4 ms·

Carbon and Oxygen, yes, but Iron? And terrestrial? Those would be something significantly new.

dalke 11y ago
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%20Isotopes.pdf 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 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/ncomms3143.html 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." Yes, I believe that's the reason the New Yorker wrote this piece. It even links to the new PNAS article at http://www.pnas.org/content/112/27/8193.abstract?sid=51595c5b-6aaf-4d85-af40-9562f2f70814 http://www.pnas.org/content/112/27/8193.abstract?sid=51595c5... , which was published only 5 months ago, which says: > 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'?
- protonfish 11y ago
  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.
  - dalke 11y ago
    I still don't know what "like this" means. I think the isotopic difference in coal layers is exactly like this. I think this quote from http://link.springer.com/referenceworkentry/10.1007/978-1-4020-9212-1_120?no-access=true http://link.springer.com/referenceworkentry/10.1007/978-1-40... "Isotopes and Geobiology" (2001): > 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. I imagine that Ca and other elements are similar.
    - protonfish 11y ago
      "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.

dalke 11y ago

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%20Isotopes.pdf 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 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/ncomms3143.html 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." Yes, I believe that's the reason the New Yorker wrote this piece. It even links to the new PNAS article at http://www.pnas.org/content/112/27/8193.abstract?sid=51595c5b-6aaf-4d85-af40-9562f2f70814 http://www.pnas.org/content/112/27/8193.abstract?sid=51595c5... , which was published only 5 months ago, which says: > 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'?

protonfish 11y ago
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.
- dalke 11y ago
  I still don't know what "like this" means. I think the isotopic difference in coal layers is exactly like this. I think this quote from http://link.springer.com/referenceworkentry/10.1007/978-1-4020-9212-1_120?no-access=true http://link.springer.com/referenceworkentry/10.1007/978-1-40... "Isotopes and Geobiology" (2001): > 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. I imagine that Ca and other elements are similar.
  - protonfish 11y ago
    "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.