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 - June

I found a number of interesting papers during June, and I am reasonably pleased that there were no significant contradictions to my ebook Planetary Formation and Biogenesis.  There were three major thrusts. The first one involved fluid flow on Mars, which my work requires, although of course its existence is generally accepted. Observations from the Curiosity rover at Gale crater showed isolated outcrops of cemented pebbles and sand. The rounded pebbles in the conglomerate indicates substantial fluvial abrasion, which led the authors (Williams et al. Science 340: 1068 – 1072) to conclude that sediment was mobilized in water that probably exceeded the threshold conditions (depth, 0.03 – 0.9 meter, velocity 0.2 – 0.75 m/s) required to transport the pebbles. They conclude that sustained liquid water must have flowed across the landscape. Unfortunately, no evidence was available as to why it flowed, or what the fluid was. (It would be water, but such water could either be heated, or it could contain something to depress its melting point.) 
 
Another major issue is, when did rocky planets get their volatiles? Volatiles that are accreted from the stellar accretion disk are almost certainly essentially lot to space due to the high energy emissions of the young star, which persist for about  0.5 Gy. My mechanism of rocky planet formation requires many of the volatiles to accompany feldsic crust formation, and I required that to happen following about 4 Gy BP, in part to ensure that the chemicals required for life were available continuously from about 4 Gy BP for another 1.5 Gy. Pujol et al. (Nature 498: 87-89) measured argon ratios from gas occluded in rock, and concluded that less than 10% of feldsic crust evolved between 170 My and 3.8 Gy BP, 80+10% of the crust formed between 3.8 Gy and 2.5 Gy BP, and < 30% crust was generated from 2.5 Gy BP to today. These results effectively confirm that my requirements were met. Interestingly, Debaille et al (Earth Planet Sci. Lett. 373: 83-92) proposed that early-formed mantle heterogeneities persisted at least 1.8 Gy after Earth's formation. The best explanation is that there was a stagnant lid regime as the crust built up. The major change in geodynamics noted at ~3 Gy BP then reflects the transition to plate tectonics.
 
In my ebook, I argued that there should be significant reduced species emitted geochemically early in a rocky planet's history, and I argued that the components in the Saturnian system would convert methanol and ammonia to methane and nitrogen. I also argued that the planetary systems formed relatively quickly, as opposed to the current theories that require at least 15 My to get a giant. I was pleased to note that Malamud and Prialnik (Icarus 225: 763-774) calculated how serpentinization would produce nitrogen and methane in Enceladus, and argued that for their calculations to be correct, because initiation requires heat from short-lived radioisotopes, the Saturnian moons had to be formed between 2.65 and 4.8 My after CAI formation. Just what I needed! Etiope et al. (Icarus 224: 276-285) showed that methane may be formed at relatively low temperatures by the Sabatier reaction catalysed by chromite minerals. More good reduced materials.
 
Finally, Pringle et al. (Earth Planet Sci. Lett. 373: 75-82) showed from consideration of silicon isotopes in meteorites from 4-Vesta that Vesta differentiated under more reducing conditions than previously considered. Again, just what I wanted.
 
Posted by Ian Miller on Jul 1, 2013 3:33 AM Europe/London

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