This website uses cookies
Find out more
Product has been added to the basket

In Brief April 2010

Joe McCall reflects on some recent geological news…

Geoscientist 20.04 April 2010 (Online Special)


Wild surmise - the Stardust Mission


Wild-2Volume 44 (10) of Meteoritics and Planetary Science (all 1681 pp of it) is entirely devoted to the results of the Stardust Mission to recover samples from the tail of the Jupiter family (short period) comet 81P/Wild-2. This is an esoteric subject of research, but the conclusions are encapsulated in a summary, ‘Insights from the unexpected’ by J P Bradley et al. 1

First the results: the modification of the cometary particles during capture in aerogel was an unforeseen complication but can be compensated for (the phenomenon mainly affected organic grains and sulphide particles, and caused “smelting out” of metallic iron). The cometary grains were larger than predicted, solid grains of more than a micrometer in size being abundant. Grains up to 40 micrometers across were sectioned and left carrot-shaped tracks. But the big surprise was the origin of the cometary materials recovered.
The general expectation was that comet solids were predominantly composed of pre-solar grains, both pristine amorphous interstellar grains and some that had experienced partial crystallisation within the solar nebula by solid-state annealing at temperatures near 1000K. Isotopically anomalous pre-solar circumstellar grains are rare in the samples recovered, and less than are found in primitive chondrites.

The most surprising finding was that most of the cometary solids were high temperature inner nebula materials commonly found in chondrite meteorites- forsterite, chondrule fragments, ‘CAI’ fragments (calcium-aluminium rich inclusions). These mostly did not form from annealing of sub-micron-sized interstellar grains, and were the material that formed by the same processes as meteoritic components.

There is a broad mix in the Wild-2 samples, but they are unequilibrated with respect to another: olivine grains separated by less than a micron can have different Fe contents. These solids were not modified by parent body processes after they became encased in ice. The whole story requires a transport of inner solar system materials to the outer solar system - very early, between the formation of the CAI’s and the chondrule formation a million or so years later, the transport being by some process as yet unknown. The big find of the project was the organic compound glycine, as reported in December last year 2 . The comet samples shed a completely new light on the problem of the origin of chondrules 3.


The philosophical implications of these surprising results are immense. Scientists have here been proved completely wrong in their predictions about comets and cheerfully accept this. There is a common supposition that if one takes a problem to a scientist one gets a single, correct answer. This fallacy permeates the Climate Change Controversy. Scientists, in fact, commonly disagree among themselves (this is healthy, and how science progresses). They may be completely wrong. It is quite possible that the complexities, interplays and feedbacks involved in the changes of global climate are such that it is quite impossible for science to give accurate predictions. There has been a lot of suggestion of scientists falsifying results in the media. This, which I call the ‘Gupta factor’, after the most famous recent geoscience practitioner of scientific fraud, may exist – but it is surely not the main problem.

A distinguished colleague of mine has suggested that the confusion is partly due to the way science is organised into compartments (disciplines): I myself believe that it is the utter complexity of the global processes involved that may be the problem. The Stardust case illustrates how very distinguished and well-qualified scientists can still find the totally unexpected in the results of brilliantly and soundly planned experiments.

Refs:

  1. Bradley, J.P. Jones. A.P. Brownlee, D.E 2009. Insight from the unexpected. Meteoritics and Planetary Science 44(10); 1403-1405.
  2. McCall, Joseph. Glycine in particles from the tail of Comet Wild-2. Geoscientist 19(12); 14.
  3. McCall, G.J.H 2005. Chondrules and calcium-aluminium rich inclusions (CAIs). In: McCall, G.J.H., Bowden, A.J., Howarth, R.J., eds. “The History of Meteoritics and Key Meteorite Collections.”. Geological Society, London, Special Publication 256; 345-361.


More about exoplanets


I attended an annual meeting of the Meteoritical Society at Zurich in 2006, and the Barringer Lecture was delivered by Michael Mayor on the search for exoplanets, those in systems of stars outside our solar system, which commenced about 1985 with the detection of sunlike star 51 Pegasi’s companion and by then had been productive of some 200 recognitions 1.

While the descriptions of the Doppler spectroscopy, transit and gravitational microlensing methods of detection were absorbing, the overall impression was “Where does it lead? Is it not a bit like stamp collecting? Four years later, with some 400 exoplanets discovered, my opinion has changed radically. There is a brief but excellent treatment of this topic in the National Geographic Magazine December 2009 issue 2,3. This article reports that now 11 have been directly observed by blocking out the star’s light. Typical of these are Fomalhaut b, a gas giant three times heavier than Jupiter and CT Cha b, twice the diameter of Jupiter. The most massive is HD 43848b, equivalent to 7948 Earths. The methods of detection are such that while large gas or ice giants may be readily “seen”, small Earth-like planets are impossible to detect at our distance from the star. Fomalhaut b’s orbital movement can be directly detected and it orbits its star in 872 years! We can expect a lot of new recognitions with the Kepler satellite searching, though it will only cover a minute triangle of our own galaxy 2.

This development in astronomy seems to be a major revolution, even though finding out more about exoplanets through close observation is obviously technically impossible or would require immense technological invention. The fact that the Gas and Ice Giants likely have Earth-sized rocky companions and that there are a myriad of such systems in the Milky way galaxy alone (let alone other galaxies!) does not mean that there are necessarily any human-like populations out there, such are the chance factors in whether the planet has an atmsophere and of what composition, the gravitational and magnetic conditions applicable to it, the chance factors such as mutation in millions of years of evolution to advanced creatures, and the external chance factors of extinction due to geofactors and life competition during the millions of years of evolution on each planet .

Human survival on our planet is conditional on a large number of coincidental chance conditions. Yet this is a scientific revolution to be marvelled at! My own feeling is that even with these myriads of possible rocky planet hosts in the universe, probably nothing at all like human beings populates any of these exoplanets. We are probably alone, despite these discoveries.

Refs:

  1. Mayor, M. 2006. From gaseous giants to rocky planets. Meteoritics and Planetary Science 41 (Supplement); A118.
  2. Mayor, M, Marcy G.,. 2009 (sources). Worlds apart. National Geographic Magazine 26(6); 79-89
  3. Ferris, T. 2009. National Geographic Magazine 26(6); 91-93.

Dinosaur eggs in India


I have reported previously on the abnormalities in dinosaur egg fossils from Henan Province, India1. The suggestion then made was that clutches repeated over time at about 65 million years ago, the time of the disappearance of the dinosaurs, at the K/T extinction event, showed abnormalities in China, which may well have led to their extinction2. Now hundreds of dinosaur egg clusters have been found by chance in an ancient riverbed in the State of Tamil Nadu of about the same age (reported by MU Ramkumur3.

The eggs are large, 13-23 cm in diameter (about the size of a football) and are buried in sandy nests. They occur in different layers, showing that the dinosaurs came back again and again to the same nest sites (as in the case in Henan). The parents were large, docile, leaf-eating Sauropod dinosaurs. Volcanic ash is found over the eggs. The eggs were unhatched and infertile. More studies are needed to estrablish the reason for this, but this echoes the findings in Henan. This has been described as a ,treasure trove’.

This finding obviously has a bearing on the extinction of the dinosaurs. Keller and others4 have provided convincing evidence that the Chixculub crater, Mexico, the supposed ‘smoking gun’ responsible for their extinction (reported in lurid terms like ‘dinosaurs frying in their own blood’) is too old to be the culprit. Keller has lately turned her attention to the Deccan trap eruptions in India which straddle this age4, and could well have been associated with toxic chemical emissions. This new find must initate further researches into the damage to the dinosaur eggs, first noted in China and now noted in India, significant evidence that seems to have been somewhat overlooked in the popular acclaim for the Chicxulub explanation. This discovery close to the Deccan traps is surely of particular significance?

Refs:

  1. McCall, J. 1997. Dinosaur egg fossils and their implications: Henan Province, China, Geoscientist 7(1), 2
  2. Zhao, Zhi-Kui; Mao, Yue-Xing; Chi, Zhi-Fang; Yang, Gao-chuang; Kong, Ping; Ebuhara, Mitsiru; Zhao, Zhen-hua 2002. A possible causal relationship between extinction of dinosaurs and K/T iridium enrichment in the Nanxiong Basin, South China: evidence from dinosaur eggshells. Palaeogeography, Palaeoclimatology, Palaeoecology 178; 1-17.
  3. http://news.bbc.co.uk/1/hi/8284695.stm
  4. Keller, G., Stinnesbeck, W, Adatie, T., Holland, B., Steuben, B., Harting, D., De Leon, M., De La Cruz, J. 2003. Spherule deposits in Cretaceous-Tertiary boundary sediments in Belize and Guaemala. Journal of Geology 160; 1-13.
  5. McCall, G.J.H. 2009. Half a century of progress in research on terrestrial impact structures: a review. Earth Science Reviews 92; 99-116.