Genesis: The Scientific Quest for Life's Origin

by Robert M. Hazen

  This dramatic contrast provides a metaphor for our own lives. Some people choose the paths of hate, war, intolerance, destruction, and chaos to hasten the triumph of entropy—the dark side of the universe. By contrast, most people use their energies to foster emergence—to build cities, feed the hungry, create art, heal the sick, promote peace, and add to human joy and well-being in countless other ways, both large and small.

  What awesome power each of us holds to do good or ill; a single cutting insult, a single winning smile. Perhaps therein lies life's meaning and value.

  Notes

  PREFACE

  p. xiii It is possible: A significant literature explores the contrasting views of life as a chance event (Monod 1971) versus a cosmic imperative (de Duve 1995a, Morowitz 2002).

  p. xvi James Trefil: Hazen and Trefil (1991), Trefil and Hazen (1992).

  p. xvii “the unfolding of life …”: Morowitz (2002, p. 84).

  p. xvii conference in Modena, Italy: The “Workshop on Life” was held September 3–8, 2000, as one of the satellite meetings before the Millennial World Meeting of University Professors in Rome, September 8–10. The conference proceedings are collected in Pályi et al. (2002).

  PROLOGUE

  p. 1 This idea had received a boost: Corliss et al. (1979, 1981). See Chapter 7 for more details on Jack Corliss's controversial claims.

  p. 2 Morowitz's dense tabulation: The table of water's dielectric constant as a function of temperature and pressure came from Tödheide (1972, Table XI, p. 492). See also Uematsu and Franck (1981), Franck (1987), Shaw et al. (1991), and Franck and Weingartner (1999) for subsequent measurements by the same group at the Institute for Physical Chemistry and Electrochemistry, University of Karlsruhe. In spite of our surprise at seeing these results, experts in petroleum chemistry had long known about water's distinctive changes in properties at elevated temperature and pressure (e.g., Simoneit 1995). Theorist Everett Shock had incorporated these effects into his calculations of hydrothermal reactions relevant to prebiotic chemistry (Shock 1990a, 1990b, 1992a, 1993; Shock et al. 1995). Nevertheless, few researchers in the origin-of-life community had made this connection, and no relevant experiments had been performed at high temperature and pressure.

  p. 2 detailed chemical scenario: Wächtershäuser (1988a, 1990a, 1992). His work is reviewed in Chapters 8 and 15.

  p. 3 His name provided: A perspective on Harold Morowitz's contributions to the founding of astrobiology is provided by Dick and Strick (2004, pp. 61-65).

  p. 4 Hat's pressure lab: The apparatus and its operation is described in Yoder (1950).

  p. 8 “Humpane”: Jack Szostak writes, “It's the normal result to obtain a mess of hundreds of compounds. The central problem of prebiotic chemistry is how to avoid the universal tar of organic chemistry, and channel the chemistry into the products needed for the origin of life.” [Jack Szostak to RMH, 21 August 2004]

  1

  THE MISSING LAW

  p. 11 “It is unlikely …”: J. H. Holland (1998, p. 3).

  p. 11 Two great laws: Von Baeyer (1998) provides a history of the laws of thermodynamics.

  p. 12 The discovery of a dozen: For a review of the principal laws of nature and their discovery, see Hazen and Trefil (1991).

  p. 12 scholars of the late nineteenth century: The history of the idea that science has learned everything of significance appears in Horgan (1996), who defends and amplifies the idiotic claim.

  p. 12 Ilya Prigogine: Prigogine's influential analyses of emergent systems, which he called “dissipative systems,” appears in his books Order Out of Chaos: Man's New Dialogue with Nature (Prigogine 1984) and Exploring Complexity: An Introduction (Nicolis and Prigogine 1989). Of special interest to Prigogine were patterns that arise spontaneously in a shallow pan of boiling water (Bénard cells) and in certain types of slowly reacting chemicals (Belousov–Zhabotinski, or B–Z, systems). These systems, which could be analyzed with mathematical rigor, are representative of a larger class of phenomena in which energy flows through a collection of interacting particles. In the words of Wicken (1987, p. 5), “dissipation through structuring is an evolutionary first principle.”

  p. 13 complex, turbulent convection: The peculiar behavior of boiling water is addressed, for example, in Nicolis and Prigogine (1989, pp. 8-15).

  p. 14 patterns in water and sand: An extensive technical literature analyzes the formation of sand patterning. Of special note are the classic works of Ralph Bagnold (1941, 1988).

  p. 14 understanding such simple systems: Several reviewers question the idea that studies of patterning in simple mechanical systems such as sand can elucidate the behavior of much more complex biological systems. Graham Cairns-Smith writes: “I think that your discussion of emergent systems could do with a more explicit reference to the two main ways in which interestingly complex systems arise in biology—development and evolution. Development is modeled by, say, the Mandelbrot set: an amazing infinitely complex product with a childishly simple specification. And incidentally I don't see any new physical law here, just mathematics.” (G. Cairns-Smith to RMH, 31 August 2004).

  Jack Szostak echoes this opinion: “Part of the problem is the lack of a clear definition or understanding of what we mean by emergent phenomena, which leads to people referring to distinct things with the same term. So, in one sense, phenomena such as vortices or sand ripples are ‘emergent' since they are collective phenomena not exhibited by the individual components of the system. On the other hand, there seem to be different kinds of phenomena one could also call ‘emergent'…. Darwinian evolution emerges from the combination of replicating informational polymers and compartmentalization.” [Jack Szostak to RMH, 21 August 2004] In other words, some scientists argue that emergent systems that become complex through a competitive selection process are fundamentally different from those that obey simple rules of interaction.

  I'm more inclined to think that all emergent systems, whether shifting sand dunes or biological evolution, may ultimately be modeled based on a small set of “selection rules” reducible to mathematical statements. Ultimately, evolution through competitive selection represents simply another (though admittedly more elaborate) way that systems tend toward the most efficient way to dissipate energy.

  p. 15 A small band of scientists: The Santa Fe Institute and its studies in emergence are discussed in Waldrop (1992) and Regis (2003).

  p. 15 John Holland: Holland's influential works include Hidden Order (J. H. Holland 1995) and Emergence: From Chaos to Order (J. H. Holland 1998).

  p. 15 BOIDS: This program is available at www.red3d.com/cwr/boids. The program tracks the flocking behavior of a hundred or so “BOIDS,” each of which moves according to three rules: separation to avoid crowding flockmates, alignment to follow the flock's average direction, and cohesion to steer toward the average position of flockmates.

  p. 15 Physicist Stephen Wolfram: Wolfram (2002).

  p. 16 Danish physicist Per Bak: Bak's most accessible writings are found in his popular book, How Nature Works: The Science of Self-Organized Criticality (Bak 1996).

  p. 16 Santa Fe theorist Stuart Kauffman: Kauffman (1993).

  p. 16 Nobel Laureate Murray Gell-Mann: Gell-Mann and Tsallis (2004). Ideas of non-extensive entropy and related definitions of complexity are provided by Lopez-Ruiz et al. (1995), Shiner et al. (1999), Gell-Mann and Lloyd (2004), Latora and Marchiori (2004), Plastino et al. (2004). See also Gell-Mann (1994, 1995).

  p. 17 fossil-rich hundred-foot-tall cliffs: The Miocene formations of Calvert County, Maryland, have been a Mecca for fossil collectors for two centuries. Details of the geology and paleontology are recorded in W. B. Clark (1904).

  p. 17 Factor 1: The relationship between concentration of agents and complexity has the qualitative form of the so-called error function. This function begins at zero complexity for low concentrations of agents. As the concentration rises, it reaches some critical value, and complexity begins to rise. Eventually, at a higher concentration of
agents, the system's complexity achieves a maximum value.

  p. 17 The relationship between the concentration of interacting agents in a system (N) and the complexity of the system (C) has the qualitative form of the error function. At low N, no emergent structures arise, but as N increases, so does C, to an upper limit.

  p. 19 One ant species: Camazine et al. (2001, pp. 256-283). [Also E. O. Wilson to RMH, 9 April 2004; B. Fisher to RMH, 5 May 2004; C. W. Rettenmeyer to RMH, 12 May 2004]

  p. 19 Studies of termite colonies: Solé and Goodwin (2000, p. 151).

  p. 19 spiral arm structure: The formation of spiral arms requires “a central mass and a velocity large enough to produce a significant shear…. You also need time for the patterns to be established. The low mass objects don't survive long enough.” [Vera Rubin to RMH, 7 April 2004]

  p. 19 Factor 2: I suspect that one of the principal difficulties in quantifying emergent complexity is related to the varied ways that agents may be interconnected. The shifting interactions by immediate contacts of adjacent sand grains are not easily equated to the persistent chemical markers of moving ants or the elaborate networks of variable impulses that connect neurons. Nor are any of these examples exactly analogous to the interactions of molecules necessary for the origin of life.

  p. 19 A rounded grain: Bagnold (1941, p. 85).

  p. 20 The conscious brain: See, for example, Johnson (2001).

  p. 20 Factor 3: The relationship between energy flow and complexity bears a qualitative similarity to a bell-shaped curve. At low energy flux, no patterning occurs and the complexity is zero. At some minimum energy flux, pattern formation begins and complexity quickly achieves a maximum value. Above a critical value, however, the energy flux is too great and the emergent patterns begin to disperse.

  p. 20 no pattern can emerge: Physicist Paul C. W. Davies examines this issue from the standpoint of gravity, which is the initial and ultimate source of ordering in the universe (Davies 1999, p. 64).

  p. 21 Factor 4: Cycling may be important in origin-of-life scenarios, but the imposition of any kind of cycle adds at least two new variables to an experiment. In the case of a temperature cycle, for example, one must select the duration of the cycle (typically on the order of minutes to days) and the two end-point temperatures. It may also be desirable to control the rate of temperature change (gradual versus abrupt), which adds additional variables. Needless to say, such added variables complicate an experiment and its interpretation.

  p. 22 amazing stone circles: Kessler and Werner (2003).

  p. 22 E(t): This expression indicates both the flow of energy through the system, E, and the cycling of that energy, which is a function of time, t.

  p. 20 The relationship between the energy flowing through a system of interacting agents (E) and the complexity of the system (C) has the form of a critical curve. At low E, no emergent structures arise, but as E increases above a critical value, structure rapidly appears and C increases. At high E, however, patterns are destroyed.

  2

  WHAT IS LIFE?

  p. 25 “I know it when I see it.”: Associate Justice Potter Stewart of the U.S. Supreme Court made this statement as part of his concurring opinion in the 6-3 ruling that overturned the ban on pornographic films, June 22, 1964: “I shall not today attempt further to define the kinds of material … but I know it when I see it.”

  p. 25 A recent origin-of-life text: Lahav (1999, pp. 117-121).

  p. 25 “What is life?”: Pályi et al. (2002).

  p. 26 “top-down” approach: Jack Szostak states “I don't think the earliest fossils tell us anything about life's earliest chemistry. These fossils are all quite sophisticated organisms.” [Jack Szostak to RMH, 21 August 2004] Gustaf Arrhenius echoes this view: “The most ‘primitive' organisms that we can lay our hands on are already hopelessly sophisticated biochemically; they are more like us than anything original.” [Gustaf Arrhenius to RMH, 23 December 2004]

  Indeed, a principal discovery of Precambrian paleontology is that modern-type cells have populated Earth for at least 80 percent of its history. The window for life's emergence is correspondingly brief.

  p. 27 “working definition”: See Joyce (1994).

  p. 28 thin molecular coating: The idea of “flat life” has been explored by Wächtershäuser (1988a, 1992) among others. For more details see Chapter 15.

  p. 28 Claude Lévi-Strauss: Lévi-Strauss, the founder of structural anthropology, argued that all humans share similar patterns of thought. His analysis of myths from various cultures, for example, stresses the common reliance on dichotomies in dealing with our role in the cosmos. See Lévi-Strauss (1969, 1978).

  p. 28 neptunists, … plutonists: This debate, as well as that between catastrophists and uniformitarianists, was fueled by a conflict between scientific and religious interpretation of natural history. See, for example, Rudwick (1976) and Laudan (1987).

  p. 29 “The unfolding of life …”: Morowitz (2002, p. 84). Several other authors, notably Christian de Duve (1995a), have adopted a similar framework of sequential episodes in life's emergence. See also Davies (1999), Maynard-Smith and Szathmáry (1999), and Bada (2004).

  p. 30 semantic question: For a fuller explanation of these ideas, see Hazen (2002). Jack Szostak writes: “I used to think of the transition from non-life to life as a discontinuous event marked by the sudden start-up of Darwinian evolution. But as I've started to work on more aspects of the problem and look at it in more detail, what I see is more of a series of smaller steps.” [Jack Szostak to RMH, 7 September 2004]

  p. 30 philosopher Carol Cleland: Cleland and Chyba (2002).

  p. 31 Saturn's recently visited moon: Evidence for volatiles at Titan's surface are presented by Lunine et al. (1999), Campbell et al. (2003), Griffith et al. (2003), and Lorenz et al. (2003). For the latest results from the Huygen's probe, see: http://saturn.jpl.nasa.gov/home/index.cfm.

  3

  LOOKING FOR LIFE

  p. 33 “Scientists turn reckless …”: Lightman (1993, p. 41).

  p. 33 meteorite from Mars: For an overview of Martian meteorites and their identification see McSween (1994). Goldsmith (1997) provides a popular account of the Allan Hills controversy.

  p. 33 Theorists maintained: Calculations by Jay Melosh and co-workers of Caltech (Melosh 1988, 1993; Head et al. 2002) reveal that, although a lot of material is vaporized in large planetary impacts, rocks at the periphery of the impact site may be hurled unscathed off the surface into space. Such a process is thought to have transferred material from Mars to Earth. Similar impacts on Earth have certainly blasted terrestrial rocks into space, though the transfer of Earth rocks to Mars is much more difficult because of two gravitational impediments: Mars is much farther from the Sun, and it has a smaller gravitational field.

  An alternative intriguing hypothesis is that cellular life may have arisen very early in Earth's history, and that some of these microbes may have been blasted into space by large asteroid impacts. Even if a subsequent globe-sterilizing giant impact occurred, life could have been reseeded by an Earth meteorite.

  p. 33 Allan Hills region of Antarctica: The ice deserts of Antarctica are ideal hunting grounds for meteorites. These clean, dry regions persist for thousands of years, and dark-colored meteorites stand out starkly against their white surface. Scientists in helicopters or on snowmobiles can collect dozens of pristine specimens in a short field season. These areas are also valuable because they provide a relatively unbiased inventory of meteorite types. In more temperate regions, stony meteorites often blend into the surrounding rocky landscape, where they just weather away; only the resistant iron meteorites stand out, so they have always constituted the majority of meteorite finds. Antarctic collecting areas reveal that stony meteorites are much more common. For an informative visual overview, see the Web site of ANSMET, the Antarctic Search for Meteorites program, cosponsored by NASA and the Smithsonian Institution: http://geology.cwru.edu/~ansmet/.

  p. 34 A team of biologists: D.
S. McKay et al. (1996).

  p. 34 On August 7, 1996: Dick and Strick (2004, pp. 179-201) provide a detailed history of this incident. The timing of the prepublication press conference was unusual because Science nearly always holds up press announcements until the afternoon before an article's publication date (in this case, Friday, August 16). However, the important story leaked more than a week before publication because, according to Goldsmith (1997), a top official in the Clinton administration told a prostitute, who, in turn, sold the information to a tabloid. Science, in agreement with the authors and NASA, therefore made the article available on their Web site eight days before print publication. [R. Brooks Hanson to RMH, 15 April 2004]

  p. 35 “Although there are alternative …”: In subsequent years, team leader David McKay elaborated on this argument by attempting to calculate the degree to which several weak lines of evidence coalesce to produce a strong probability when taken together. See, for example, D. S. McKay et al. (2002).

  p. 36 aggressively challenged: Science received dozens of letters to the editor and technical comments challenging aspects of the D. S. McKay et al. (1996) paper. Of these submissions, three letters were published in the September 20, 1996, issue and a technical comment appeared in the December 20, 1996, issue.

  p. 36 Point number one: The most abundant organic molecules in the Allan Hills meteorite are polycyclic aromatic hydrocarbons, or PAHs, which are a ubiquitous component of carbon-rich meteorites as well as of soot, diesel exhaust, and myriad industrial processes. See, for example, Allamandola et al. (1985, 1989).