p. 36 Point two: An extensive and often contradictory literature has arisen around the question of Allan Hills' carbonate origins, particularly the temperature of their formation. See, for example, Harvey and McSween (1996) and Scott et al. (1997).
p. 36 Skeptical experts: The distinctive magnetite crystals, which possess a purity, crystal form, magnetic structure, and chainlike distribution characteristic of Earth microbes, provide the greatest remaining hope for proponents of the Martian life hypothesis. No plausible nonbiological explanation for these features has yet been proposed.
p. 36 purported fossil microbes are too small: Morowitz (1996). See also Schopf (1999, pp. 317-320).
p. 36 The story became even more confused: Steele et al. (2000a, 2000b).
p. 37 J. William Schopf: Schopf (1999, pp. 304-325).
p. 37 “I was like Daniel …”: Schopf (1999, p. 309).
p. 37 “The minerals can't prove it …”: Schopf (1999, p. 316).
p. 37 “There are fine lines …”: Schopf (1999, p. 325).
p. 38 Such catastrophic events: Maher and Stevenson (1988), Sleep et al. (1989). Estimates of the rate and magnitude of large impacts come largely from statistical studies of the sizes and ages of lunar craters.
p. 38 We don't know: Jack Szostak notes that “some people now think that a Hadean origin is likely, and that totally sterilizing impacts may have ended earlier than previously thought. And even following a sterilizing event, cells blasted into space might have reseeded the Earth.” [Jack Szostak to RMH, 21 August 2004]
p. 38 oldest known fossilized penis: The original report was Siveter et al. (2003). The story appeared in USA Today on December 12, 2003. There was much scientific interest in this discovery because highly varied penile appendages constitute the basis for classifying the group of crustaceans called copepods.
p. 39 Apex Chert: Schopf (1993). Apex Chert fossils had been reported earlier, for example in Awramik et al. (1983) and in Schopf and Packer (1987). The 1993 paper was the first to enumerate 11 species of ancient Apex microbes.
Bruce Runnegar writes, “Although it is more dramatic to highlight the 1993 announcement of Schopf's discovery of Earth's oldest fossils, one should be aware that the same kind of announcement came out of the Schopf lab in the late 1970s from rocks of about the same age in the North Pole area of Western Australia. These were discovered by Stan Awramik at UC Santa Barbara and some people still believe these are the ‘best of the oldest.' However, there are problems with these as well.” [B. Runnegar to RMH, 4 March 2005]
p. 39 world's leading experts: Among Schopf's most noted works is the volume he edited on Precambrian paleontology, Earth's Earliest Biosphere: Its Origin and Evolution (Schopf 1983). In that work he presents his own review of the earliest known microbes (Schopf and Walter 1983).
p. 39 UCLA protocol: Schopf (1999, pp. 71-100).
p. 40 Bonnie Packer: [James Strick to RMH, 1 September 2004] The initial publication was Schopf and Packer (1987). Packer was the first person to observe unusual microstructures in Apex Chert samples.
p. 40 Controversy erupted: Brasier et al. (2002). An account of the controversy is presented by Knoll (2003, pp. 60-65).
p. 41 Further study: The geology of the Apex Chert site is still a matter of considerable debate. Brasier and Australian geologist John Lindsey highlighted these concerns at subsequent seminars, including a joint presentation at the Carnegie Institution's Geophysical Laboratory on July 1, 2002. For opposing viewpoints see Lindsay et al. (2003a, 2003b), Brasier et al. (2004), and Schopf et al. (2002).
p. 41 “We reinterpret …”: Brasier et al. (2002, p. 77).
p. 41 a rebuttal: Schopf et al. (2002).
p. 42 “News and Views”: Gee (2002). See also Dalton (2002).
p. 42 This debate: The Astrobiology Science Conference 2002 (the second such meeting) took place from April 7 to April 11 at NASA Ames Research Center. Abstracts of the meeting are available at http://web99.arc.nasa.gov/abscon2.
p. 42 Schopf spoke: The original NASA videotape of this debate was provided by Lynn Rothschild of the NASA Ames Research Center. A description of the session, including a photograph of Schopf peering at Brasier, appears in Dalton (2002).
p. 42 soften his assertion: While Schopf did back off his claim of fossil cyanobacteria in the lecture, he repeated the arguments in a later article, claiming that “Several of the Apex species seem almost indistinguishable from living cyanobacteria.” (Schopf 2002, p. 173).
p. 43 Raman spectroscopic data: see also Pasteris and Wopenka (2003).
p. 44 equally difficult to disprove: Scientists are taught to evaluate alternative hypotheses based on Occam's razor: Accept the hypothesis that requires the fewest assumptions. But how does one choose between evidence for and against the existence of ancient microbial life, or life in a Martian meteorite, for that matter? If your philosophical bias is that life emerges rapidly and is thus ubiquitous in the universe, then any tantalizing sign of life—carbon smudges or scrappy fossils—will provide encouraging supporting evidence. If you think life rare or unique, then the tenuous character of the same data will prevail. Consequently, to prove either case—that an ancient rock does or does not hold evidence for life—is extraordinarily difficult. Brasier et al. were successful in casting doubt on Schopf's claims of microbial fossils, but they came nowhere close to disproving that the carbon residues were biogenic in origin.
p. 44 Meanwhile, paleontologists: Claims of 3.5-billion-year-old microfossils from South Africa were published by Furnes et al. (2004).
4
EARTH'S SMALLEST FOSSILS
p. 47 “Millions of brutal years …”: Simpson (2003, p. 72).
p. 48 Andrew Knoll: The “Origin of Life” Gordon Research Conference took place from July 27 to 31, 1997. Two of Knoll's reviews (Knoll 1996, 2003) provide accessible overviews of Earth's earliest fossil cells.
p. 50 severe analytical challenge: Simultaneously with our efforts, Derek Briggs and co-workers at the University of Bristol produced similar electron microprobe maps of fossils (Orr et al. 1998).
p. 51 Rhynie, Scotland: The fossils of the Rhynie Chert are documented in the classic studies of Kidston and Lang (1917-1921).
p. 51 Kevin Boyce: Boyce's analytical work on Devonian plant fossils is described in Boyce et al. (2001, 2003).
p. 54 Analytical studies: Schidlowski et al. (1983), Schidlowski (1988).
p. 54 mammoth bones: Koch (1998).
p. 54 fossil coal: McRae et al. (1999).
p. 54 Burgess Shale: Butterfield (1990) reports bulk isotopic values of approximately -27 for the Burgess Shale. The classic 525-million-year-old Burgess Shale deposits of British Columbia preserve a diverse soft-bodied fauna in exquisite detail. These fossil forms are vividly described in Gould (1989).
p. 55 Values as low as -50: The distribution of ancient carbon isotope values has been tabulated, for example, by Schidlowski et al. (1983) and H. D. Holland (1997).
p. 55 Walter's work: See, for example, Walter et al. (1972), Walter (1976, 1983).
p. 55 “It's Strelley Pool Chert …”: The age and geological setting of the Strelley Pool Chert has been described by C. P. Marshall et al. (2004) and Allwood et al. (2004).
p. 59 Earth's Oldest “Fossils”?: Bruce Runnegar writes, “I would prefer to title this section “Earth's Oldest Life” …. Fossils have been reported, even named (Isuasphaera), from the Isua rocks by Hans-Dieter Pflug but no one accepts them as remains of living organisms. What is being discussed here is only, at best, ‘isotopic fossils.'” [B. Runnegar to RMH, 4 March 2005]
p. 59 oldest known rocks: Moorbath et al. (1986), Nutman et al. (1996, 1997).
p. 59 Stephen J. Mojzsis: Mojzsis et al. (1994, 1996). See also E. K. Wilson (1996) and H. D. Holland (1997) for analyses of the report.
Bruce Runnegar writes, “This is a dramatic way to present the discovery, but light carbon had been reported from the Isua rocks since the 1960s, I believe. Manfred Schidlowski, in particular, pu
blished many articles arguing that Isua provided evidence for life on Earth prior to the Mojzsis et al. article in Nature.” [B. Runnegar to RMH, 4 March 2005]
p. 59 Akilia rocks posed problems: Fedo and Whitehouse (2002). See also Whitehouse (2000), Lepland et al. (2005). Kerr (2002a), Simpson (2003), and Dick and Strick (2004) provide analyses of the controversy. Aivo Lepland of the Geological Survey of Norway, who spent five years attempting to duplicate Mojzsis's results without success, has raised additional questions about the validity of the results. As a consequence, Gustaf Arrhenius, a coauthor on the 1996 paper, has distanced himself from the original conclusions (Lepland et al. 2005). “I think there must have been a mix-up of the samples,” he says (Dalton 2004, p. 688).
More convincing evidence for ancient biogenic carbon is provided by Rosing (1999), who reported negative carbon isotope values from 3.7-billion-year-old sediments from the Isua region of Greenland. [Gustaf Arrhenius to RMH, 8 August 2004]
p. 60 plausible explanations: See, for example, van Zuilen et al. (2002). Negative carbon isotope fractionation is known to occur inorganically, for example, at high temperature, when iron carbonate breaks down to graphite plus iron oxide.
5
IDIOSYNCRASIES
p. 61 “The ability of …”: Lahav (1999, p. 64).
p. 62 industrial chemists: The standard industrial process for synthesizing chainlike carbon molecules is called Fisher–Tropsch synthesis.
p. 62 Life builds hydrocarbons: The biochemical process for synthesizing chainlike molecules is detailed in Lehninger et al. (1993, pp. 642-649).
p. 62 produced abundantly: Allamandola et al. (1985, 1989, 1997), Allamandola and Hudgins (2003). PAHs are identified by their distinctive infrared emission spectra.
p. 63 4-ring molecules called sterols: Lehninger et al. (1993, pp. 669-674).
p. 64 A crucial requirement: For a survey of molecular biomarkers see K. E. Peters and Moldowan (1993).
p. 65 The Hopane Story: Hopanes were discovered by Guy Ourisson of the Université Louis Pasteur and co-workers (Rohmer et al. 1979, Ourisson and Albrecht 1992, Ourisson and Rohmer 1992, Tritz et al. 1999). The identification of hopane-related compounds in ancient Australian rocks is reported by Summons et al. (1999), with a commentary by Knoll (1999). For related work on ancient biomolecules from Australian rocks, see Summons and Walter (1990), Summons et al. (1996), and Buick et al. (1998).
p. 65 In 1999: Brocks et al. (1999).
p. 67 2-methylhopanoid: Bruce Runnegar writes, “As all extant cyanobacteria, so far as is known, make 2-methylhopanes, the time of origin of this innovation may significantly predate the origin of the last common ancestor of living cyanobacteria.” [B. Runnegar to RMH, 4 March 2005]
p. 67 Biosignatures and Abiosignatures: This section is adapted from Hazen et al. (2002).
p. 70 biomolecular fragment: See the Web site www.biocyc.org for a database that illustrates many of the hundreds of common small molecules found in cells.
p. 72 microbial corrosion: Steele et al. (1994).
p. 72 Steelie's assignment: Steele et al. (2000a, 2000b).
p. 73 the term “astrobiology”: Dick and Strick (2004, p. 205).
p. 73 Enspel, Germany: Toporski et al. (2002).
p. 75 MASSE: For information on the project development visit http://astrobiology.ciw.edu/main.php. The group proposes to look for morphological as well as chemical evidence (Cady et al. 2003). For an overview of Andrew Steele's life-detection experiments, see Whitfield (2004). The difficulties of detecting life remotely on Mars are underscored by the ambiguous results of the Viking mission in the 1970s (Levin and Straat 1976, 1981).
INTERLUDE—GOD IN THE GAPS
p. 77 Darwinists rarely mention the whale: This quote comes from Alan Haywood's (1985) Creation and Evolution. These sentiments are echoed in Duane T. Gish's (1985) Evolution: The Challenge of the Fossil Record, in which he says: “There are simply no transitional forms in the fossil record between marine mammals and their supposed land mammal ancestors…. It is quite entertaining, starting with cows, pigs, or buffaloes, to attempt to visualize what the intermediates may have looked like. Starting with a cow, one could even imagine one line of descent which prematurely became extinct, due to what might be called an “udder failure” (pp. 78-79).
p. 78 35-million-year-old Basilosaurus: Gingerich et al. (1990).
p. 78 Rodhocetus: Gingerich et al. (1994).
p. 78 Ambulocetus: Thewissen et al. (1994).
p. 78 new proto-whale species: Thewissen et al. (2001). See also the companion commentary by Muizon (2001).
p. 80 Michael Behe and William Dembski: Behe (1996) and Dembski (1999, 2004). For opposing views see, for example, Pennock (2002) and Forrest and Gross (2004).
p. 80 deeper problem: K. R. Miller (1999) presents a compelling case against the idea of “God in the gaps.”
6
STANLEY MILLER'S SPARK OF GENIUS
p. 83 “The idea that …”: S. L. Miller (1953, p. 528). Günter Wächtershäuser writes: “Oparin, in fact, never suggested such an atmosphere, as can be verified by reading his books of 1924 and 1938” [Günter Wächtershäuser to RMH, 24 June 2004]
p. 83 spontaneous generation: The complex story of spontaneous generation, a theory that persisted throughout the nineteenth century, is described by Farley (1977), Fry (2000), and Strick (2000).
p. 83 seventeenth-century invention: The invention of the microscope was to biology what the invention of the telescope was to astronomy. Discoveries of microorganisms, the cell, and even smaller internal cellular structures transformed biology. See Ford (1985).
p. 84 Lazzaro Spallanzani: See, for example, Dolman (1975) for a biographical account and bibliographic citations.
p. 84 Englishman John Needham: Westbrook (1974) provides a biographical sketch and bibliographic sources.
p. 84 Louis Pasteur: Pasteur's motivation for these experiments in spontaneous generation is explored in Geison (1974), who also provides extensive bibliographic citations.
p. 85 In 1871, Charles Darwin: The letter is item 7471 in the Darwin online database: http://darwin.lib.cam.ac.uk. For a discussion of Darwin's views, see Fry (2000, pp. 54-57).
p. 85 life requires liquid water: See, however, the intriguing speculations of Steven Benner of the University of Florida (Benner 2002), who warns against “Earth-o-centrism.” Perhaps, he notes, some other medium, such as liquid ammonia, might foster an alternative biochemistry on other worlds. Exploring this idea further, The Royal Society of London held a conference on “The Molecular Basis of Life: Is Life Possible Without Water?” December 3–4, 2003 (Ball 2004).
p. 86 Alexander Oparin: Oparin's 1924 work first appeared in English in 1938 (Oparin 1924, 1938), but it was not widely available to English-speaking audiences until Bernal (1967), which included a translation. According to Günter Wächtershäuser, the rarely cited book Mechanische-Physiologische Theorie der Abstammungslehre by Swiss botanist Carl Wilhelm von Nägeli (1884) includes a prescient description of “the origin of life in a broth of emerging, growing and evolving protein particles.” [Günter Wächtershäuser to RMH, 24 June 2004]
p. 86 “primordial soup”: This phrase follows J. B. S. Haldane's (1929) description of the early ocean as achieving “the consistency of hot dilute soup” (p. 247).
p. 86 J. B. S. Haldane: Haldane's choice of The Rationalist Annual, a periodical largely devoted to the promotion of rationalism and secular education, may seem an odd one for a theoretical paper on origin-of-life chemistry. Cooke (2004) chronicles the colorful history of the Rationalist Press Association, including Haldane's participation.
p. 87 chemist Harold Urey: Urey, a scientist of unusual breadth, won the 1934 Nobel Prize in chemistry for his discovery of deuterium, the heavy isotope of hydrogen and the essential component of “heavy water.” He was also an authority on Earth's primitive atmosphere (Urey 1951, 1952), which led to his speculations about the prebiotic formation of organic compounds.
p
. 87 Jeffrey Bada: Wills and Bada (2000).
p. 87 Scientists revere simple: Miller's original article (S. L. Miller 1953) contains a rather sketchy outline of the experiment. Additional details are provided by S. L. Miller (1955) and Wills and Bada (2000).
p. 90 mid-February: Wills and Bada (2000, p. 47) quote Stanley Miller's recollection of a mid-December 1953 submission. However, records in the Harold Clayton Urey papers (Scripps Institution of Oceanography Archives) include a manuscript receipt from Science dated February 16, 1953. [Antonio Lazcano to RMH, 30 August 2004; Jeffrey Bada to RMH, 1 September 2004]
p. 90 Miller's first publication: S. L. Miller (1953). The New York Times article, “Life and a glass Earth,” appeared on May 17, 1953, page E10.
p. 90 The Miller–Urey experiment: Historical perspectives are provided by Wills and Bada (2000) and Bada and Lazcano (2003).
While Miller has received widespread acclaim for his experiment, some scientists and historians are less convinced of the originality of the Miller–Urey research. Similar experiments were conducted decades earlier by the German chemist Walter Löb (1906, 1914), who employed similar apparatus and also succeeded in synthesizing the amino acid glycine (see Mojzsis et al. 1998). Löb's research, however, was not designed to probe the chemistry of life's origins, nor was it meant to mimic prebiotic environments.
p. 90 Independent confirmation: Miller's experiments were repeated first by Hough and Rogers (1956) and Abelson (1956).
p. 90 Walter Löb: Löb (1906, 1914). Gustaf Arrhenius decries the lack of credit given to Löb. He states that the reverence accorded to the Chicago work is “an American myth originally based on cultural and linguistic ignorance, later on unwillingness to acknowledge the original work.” [Gustaf Arrhenius to RMH, 26 December 2004] In addition, Löb died at a relatively early age and was thus unable to promote his findings.
p. 91 John Oró: Oró (1960, 1961a). Rensselaer Polytechnic Institute chemist James Ferris and co-workers elaborated on the role of HCN in prebiotic chemistry (Ferris et al. 1978).
Genesis: The Scientific Quest for Life's Origin Page 29