Metadata of the Chapter That Ill Be Visuali Ed Online

!"#$%$#$&'(&#)"&*)$+#",&#)$#&-.//&0"&1.23$/.4"%&'5/.5"

!"#$%&'()*%+& ,'*-.'/*#+(0.1$ !.$2'*3"%(4&#' 5677 !.$2'*3"%(8.+/&' 0$'*93&':;&'+#3(<&'+*9(8&*/&+=&'3 !.''&C$.9/*93(D1%".' >#-*+2(?#-& 6$4*$5' ,#'%*@+& A*B&9(?#-& 75#'5.' 01EE*F G*B*C*.9 H'3#9*I#%*.9 J9*B&'C*/#/(?#@*.9#+(D1%K9.-#(/&(LMF*@.(NJ?DLOP(!/Q J9*B&'C*%#'*# D//'&CC L&F*@.(GQ>P(L&F*@. R-#*+ #+#'S@*&9@*#CQ19#-Q-F Comp. by: DMuthuKumar Stage: Galleys Chapter No.: 1275 Title Name: EAB Page Number: 0 Date:28/10/10 Time:11:12:50

1 P

argued in 1929 that the origin of life had been preceded 38 2 Primordial Soup by the synthesis of organic compounds. Based on experi- 39 ments by E. C. C. Baly, an English chemist who had 40 3 ANTONIO LAZCANO reported the formation of amino acids and sugars as 41

4 Universidad Nacional Auto´noma de Me´xico (UNAM), a result of the UV irradiation of a solution of CO2 in 42 5 Cd. Universitaria, Mexico D.F, Mexico water, Haldane suggested that the absence of oxygen in 43

a CO2-rich primitive atmosphere led to the synthesis of 44 organic compounds and their accumulation in the prim- 45 6 Synonyms itive waters of the Earth, which he wrote had “the consis- 46 7 Prebiotic soup; Primitive broth tency of hot dilute soup.” The discovery of phages led 47 Haldane to argue that viruses represented an intermediate 48 8 Keywords step in the transition from the prebiotic broth to the first 49 9 Abiotic organic synthesis, Darwin’s warm little pond, heterotrophic cells (Farley 1977; Lazcano 2010a). 50 10 Oparin–Haldane, origin of life, primordial heterotrophs A Darwinian Warm Little Pond 51 11 Definition In 1871, Charles Darwin mailed a letter to his close friend 52 12 The primordial soup is a generic term that describes the Joseph Dalton Hooker in which he mentioned Pasteur’s 53 13 aqueous solution of organic compounds that accumulated work on the absence of spontaneous generation, and 54 14 in primitive water bodies of the early Earth as a result of added that “It is often said that all the conditions for the 55 15 endogenous abiotic syntheses and the extraterrestrial first production of a living organism are now present, 56 16 delivery by cometary and meteoritic collisions, and from which could ever have been present. But if (and oh what 57 17 which it is assumed that the first living systems evolved. a big if) we could conceive in some warm little pond with 58 all sorts of ammonia and phosphoric salts,–light, heat, 59 18 Overview electricity &c. present, that a protein compound was 60 19 The term “primordial soup” and its synonyms are linked chemically formed, ready to undergo still more complex 61 20 to the proposal of the heterotrophic theory of the origin of changes, at the present day such matter would be instantly 62 21 life, which was suggested independently in the 1920s by devoured, or absorbed, which would not have been the 63 22 Alexandr I. Oparin, John B. S. Haldane, and few others. case before living creatures were formed.” 64 23 Based on the simplicity and ubiquity of fermentative reac- However, the “hot dilute soup” concept formulated by 65 24 tions, Oparin and Haldane proposed that the first organ- Haldane developed independently of Darwin’s warm little 66 25 isms must have been heterotrophic bacteria that could not pond. During the first part of the twentieth century, most 67 26 make their own food but obtained organic material pre- authors assumed, at least implicitly, that the origin of life 68 27 sent in the primitive milieu. In order to support his pro- had taken place in an aqueous environment. When Wins- 69 28 posal, Oparin appealed not only to astronomical low Herschel discussed the consistency of colloids, which 70 29 observations that had shown that hydrocarbons and by then were assumed to explain many of the properties of 71 30 other organic material were present in meteorites and protoplasm (Podolsky 1996), he wrote that “How many 72 31 cometary nuclei, but also to the nineteenth century exper- factors determine consistency is a matter of controversy, 73 32 imental syntheses of organic molecules by Wohler, but the colloquial meaning of the word is well understood 74 33 Butlerow, and Mendeleyeev, among others (Lazcano and may be illustrated by the description, from a recent 75 34 2010a). novel, of ‘Flanders mud after a thaw’. As the flow 76 35 Similar ideas were being developed independently at increased, the side of the trenches began to fall in; the 77 36 the same time by other researchers. Like Oparin, the earth thus mixed with the water thickened it to 78 37 British biochemist and geneticist John B. S. Haldane

Muriel Gargaud (ed.), Encyclopedia of Astrobiology, DOI 10.1007/978-3-642-11274-4, # Springer-Verlag Berlin Heidelberg 2011 Comp. by: DMuthuKumar Stage: Galleys Chapter No.: 1275 Title Name: EAB Page Number: 0 Date:28/10/10 Time:11:12:50

2 P Primordial Soup

79 a consistency which might be liked to a very rich soup” substantial yield. The ▶ Miller–Urey experiment marked 129 80 (Herschel 1926). not only a new epoch in the study of the origin of life but 130 81 There is nothing that suggests that Herschel, Haldane, also led to surprisingly rapid acceptance by the public of 131 82 or Oparin had read Darwin’s remarks about the origin of both the heterotrophic theory and the idea of a primitive 132 83 life and the warm little pond. Darwin’s letter was included soup (Bada and Lazcano 2003). 133 84 by his son Francis as a footnote in the 3rd volume of his 85 father’s book Life and Letters published in 1887, but it was Was There a Primitive Soup? 134 86 not until 1969 that Melvin Calvin published it in his book Although it is generally agreed that free oxygen was absent 135 87 on chemical evolution (Calvin 1969), calling it to the from the primitive Earth, there is no agreement on the 136 88 attention of the origins-of-life community (Pereto´ et al. composition of the primitive atmosphere; opinions vary 137

89 2009). By then, the concept of a prebiotic broth and from strongly reducing (CH4 + NH3 +H2O, or CO2 +H2 138 90 a heterotrophic origin of life, which had been developed +N2 +H2O) to neutral (CO2 +N2 +H2O). In general, 139 91 by Oparin and Haldane within the framework of an evo- nonreducing atmospheric models were favored by plane- 140 92 lutionary perspective, had gained considerable support tary scientists, while prebiotic chemists leant toward more 141 93 from the development of a multidisciplinary research reducing conditions, under which the abiotic syntheses of 142 94 program on the emergence of the first living systems. amino acids, purines, pyrimidines, and other compounds 143 are very efficient. Prior to the recognition that organic 144 95 Defining the Soup compounds can be synthesized under the neutral condi- 145 96 The proposal that life was the outcome of prebiotic chem- tions of a CO2-rich atmosphere (Cleaves et al. 2008), the 146 97 istry and the evolution of precellular systems was further difficulties involved with the endogenous synthesis of 147 98 elaborated and refined by Oparin in a more extensive book amino acids and nucleobases have led to the development 148 99 that was published in Russian in 1936 and translated 2 of alternatives. 149 100 years later into English (Oparin 1938). In his new book, In the early 1990s, Chyba and Sagan reanalyzed Oro´’s 150 101 Oparin suggested that the ▶ primitive Earth was a highly 1961 proposal on the role of cometary nuclei as sources of 151 102 reducing milieu in which iron carbides of geological origin volatiles to the primitive Earth, and based on the chemical 152 103 would react with steam to form hydrocarbons. Their oxi- composition of carbonaceous meteorites proposed that 153 104 dation would yield alcohols, ketones, aldehydes, etc., that the exogenous delivery of organic matter by asteroids, 154 105 would then react with ammonia to form amines, amides, comets, and interplanetary dust particles could have 155 106 and ammonium salts. The resulting protein-like com- played a significant role in forming the primitive soup, 156 107 pounds and other molecules would form a hot dilute by seeding the early Earth with the compounds necessary 157 108 soup, in which they would aggregate to form colloidal for the origin of life (Chyba and Sagan 1992). On the other 158 109 systems such as coacervates, from which the first hetero- hand, proponents of an autotrophic theory of the origin of 159 110 trophic microbes evolved. Others, like John D. Bernal life (Wa¨chtersha¨user 1988) have dismissed the role of 160 111 argued that the compounds were concentrated on the ▶ prebiotic synthesis and accumulation of organic com- 161

112 surfaces of minerals like clays, where the higher density pounds. However, since the FeS/H2S combination is 162 113 would favor their chemical interaction (Bernal 1944). a strong reducing agent that has been shown to reduce 163 114 Experimental evidence in support of Oparin’s pro- nitrate and acetylene, induce the formation of peptide 164 115 posal came first from Harold C. Urey’s laboratory, at the bonds between amino acids activated with carbon mon- 165 116 University of Chicago, who had considered the origin of oxide and (Ni, Fe)S (Maden 1995; Huber and 166 117 life in the context of his proposal of a highly reducing Wa¨chtersha¨user 1998), and catalyze the synthesis of acetic 167 118 terrestrial atmosphere (Urey 1952). The first successful acid and pyruvic acid from CO under simulated hydro- 168 119 prebiotic amino acid synthesis was carried out with an thermal conditions (Huber and Wa¨chtersha¨user 1997; 169 120 electric discharge and a strongly reducing model atmo- Cody et al. 2000), the role of Fe/S minerals is also com- 170

121 sphere of CH4, NH3,H2O, and H2 (Miller 1953). The patible with a more general, modified model of the prim- 171 122 result of this experiment was a significant yield of itive soup in which pyrite formation is recognized as an 172 123 a racemic mixture of amino acids, together with hydroxy important source of electrons for the reduction of organic 173 124 acids, short aliphatic acids, and urea. One of the surprising compounds (Bada and Lazcano 2002). 174 125 results of this experiment was that the products were not There has been no shortage of discussion about how 175 126 a random mixture of organic compounds; rather, the formation of the primitive soup took place. However, 176 127 a relatively small number of compounds, most of which it is likely that no single mechanism can account for the 177 128 were of biochemical significance, were produced in wide range of organic compounds that may have 178 Comp. by: DMuthuKumar Stage: Galleys Chapter No.: 1275 Title Name: EAB Page Number: 0 Date:28/10/10 Time:11:12:51

Primordial Soup P 3

179 accumulated on the primitive Earth, and that the prebiotic liposomes. Our ideas on the prebiotic synthesis of organic 229 180 soup was formed by contributions from endogenous syn- compounds are based largely on experiments in model 230 181 theses in a reducing atmosphere, metal sulfide-mediated system, and the evidence suggests that the remarkable 231 182 synthesis in deep-sea vents, and exogenous sources such as coincidence between the molecular constituents of living 232 183 comets, meteorites, and interplanetary dust. This eclectic organisms and those synthesized in prebiotic experiments 233 184 view does not beg the issue of the relative significance of is too striking to be fortuitous. The robustness of this type 234 185 the different sources of organic compounds, but it simply of chemistry is supported by the occurrence of many of 235 186 recognizes the wide variety of potential sources of organic these biochemical compounds in the 4.5 billion-year-old 236 187 compounds, the raw material required for the emergence Murchison carbonaceous chondrite and other carbon- 237 188 of life (Bada and Lazcano 2009; Lazcano 2010b). rich meteorites, suggesting that similar synthesis took 238 place on the primitive Earth (Miller and Lazcano 2002). 239 189 The Prebiotic Broth: A Risky Metaphor? 190 Synonymous terms like “primitive soup,” “primordial Conclusions 240 191 broth,” or “Darwin’s warm little pond” have led in some How the first life evolved is not known, but analysis of 241 192 cases to major misunderstandings, including the simplis- carbonaceous chondrites and the laboratory simulations 242 193 tic image of a worldwide ocean, rich in self-replicating of the primitive Earth suggest that prior to the emergence 243 194 molecules and accompanied by all sorts of biochemical of the first living systems the prebiotic environment was 244 195 monomers. However, nowadays, it refers to parts of the endowed with (1) a large suite of organic compounds of 245 196 prebiotic environment where the accumulation and inter- biochemical significance; (2) many organic and inorganic 246 197 action of the products of abiotic synthesis may have taken catalysts (such as cyanamide, metallic ions, sulfur-rich 247 198 place, including oceanic sediments, intertidal zones, shal- minerals and clays); (3) purines and pyrimidines, that is, 248 199 low ponds, membrane-bound systems, freshwater lakes, the potential for template-dependent polymerization 249 200 and lagoons undergoing wet-and-dry cycles. The soup reactions; (4) membrane-forming compounds; and 250 201 may have been semi-frozen, and glacial ponds where (5) the availability of many possible sources of carbon 251 202 evaporation, eutectic separations, or other physicochem- and nitrogen for primordial heterotrophs. Once life 252 203 ical mechanisms, such as the adherence of biochemical appeared and biosynthetic pathways developed, the reser- 253 204 monomers to active surfaces, could have raised local con- voir of organic material present on the Earth then shifted 254 205 centrations and promoted polymerization (Bada and from one initially characterized by compounds of abiotic 255 206 Lazcano 2009). origin to one made up entirely of biologically derived 256 207 Given adequate expertise and experimental condi- components (Lazcano 2010b). 257 208 tions, it is possible to synthesize almost any organic mol- The existence of different abiotic mechanisms by 258 209 ecule. However, the fact that a number of molecular which biochemical monomers can be synthesized under 259 210 components of contemporary cells can be formed plausible prebiotic conditions is well established. Of 260 211 nonenzymatically in the laboratory does not necessarily course, not all prebiotic pathways are equally efficient, 261 212 mean that they were also essential for the origin of life, or but the wide range of experimental conditions under 262 213 that they were available in the prebiotic environment. The which organic compounds can be synthesized demon- 263 214 primitive soup must have been a bewildering organic strates that prebiotic syntheses of the building blocks of 264 215 chemical wonderland, but it could not include all the life are robust, that is, the abiotic reactions leading to them 265 216 compounds or molecular structures found today in even do not take place under a narrow range defined by highly 266 217 the seemingly most primitive prokaryotes. It is possible selective reaction conditions, but rather under a wide vari- 267 218 that some compounds, including perhaps RNA itself, may ety of experimental settings. Like other scientific meta- 268 219 not have been synthesized prebiotically, so their occur- phors, the term “primitive soup” is risky but useful, and 269 220 rence in living systems may have been the result of early has become a part of popular lore. For all the uncertainties 270 221 metabolic syntheses. surrounding the emergence of life, it appears that the 271 222 The existence of different abiotic mechanisms by formation of the prebiotic soup is one of the most firmly 272 223 which biochemical monomers can be synthesized under established events that took place in the primitive Earth. 273 224 plausible prebiotic conditions is well established. During 225 the past few years, laboratory simulations of prebiotic See also 274 226 synthesis have been developing models of specific detailed ▶ Heterotrophic Hypothesis 275 227 environments, including those that may have been pro- ▶ Miller–Urey experiment 276 Au1 228 vided by the surface of clays, small volcanic ponds, and Comp. by: DMuthuKumar Stage: Galleys Chapter No.: 1275 Title Name: EAB Page Number: 0 Date:28/10/10 Time:11:12:51

4 P Primordial Soup

277 ▶ Prebiotic Synthesis Huber C, Wa¨chtersha¨user G (1997) Activated acetic acid by carbon 310 fixation on, Fe, Ni, S under primordial conditions. Science 311 278 ▶ Primitive Earth 276:245–247 312 279 ▶ RNA World Huber C, Wa¨chtersha¨user G (1998) Peptides by activation of amino acids 313 with CO on Ni, Fe, S surfaces and implications for the origin of life. 314 280 References and Further Reading Science 281:670–672 315 281 Bada J, Lazcano A (2002) Some like it hot, but not biomolecules. Science Lazcano A (2010a) Historical development of origins of life. In: Deamer 316 282 296:1982–1983 DW, Szostak J (eds) Cold spring harbor perspectives in biology: 317 283 Bada JL, Lazcano A (2003) Prebiotic soup: revisiting the Miller experi- the origins of life. Cold Spring Harbor Press, Cold Spring Harbor, 318 284 ment. Science 300:745–746 pp 1–16 319 285 Bada JL, Lazcano A (2009) The origin of life. In: Ruse M, Travis J (eds) The Lazcano A (2010b) The origin and early evolution of life: did it all start in 320 286 harvard companion of evolution. Belknap/Harvard University Press, Darwin’s warm little pond? In: Bell MA, Futuyma DJ, Eanes WF, 321 287 Cambridge, pp 49–79 Levinton JS (eds) Evolution since Darwin: the first 150 years. Sinauer, 322 288 Bernal JD (1944) The physical basis of life. Routledge and Kegan Paul, Sunderland, pp 353–375 323 289 London Maden BEH (1995) No soup for starters? Autotrophy and origins of 324 290 Calvin M (1969) Chemical evolution: molecular evolution towards metabolism. Trends Biochem Sci 20:337–341 325 291 the origin of living systems on the earth and elsewhere. Oxford Miller SL (1953) A production of amino acids under possible primitive 326 292 University Press, New York Earth conditions. Science 117:528 327 293 Chyba CF, Sagan C (1992) Endogenous production, exogenous delivery, Miller SL, Lazcano A (2002) Formation of the building blocks of life. In: 328 294 and impact-shock synthesis or organic compounds, an inventory for Schopf JW (ed) Life’s origin: the beginnings of biological evolution. 329 295 the origin of life. Nature 355:125–132 California University Press, Berkeley, pp 78–112 330 296 Cleaves JH, Chalmers JH, Lazcano A, Miller SL, Bada JL (2008) Prebiotic Oparin AI (1924) Proiskhozhedenie Zhizni. Mosckovskii Rabochii, 331 297 organic synthesis in neutral planetary atmospheres. Orig Life Moscow. Reprinted and translated in Bernal JD (1967) The origin 332 298 Evol Biosph 38:105–155 of life. Weidenfeld and Nicolson, London 333 299 Cody GD, Boctor NZ, Filley TR, Hazen RM, Scott JH, Sharma A, Oparin AI (1938) The origin of life. McMillan, New York 334 300 Yoder HS Jr (2000) Primordial carbonylated iron-sulfur compounds Pereto´ J, Bada JL, Lazcano A (2009) Charles Darwin and the origins of life. 335 301 and the synthesis of pyruvate. Science 289:1337–1340 Orig Life Evol Biosph 39:395–406 336 302 Darwin F (ed) (1887) The life and letters of Charles Darwin, including an Podolsky S (1996) The role of the virus in origin-of-life theorizing. J Hist 337 303 autobiographical chapter, vol 3. Murray, London Biol 29:79–126 338 304 Farley J (1977) The spontaneous generation controversy from descartes to Urey HC (1952) On the early chemical history of the earth and the origin 339 305 oparin. John Hopkins University Press, Baltimore/London of life. Proc Natl Acad Sci USA 38:351–363 340 306 Haldane JBS (1929) The origin of life. Rationalist Annu 148:3–10 Wa¨chtersha¨user G (1988) Before enzymes and templates, theory of surface 341 307 Herschel W (1926) Consistency. In: Alexander J (ed) Colloid chemistry, metabolism. Microbiol Rev 52:452–484 342 308 vol 1, Theoretical and Applied. Chemical Catalog, New York, 309 pp 727–738 Comp. by: DMuthuKumar Stage: Galleys Chapter No.: 1275 Title Name: EAB Page Number: 0 Date:28/10/10 Time:11:12:51

Author Query Form

Encyclopedia of Astrobiology Chapter No: 1275 ______

Query Refs. Details Required Author’s response AU1 The entry titles “Miller–Urey experiment, Prebiotic Synthesis, Primitive Earth” are not in the entry list. Please check if appropriate.