A search for prebiotic signatures with the Mars 2020 rover David Catling (U. Washington, Seattle) , +Tanja Bosak, Woody Fischer, John Grotzinger, Joel Hurowitz, Dimitar Sasselov, Roger Summons, John Sutherland, Jack NOTE ADDED BY JPL WEBMASTER: Szostak, & the Simons Collaboration on the This content has not been approved or adopted by NASA, Origins of Life JPL, or the California Institute of TechnoloGy. This document is = Group of organic chemists + biochemists + being made available for chemists + geoscientists + astronomers information purposes only, and any views and opinions expressed herein do not necessarily state or reflect those of NASA, JPL, or the California Institute of Technology. Overview • Motivation – Even if Mars didn't evolve life (no black shales yet!) it can provide insight into prebiotic chemistry: Consider for 2020 & sample return – Can we find traces of prebiotic feedstocks or biomolecules from prebiotic chemistry? This seems like an under-studied issue. Part 1) Environments for the origin of life – Little time here to weigh pros & cons of all proposed environments – We focus on an environment (lacustrine) that has the strongest experimental support of biomolecules made with specificity & yield Part 2) What to look for? Will discuss traces of ingredients and products of prebiotic chemistry. Part 3) Where to look? Lithologies of best preservation Part 1: Environments for Origin of Life The prebiotic is hidden on Hadean Earth from lack of rocks Do prebiotic traces exist on Noachian (4.1 to ~3.7 Ga) Mars? Darwinian evolution Post-Moon Stable Prebiotic RNA DNA in Black Photosynthetic impact ocean chemistry World cells shale life (stromatolites) 4.5 4.4-4.3 4.4 4.0 3.8 3.5 Billions of years ago (Ga) + arguments that an origin of life anywhere would have similar organic molecules: e.g., Pace (2001) The universal nature of biochemistry. P. Natl. Acad. Sci. Updated from Joyce (2002, Nature) Many proposed environments for life’s origin Deep-sea vents? Surface vents/hot springs? Sea ice? Evaporative lakes? Lost City, mid-Atlantic Yellowstone carbonate chimney What does the most successful lab prebiotic chemistry imply about the geochemical environment? Prebiotic chemistry to geochemical scenario The problem: How (geo)chemistry transitioned into biology Work backwards: How necessary prebiotic chemistry informs geochemistry proteins ribonucleotide (amino acids) A, G (purine), C, U (pyrimidine) base lipids Systems Chemistry approach (pioneered by John Sutherland, Univ. of Cambridge) 1) Examine subsystem synthesis separately 2) Merge common chemistry 3) Thus make all pieces in one go (ribonucleotides, amino acids, lipids) 4) Infer a geological scenario that accommodates this chemistry Demonstrated in lab: Simple “feedstock” molecules to biomolecules Last decade: A series of papers shows that ribonucleotides, lipid precursors, and amino acids form from simple, common ingredients in cyanosulfidic photoredox chemistry: 3- HCN reductant H2S, phosphate groups (PO4 ), UV (200-300 nm) CN- nucleophile: donates e- pair to make e- release, photoexcitation C-C chains into big molecules with N H2CO à sugars drives reactions NC NC – O– –O OH OH O OH O – – –O P OCOC H P O O P NH2 HO 7 15 O O OH O O O O + OH/COC7H15 HO CN H2N S HO OH OH Thr HO O OH O + + O Ala C7H15 C7H15 C7H15 O– NC NH2 NC OH O P OH O Leu H2N S NH2 O HO H2N CN S O OH NH Ser 2 OH OH Val Gly NC NH2 H2N CN CN CN HO HO HO OH amino acids OH OH NH OH O HO 2 HO + CN S S H2S S O NC OH lipid precursors CN NH2 H2S O HO O NH2 N OH OH HCN H2CO NH2 O Pi H2N HO CN CN HO HO Powner+ HO HO NH2 O O O O N O N N N N NH Pi hν NH2 NH2 N O O (2009) Nature HO O HO O O O O O ribo- P P Ile NH H2N NH2 – – O 2 O O O O CN Arg O nucleotides CuCl2 NC OH NC CN NC CN NC NC Patel+ (2015) O O H2N CN HCN + CuC3N CN + NH OH NH CuCl HCN 2 Asn, Nature Chem. H2N NH2 Asp O NC CN NC CN NC NH NH 2 3 NC + H2N CN H N OH HN OH NH H N CN O 2 O CN 2 H2N NC Ritson+ (2018) H2N OH S H2N CN Gln, Nature Comm. Glu amino acids H2N S H2N S H2N HN OH NH NH NH CN NH Pro CN H2N NH2 H2N HO NH2 H2N HO H N N S N 2 H H Implied geochemistry A key need: concentrated cyanide Toner & Catling (2018), in review Impacts or anoxic photochemistry B. A. HCN NaHCO3 alkaline brine concentrates 4- Evaporite: carbonate, Na/KCl, sulfate, cyanide as ferrocyanide (Fe(CN)6 ) Na-ferrocyanide, clays Typical mafic/ultramafic closed basin waters NaCN CaO, MgO, FeO + à NaCl, KCl, Na CO FeC , C water C. shock/contact 2 3, 3 metamorphism Aqueous: Na+, CN-, Cl-, carbonate (high pH) Solids: Ca(OH)2, Mg(OH)2, Fe(OH)2 FeC3, C Pyrite + cyanide à HS- + ferrocyanide 3- Fe-phosphate + cyanide à PO4 + ferrocyanide Part 2: What to look for: (a) minerals 1) Generally: Sedimentary minerals in evaporite environments that concentrate prebiotic precursors. • Are they in your spectral library? 2) Specific minerals: 4- • Ferrocyanide (Fe(CN)6 ) salts (Na-, Cu-, Fe- ) • Associated with Fe/Ca/Mg carbonates, halite, sulfates • Associated impact shocK products: Iron carbide, elemental carbon 3) Signs of anoxic environments: • Elemental sulfur (S8) could indicate a reducing atmosphere • Anoxia: Detrital sulfide, authigenic Fe2+-clays, siderite, magnetite 4) Aside: Has cyanide already been detected on Mars? Eigenbrode+ (2018) MSL data has mass = 27 (HCN) Part 2: What to look for: (b) organics The 2020 payload limits in situ analysis, but what if samples for return had signs of 3 prebiotic subsystems: Nucleic acids, peptides & lipids? It could revolutionize our understanding of origin of life. E.g.: RNA precursors (steps to RNA World) Uracil base inosine nucleoside peptide & protein precursors hydrolytically stable amino acids, e.g. valine Indicative of C3 glyceraldehyde precursor of amino acids, e.g., RNA lipids, and ribonucleotides Glycerol (C3) glyceraldehyde C4 acid related to amino acid aspartate & used in the malic acid (reverse) citric acid cycle Part 2: What to look for: (b) organics Organic-preserving (returned) samples may allow us to distinguish: 1. meteorite organics: kerogen pyrolysis dominated by 1-3-ring aromatics with less aliphatic substitution than 4-5 rings in biology; amino acids 13C- 15N-rich vs. depleted in biology (Engel & Macko, ’90,’97) 2. cyanosulfidic prebiotic: limited assemblage of small organics (Patel+ 2015) 3. Fischer-Tropsch-type (FTT): isomeric mixtures vs. favored isomers of molecular series in biology (Mißbach+ 2018). Exponential drop off with Cnumber modified by loss of Clow volatiles. 4. biology is selective with a Lego principle of tail-head repeat units: lipids of C16H32O2 palmitic acid (palm oil) 1) acetyl (C2) polymers a C40 carotenoid 2) isoprene (C5H8) polymers. Part 3: Where to look? Evaporites: Silica Clays Carbonates, halite, sulfates Pros • Carbonates & sulfates in marine environments and playas incorporate & protect Fine-grained, ideally opaline organics (O’Reilly+ 2016; SiO2 deposited under reducing, Cabestrero+ 2018) non-acidic conditions Fine-grained sediments rich in clay minerals • Carbonates can preserve • Adsorbs proteins, RNA • Smectites can protect microbial textures (Biondi+ 2016), lipids, organics from degradation nucleotides (e.g., Ogawa and Kuroda, • Ancient halite can preserve 1997) nucleic acids (Jaakkola+ • Can adsorb intermediates of 2016). prebiotic chemistry • Can adsorb nucleobases, nucleotides (Ferris, 1989; • Borate proposed prebiotic • Stabilizes C sugars in the 5 Feuillie+ 2013; Pedreira- chemistry (Ricardo+ 2004; formose reaction (sugar Segade+ 2016), proteins, Kim & Benner, 2017). formation from amino acids (Aufdenkamp+ Cons formaldehyde) (Lambert+ 2001), organoammonium • If minerals later dissolve, loss 2010) (Ogawa & Kuroda, 1997) of organic matter is possible Look for sedimentary. If hydrothermal, may have less or no prebiotic organics Summary • In the last decade, common feedstock prebiotic chemistry has generated ribonucleotides, lipid precursors & amino acids – CN-, sulfide, and UV are key to this successful scheme – Could have happened on Mars. Even if life didn’t evolve, we might learn much about life’s origins from prebiotic chemical traces on Mars. • Prebiotic chemistry implies the plausible geochemistry - – Alkaline, NaHCO3-rich evaporite lakes best concentrate CN as ferrocyanide “storage” that can be released later – Such lakes commonly form in (ultra)mafic closed basins – Arid, low-temperature (≤ 25ºC) places are favored Mars • What to look for: – Sedimentary minerals: Ferrocyanides in carbonate & Cl- evaporites – Organics: Meteorite vs. cyanosulfidic vs. Fischer-Tropsch vs. biology • Where to look: – Preserved in fine grained sedimentary silica or clays or evaporites Back-up slides follow Aqueous model results • Concentration of cyanide by closed-basin lake water (Toner & Catling, in review) C–C bond formation and C1 feedstocks HS• e– hν aq. + – HS• H2S HS H2S H N• H H net two-electron reduction Iminomethane NH H C N H+ + –C N H weak good electrophile nucleophile H O NH 2 3 formaldehyde H H C HO N glycolonitrile hydrolysis O cyanohydrin (simplest cyanohydrin) formation good electrophile difficult, needs x 2 umpolung HO glyceraldehyde HO HO HO O O NH glycolaldehyde glycolaldehyde imine.