions between microorganisms and dissolved ferrous iron in the ancient oceans offer one plausible means of mineral precipitation, in which bacteria directly generate ferric iron either by chemolithoautotrophic iron oxidation or by photoferrotrophy. On the basis of chemical analyses from BIF units of the 2.5 Ga Hamersley Group, Western Australia, we show here that even during periods of maximum iron precipitation, most, if not all, of the iron in BIFs could be precipitated by iron-oxidizing bacteria in cell densities considerably less than those found in modern Fe-rich aqueous environments. Those ancient microorganisms would also have been easily supported by the concentrations of nutrients (P) and trace metals (V, Mn, Co, Zn, and Mo) found within the same iron-rich bands. These calculations highlight the potential importance of early microbial activity on ancient metal cycling.

Micro-scale tracing of Fe and Si isotope signatures in banded iron formation using femtosecond laser ablation

“…Oxidation and subsequent precipitation of ferric oyxhydroxide was most likely caused by anaerobic photosynthesis (e.g. Konhauser et al, 2002;Kappler et al, 2005) or atmospheric oxygen (e.g. Holland, 1973;Drever, 1974;Ehrenreich and Widdel, 1994;Kaufman et al, 2007).…”

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

“…Despite the consensus amongst workers that the precursor phase during the sedimentation of IF was most likely Fe(III)-oxyhydroxides (e.g., Konhauser et al, 2002;Kappler et al, 2005;Posth et al, 2014;Sun et al, 2015) or an Fe(III)-Si gel (e.g., Percak-Dennett et al, 2011;Zheng et al, 2016), there is renewed interest in possible alternative phases that may have influenced or been important for BIF sedimentation. These alternative authigenic phases include dominantly Fe(II) or mixed-valence phases, such as greenalite and various "green-rust" phases.…”

Fossilized iron bacteria reveal a pathway to the biological origin of banded iron formation

“…I t is generally believed that banded iron formations (BIFs), the bulk of which was formed in the late Archaean/ Palaeoproterozoic marine basins, occurred in stratified water columns deep in the ocean and on continental shelf margins [1][2][3][4] . Soluble ferrous iron, supplied from mid-ocean ridges and hydrothermal vents, was oxidized by various processes to ferric iron and deposited in association with varying silica ratios as BIFs [1][2][3][4] .…”

“…Soluble ferrous iron, supplied from mid-ocean ridges and hydrothermal vents, was oxidized by various processes to ferric iron and deposited in association with varying silica ratios as BIFs [1][2][3][4] . But the mechanism that drove and sustained the massive and sporadic deposition of BIFs throughout much of the Precambrian remains a mystery, despite decades of research.…”

“…Instead, biotic, anoxygenic photoferrotrophic precipitation according to the equation 4Fe 2 þ þ CO 2 þ 11H 2 O þ light-[CH 2 O] þ 4Fe(OH) 3 þ 8H þ has been proposed [6][7][8][9][10][11][12][13][14] . With the exemption of proxies such as iron isotopes 12,13 , there exists no direct environmental evidence-neither in ancient nor in modern ecosystems-demonstrating how photoferrotrophs could have accounted for vast-scale biological BIF deposition, including the formation of their spectacular banded consistency.…”