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Bacteria created iron deposits by metabolizing iron?


Researchers: Half of iron atoms in some cores were processed by microbes 2.5 bya/Clark Johnson 2.5 billion years ago?

That’s the theory here:

These ancient deposits, up to 150 meters deep, were begging for explanation, says Johnson.

Scientists thought the iron had entered the ocean from hot, mineral-rich water released at mid-ocean vents that then precipitated to the ocean floor. Now Johnson and Li, who is currently at Nanjing University in China, show that half of the iron in banded iron was metabolized by ancient bacteria living along the continental shelves.


Biologists say this process “is really deep in the tree of life, but we’ve had little evidence from the rock record until now,” Johnson says. “These ancient microbes were respiring iron just like we respire oxygen. It’s a hard thing to wrap your head around, I admit.”

The research also clarifies the evolution of our planet — and of life itself — during the “iron-rich” era 2.5 billion years ago. “What vestiges of the iron-rich world remain in our metabolism?” Johnson asks. “It’s no accident that iron is an important part of life, that early biological molecules may have been iron-based.”

Hmmm. Maybe we better get some corroborating studies.

Iron is an important part of life but it could be so for a variety of reasons. Still, this is interesting.

Here’s the abstract:

Banded iron formations (BIFs) record a time of extensive Fe deposition in the Precambrian oceans, but the sources and pathways for metals in BIFs remain controversial. Here, we present Fe- and Nd-isotope data that indicate two sources of Fe for the large BIF units deposited 2.5 billion y ago. High-eNd and -d56Fe signatures in some BIF samples record a hydrothermal component, but correlated decreases in eNd- and d56Fe values reflect contributions from a continental component. The continental Fe source is best explained by Fe mobilization on the continental margin by microbial dissimilatory iron reduction (DIR) and confirms for the first time, to our knowledge, a microbially driven Fe shuttle for the largest BIFs on Earth. Detailed sampling at various scales shows that the proportions of hydrothermal and continental Fe sources were invariant over periods of 100–103 y, indicating that there was no seasonal control, although Fe sources varied on longer timescales of 105–106 y, suggesting a control by marine basin circulation. These results show that Fe sources and pathways for BIFs reflect the interplay between abiologic (hydrothermal) and biologic processes, where the latter reflects DIR that operated on a basin-wide scale in the Archean. (paywall) – Weiqiang Li, Brian L. Beard, Clark M. Johnson. Biologically recycled continental iron is a major component in banded iron formations. Proceedings of the National Academy of Sciences, 2015; 201505515

See also: Where are we with origin of life?

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