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A Shake Up of Accretion Theory

8 September 2013

Keeping climate science at bay with a very long pole Nature also has an article on sulphur in the Mantle which might be important – see http://phys.org/print297597610.html. This seems to overturn the prevailing view that most sulphur in the Mantle has an origin in chondrites. Basically, they took soil samples from the Mid Atlantic Ridge in the South Atlantic, seeking out rock that had welled up out of the Mantle, and it emerges this contained sulphur of a kind unlike what is found in chondrites (a type of meteor).

This is important research as the view is that most metals in the Mantle were pulled inwards once the core had developed – and it required all the iron friendly elements it could get if it hoped to grow to the hypothetical size of the mostly iron core. The effect was to leave the Mantle depleted of metals and sulphides. All of this is of course conjecture, a hypothesis, but one that is taken deadly serious all the same, and dissension is generally unwelcome. In contrast, rocks that have been driven out of the Mantle, to the surface, actually contain metals and to explain this anomaly academic scientists latched onto chondrites, pointing a finger at a primeval meteor bombardment, taking on board the proportion of metals in such meteorites being almost exactly the same as in the Mantle rock that had been studied (which was a small proportion of the whole). Hence, the core pulled metals out of the Mantle to make the core grow and the Mantle itself was replenished by millions of chondrite meteorites. Who said science was sober, reasonable, and sensible, and the deduction involved is comparable to a veritable Sherlock Holmes.

All well and good, cracks papered over – temporarily keeping the critics at bay. Along comes this study and blows the cosy ad hoc theory out of the water. It is basically saying that the prevailing view of raining chondrites is an explanation too far – and is probably a hypothesis up a gum tree. They are not saying this outright – that would be rude, undiplomatic. The original hypothesis requires another explanation to account for the fact that the Mantle rock examined in the South Atlantic contained sulphur that was different to that commonly found in chondrites. It is not just the strange idea of mass bombardment and replenishment that is threatened but the whole idea of core-mantle differentiation during the process of planetary accretion (which is thought to be how the planets were formed). Core segragation, it is alleged, scavenged around for iron loving elements such as tungsten, cobalt, and sulphur. The theory claims 97 per cent of Earth's sulphur is locked up in the iron rich core. Now it seems that might not be so. Is it back to the drawing board?

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