Abiogeneses e Bioquimica: A busca pelo Universo tunelado para a Vida. Material a Pesquisar

Nautillus Magazine

Goodbye Copernicus, Hello Universe

http://nautil.us/issue/1/what-makes-you-so-special/goodbye-copernicus-hello-universe

– Varios importantes links no post abaixo para ler:

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Torbjörn Larsson • 17 days ago

And that’s how you frame an issue on a new site!

But moving on to the details, I differ a bit on the view of the many potential pathways that could lead from chemical evolution to biological evolution. “Selection bias”, likelihoods, would be front and center. For example, there are thermodynamic reasons why RNA could have been favored as the first genetic material, if that was what happened. [“Statistical Physics of Self-Replication”, England, TBP; “Thermodynamic Basis for the Emergence of Genomes”, Woo et al, PLOS Comp. Biol. 2012.]

That is where I think Spiegel and Turner fails. As I remember my problem at the time was that they had to posit different pathways on different locales in order to make the result less constrained. Eg a failure to find life on Mars would be due solely to the pathway.

But for the same reason we should expect evolution, differential reproduction, to be a universal process among life because it promotes the most successful populations by its very nature, we should expect a successful pathway to life to be dominant. The recent find of earliest, even metamorphic, BIFs of Isua @ 3.8 Ga bp as likely result of anoxygenic photosynthesis pushes life within 1 Ga from Earth formation. [ http://www.sciencedirect.com/s… ] That is early enough to find our pathway, likely alkaline hydrothermal vent biochemistry by homology with early autotroph metabolism as per Lane and Martin, easy so likely generic.

Small nitpick which do not detract from environmental theory/selection bias (aka various “Anthropic Principles”): “Without all these ducks lined up in a row, there would be no carbon.”

Not all carbon is synthesized by the resonant pathway. This even seems to have been a problem, since too easy direct three-body formation at low temperatures would have been inconsistent with astronomical observations. Luckily it is sufficiently low in production. [http://arxiv.org/pdf/1112.2136… ]

I don’t know if this alternative pathway production rate is too low to prohibit more massive element formation in all kinds of potential universes where the resonant process is suppressed or vanished.

And while I looked for the non-resonant process reference which I had misplaced, I found an article that could be of interest re the apparent selection bias in carbon production. It seems it is not too fine-tuned, the excited state could vary with a factor 3 in energy excess. [http://www.csicop.org/sb/show/… ]

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PESQUISA:

http://www.sciencedirect.com/science/article/pii/S0012821X1200711X – (Artigo nao lido: precisa subscricao)

Biological Fe oxidation controlled deposition of banded iron formation in the ca. 3770 Ma Isua Supracrustal Belt (West Greenland) – 

Abstract

The redox balance of the Archean atmosphere–ocean system is among the most significant uncertainties in our understanding of the earliest history of Earth’s surface zone. Most workers agree that oxygen did not constitute a significant proportion of the atmosphere until after ca. 2.45 Ga, after the Great Oxidation Event, but there is less agreement on when O2 production began, and how this may have been consumed by reduced species such as Fe(II) in the oceans. The Fe redox cycle through time has been traced using banded iron formations (BIFs), and Fe isotopes are increasingly used to constrain the conditions of Earth’s paleoenvironments, including the pathways of formation of BIFs. Iron isotope analyses of BIFs from the 3.7 to 3.8 Ga Isua Supracrustal Belt (ISB), obtained by micro-sampling of magnetite-rich layers and conventional analysis, as well as by in situ femtosecond laser ablation (fs-LA-ICP-MS), indicate a consistently narrow range of non-zero δ56Fe values. Analysis of magnetite by fs-LA-ICP-MS allows for precise and accurate micron-scale analyses without the problems of orientation effects that are associated with secondary ion mass spectrometry (SIMS) analyses. Magnetite δ56Fe values range from +0.4‰ to +1.1‰ among different bands, but within individual layers magnetite grains are mostly homogeneous. Although these BIFs have been metamorphosed to amphibolite-facies, the metamorphism can neither explain the range in Fe isotope compositions across bands, nor that between hand samples. The isotopic compositions therefore reflect “primary”, low-temperature sedimentary values. The positive δ56Fe values measured from the ISB magnetites are best explained by deposition of Fe(III)-oxides produced by partial oxidation of Fe(II)-rich ocean water. A dispersion/reaction model, which accounts for rates of hydrothermal Fe(II)aq input, rates of oxidation, and rates of Fe(OH)3 settling suggests exceptionally low O2 contents, <0.001% of modern O2contents in the photic zone. Such low levels suggest an anoxygenic pathway is more likely, and the data can be well modeled by anoxygenic photosynthetic Fe(II) oxidation. Comparison of the Fe isotope data from the Isua BIFs with those from the 2.5 Ga BIFs from the Hamersley and Transvaal basins (Australia and South Africa, respectively) suggests a striking difference in Fe sources and pathways. The 2.5 Ga magnetite facies BIFs of Australia and South Africa have δ56Fe values that range from −1.2‰ to +1.2‰ over small scales, and are on average close to 0‰, which is significantly lower than those reported here from the Isua BIFs. The wide range in Fe isotope compositions for the Hamersley and Transvaal BIFs, in concert with C and O isotope data, have been interpreted to reflect bacterial dissimilatory Fe(III) reduction (DIR). The absence of low δ56Fe values in the Isua BIFs, as well as the lack of fine-scale isotopic heterogeneity, may indicate formation prior to widespread DIR.


Highlights

► Analysis by fs-laser-ablation allows for precise and accurate micron-scale analyses. ► Iron isotope analyses of BIFs from Isua indicate a narrow range of positive δ56Fe values. ► Narrow range of positive magnetite δ56Fe values reflect primary sedimentary values. ► Positive δ56Fe values best explained by anoxygenic photosynthetic Fe(II) oxidation. ► Iron in Isua BIFs has a different source and pathway than that of 2.5 Ga BIFs.

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