It's new because the field is only about 20 years old and everything in it is new. I gave you a link to one source, with details. Here's the link again to that 2005 piece from University of Wisconsin-Madison http://www.geology.wisc.edu/outcrop/05/05_pdfs/11%20Iron%20I... :
> [In 1996] there was almost no information on the isotopic composition of iron. Previous studies had not been able to identify naturally occurring mass dependent fractionation, within the error of the mass spectrometry measurements. Therefore it was necessary to develop new analytical methods that were highly precise. ... . Although the field of Fe isotopes is currently in its developmental stage, much like oxygen isotopes was five decades ago; it is rapidly becoming a common geochemical tool.
Here's a PhD thesis from 2004, http://dspace.mit.edu/handle/1721.1/53550 , which concludes "The observed range in the Fe isotopic composition of the natural samples including biological and aqueous samples demonstrates that significant and useful fractionation is associated with Fe biogeochemistry in the environment". Note that the author received a MS from University of Wisconsin-Madison, which the 2005 article is about, and the New Yorker piece also concerns the Wisconsin group.
So looking to a more recent Nature article which doesn't mention direct ties to the Wisconsion group, http://www.nature.com/ncomms/2013/130719/ncomms3143/full/nco... titled "Distinct iron isotopic signatures and supply from marine sediment dissolution" (2013):
> Microbial sediment respiration supports a major flux of dissolved and isotopically light Fe to the global ocean8, 9, 10, by catalysing the reductive dissolution (RD) of Fe oxyhydroxide minerals during organic matter decomposition11
You asked 'And terrestrial?', but you statement was a flat 'there's no evidence for it', which includes in the ocean. Note that the New Yorker article says "The ancient iron formations share many characteristics with modern limestones, which suggests that they accumulated in a marine environment".
But even then, you say "Those would be something significantly new."
> 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.
So again, could you explain what you mean by 'not supported by anything else we know about this time period, or life on Earth in general'?
I don't mean "new" in the sense of the studies are new. I mean "new" in the sense that nothing like this has even been observed in nature.
I misread the article about the terrestrial part.
I responded to your parent comment about localized high concentrations being required for chemotrophs. In deep sea vents, oxidizable chemicals are fresh. Organisms have time to harness their energy before it is naturally depleted through chemical reactions. This would not happen in the proposed scenario as the iron would have plenty of time to react before being washed into the ocean.
> It has long been recognized (e.g., Thode et al. (1949), Craig (1953) and Wellman et al. (1968)) that biological processes significantly fractionate the isotopes of C, N, and S, leading to characteristic biosignatures in sedimentary rocks that will be more or less preserved in the geological record. In the following, a brief overview is given of the major isotope fractionation processes in the biosphere and the geosphere.
is also "like this". But there's a 50 year head start with those elements.
"Like this" refers to the proposal that there were large numbers of iron chemotrophic organisms in the Precambrian.
Some elements (like Carbon) are known to be essential elements in the metabolism of biological organisms. This is why we would expect elements like Al and U to never show isotopic ratios associated with biological activity. Fe is used in living things, but only rarely. (The human body is 0.0006% Fe by weight.) To propose a biological origin for massive iron deposits is so far outside of what we know about biochemistry that it is not a legitimate proposal as is. The outlandishness of these proposed organisms equates to a very poor hypothesis that is not rigorous enough to be legitimately considered yet.
I am gobsmacked. By your comments you haven't read or know much about the topic, yet you insist that your personal beliefs trump the published work of scores of papers on the topic. But there's no reason to go to those papers when The New Yorker piece addresses your concerns:
> The ancient iron formations share many characteristics with modern limestones, which suggests that they accumulated in a marine environment. In today’s oceans, iron is in such short supply that it is a limiting nutrient—an essential element whose scarcity holds biological productivity in check. (A controversial climate-engineering scheme is even based on this fact; the idea is that if the oceans were fertilized with iron powder, plankton would bloom enthusiastically and then die, sinking to the ocean floor and sequestering large amounts of carbon there without, fingers crossed, wreaking havoc on the rest of the marine biosphere.) The primordial oceans, by contrast, must have been awash with iron. The richness of the rock formations—imagine all the steel in cars, cutlery, airplanes, buildings, bridges, and railroads—attests to that.
Thus when you write 'Fe is used in living things, but only rarely', the interpretation should be 'iron is so important to living systems that a biosystem will use all of the biologically available iron. There is so little iron available that it's a limiting factor to the ecosystem.'
With the plankton bloom being an example of 1) how iron is a limiting factor, and 2) a process by which iron is removed from the biosphere.
