Citation format: Mignan, A. (2011), Claims of Indigenous Life Forms in Meteorites: A Short Review. Meteorite magazine, vol. 17, no. 4, pp. 34-38.
The full text is reproduced from Meteorite magazine with permission from the publisher.
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Are we alone in the Universe? The answer has eluded mankind until now. Or did it? From time to time, scientists claim to have found the proof of extraterrestrial life. The latest to date is Richard B. Hoover, a NASA scientist, who has supposedly found the evidence for indigenous microfossils in carbonaceous meteorites1 (Hoover, 2011). Claims of alien life in meteorites are some of the most fascinating since they are linked to something tangible. How better prove the existence of extraterrestrial life than having a piece of rock that contains some kind of alien form, fossil or alive, in it.
The histogram shown in Figure 1 depicts the chronology of claims of indigenous life forms, past or present, found in meteorites and of the subsequent debates, from the early age of Meteoritics to the present day. What strikes the eye is the histogram’s cycle-like structure. Each cycle starts with one extraordinary claim: meteoritic stones and irons contain fossils of multi-cellular invertebrates (Hahn, 1880), chondrites contain living indigenous bacteria (Lipman, 1932; Geraci et al., 2001), microfossils can be found in carbonaceous meteorites (Nagy et al., 1961; Hoover, 2011) as well as in Martian meteorites (McKay et al., 1996). Other studies always follow to whether refute or corroborate the initial claim. Finally, the hypothesis dies off, to maybe be revitalized decades later in a new cycle. Interestingly, this structure follows the famous Thomas Kuhn’s Structure of Scientific Revolutions2 (e.g., Kuhn, 1970).
"La Paléontologie reste pour nous unique en son genre et dépourvue encore de terme de comparaison. Mais comme, en réalité, rien n’est unique dans la nature, sinon la nature elle-même, la seule question possible est de savoir si des termes de comparaison, qui existent certainement quoique nous les igorions, viendront ou ne viendront pas à notre connaissance"3 – Stanislas Meunier (1871)
In the late 19th century, Otto Hahn, not to be confused with the German chemist and Nobel laureate of the same name, claimed the presence of fossils in meteorites. He thought to have identified in thin sections fossils of sponges, corals and crinoids in ordinary chondrites and even in irons (Hahn, 1880). Hahn’s idea was later rejected by most of his contemporaries. J. Lawrence Smith4 stated: "Although I have probably examined more microscopic plates of (…) meteorite than any other person, still I have never discovered anything like organic remains" (Louisville Courier Journal, 1881). As can be seen in Figure 2a, the author clearly misinterpreted chondrules as being fossilized corals. This is a clear example of pareidolia, the same process that makes you see animal shapes in clouds. One other notable obscure theory based on this trick of the mind is the Nummulosphere of Randolph Kirkpatrick (1912), according to which all rocks on Earth would have formed from the accumulation of foraminifera5. In his work, Kirkpatrick ironically criticizes Hahn by stating: "Dr. Otto Hahn believed in the organic origin of meteorites, but he fails to produce any evidence in support of his theory. He mistook the chondrules of aerolites for Sponges, Corals, and Crinoids (…) Further, he considered the Widmanstatten figures of siderites to be for the most part plant-cells and not crystals". At the same time, Kirkpatrick indicates: "Nummulitic structure is clear enough to my practiced sight in meteorite sections containing stone and iron (…) (Meteorites) are lumps of mineralized and ore-enriched nummulitic rock (…) In my opinion, meteorites have no more to do with nebular and prenebular theories than have lumps of chalk".
Hahn’s idea did not survive. It was however (kind of) resurrected in the 1960s by Bartholomew Nagy’s group who proposed the catchy term organized elements (OEs) for what they believed to resemble unicellular microfossils in carbonaceous chondrites (Claus & Nagy, 1961). Their 1961 paper led to a hectic debate published in the prestigious Nature and Science journals and which lasted for several years (Figure 3). In 1962, Fitch et al. (1962) refuted the claim; OEs consist in fact of mineral grains. The authors stated: “although the work of Claus and Nagy was done with much greater care and competence than the early work of Hahn, the decision whether a certain form is of biological or inorganic origin is once again purely subjective”. Nagy et al. (1962) responded that Fitch et al. had not looked at the right place and proposed four more experiments to corroborate their hypothesis. Anders & Fitch (1962) then discriminated OEs in two classes: (1) simple shapes, indigenous and inorganic and (2) complex shapes of biological origin but most likely spore contaminants. Nagy et al. (1963) verified that the complex OEs were not contaminants and Fitch & Anders (1963) that they really looked like contaminants. And the story went on... until it died off.
The Martian meteorite, code name ALH84001, first find made in the Allan Hills of Antarctica in a 1984 expedition, has been made famous by a team from NASA (McKay et al., 1996) for it contains "elongate forms (that) resemble some forms of fossilized filamentous bacteria" (Figures 2b). ALH84001 is now part of the pop culture (Figure 4) in contrast with other claims, maybe due to the fact that the existence of Martians would make more sense to the layman than the existence of "Asteroidians" or "Cometians", but it is most probably due to the frantic media attention at the time6. Ashley & Delaney (1999) give a simple answer to the ALH84001 enigma, in agreement with a number of previous studies: "The ultrabasic igneous rock, ALH84001, is (…) an extremely poor candidate in which to search for Martian life as it is more likely to show terrestrial contamination signatures than Martian biogenic signatures".
The most recent claims of indigenous fossils in meteorites come from Hoover (2011) and while it is considered now by the medias as some exclusive news1, his work on the topic spans for over a decade (e.g., Hoover et al., 1998). Hoover (2008) claimed: "The CI and CM carbonaceous meteorites contain a large number of complex and embedded coccoidal and filamentous forms consistent in size, shape and morphology with known species of cyanobacteria, sulfur bacteria and other morphologically convergent prokaryotes". In regards of Nagy’s OEs, Hoover (2011) indicated: "(Nagy et al.) failed to recognize a pollen grain and erroneously included an image of it in their original paper. This resulted in their work being discredited". Although the shapes observed by Hoover are likely to be indigenous, the problem with pattern recognition is always the same and the lesson should have been learned by now.
"I fail to find in Dr. Lipman’s experiments any good evidence of the presence of bacteria in the interior of (meteorites) (…) It is very questionable whether all contaminations from the air can be excluded" – Nininger (1933)
"(The claim of bacteria of extraterrestrial origin in meteorites was) received by the layman with philosophical interest and by geologists and bacteriologists with skepticism" – Roy (1935)
If meteorites could contain relics of the past life on their parent body, why not living organisms? Following the panspermia hypothesis, meteorites are potential vectors of life (e.g., Wickramasinghe et al., 2003). The subject goes beyond the scope of the present paper since most arguments are only conjectural. Evidence of living organisms in meteorites has been nevertheless claimed in a few studies, which are worth mentioning. Lipman (1932) stated having found living bacteria in ordinary chondrites (Figure 5). His work was immediately refuted, the most plausible origin for the bacteria being a laboratory contamination (e.g., Nininger, 1933; Roy, 1935). A more recent work is by Geraci et al. (2001), which experiment protocol is basically similar to the one used by Lipman 70 years before. The authors indicate: "A (…) search for the presence of microbes in meteorites shows that (they) are rich in microorganisms, indicating that these already existed in early Earth formation stages (… and these are) found to be not essentially different from present day organisms". Really? How interesting!
"The intense controversy which once surrounded the origin of (CI chondrite) organic matter has subsided. Most authors now agree that this material represents primitive prebiotic matter, not vestiges of extraterrestrial life" – Anders et al. (1973)
"The complex polymer-like organic matter similar to kerogen in the carbonaceous meteorites (…) constitutes an important biomarker" – Hoover (2011)
While microphotographs of pretended life forms appear as dramatic pieces of evidence (Figure 2), conclusions based on morphology alone are insufficient. Carbonaceous meteorites (Figure 6) are known to contain a multitude of complex organic compounds, such as the building blocks of proteins and of DNA (e.g., Anders et al., 1973). Proponents of life in meteorites consider them as strong biomarkers to support their sensational biomorphic findings (Hoover, 2011 and references therein). Mainstream scientists agree however that they are synthesized from non-biological processes, as proven by the Miller-Urey and Fischer-Tropsch experiments (e.g., Anders et al., 1973).
The Martian life scenario is different. To prove their case, McKay et al. (1996) described, in addition to their nanobacteria shape-like features, other finds such as Polycyclic Aromatic Hydrocarbons (PAHs), carbonates and magnetite crystals. However they conclude: "None of these observations is in itself conclusive (…) When they are considered collectively (…), we conclude that they are evidence for primitive life on early Mars". Again, not the most elegant scientific result we might expect.
"Extraordinary claims require extraordinary evidence" – Carl Sagan
Following Occam’s razor, of two hypotheses that lead to the same result, the simplest one is always to be preferred. Thus complex shapes observed in meteorites, be them from asteroids, comets or from the planet Mars, are likely to be mineral concretions of random forms or terrestrial contaminants. However the study of the strange and the unknown has clearly some appeal and research will continue. Although the claim of life in meteorites can be considered at the present time as fringe science, this might change in the future. So now, let’s wait for a sedimentary Martian meteorite7 to fall on Earth and, maybe, find some undeniable proof of alien life, past or present8.
Acknowledgements: I would like to thank Editor Robert Beauford for giving me the opportunity to publish this review in Meteorite magazine as well as Jörn Koblitz for his comments.
|1||Hahn (1879)||I||P||35||Nagy et al. (1963)||I||P|
|2||Hahn (1880)||I||P||36||Anders et al. (1964)||I||O|
|3||Birgham (1881)||I||P||37||Vdovykin (1964)||I||O|
|4||Louisville Courier J. (1881)||I||O||38||Oro & Tornabene (1965)||II||O|
|5||Weinland (1882)||I||P||39||VanLandingham (1965)||I||P|
|6||Anonymous (1882)||I||O||40||Manten (1966)||I||-|
|7||Smith (1882)||I||O||41||Nagy (1966)||I||-|
|8||Vogt (1882)||I||O||42||Urey (1966)||I||-|
|9||Weinland (1882)||I||P||43||Nagy (1967)||I||-|
|10||Kirkpatrick (1912)||I||P||44||VanLandingham et al. (1967)||I||P|
|11||Lipman (1932)||II||P||45||Tan & VanLandingham (1967)||I||?|
|12||Farrell (1933)||II||O||46||Rossignol-Strick & Barghoorn (1971)||I||O|
|13||Nininger (1933)||II||O||47||Nagy (1975)||I||P|
|14||Roy (1935)||II||O||48||McKay et al. (1996)||I||P|
|15||Lipman (1936)||II||P||49||Anders (1996)||I||O|
|16||Roy (1937)||II||O||50||Bradley et al. (1997)||I||O|
|17||Claus & Nagy (1961)||I||P||51||McKay et al. (1997)||I||P|
|18||Anders (1962)||I||O||52||Zhmur et al. (1997)||I||P|
|18||Anders & Fitch (1962)||I||O||53||Hoover et al. (1998a)||I||P|
|20||Briggs & Kitto (1962)||I||-||54||Hoover et al. (1998b)||I||P|
|21||Fitch et al. (1962)||I||O||55||Sears & Kral (1998)||I||O|
|22||Gregory (1962)||I||O||56||Westall et al. (1998)||I||-|
|23||Morrison (1962)||I||P||57||Westall (1999)||I||-|
|24||Mueller (1962)||I||O||58||Steele et al. (2000)||II||O|
|25||Nagy et al. (1962)||I||P||59||Geraci et al. (2001)||II||P|
|26||Nagy & Claus (1962)||I||P||60||Gibson et al. (2001)||I||P|
|27||Palik (1962)||I||P||61||Hoover & Rozanov (2003)||I||P|
|28||Pearson (1962)||I||O||62||Hoover et al. (2004)||I||P|
|29||Staplin (1962)||I||P||63||Hoover (2005)||I||P|
|30||Briggs & Mamikunian (1963)||I||-||64||Hoover (2006)||I||P|
|31||Claus et al. (1963)||I||P||65||Hoover (2008)||I||P|
|32||Fitch & Anders (1963a)||I||O||66||Rozanov (2010)||I||P|
|33||Fitch & Anders (1963b)||I||O||67||Hoover (2011)||I||P|
|34||Mamikunian & Briggs (1963)||I||-|
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1. "Exclusive: NASA Scientist Claims Evidence of Alien Life on Meteorite", FoxNews, published online March 5, 2011.
2. Kuhn’s structure of scientific revolutions consists of three phases: (1) the "pre-paradigm" phase, characterized by several incompatible and incomplete theories, (2) "normal science" in which observations are explained by a consensus and (3) "revolutionary science" if some difficulties emerge and new assumptions are required.
3. "Paleontology remains unique and free of comparison. But since, in reality, nothing is unique in Nature, except Nature itself, the only possible question is to know whether terms of comparison, which probably exist but that we are unaware of, will come to our knowledge or not".
4. Smith’s private meteorite collection was one of the largest in the world and he was regarded in his time as one of the highest authorities in the field of Meteoritics (Mignan, 2011).
5. Kirkpatrick looked at thin slides of a variety of rocks and observed shapes, which reminded him of 2-D sections of Foraminifera.
6. President Clinton Statement Regarding Mars Meteorite Discovery: "(…) Today, rock 84001 speaks to us across all those billions of years and millions of miles. It speaks of the possibility of life (…)", at http://www2.jpl.nasa.gov/snc/clinton.html.
7. If a meteorite of Martian sandstone hit you on the head would you recognize it? by Ashley & Delaney (1999).
8. NASA spacecraft data suggest water flowing on Mars at http://www.nasa.gov/mission_pages/MRO/news/mro20110804.html.