Is science sometimes in danger of getting tunnel vision? Recently published ebook author, Ian Miller, looks at other possible theories arising from data that we think we understand. Can looking problems in a different light give scientists a different perspective?

Planetary Formation Update - March

What for me were the most important papers that I found during March were papers relating to the oxidative state of the Earth during accretion. In my ebook, Planetary Formation and Biogenesis, I argued that the availability of reduced organic material is critical for biogenesis, and that as far as carbonaceous and nitrogenous materials were concerned, the Earth's mantle was reducing. Part of the reason was because the isotope composition of Earth's materials is closest to that of enstatite chondrites, which are highly reducing, and because meteorites that have originated from bodies closer to the star than the asteroid belt have increasingly reduced compositions, thus phosphorus occurs as phosphides. A further reason is that water on the ferrous ions in many olivines produces hydrogen, and is the source of methane of geochemical origin. The great bulk of the outer Earth has reduced iron, e.g. in the ferrous state in olivines and pyroxines, and the overall oxidation state of a closed system is constant. The Earth is gradually oxidizing because water reacts with ferrous to make ferric and hydrogen, and while hydrogen in the presence of carbon or nitrogen makes reduced compounds, it can also be lost to space. Geologists seem very keen on the oxidized mantle and argue that gases initially produced by volcanoes were carbon dioxide and molecular nitrogen.
The first of the papers, (Siebert et al. Science 339: 1194-1197) argued that the abundance of certain slightly siderophile elements such as V and Cr are better explained through initial oxidizing conditions, which were subsequently reduced to present values by transfer of oxygen to the core. They argue that reduced conditions leads to more Si in the core than is compatible with sonic measurements. For me, there were a number of difficulties with this argument, one being that too many components known to be present were left out of the calculations, and secondly, the effect of water seemed to be omitted. Water would oxidize silicon, thus reducing that available to the core, and make hydrogen. In the second paper, Vočlado (Nature 495: 177-178) carried out a theoretical study using the conditions at the present boundary between inner and outer core (330 billion pascals and a temperature up to 6000 degrees K) and argued that Si is equally probable in the inner solid core and outer liquid core and iron oxide is also there to account for oxygen. Perhaps, but the seismic properties and density of the core have yet to be matched with this proposal. It is also not exactly clear how the properties ascribed to components at these conditions were obtained (there will be no experimental data!) and finally, these calculations left out a number of components, including nickel.
Two papers were more helpful to my cause. Bali et al. (Nature 495: 220 – 222) showed that water and hydrogen will exist as two immiscible phases in the mantle, which explains why there can be very reducing conditions while the upper mantle can appear to be readily oxidized in relation to minor components like V and Cr. Meanwhile, Walter and Cottrell (Earth Planet Sci Let. 365: 165-176) note that while multi-variable statistical modeling of siderophile element partitioning between core-forming metallic liquids and silicate melts form the basis for physical models of core formation, experimental data are too imprecise to discriminate between current models and variations in statistical regression of partitioning data exerts a fundamental control on physical model outcomes. Such modeling also invariably depends on the assumption of the magma ocean.
To summarize these papers, on balance I do not think they falsify my proposal, however some geologists may not agree with that assessment. On the other hand, with slightly good news for my proposal, NASA Science announced Curiosity has drilled into a sedimentary rock in Gale Crater at a place where water was assumed to have formed a small lake and found in amongst the rock, nitrogen, hydrogen, oxygen, phosphorus and carbon, the elements necessary for forming life. What I found important was the presence of nitrogen, because that almost assures us that there was originally reduced nitrogen, as my proposal requires. The nitrogen is most unlikely to have come from N2 in the atmosphere, because the atmosphere contains so little of it. Only a radically different atmosphere in earlier times would deliver sufficient to fossilize nitrogen. The nature of the clay present is consistent with water of relatively low salinity weathering olivine. Also present was calcium sulphate, which is suggestive of neutral or mildly alkaline conditions at the time. Link:
Posted by Ian Miller on Apr 8, 2013 3:17 AM Europe/London

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