Back here? From Phys.org:
“What we concluded is that, by discounting hydrogen peroxide oxidation, anoxygenic photosynthetic micro-organisms are the most likely mechanism responsible for Earth’s oldest iron formations,” Ernesto Pecoits of the Université Paris Diderot and lead author on the study told astrobio.net.
Microorganisms that photosynthesize in the absence of oxygen assimilate carbon by using iron oxide (Fe(II)) as an electron donor instead of water. While oxygenic photosynthesis produces oxygen in the atmosphere (in the form of dioxygen), anoxygenic photosynthesis adds an electron to Fe(II) to produce Fe(III).
“In other words, they oxidize the iron,” explains Pecoits. “This finding is very important because it implies that this metabolism was already active back in the early Archean (ca. 3.8 Byr-ago).”
Here’s the abstract:
It is widely accepted that photosynthetic bacteria played a crucial role in Fe(II) oxidation and the precipitation of iron formations (IF) during the Late Archean–Early Paleoproterozoic (2.7–2.4 Ga). It is less clear whether microbes similarly caused the deposition of the oldest IF at ca. 3.8 Ga, which would imply photosynthesis having already evolved by that time. Abiological alternatives, such as the direct oxidation of dissolved Fe(II) by ultraviolet radiation may have occurred, but its importance has been discounted in environments where the injection of high concentrations of dissolved iron directly into the photic zone led to chemical precipitation reactions that overwhelmed photooxidation rates. However, an outstanding possibility remains with respect to photochemical reactions occurring in the atmosphere that might generate hydrogen peroxide (H2O2), a recognized strong oxidant for ferrous iron. Here, we modeled the amount of H2O2 that could be produced in an Eoarchean atmosphere using updated solar fluxes and plausible CO2, O2, and CH4 mixing ratios. Irrespective of the atmospheric simulations, the upper limit of H2O2 rainout was calculated to be paywall)
This is despite the complexities of photosynthesis?
See also: Does nature just “naturally” produce life?
Can all the numbers for life’s origin just happen to fall into place?
Hat tip: Phillip Cunningham