4.1 Classification of Carbonaceous Meteorites. The type meteorites for the different clans of carbonaceous chondrites are CI (Ivuna), CM (Mighei), CO (Ornans), CV (Vigarano), CR (Renazzo) and CK (Karoonda). Wiik (1956) and Van Schmus & Wood (1967) classified carbonaceous chondrites based upon their chemical composition and petrology. In the Wiik classification system, the Group I carbonaceous chondrites have ~7% C, 20% H2O, and ~22% SiO2; the Wiik Group 2 (e.g. Murchison, Mighei and Cold Bokkeveld) chondrites, have ~ 4% C, 13% H2O, and 27.5% SiO2 and the Group 3 (e.g. Mokoai & Felix) have <1% C. Carbonaceous chondrites are further subdivided into petrologic types (1-7). The petrologic type is an indicator of the degree of chemical equilibrium within the meteorite minerals. In this system, the type 3 chondrites have not been significantly altered by either water or thermal metamorphism. Unequilibrated chondrites from lack of thermal metamorphism are of petrologic types 1-3 and types 4 to 7 are increasingly equilibrated due to extended thermal processes. The petrologic types 2 and 1 are found only in the carbonaceous chondrite clan and they have been subjected to an increasing degree of aqueous alteration. Carbonaceous chondrites of petrologic type 1 have been so extensively altered by water that chondrules are entirely absent, even though they have chondritic composition and must have contained chondrules during their early history before the aqueous alteration occurred. The type 2 chondrites have few somewhat less aqueously altered chondrules. The chondrules of type 3 are numerous, unaltered and very distinct, whereas those of types 4 to 6 again become more indistinct due to thermal metamorphism and re-crystallization. By petrologic type 7 the chondrules are again absent due to thermal destruction.
4.2 Mineralogy, Petrology and Organic Chemistry of CI1 Carbonaceous Meteorites. Cloëz and Pisani conducted the first detailed chemical analysis and study of the mineralogy and the Orgueil meteorite. Pisani (1864) concluded that Orgueil silicate minerals are more properly designated as serpentine rather than peridotite. Cloëz (1864a,b) found the Orgueil meteorite to be comprised of a soft, black, friable material, with 5.92% carbon, humic substances, magnetite, silicic acid, hygroscopic water (5.2-6.9%) and 8-10% indigenous water of hydration that is liberated only at a temperature > 200 oC. He also reported the detection of a variety of evaporite minerals including magnesium, ammonium, calcium and sodium salts. Microscopic and chemical analysis led Cloëz to conclude that the dominant portion of the carbonaceous material within the Orgueil meteorite was in the form of complex polymeric carbon insoluble in water and similar to humic substances, peat, and coal but unlike living organic matter (TABLE III).
Since these early studies a great deal of research has been dedicated to a detailed study of the mineralogy, petrology, and organic chemistry of the CI1 carbonaceous meteorites. This work has been summarized in detail by (Tomeoka and Buseck, 1988; Nagy, 1975; Kissin, 2003; Sephton, 2005). It is now established that the CI1 carbonaceous meteorites contain ~65 wt% fine scale phyllosilicate aggregates and intergrowths of serpentine and smectite/saponite, 10% magnetite, sulfides such as aqueously altered iron-nickel sulfides 7% pyrrhotite ([Fe,Ni]1-xS), and 5% ferrihydrite (5Fe2O3 . 9H2O) and troilite (FeS) as well as 5% recomposed carbonates like Breunnerite (Mg,Fe)CO3 and a small fraction (<1%) of olivine and pyroxene crystallites (Endre and Bischoff, 1996, Bland et al., 2004). The Orgueil meteorite also contains 4.56 Gy magnetites (as individual crystals, framboids, stacks of platelets) and presolar diamonds, silicon carbide and graphite (Huss and Lewis, 1994). Magnetite and pyrite framboids and platelets are present in the CI1 (Alais, Ivuna, and Orgueil) and C2 Ungrouped (Tagish Lake) carbonaceous meteorites that have been investigated in this research. Spectacular platelets and magnetite framboids with extremely well preserved uniform crystallites are common in the Tagish Lake meteorite. Studies carried out at the Paleontological Institute in Moscow by Academician Alexei Yu. Rozanov has revealed that framboids are present in the upper Permian black shales of the Berents Sea shelf which are similar in similar size distribution and characteristics as those found in the Alais and other carbonaceous meteorites.
Independent studies confirmed the very early findings that the CI1 carbonaceous meteorites contained a complex insoluble organic matter very similar to kerogen as is typically encountered in coal. Boström and Frederickson (1966) described the Orgueil meteorite as a“bituminous clay with a breccia structure and clastic texture.” They concluded there were three main stages of mineral formation on the meteorite parent body -
2. Middle stage with minerals like chlorite and limonite forming below 170 oC
3. Late stage with carbonates and sulphates forming below 50 oC.
Guo et al. (2007) used carbonate clumped isotope thermometry to determine the conditions of aqueous alteration sequence (of calcite to dolomite to bruennerite) as the carbonaceous meteorite parent bodies were cooling. They concluded the Orgueil dolomite formed at 26 oC and the bruennerite formed at -6 oC. The Orgueil and Ivuna CI1 meteorites appear to have experienced an extended period of aqueous alteration by acidic hydrothermal fluids that completely destroyed the pentlandite ([Fe,Ni]9S8) which is present in the Alais and Tonk meteorites, which probably experienced a shorter period of alteration (Bullock et al., 2003, 2005). The dissolved nickel was eventually re-combined with sodium to form sodium nickel sulfate (Ni-bloedite) or iron to form ferrihydrite. These diverse mineral grains and particulates contained within the CI1 carbonaceous are typically cemented together by epsomite and other water soluble salts.
4.3 Heating of CI1 Carbonaceous Meteorites during Atmospheric Transit. Immediately after the fall of the Orgueil CI1 carbonaceous meteorite, the villagers collected more than 20 jet-black stones. Many of these stones had complete fusion crusts and a few were quite large (one with mass ~11 kg). Leymeri (1864a) related that one of the stones “fell into a farmer’s attic, and this man burned his hand when he touched it.” He also described using a knife to cut one of the Orgueil stones soon after the fall: “The knife cut creates smooth and shiny surfaces which is an indication of a fine, paste-like matter” (Leymeri, 1864b). These observations indicate that the interior of the Orgueil stones had the consistency of wet clay-like just after the fall. Even though a thin fusion crust was formed on the exterior of the stones by intense heating during the transit through the atmosphere, it is clear that the interior of the stones never became hot. (Some of the Orgueil stones (as well as those of the Murchison CM2 meteorite that landed in Australia in 1969) were found a few hours after the fall with a thin coating of frost on the outer surface. This finding indicates that the inner portions of the stones were below zero after transit though the atmosphere. The interior portions of these stones were apparently protected by ablative cooling during atmospheric transit in a manner analogous to that experienced during the re-entry of an Apollo Command Module. This is important with regard to the possible transport of bacteria remaining viable during atmospheric entry.
4.4 Amino Acids and Chiral Biomarkers Modern Bacteria and Carbonaceous Meteorites. A suite of 20 life-critical amino acids are present in the proteins of all life forms known on Earth. The protein amino acids exhibit homochirality in that they are exclusively the L-enantiomer. Table IV shows the protein L-amino acids in the exopolysaccharide (EPS) slime sheath of the cyanobacterium Microcystis aeruginosa K-3A; living cells of the bacteria E. Coli and Salmonella sp. and ancient terrestrial biology (e.g., a Fly in amber and teeth of a Cretaceous Duck-Billed Hadrosaur) for comparison with extraterrestrial amino acids detected in the Murchison, Murray, Orgueil and Ivuna meteorites reported by Ehrenfreund et al., Engel et al. and Cronin and Pizarello. The amino acids of Table IV shown in italics or marked with “-“ or “n.d.” were either not detected or present at only trace levels in the fossils in terrestrial rocks and carbonaceous meteorites. Even though there is no doubt that the amber encased fly and the Hadrosaur teeth are biological in origin, it is seen that these fossils are also missing several of the same amino acids that absent in the carbonaceous meteorites. Only 8 of the 20 life-critical protein amino acids are detectable in water/acid extracts of carbonaceous meteorites. The fact that several of the amino acids missing in meteorites and ancient terrestrial fossils are abundant in living bacteria provides strong evidence that the meteorites are not contaminated by modern biological materials. If modern bio-contaminants were present, all 20 protein amino acids should be detected.
The data of Table IV indicates that the most abundant (by weight%) amino acids in the cyanobacterium Microcystis sp. are GLU, ASP, ALA, GLY and LEU (all above 8%) followed closely by THR, SER, VAL, ILEU and PRO (all above ~5%). However, GLY is by far the most abundant protein amino acid in the Murchison (CM2), Murray (CM2), Orgueil (CI1) and Ivuna (CI1) carbonaceous meteorites and it is followed by ALA, GLU and ASP. However, in these carbonaceous meteorites, the protein amino acids LEU, THR, SER, VAL, ILEU and PRO, which are abundant in all life on Earth, are either totally absent or detected only at trace levels. As has been pointed out by Engel and Macko (2005) these missing protein amino acids provide clear and convincing evidence that the interior portions of the CI1 and CM2 carbonaceous meteorites are not contaminated by modern cyanobacteria, pollen, fingerprints or other microbial contaminants. Isovaline (IVA), α-aminoisobutyric acid (AIB) and γ -Aminobutyric Acid (GABA) are the most abundant non-protein amino acids in carbonaceous meteorites. While they are not protein amino acids it is wrong to conclude that they are not biological in nature. The amino acids IVA and AIB are formed on Earth by the diagenetic alteration of ancient biological materials and γ -Aminobutyric Acid is synthesized by organisms on Earth. However, most protein amino acids are absent in meteorites and terrestrial fossils and only 8 of the 20 life-critical protein amino acids have been found in carbonaceous meteorites using the most sensitive modern methodologies available.
4.5 Comets as Parent Bodies of CI1 Carbonaceous Meteorites. The CI1 carbonaceous meteorites are jet-black stones that contain indigenous extraterrestrial water. The albedo of the Orgueil meteorite is extremely low (~0.05) and comparable to that of the very dark C-type asteroids and the nuclei of comets. This is blacker than asphalt which has an albedo of ~ 0.07. The European Space Agency Halley Multicolor Camera aboard the Giotto Spacecraft obtained images at the closest approach (00:03:01.84 UT on March 14, 1986) at a distance of 596 km from the centre of the nucleus revealing detailed topographic features on the black (albedo 0.04) surface and jets Lamarre et al. (1986) reported that IKS-Vega data indicated the temperature of nucleus of comet Halley was 420 K +/- 60K at 0.8 A.U which was consistent with “a thin layer of porous black material covering the comet nucleus.” The Deep Space 1 spacecraft found the 8 km long nucleus of Comet 19P/Borrelly to be very hot (~345 K) with prominent jets aligned with the orientation of the rotation axis of the nucleus and albedo of 0.01 to 0.03 (Soderbloom et al. 2002). Ices of water, carbon dioxide, methane and other volatiles in the cold nucleus in proximity to the hot crust would melt and then boil to produce high pressure beneath the crust if gas is released faster than it can escape through the porous crust. In regions where the pressure exceeds the strength of the crust, localized failure of portions of the crust could result in explosive release of the gas giving rise to the observed flaring of comets and the dramatic jets.
Once a comet enters the inner solar system, it becomes hot from solar radiation on the black nucleus and loses mass rapidly. The European Space Agency Infrared Space Observatory (ISO) showed that water was the primary volatile (75-80 %) of the 40-50 km diameter nucleus of Comet Hale-Bopp. Minor volatile fractions detected (CH4, NH3 and H2CO) could have come from clathrates (H2O ice with simple gasses like CO2 and NH3 in a stable lattice structure) or result from atmospheric chemistry. ISO found that Hale-Bopp released water vapor, carbon monoxide and carbon dioxide at a rate of 2 x 109 kg/sec and detected olivine in the dust. Olivine is commonly encountered in meteorites. As comets lose ices they develop an inert outer crust from the less volatile material. The nuclei of comets are extremely complex – they exhibit rugged terrain, smooth rolling plains, deep fractures and are composed of very dark material. This black crust becomes very hot while the comet is in the inner regions of the Solar System.
Figure 7.a. is a NASA Deep Space 1 spacecraft composite false color image showing geyser-like jets erupting from the long prolate nucleus (8 km) of comet 19P/Borrelly on Sept. 22, 2001. (The colors indicate three orders of magnitude in light level (red is 1/10, blue 1/100 and purple 1/1000 the intensity of the comet nucleus). The red bumps on the nucleus are real and show where the main jet resolves into three distinct narrow jets coming from distinct sources on the comet nucleus. These narrow jets are entirely consistent with the hypothesis that internal pressures generated by steam produced by melting of internal ices which then boil into gases as they are vaporized as heat conducts through hot crust. The NASA Deep Impact probe obtained the valuable data about the nature of comets as it approached and when the impactor collided with the nucleus of comet 9/P Temple 1 on July 4, 2005. Fig. 7.b is a Deep Impact image of the nucleus of comet Temple 1. The regions shown in blue are where exposed deposits of water ice that were detected on the surface of the comet nucleus Sunshine et al. (2005). These water ice regions ere observed to be ~30% brighter than the surrounding areas and probably were exposed when portions of the black crust was blown off into space by the explosive eruptions such as were recorded in a video by the spacecraft. The Deep Impact measurements of the temperature profile of comet P/Temple 1 nucleus at 1.5 AU is shown in Figure 7.c. Even as far away from the Sun as Mars the jet-black comet nucleus reaches temperatures as high as 330 K (57 oC). Furthermore, the lowest temperatures measured on the crust were ~ 280 K (7 oC) which is slightly above the temperature at which water ice changes from solid to liquid phase. Prior to the impact, the ambient outgassing of Temple 1 was ~6x1027 molecules/s of water. However, the free sublimation of ice calculated above (~200 K) was only ~4.5 x 1021 molecules/m2/s indicating that the ambient outgassing had significant subsurface sources. The Deep Impact spacecraft also observed numerous events of flaring of the nucleus and eruption of geyser-like jets as the comet was approached and before the collision of the impactor. On November 4, 2010, the NASA EPOXI extended mission of the Deep Impact Spacecraft passed within 435 miles of the 2.2 km long nucleus of comet Hartley 2 and revealed bright jets of carbon dioxide gas and dust.
These observations of comets are consistent with the hypothesis that the comet crust impedes the flow of gasses such that pressures develop as ices melt and vaporize in pockets and cavities beneath the crust. This provides the pressures needed to allow water to transition from the solid to the liquid state and then into the gaseous state. This would create micro-niches with pools of liquid water trapped within pockets in rock and ice, very much analogous to the cryoconite and ice bubble ecosystems contained psychrophilic microbial extremophiles such as those described from the glaciers and frozen Pleistocene thermokarst ponds of Alaska and Siberia and the glaciers and perennially ice covered lakes of the Schirmacher Oasis and Lake Untersee in East Antarctica (Hoover, 2008; Hoover and Pikuta, 2010; Pikuta et al. 2005). If gas is produced faster than it can escape through the porous crust, it could high pressures resulting in localized failure of weaker portions of the crust and the violent eruption into space of carbon dioxide, water vapor and chunks of crust and particles of ice and dust propelled into space and directed into the dust tail of the comet. These dust particulates could give rise to meteor showers as the comet passes through the tail. From time to time, larger chunks of the ejected may survive passage through the Earth’s atmosphere and this could be the link between comets and the CI1 (and possibly the CM2) carbonaceous meteorites. The fact that the CI1 meteorites contain minerals that were extensively altered by liquid water on the parent body and that the stones have been found to contain a large amount of indigenous extraterrestrial water clearly establishes that their parent bodies were most likely comets or water-bearing asteroids. It is now well known that the black nuclei of comets get very hot (significantly above >273 K where water ice melts) as they approach the Sun.
Gounelle et al. (2006) used the eyewitness accounts to compute the atmospheric trajectory and orbit of the Orgueil meteoroid and concluded that the orbital plane was close to the ecliptic and that entry into the atmosphere took place at a height of approximately 70 km and an angle of ~20°. Their calculations indicated the meteoroid terminal height was ~20 km and the pre-atmospheric velocity was > 17.8 km/sec. They found the aphelion to be 5.2 AU (the semi-major axis of orbit of Jupiter) and perihelion ~0.87 AU, which is just inside the Earth's orbit as would be expected for an Earth-crossing meteorite. This calculated orbit suggests the Apollo Asteroids and the Jupiter-family of comets are likely candidates for the Orgueil parent body include (although Halley-type comets are not excluded).
The cosmochemistry data for a cometary parent body is entirely consistent with the composition and characteristics of the CI1 meteorites. This suggestion that the parent body of the CI1 carbonaceous meteorites were possibly comets is significant with regard to possible existence of indigenous microfossils in the Alais, Ivuna and Orgueil meteorites. From the extensive evidence of aqueous alteration on the Orgueil parent body and the presence of indigenous water in the Orgueil meteorite it is clear that the parent body was either a water-bearing asteroid or a comet. However the Giotto and Vega observations of Halley and the Deep Impact Observations of the nucleus of 9P/Temple-1 have clearly established that these bodies get very hot as they enter the inner regions of the Solar System. It is now clear that any water bearing asteroid with an albedo of the Orgueil meteorite would reach a temperature above 100 C at 1AU. At these temperatures, water ice and other volatiles would be converted to liquid water, steam, and produce an expanding cloud of gas and expelled particulates. Any planetessimal orbiting the Sun and possessing a gaseous envelope and dust tail is traditionally refered to as “comet” rather than an asteroid, and therefore it seems logical that comets represent the most probable parent bodies for these water rich, black meteorites that travel in trajectories that cross the orbit of planet Earth.
4.6 Role of Comets and Carbonaceous Meteorites in the Origin and Evolution of the Earth’s Atmosphere, Hydrosphere, and Biosphere The relationship of comets with carbonaceous meteorites and their role in the origin and evolution of the atmosphere, hydrosphere, and biosphere of Earth has become better understood during the past few decades. The cratered surface of the moon provides clear evidence of the intense Hadean bombardment of the inner planets and moons by comets, asteroids and meteorites during the early history of the Solar System. Watson and Harrison (2005) interpreted the crystallization temperatures of 4.4 Ga Zircons from Western Australia as providing evidence that liquid water oceans were present on the early Earth within 200 million years of the formation of the Solar System. It has recently become more widely recognized that comets played a crucial role in the formation of the atmosphere and oceans of early Earth during the Hadean bombardment (Delsemme, 1997; Steel, 1998; Owen, 1997).
In 1978, Sill and Wilkening proposed that comets may have delivered life-critical biogenic elements carbon and nitrogen trapped within clathrate hydrates in their icy nuclei. In the same year, Hoyle and Wickramasinghe (1978, 1981, 1982, 1985) have proposed that comets delivered not only water, biogenic elements and complex organic chemicals to the surface of planet Earth, but that they also delivered intact and viable microorganisms. The detection of microfossils of cyanobacteria and other filamentous trichomic prokaryotes in the CI1 carbonaceous meteorites (which are likely cometary crustal remnants) may be interpreted as direct observational data in support of the Hoyle/Wickramasinghe Hypothesis (Wickramasinghe 2011) of the role of comets in the exogenous origin of terrestrial life.
Eberhardt et al. (1987) measured the deuterium/hydrogen ratios in the water of comet P/Halley. Delsemme (1998) found that that the D/H ratio of the water molecules of comets Halley, Hale–Bopp and Hyakutake were consistent with a cometary origin of the oceans. Dauphas et al., (2000) interpreted the deuterium/hydrogen ratios indicate that the delivery of water and ice to the early Earth during the late Hadean heavy bombardment by comets, asteroids and meteorites helped to cool the Earth’s crust and form the early oceans. Table V shows data extracted from the Robert et al. (2000) compilation of Deuterium/Hydrogen ratios of selected components of the Cosmos.
When these bodies are grouped in accordance with their D/H ratio it is easily seen that the telluric inner planets and the LL3 (stony) and SNC (Mars) meteorites have high (~500-16,000) ratios and the gas giants, protosolar nebula, ISM and Galaxies are very low (~15-65). The D/H ratios of the comets (~290-330) and carbonaceous meteorites (~180-370) are much closer to that of Earth (~149) and support the hypothesis that they may have made significant contributions to the formation of the oceans of our planet. It is interesting that the D/H ratios of comets are very similar to the ratios measured in the kerogen, amino acids and carboxylic acids of the Orgueil (CI) and other (CM, CV, and CR) carbonaceous meteorites. This supports the view that although stony meteorites are most probably derived from rocky asteroids, the carbonaceous meteorites most probably are derived from water-bearing asteroids or the nuclei of comets. The 30 m diameter fast-spinning carbonaceous asteroid 1998 KY26 that was discovered on June 2, 1998 has been found to contain 10-20% water. However, the small carbonaceous, water-rich asteroid 1998 KY26 also has color and radar reflectivity similar to carbonaceous meteorites and it may be a spent comet. Near IR observations indicated the presence of crystalline water ice and ammonia hydrate on the large Kuiper Belt object (50000) Quaoar with resurfacing suggesting cryovolcanic outgassing. The Cassini/Huygens spacecraft has recently obtained data indicating that a vast liquid water ocean may also exist beneath the thick frozen crust of Titan. Cassini/Huygens has also detected evidence for cryovolcanic water-ice geysers on Titan and Saturn’s moon Enceladus.
5. EVIDENCE OF MICROFOSSILS IN CI1 METEORITES AND LIFE IN ICE: IMPLICATIONS TO POSSIBLE LIFE ON COMETS, EUROPA, AND ENCELADUS
The detection of evidence of viable microbial life in ancient ice (Abyzov et al., 1998, 2003; Hoover and Pikuta, 2010) and the presence of microfossils of filamentous cyanobacteria and other trichomic prokaryotes in the CI1 carbonaceous meteorites has direct implications to possible life on comets and icy moons with liquid water oceans of Jupiter (e.g. Europa, Ganymede or Callisto) and Enceladus (Fig. 8.a) Saturn’s spectacular moon that is exhibiting cryovolcanism and spewing water, ice and organics into space from the region of the blue and white “tiger stripes.” Europa exhibits red, orange, yellow and ochre colors and fractured regions indicating the icy crust is floating on a liquid water ocean. The possibility of life on Europa has been discussed by Hoover et al. (1986): Chyba et al. (2001) Dalton et al. (2003), and in edited books by Russell (2011), and Wickramasinghe (2011) and in Volumes 5, 11, and 13 of the Journal of Cosmology. Hoover et al. (1986) argued while deep blue and white colors in the Galileo images of the Jovian moon Europa were typical of glacial ice, ice bubbles and snow on Earth as seen in this image of ice bubbles from the Schirmacher Oasis of East Antarctica (Fig, 8.b). The red, yellow, brown, golden brown, green and blue colors detected by the Galileo spacecraft in the Conamara Chaos region (Fig. 8.c.) and the deep red lines of the icy crust of Europa (Fig. 8.d.) are consistent with microbial pigments rather than evaporite minerals. The 1986 paper suggested that the colors seen in Europa images resulted from microbial life in the upper layers of the ice. A number of more recent studies and books have been published concerning the significance of ice microbiota to the possibility of life elsewhere in the Solar System (e.g. Russell 2011; Wickramasinghe 2011; Volumes 5, 7, 13 of the Journal of Cosmology).
Diatoms are golden brown and cyanobacteria exhibit a wide range of colors from blue-green to red, orange, brown and black. Bacteria recovered from ice are often pigmented. For example, the extremophiles isolated from the ancient Greenland ice cores produce pigmented colonies. Herminiimonas glaciei colonies are red (Fig. 8.e) and the colonies of “Chryseobacterium greenlandensis” exhibit yellow pigments (Fig. 6.b.). Figure 5.c. shows the red pigmented colonies of the new genus of psychrophile, Rhodoglobus vestali isolated from a lake near the McMurdo Ice Shelf, Antarctica (Sheridan et al. 2003). Colonies of Hymenobacter sp. (Fig. 6.d.) isolated from the Schirmacher Oasis Ice Cave are red-ochre in color (Hoover and Pikuta, 2009, 2010). The possibility of life on Enceladus and the detection of biomarkers in the plumes of water, ice and organic chemicals ejected from the “Tiger Stripes” of Enceladus has been discussed by McKay et al., (2008) Hoover and Pikuta ( 2010) and in a number of articles published in volumes 5, 7, and 13 of the Journal of Cosmology.
It is concluded that the complex filaments found embedded in the CI1 carbonaceous meteorites represent the remains of indigenous microfossils of cyanobacteria and other prokaryotes associated with modern and fossil prokaryotic mats. Many of the Ivuna and Orgueil filaments are isodiametric and others tapered, polarized and exhibit clearly differentiated apical and basal cells. These filaments were found in freshly fractured stones and are observed to be attached to the meteorite rock matrix in the manner of terrestrial assemblages of aquatic benthic, epipelic, and epilithic cyanobacterial communities comprised of species that grow on or in mud or clay sediments. Filamentous cyanobacteria similar in size and detailed morphology with basal heterocysts are well known in benthic cyanobacterial mats, where they attach the filament to the sediment at the interface between the liquid water and the substratum. The size, size range and complex morphological features and characteristics exhibited by these filaments render them recognizable as representatives of the filamentous Cyanobacteriaceae and associated trichomic prokaryotes commonly encountered in cyanobacterial mats. Therefore, the well-preserved mineralized trichomic filaments with carbonaceous sheaths found embedded in freshly fractured interior surfaces of the Alais, Ivuna, and Orgueil CI1 carbonaceous meteorites are interpreted as the fossilized remains of prokaryotic microorganisms that grew in liquid regimes on the parent body of the meteorites before they entered the Earth’s atmosphere.
The Energy Dispersive X-ray spectroscopy data reveals that the filaments detected in the meteorites typically exhibit external sheaths enriched in carbon infilled with minerals enriched in magnesium and sulfur. These results are interpreted as indicating that the organisms died on the parent body while aqueous fluids were present and the internal cells were replaced by epsomite and other water soluble evaporite minerals dissolved in the liquids circulating through the parent body. The nitrogen level in the meteorite filaments was almost always below the detection limit of the EDS detector (0.5% atomic). However, nitrogen is essential for all amino acids, proteins, and purine and pyrimidine nitrogen bases of the nucleotides of all life on Earth.
Extensive EDS studies of living and dead cyanobacteria and other biological materials have shown that nitrogen is detectable at levels between 2% and 18% (atomic) in cyanobacterial filaments from Vostok Ice (82 Kya) and found in stomach milk the mammoth Lyuba (40 Kya); mammoth hair/ tissue (40-32 Kya); pre-dynastic Egyptian and Peruvian mummies (5-2 Kya) and herbarium filamentous diatom sheaths (1815). However, Nitrogen is not detected in ancient biological materials such as fossil insects in Miocene Amber (8 Mya); Cambrian Trilobites from the Wheeler Shale (505 Mya) or cyanobacterial filaments from Karelia (2.7 Gya). Consequently the absence of nitrogen in the cyanobacterial filaments detected in the CI1 carbonaceous meteorites indicates that the filaments represent the remains of extraterrestrial life forms that grew on the parent bodies of the meteorites when liquid water was present, long before the meteorites entered the Earth’s atmosphere. This finding has direct implications to the distribution of life in the Cosmos and the possibility of microbial life in liquid water regimes of cometary nuclei as they travel within the orbit of Mars and in icy moons with liquid water oceans such as Europa and Enceladus.
ACKNOWLEDGEMENTS I want to thank Gregory Jerman and James Coston of the NASA Marshall Space Flight Center for FESEM and EDS analysis support and Dr. Claude Perron, Musée Nationale d’Histoire (Paris) for samples of the Alais and Orgueil meteorites and Dr. Paul Sipiera of the Planetary Studies Foundation and the Field Museum for samples of the Orgueil and Ivuna CI1 meteorites. I also thank Academician Alexei Yu. Rozanov the Paleontological Institute (Russian Academy of Sciences), Academician Erik Galimov of Vernadsky Institute, (Russian Academy of Sciences), Prof. John F. Lovering of the University of Melbourne; and Dr. Rosemarie Rippka of Pasteur Institute, Paris for many helpful discussions concerning meteorites, bacterial paleontology, and cyanobacteria.
Abyzov, S.S., Mitskevich, I.N., Poglazova, M.N., Barkov, M.N., Lipenkov, V.Ya., Bobin, N.E., Koudryashov, B.B., Pashkevich, V.M., (1998). Antarctic ice sheet as a model in search of Life on other planets. Advances in Space Research, 22, 363-368.
WM's Note: Due to huge listings of references, they are deleted here in this webpage.
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|49||DNA's Trap for Investors: A Race to the Bottom ||2012.07.19||운영자||2012.07.19||2183|
|48||NASA rover Curiosity makes historic Mars landing ||2012.08.06||운영자||2012.08.06||2002|
|47||Universe, through the ESA Herschel Space Telescope||2012.08.06||운영자||2012.08.06||4317|
|46||Birds-of-Paradise - Cornell Lab of Ornithology ||2012.12.22||운영자||2012.12.22||3413|