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 Update: September

Since I found no papers that falsified the major premises, my alternative theory on planetary formation survived September! Of course the skeptic might say (a) I never found them, or (b) I ignored them. I cannot guarantee that (a) did not apply because I do not have access to every journal (nor the time to read them), but some, having read this month's Chemistry World, may accuse me of (b). This paper (Alexander et al. (2012) Science 337: 721) determined the isotope ratios of hydrogen and nitrogen in various bodies from the solar system with the goal of deciding from where Earth's water came. In particular, they determined that water from the outer solar system has a higher D/H ratio than Earth's water, and since hydrogen on Earth escapes to space, anything that creates hydrogen from water, such as UV photolysis, raises the D/H ratio. There is no known mechanism to lower it. Accordingly, they decided that their determinations falsify some modeling work, which has the volatiles arriving due to the influx of a massive amount of icy bodies during a period when Jupiter and Saturn migrated outwards (having previously migrated inwards!).  (For a planet to migrate outwards, conservation of angular momentum and energy require massive amounts of material from further out to be thrown inwards.)
 
So, where did Earth's volatiles come from? These authors determined the D/H ratio and the 15N/14N ratio in various types of asteroidal bodies, and found the ratios in CI chondrites closely matched the ratios of Earth's hydrogen and nitrogen. Therefore, on the basis that there were no further possible sources, they decided CI chondrites were the source of Earth's volatiles. If so, that falsified my theory. So, why did I ignore it? Basically because, in my ebook, I devoted a whole chapter with fifty-six references to this issue and most of the critical issues were ignored by this paper, which makes me a little grumpy about both the paper and the refereeing.
 
What can go wrong with this logic? First, simply matching two ratios runs into the possibility of the fallacy of false cause. The asteroidal bodies have a wide range of results, although the enrichment of one element tends to follow the other. Given a wide range, the value for Earth is likely to match one of them. However, if we compare total mass, the nitrogen/carbon ratios in such chondrites do not match the ratio on Earth by a factor of approximately four, which strongly suggests they are not the origin. Worse, the nitrogen/carbon ratio is almost four times higher on Venus, and two orders of magnitude lower on Mars, which requires each body to be struck almost solely by bodies of different origin and totally different composition. Then, to get the Earth's volatiles, Earth has to be struck by at least 10^23 kg of chondrite, and based on area the Moon would have been struck by about 7x10^21 kg of chondrite. There is no evidence to support this. Of course, CI chondrites are relatively rare in the asteroid belt, so we have to also ask, why did virtually all these collide with Earth, while the other asteroids were not disrupted from their orbits (and the CI chondrites are further out), or alternatively, if the entire asteroid belt was disrupted, why were we not struck predominantly by the predominant silicaceous bodies? Then, previous work by Drake and Righter (Nature 416: 39) showed that, based on isotopes of other elements, no asteroidal body could have delivered Earth's volatiles, and the problem becomes much worse if the predominant asteroids devoid of volatiles also struck Earth. Oxygen isotopes alone characterize both the Earth and the Moon as being different from all other bodies for which data are available.
 
There is a further problem: why do we think that the D/H ratio on Earth is primeval? On Mars, and particularly on Venus, D enrichment must have occurred, so why did it not occur here? Genda and Ikoma (Icarus 194: 42) showed that there should have been an enhancement of between 2-9 times on Earth; nine times would mean that the current Earth's hydrogen was originally of nebular composition.
 
The problem with this paper is that conclusions were drawn from a very minor subset of available data, it focused on isotope ratios of hydrogen for water but ignored oxygen, which are known to be characteristic, and worse, the conclusion was reached based on the premise that the set of possible source of water was {comets, asteroids}. The real set is {comets, asteroids, accretion disk}. Just because the current paradigm ignores the accretion disk as the answer does not mean it was not the source. Finally, in my opinion it is extremely wrong to reach a conclusion based on genuinely good analytical data, and then ignore all the previous papers that call the conclusion into question. If referees have any function at all, surely this is one of them?
 
Accordingly, I ignored it in my claim because it was too complicated to show why in a blog. The chapter in the ebook that dealt with this issue took over 11,000 words, and that assumed that some material from previous chapters had been read. In short, this paper would not have changed that chapter, so as far as I am concerned, the conclusions of the chapter stand.
Posted by Ian Miller on Oct 6, 2012 3:35 AM Europe/London

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