4 ms·

Jumping to the conclusion that there were ancient terrestrial microorganisms that metabolized iron as an energy source to explain odd isotopic ratios seems like

Jumping to the conclusion that there were ancient terrestrial microorganisms that metabolized iron as an energy source to explain odd isotopic ratios seems like a stretch to me. In the same way that it is unnecessary to pad out a science article with questionable metaphors.

nitrogen 11y ago
What is your alternative explanation for the claimed isotope imbalance?
- protonfish 11y ago
  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'?
dalke 11y ago
This is not a "jump". This is ongoing research in a relatively young field (about 20 years old), with multiple views. But you can read 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... concerning work being done in 2005 on the topic, which shows that the New Yorker is no distant leap beyond what people in that field have been saying for over a decade, and with efforts to fill in the details.

nitrogen 11y ago

What is your alternative explanation for the claimed isotope imbalance?

protonfish 11y ago
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'?

dalke 11y ago

This is not a "jump". This is ongoing research in a relatively young field (about 20 years old), with multiple views. But you can read 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... concerning work being done in 2005 on the topic, which shows that the New Yorker is no distant leap beyond what people in that field have been saying for over a decade, and with efforts to fill in the details.