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They mention in the article non-biological process that can affect isotope ratios. This seems much more plausible. Suggesting that there were large enough amoun

They mention in the article non-biological process that can affect isotope ratios. This seems much more plausible. Suggesting that there were large enough amounts of terrestrial chemotrophs to change isotopic ratios is not supported by anything else we know about this time period, or life on Earth in general. The burden of proof is still in their camp to demonstrate: 1. Any evidence to suggest biological origin 2. Reasons why biological process are more likely to account for the observed iostope ratio that non-biological. Until then, this is only an interesting, though unlikely, explanation.

dalke 11y ago
Could you explain what you mean by 'or life on Earth in general'? Kinetic fractionation is a well-known process. Quoting https://en.wikipedia.org/wiki/Kinetic_fractionation https://en.wikipedia.org/wiki/Kinetic_fractionation : > Biological processes are generally unidirectional and are very good examples of "kinetic" isotope reactions. All organisms preferentially use lighter isotopic species, because "energy costs" are lower, resulting in a significant fractionation between the substrate (heavier) and the biologically mediated product (lighter). As an example, photosynthesis preferentially takes up the light isotope of carbon 12C during assimilation of an atmospheric CO2 molecule. This kinetic isotope fractionation explains why plant material (and thus fossil fuels, which are derived from plants) is typically depleted in 13C by 25 per mil (2.5 per cent) relative to most inorganic carbon on Earth. That sounds like life on Earth in general can form large geological concentrations of isotopically shifted material, and it's well accepted.
- protonfish 11y ago
  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.
- protonfish 11y ago
  Also, you can't make the same assumptions with chemotrophs as you can with phototrophs. Photosynthetic organisms use sunlight to power their chemical reactions so they can thrive anywhere there is sunshine, water and CO2. Chemotrophs can only thrive where there is a local concentration of their "food" (iron, in this case) compared to the average concentration. Let me explain it this way. Say you have an environment rich in elemental oxygen and iron. What's to stop the oxidation from occurring naturally before an organism can facilitate it and harness the energy? Nothing. This is why you only see chemotrophs around local high concentrations (like deep sea vents.) This means it is inherently impossible for chemotrophs to ever become widespread.
  - dalke 11y ago
    Do you have any evidence that chemotrophs do not have an isotopic preference? That would contradict the "all life" from the Wikipedia quote, and contradict what little I know about the universality of the mechanism. A quick search finds: Detmers, J., Brüchert, V. Habicht, K.S. and Kuever, J. (2001) Diversity of Sulfur Isotope Fractionations by Sulfate-Reducing Prokaryotes, Applied and Environmental Microbiology, 67, 888-894. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC92663/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC92663/ > All of the 32 sulfate-reducing bacteria discriminated against 34S during sulfate reduction. Desulfonema magnum showed the largest fractionation (ɛ = 42.0‰), and Desulfovibrio halophilus showed the smallest (ɛ = 2.0‰) It looks like the scientists working in this field have not made the assumption but have actually tested it. > This is why you only see chemotrophs around local high concentrations I lack the biochemistry knowledge. My limited understanding is that life was restricted to the ocean. If the Fe and O react on land (with limited oxygen, that produces iron(II), yes?), then it will be dissolved in fresh water. But when it hits the ocean, it's going to interact with the salts and other substances which a billion years of rain bought into the sea. In that case, the ocean edge will have the local high chemical concentrations. Sure, over time that will equilibrate. But any life at that boundary will be able to take advantage of the chemical gradient in the way you mentioned. We see this now, where continental runoff is a source of nutrients for ocean life, similar to how volcanic eruptions can add nutrients to soil through the weathering process of volcanic rocks.

dalke 11y ago

Could you explain what you mean by 'or life on Earth in general'? Kinetic fractionation is a well-known process. Quoting https://en.wikipedia.org/wiki/Kinetic_fractionation https://en.wikipedia.org/wiki/Kinetic_fractionation : > Biological processes are generally unidirectional and are very good examples of "kinetic" isotope reactions. All organisms preferentially use lighter isotopic species, because "energy costs" are lower, resulting in a significant fractionation between the substrate (heavier) and the biologically mediated product (lighter). As an example, photosynthesis preferentially takes up the light isotope of carbon 12C during assimilation of an atmospheric CO2 molecule. This kinetic isotope fractionation explains why plant material (and thus fossil fuels, which are derived from plants) is typically depleted in 13C by 25 per mil (2.5 per cent) relative to most inorganic carbon on Earth. That sounds like life on Earth in general can form large geological concentrations of isotopically shifted material, and it's well accepted.

protonfish 11y ago
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.
protonfish 11y ago
Also, you can't make the same assumptions with chemotrophs as you can with phototrophs. Photosynthetic organisms use sunlight to power their chemical reactions so they can thrive anywhere there is sunshine, water and CO2. Chemotrophs can only thrive where there is a local concentration of their "food" (iron, in this case) compared to the average concentration. Let me explain it this way. Say you have an environment rich in elemental oxygen and iron. What's to stop the oxidation from occurring naturally before an organism can facilitate it and harness the energy? Nothing. This is why you only see chemotrophs around local high concentrations (like deep sea vents.) This means it is inherently impossible for chemotrophs to ever become widespread.
- dalke 11y ago
  Do you have any evidence that chemotrophs do not have an isotopic preference? That would contradict the "all life" from the Wikipedia quote, and contradict what little I know about the universality of the mechanism. A quick search finds: Detmers, J., Brüchert, V. Habicht, K.S. and Kuever, J. (2001) Diversity of Sulfur Isotope Fractionations by Sulfate-Reducing Prokaryotes, Applied and Environmental Microbiology, 67, 888-894. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC92663/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC92663/ > All of the 32 sulfate-reducing bacteria discriminated against 34S during sulfate reduction. Desulfonema magnum showed the largest fractionation (ɛ = 42.0‰), and Desulfovibrio halophilus showed the smallest (ɛ = 2.0‰) It looks like the scientists working in this field have not made the assumption but have actually tested it. > This is why you only see chemotrophs around local high concentrations I lack the biochemistry knowledge. My limited understanding is that life was restricted to the ocean. If the Fe and O react on land (with limited oxygen, that produces iron(II), yes?), then it will be dissolved in fresh water. But when it hits the ocean, it's going to interact with the salts and other substances which a billion years of rain bought into the sea. In that case, the ocean edge will have the local high chemical concentrations. Sure, over time that will equilibrate. But any life at that boundary will be able to take advantage of the chemical gradient in the way you mentioned. We see this now, where continental runoff is a source of nutrients for ocean life, similar to how volcanic eruptions can add nutrients to soil through the weathering process of volcanic rocks.