FOSSIL DIATOMS IN A NEW CARBONACEOUS METEORITE
N. C. Wickramasinghe, J. Wallis, D.H. Wallis and Anil Samaranayake
1. The Polonnaruwa meteorite
Minutes after a large fireball was seen by a large number of people in the skies over Sri Lanka on 29 December 2012, a large meteorite disintegrated and fell in the village of Araganwila, which is located a few miles away from the historic ancient city of Polonnaruwa. A small piece of the meteorite was sent by one of us (AS) for study at the Buckingham Centre for Astrobiology and Cardiff University.
The meteorite when examined under a light microscope exhibits a highly porous and composite structure characteristic of a carbonaceous chondrite, with fine-grained olivine aggregates connected with mineral intergrowths. A few percent carbon as revealed by EDX analysis confirms the status of a carbonaceous meteorite. The general characteristics of the new meteorite bear a striking similarity to those of the unusual Maribo CM chondrite that fell over Denmark on January 17, 2009 (Haach et al, 2011). This meteorite was identified as arising from an extinct cometary fragment in the Taurid complex associated with comet Encke. In view of the proximity of occurrence within the calendar year between the Maribo and Polonnaruwa events we provisionally identify the latter as arising from an extinct cometary fragment belonging to the same Taurid complex. We shall henceforth refer to this meteorite as the Polonnaruwa CM chondrite or the Polonnaruwa meteorite.
2. Meteorite analysis
Fragments from a freshly cleaved interior surface of the Polonnaruwa meteorite were mounted on aluminium stubs and examined under an environmental scanning electron microscope at the School of Earth Sciences at Cardiff University. Images of the sample at low magnification displayed a wide range of structures that were distributed and enmeshed within a fine-grained matrix, of which Fig.2 is an example. EDX studies on all the larger putative biological structures showed only minor differentials in elemental abundances between the structures themselves and the surrounding material, implying that the larger objects represent microfossils rather than living or recently living cells. For the smallest structures, however, such a distinction could not be easily made from EDX studies alone. Other criteria will be required.
The donut-shaped structure seen in the bottom left corner of Fig.2 is one of many that were found in the Polonnaruwa meteorite that bears a striking similarity to the SEM images of the Kerala red rain cells (Louis and Kumar, 2004; Gangappa et al, 2010). We discuss elsewhere the possible link between these structures and the red rain that followed the meteorite fall.
- Diatom 1.jpg (39.97 KiB) Viewed 4049 times
Fig.2
Other structures of various shapes, including large numbers of slender cylinders of lengths 5 -10[j,m, and a few micrometres in diameter are seen to be distributed extensively throughout the sample. It is of interest to note that precisely such types of dielectric particles, which may have a pre-solar origin, have been invoked to explain both the linear and circular polarization of starlight (Wickramasinghe, 1967). As early as 1976 the presence of clumps of biogenic material in carbonaceous chondrites was inferred from spectroscopic studies at ultraviolet wavelengths (Hoyle and Wickramasinghe, 1976). The identification of infrared spectroscopic features of interstellar and cometary dust with the spectra of diatoms has also been discussed (Hoover, Hoyle, Wickramasinghe et al 1986). The discovery of diatoms in a carbonaceous chondrite therefore comes as no surprise.
The larger ovoidal object in Fig 2 possesses a microstructure and morphology characteristic of a wide class of terrestrial diatoms. Diatoms are unicellular phytoplankton characterised by elaborately sculptured frustules comprised of a hydrated silicon dioxide polymer. The intricately woven microstructure of these frustules would be impossible to generate abiotically, so the presence of structures of this kind in any extraterrestrial setting could be construed as unequivocal proof of biology. Diatom fossils of a wide range of types are found marine sediments dating back to the Cretaceous Tertiary boundary 65 million years ago.
- Diatom 2.jpg (57.79 KiB) Viewed 4049 times
Fig3
In the higher resolution image of Fig3 we can unambiguously identify an object as being a a diatom from its complex and highly ordered microstructure and morphology, that cannot result from any conceivable mineralisation or crystallisation process. The structure has been mineralised to a high degree over millions of years and displays close similarities in elemental abundances with the surrounding material.
One of the many of the slender cylinders seen in Fig.2 is examined under higher magnification in Fig.5. The intricacy of the regular patterns of "holes", ridges and indentations are again unquestionably biological, and this is impossible to interpret rationally as arising from an inorganic crystallisation process. Here too the near identity of elements inside and outside the structures point to a mineralised fossil rather than a recent diatom.
- Diatom 3.jpg (34.83 KiB) Viewed 4049 times
Fig5
3. Microfossil identifications
Reports of microfossil discoveries in meteorites have a long and tangled history stretching over half a century. Early claims of microfossils in carbonaceous chondrites by Claus and Nagy (1961) were quickly dismissed as arising from contaminants because there were indeed some instances in which contaminants (eg pollen grains) were mistakenly attributed to microfossils (Anders, 1962; Anders and Fitch, 1962). H.D. Pflug's more careful studies in the 1980's provided much stronger evidence of microfossils (Pflug, 1984; Hoyle and Wickramasinghe, 1982). Richard Hoover at NASA Marshall Space Flight Centre has continued to discover structures in carbonaceous meteorites that he identified as fossils of cyanobacteria (Hoover, 2005,2011). Despite the growing strength of Pflug's and Hoover's evidence counter claims that they are most likely to be crystallographic artefacts still dominate the literature, and the matter is seen at best as being unresolved. Whilst cyanobacterial filaments of the type found by Hoover may, by stretching credulity to a limit, be perceived as possible mineralogical artefacts, the highly characteristic diatom morphologies and microstructure seen in Figures 3 and 5 cannot be remotely construed as anything other than biologically defined structures that have undergone a high degree of fossilisation.
Comparison of the SEM images of another fossil diatom in the Polonnaruwa meteorite with a modern diatom Sellaphora blackfordensis (Mann, 1989,1999) leaves scarcely any room to doubt the identity of the former. Again we stress that contamination is decisively ruled out because the structure in the meteorite is deemed to be a fossilised object, and fossils diatoms were not present near the surface of the Earth to contaminate a new fall of meteorites.
We conclude therefore that the identification of fossilised diatoms in the Polonnaruwa meteorite is firmly established and unimpeachable. Since this meteorite is considered to be an extinct cometary fragment, the idea of microbial life carried within comets and the theory of cometary panspermia is thus vindicated (Hoyle and Wickramasinghe, 1981,.1982, 2000; Wickramasinghe, Wickramasinghe and Napier, 2010). The universe, not humans, must have the final say to declare what the world is really like.
[Complete article to be seen here:
http://www.buckingham.ac.uk/wp-content/ ... eorite.pdf]