The Space-Soup Theory of Life: Tiny Primordial Soups on Interstellar Dust

Preprint release. 18 March, 2015

The space-soup theory of life: Tiny primordial soups on interstellar dust

Alexandre Harvey-Tremblay [email protected]

Abstract: In the abiogenesis hypothesis, self-replicating RNA is generally assumed to have arisen out of a primordial soup of amino acids no later than 500 million years before life on Earth. Prebiotic molecules such as glycolaldehyde and amino acetonitrile are found to be abundant in nebulas such as Sagittarius B2. In this paper I show how icy grains within nebulas can act as tiny primordial soups. I further show that a typical nebula would be 1011 times more likely to create a self-replicator than the combined iterative power of Earth’s primitive oceans. Finding the first self-replicator could be a problem significantly more difficult than previ- ously envisioned, requiring the contribution of a larger primordial soup spread across a nebula and operating for 8 billion years prior to life on Earth. This could explain why life lagged the Big Bang by 10 billion years and solve the Fermi paradox.

Introduction The spectroscopy of meteorites has revealed the presence served in space8. The icy grain model is further supported of indigenous amino acids1. More than 70 amino acids by laboratory experiments analogous to outer space condi- have been found in the Murchison meteorite alone2. Sagit- tions, which reproduced part of the observed organic rich- tarius B2, a nebula 390 light years away from the centre of ness of nebulas9, 10, as well as produced the amino acids the Milky Way, exhibits the richest organic composition serine, glycine and alanine in one experiment11 and over observed to date in a nebula. In fact, over 70 organic com- 16 amino acids in another12. In the Bernstein experiment, pounds have been reported to be present in it3 and the the carbon yield of glycine was 0.5% in comparison to a numbers are growing. More recently, glycolaldehyde yield of 1.2 to 4.7% for revised Miller-Urey type experi-

CH2OHCHO, the first interstellar sugar, and amino ace- ments13. tonitrile NH2CH2CN, a direct precursor of the simplest Organic matter is found almost everywhere in amino acid glycine, were also detected in this nebula4, 5. space: diffuse clouds, planetary nebulas, star forming re- The concentration of gas within a typical nebula gions, comets, asteroids and meteorites14. Space probes is thought to be too low to explain the rich organic chem- from the Stardust NASA mission returned to Earth with a istry. An icy grain model is instead suggested. A typical measurable deposition of indigenous organics15. An interstellar icy grain has a size of 0.01µm3 to 0.1µm3 and emerging view is that comets may have sprinkled organic would equal 0.5 to 1% of the hydrogenous mass of the space dust on primitive Earth, helping kickstart life16. nebula6. Infrared measurements from space telescopes Meanwhile on Earth, the search for a self-repli- confirmed that frozen materials envelope the grain, of cating molecule continues in laboratories. How amino which H2O is the most abundant7. According to the grain acids and organic polymers first assembled into a structure chemistry model, icy grains accumulate ambient organics undergoing natural selection remains the great unanswered on their surfaces. Cosmic ray ionization, surface diffusion question of abiogenesis. Ribozyme-like structures, able to effects and ambient temperature changes will cause the both encode information and catalyze reactions - two core simple organics to react, creating the rich products ob- requirements of life, may provide the best investigative

Page 1! of !6 path17. Primitive Earth served as an incubator for organic total time (t) the soup is iterating and c) the efﬁciency materials in what is called the primordial soup, where or- (k) of the process: ganic compounds were chemically interacting to form progressively more complex structures. (1) Ic ∝ k · m · t

The origins of the first self-replicator From these assumptions, many environments of Once a self-replicating molecule originates, it undergoes different nature, composition or ambient temperature could natural selection and can quickly evolve into complex sys- iterate over the problem. Since nebulas are producing a tems. But how hard is it to generate the first self-replica- complex organic chemistry and that amino acids are likely tor? In a primordial soup, simple organic molecules inter- on icy grains, this opens the possibility that they are con- act to form products of random complexities. Under the tributing to the search for a self-replicator. Here I propose worse case scenario, the first self-replicator can be pro- that in nebulas, with an environment rich in organic com- duced by an iterative process over the set of all possible pounds, icy grains form a primordial soup on their sur- atomic arrangements of organic matter. As each arrange- faces. ment has to be tried until a self-replicator is found, finding it would be a NP-hard problem akin to the traveling sales- Explanation of the model man problem. The primordial soup acts as an iteration en- In nebulas such a Sagittarius B2 icy grains travel through a gine that traverses the set of possible atomic arrangements thin gas of 3000 particles/cm3. Over time, ambient organic in search of a self-replicator. Since every drop of water in molecules will accumulate over the surface of the grain. A the ocean contains approximately 1.5x1021 molecules, the micro-environment will exist where organics interact search is massively parallel. Creating life can be seen as a through diffusion to create products of various complexi- computational problem. ties. As the resulting products of each individual collision Some factors could simplify the problem. Many are random there is a non-zero chance that it will produce arrangements of organic matter could lead to a working a self-replicator. Therefore, the grain acts as a minuscule self-replicator. This would reduce the number of iterations primordial soup. required for a solution as it only needs to find one out of If and when a self-replicator is created, asexual all possible self-replicators. Additionally, complex but reproduction will subject it to natural selection. The self- stable molecular arrangements could be created during the replicator will quickly evolve to adapt its physiology for process, resulting in islands of stability. Each island would its current environment. If it fails to adapt, it will go ex- be a milestone along the path of increased complexity, tinct and will serve as reagents for a future reaction. If it dividing the number of iteration required to find the first does adapt, numerous copies of it will be produced by self-replicator. consuming the remaining organic matter on the icy grain. For the search to be an NP-Hard problem, certain The grain will hereafter be called a producer. The repro- assumptions are made: duction will continue until it runs out of food or out of 1) Any single collision between sufficiently complex space on the producer. organic molecules yields products with varying proba- Some of the self-replicators will evaporate into bilities and serves as one iteration. space due to thermodynamics. Eventually one will land on 2) Each iteration has a non-zero chance of producing a a neighbouring icy grain. Once landed, the self-replicator self-replicator. will transform it into a producer and the evaporative-land- 3) Any region of space where iteration takes place over ing cycle will repeat itself. time will be considered a primordial soup whose itera- As the volume occupied by producers grows

tive contribution (Ic) is proportional to a) the mass (m) through the nebula, it will traverse different climate-zones, of iterating organic material within the soup, b) the delimited by temperature, ambient radiation, bath compo-

Page 2! of !6 sition, organic matter type, concentration levels, etc. The it to that provided by a nebula. To do so, I used equation self-replicators will, if possible, adapt to the changing cli- (1) that I derived in an earlier paragraph. mate and continue to grow. If they cannot adapt, the vol- With this equation and by using the Earth as a ume of producers will seize to grow at the frontier of the reference, the iteration contribution of a primordial soup new climate. After an extended period of time, a fixed vol- on an icy-grain is proportional to its mass of organics (m), ume of space within the nebula will be occupied by pro- to an efficiency ratio (k") referenced against Earth and to ducers. This will be called the habitable zone. the time spent iterating (t). The habitable zone may be very large. Wind cur- rents, turbulence or collisions could carry producers across (2) Ic (Earth) ∝ m · t large distances, perhaps even across light years and over (3) Ic (icy-grain) ∝ k" · m · t the span of centuries. Regions of higher temperatures in nebulas are found in areas of intense star and planetary The value of k" is measured experimentally from formations. As the rate of chemical reactions increases the experiments of Miller-Urey18 and Bernstein9. Carbon with temperature, those areas are more likely to have more yields of amino acids of 0.5% vs an average of 2.95% are efficient producers. within 1 order of magnitude. The speed of the reaction During this process, stars and planets may form however, is very different. In the Bernstein experiment, the within the habitable zone. As planets accrete, they reach reaction is accelerated by an ultra-violet dose correspond- temperatures above the melting point of metals, vaporizing ing to between 500 years (at the edge of a dense cloud) to most of the complex organic matter. Self-replicators might 500,000 years (deep within the cloud) of natural emis- not survive the planetary accretion process, but comets sions. In the Miller-Urey, the reaction is occurring over a 1 orbiting star systems will accumulate producers as they week period. It is unclear if these experiment times are the travel through space. The comets will then outgas their minimum required to obtain these yields or if they were contents on nearby planets as they travel inwards. exaggerated to guarantee yield. With these considerations If this model is correct, then a producer or a self- in mind, I calculated a value for k" between 6.4e-6 and replicator would have landed on primordial Earth. It would 6.4e-9. have supplied a solved self-replicating structure to Earth’s An 8 billion years old nebula of 106 solar masses, bath of organic matter. The structure would have replicated where 1% of its mass is in the form of icy grains, would by consuming the primordial soup as food and would have have an iteration rate many times higher than that of Earth. evolved into a more complex stage - possibly an RNA I calculated that the odds of the first self-replicator occur- world. ring in the nebula, rather than on Earth, are of magnitude To understand the purpose of icy grains in the 1011 to 1 in favour of the nebula. creation of life, it helps to treat them as computational engines solving a massively parallel algorithmic problem. Discussion and the Fermi paradox The icy grains have the role of a computing node. Once a Life on Earth is often thought to have evolved from inor- solution is found, it is shared with the other nodes by the ganic matter over the course of 4 billion years. The initial process of diffusion. Agglomerations of nodes that provide 500 million years of the process is the abiogenesis phase the largest share of computing power have the highest and is believed to have occurred in the primordial soup of chances of finding the first self-replicator. Earth. If true, the process would be self contained to the planet, be mostly independent of the surrounding interstel- Results lar environment and could easily be repeated on any other By applying a mathematical description to the model here- Earth-like planet within a comparable time frame. This in described, I was able to estimate the relative contribu- assumption leaves two unanswered questions. 1) Why did tion of Earth’s oceans to the iteration process and compare it occur 10 billion years after the Big Bang and not as soon

Page 3! of !6 as the first batch of planets was formed 7 billion years ago Earth’s life. This descendant should predate the first bacte- - many of them surely Earth-like? 2) If life did evolve rias on Earth. Failure to share a common descent predating sooner on other planets, why is there a lack of evidence for bacterias would suggest one of two things. intelligent extraterrestrial civilizations - the Fermi para- 1. If a common descent does exist but postdates the first dox. If intelligent life is rare, we would except it to take all bacterias, it would be suggestive of panspermia from of the available time since the Big Bang to evolve. one planet to the other. This result is neutral. In this paper I presented a preliminary step that 2. If no common descent exists, it would suggest that would be required before life could evolve on an Earth- self-replicators appeared twice: once on Earth and like planet. The problem of finding the first self-replicator once elsewhere. This would contradict the rare self- could be significantly more difficult than originally as- replicator premise of this theory. sumed, such that an ocean-sized primordial soup would e) A generalization of d): Finding life that does have no reasonable chances to iterate over a self-replicator. not share a common descent with life on Earth. If self- There may be thousands of Earth-like planets stuck in a replicators are truly the hardest problem to solve for life, state of primordial soup waiting for a self-replicator to be then finding multiple self-replicators having an anatomy/ created. Only a galaxy-wide process over stellar nebulas, physiology that cannot be explained from common descent iterating for 8 to 10 billion years, would have a reasonable with Earth’s life, would suggest that self-replicators can chance to produce one. Earth would have formed in an easily originate from prebiotic matter. area of the galaxy relatively shortly after a self-replicator was created in space. Methods This section provides a detailed account of the calculations Falsifiability supporting the results of this paper. The method described Here I suggest future observations or findings that could relates specifically to the determination of the odds that a falsify the space-soup hypothesis: self-replicator is created in the solar nebula versus the a) Finding an easy way to create self-replicators odds that it is created in the primitive oceans of Earth. I from simpler organics compatible with the environment of will call this result the contribution ratio. To obtain it, I primitive Earth would invalidate it. It would mean that used a list of common values, most of them derived empir- self-replicators are easy to make. Hence the problem ically about the Earth and a solar nebula of typical proper- would not be NP-Hard and life would not be significantly ties - hereafter called Nebula I. The list of values is shown delayed by the slow process of finding a self-replicator. below. The description of the method will be divided into b) As all planets in our solar system and neigh- two sections. In the first section, I set a lower bound for bouring stellar regions originated from the same nebula, the contribution ratio. In the second section, I calculate a we would expect to find primitive life on many of them realistic value for it. and certainly on those having water. If no such life is found, it would be a strong indicator that the first self- List of used values replicator arose on Earth and Earth alone. A. Mass of water on Earth...... 1.35e21 kg c) Star systems originating from a different nebu- B. Mass of the Sun...... 1.989e30 kg la than ours are likely to be void of life. In them, we may C. Mass of Nebula I...... 2e36 kg find planets stuck in a primordial soup with no self-repli- D. Percentage of mass in the form of icy grain for Nebula cators. Such planets would be a self-replicator’s dream and I ...... 1% the lack of predators or even resource-competitors would E. k"...... 6.4e-9 make it highly conductive to be seeded with Earth’s life. F. Time spent iterating on Earth...... 5e8 years d) If indigenous bacterias are found elsewhere G. Time spent iterating in Nebula I ...... 5e9 years than on Earth, they should share a common descent with

Page 4! of !6 H. Ice to rock mass ratio of interstellar dust. From the The relative iteration contribution of Nebula I is given by: literature, a mass ratio of ice/rock of 2-3 to 1 of inter- k" · 1.32e34 kg · 5e9 years ≈ 1.33e43 kg · s stellar dust and comets is generally reported19 ..... 66% The normalized iteration contribution of Earth is given by: I also put forward two assumptions; 1.35e21 kg · 5e8 years ≈ 2.13e37 kg · s 1) The mass of organics on an icy grain is proportional to its volume of ice. 1c) From the above values, I obtain the following ratio:

2) Since the medium holding the organics is water in Ic (nebula) / Ic (Earth) = 1.33e43 kg · s / 2.13e37 kg · s ≈ 6.2e5 each environment, the organics on the grains have a similar concentration to those in Earth’s primitive 1d) Conclusion: The odds that a self-replicator is found oceans. inside Nebula I rather than on Earth are at least 6.2e5 to 1 in favour of Nebula I. This value serves as a lower bound. Calculation of k": k" is the efficiency constant relative to Earth. To determine its value, I compare the experiments Section 2 - Realistic value: Accepting the hypothesis that of Bernstein9 to the revised experiments of Miller-Urey13. the primordial soup was only effective on ocean’s shores Since the Bernstein experiment is significantly less effi- (see “Sandwich theory of life”20) and/or at hydrothermal cient, the constant k" will be below 1. oceanic vents (see “Deep sea vents hypothesis”21), we must reduce the mass available for iteration on Earth ac- Miller-Urey Bernstein cording to: Yield 0.5% 2.95%

Time 500y-500,000y 0.019y (1 week) m = mwater · (fs + fv) where,

k"- = (0.5% * 0.019y) / (2.95% * 500y) ≈ 6.4e-6 fs is the fraction of Earth’s oceans covering the shore, and k"+= (0.5% / 2.95%) * (0.019y / 500000y) ≈ 6.4e-9 fv is the fraction of Earth’s oceans dominated by hydrothermal effects. k" is between 6.4e-6 and 6.4e-9.

2a) How to estimate fs? Measurements of shore lines are Section 1 - Lower bound: I take the most conservative difﬁcult because of the coastline paradox. However, stan- approach: where all of Earth’s oceans equally contribute to dard workarounds used by the United States Defence the iterative process. This assumption will likely result in a Mapping Agency and the World Resources Institute pro- massive overestimation of the contribution of the Earth, vide the value of 1,162,306 km of coastline for the but it will serve as a lower bound. world22. I further suppose that primordial soup iterations happen up to 1 meter deep and up to 1 km away from the 1a) Mass available for iteration. shore. From that, I obtain an iterative water mass of: The mass of ice in Nebula I available for iteration is given by: 1162306 km · 1 m · 1 km · 1 g/cm3 ≈ 1.16e15 kg

mnebula · 1% · 66% = 1.32e34 kg 2b) How to estimate fv? It is estimated that approximately The mass of water on Earth available for iteration is given 1000 hydrothermal vents exist at the bottom of the ocean by: today and are located at the junctions of tectonic plates or 23 mwater = 1.35e21 kg regions of signiﬁcant geothermal activities . These vents smoke large quantities of organics over a volume of water. 1b) Relative iteration contribution. A review of the literature revealed no vents larger than a

Page 5! of !6 cylinder with the height of 1 km and radius of 1 km. As an cules in Solid Methane (CH4), Ethylene (C2H4), and Acetylene (C2H2). ApJ 503:959 (1998). additional safety margin I will assume these values for all 11. Bernstein, M. P., Dworkin, J. P., Sandford, S. A., Cooper, G. W. & vents. From that I obtain an iterative water mass of: Allamandola, L. J.. Racemic amino acids from the ultraviolet pho- tolysis of interstellar ice analogues. Nature 416:401-403 (2002). 1000 · 1 km · π · (1 km)2 · 1 g/cm3 ≈ 3.14e15 kg 12. Muñoz Caro, G. M. et al. Amino acids from ultraviolet irradiation of interstellar ice analogues. Nature 416:403-406 (2002). 13. Miller, S. L. & Schlesinger, G. The atmosphere of the primitive 2c) Reassessment of the normalized contribution of Earth Earth and the prebiotic synthesis of organic compounds. Advances to the iterative process. in Space Research. 3.9:47-53 (1983). 14. Herbst, E. & van Dishoeck, E. F.. Complex Organic Interstellar Molecules. Annual Review Astronomy and Astrophysics. 47:427– (1) Iterative-mass = 1.16e15 kg + 3.14e15 kg = 4.3e15 kg 80 (2009)

(2) Ip (Earth) = 4.3e15 kg · 5e8 years ≈ 6.79e31 kg · s 15. Sandford, S. A. et al. Organics Captured from Comet Wild 2 by the Stardust Spacecraft. Science 15:1720-1724 (2006) 16. Anders, E.. Pre-biotic organic matter from comets and asteroids. 2d) New Ratio Nature 342:255-257 (1989)

Ip (nebula) / Ip (Earth) = 17. Robertson, M. P. & Joyce, G. F. The origins of the RNA world. 1.33e43 kg · s / 6.79e31 kg · s ≈ 1.96e11 Cold Spring Harb Perspect Biol. 1:4(5) (2012) 18. Warneck, P. A. microwave-powered hydrogen lamp for vacuum ultraviolet photochemical research. Appl. Opt. 1:721–726, 1962. 2e) Conclusion: The odds that a self-replicator is found 19. H.U. Keller. Comets: Dirty snowballs or icy dirtballs. Physics and inside Nebula I rather than on Earth are likely to be ap- Mechanics of Cometary Materials (1989) 20. Wächtershäuser G. The origin of life and its methodological chal- proximately 2e11 to 1 in favour of Nebula I. lenge. J Theor Biol. 187(4):483-94 (1997) 21. Corliss, J. B., Baross, J. A. & Hoffman, S. E. Oceanologica Acta 4 References suppl. 59−69 (1981). 22. World Vector Shorelines. NOAA - National Oceanic and Atmos- 1. Cronin, J. R. & Pizzarello, S. Amino acids in meteorites. Adv. pheric Administration. (1995) Space res. 3:5-18 (1983) 23. Edward T. Baker, Christopher R. German. On the Global Distribu- 2. Cronin, J. R. & Chang, S. Organic Matter in Meteorites: Molecular tion of Hydrothermal Vent Fields. Mid-Ocean Ridges: Hy- and Isotopic Analyses of the Murchison Meteorite. The Chemistry drothermal Interactions Between the Lithosphere and Oceans, Geo- of Life’s Origins. 416:209-258 (1993) physical Monograph 148:245–266 (2004) 3. Nummelin, A. et al. A three-position spectral line survey of sagittarius b2 between 218 and 263 GHz. II. Data analysis. The Astrophys- Author Information Correspondence and requests for ical Journal Supplement Series, 128:213 (2000) 4. Halfen, D. T., Apponi, A. J., Woolf, N., Polt, R. & Ziurys, L. M. A materials should be addressed to Alexandre Harvey-Trem- systematic study of glycolaldehyde in Sagittarius B2(N) at 2 and 3 blay at [email protected]. mm: Criteria for detecting large interstellar molecules. The Astro- physical Journal, 639:237-245 (2006) 5. Belloche, A. et al. Detection of amino acetonitrile in Sgr B2(N). 482.1:179-196 (2008) 6. Savage, B. D. & Mathis, J. S. Observed Properties of Interstellar Dust. Ann. Rev. Astron. Astrophys. 17:73-111 (1979) 7. Gibb, E. L., Whittet, D. C. B., Boogert, A. C. A., Tielens, A. G. G. M.. Interstellar ice: The infrared space observatory legacy. The astrophysical journal supplement series, 151:35-73 (2004) 8. Garrod, R. T., Widicus Weaver, S. L. & Herbst, E.. Complex Chem- istry in Star-Forming Regions: An Expanded Gas-Grain Warm-up Chemical Model. The Astrophysical Journal, 682:283–302 (2008) 9. Bernstein, M. P., Allamandola, L. J. & Sandford, S.A. Complex organics in laboratory simulations of interstellar/cometary ices. Advances in Space Research. 19:991-998 (1997) 10. Kaiser, R. I. & Roessler, K. Theoretical and Laboratory Studies on the Interaction of Cosmic-Ray Particles with Interstellar Ices. III. Suprathermal Chemistry-Induced Formation of Hydrocarbon Mole-

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