Roger Summons Department of Earth, Atmospheric and Planetary Sciences MIT

1. Preservation of Organic Biomarkers on Earth: Generic Biosignatures, Petroleum Source Rocks, Early Earth Organic Record, OM & Hydrothermal Ecosystems OM & Deep Biosphere, Roger Summons Department of Earth, Atmospheric and Planetary Sciences MIT

2. Topics • What is a biomarker? • Criteria for discriminating biogenic vs non-biogenic organic compounds on Earth & Mars • Petroleum Source Rocks • Potentially useful analogues for understanding organic matter concentration & preservation on Earth • OM in Ancient Sediments • OM & Hydrothermal Ecosystems • OM & Deep Biosphere

3. Non-biogenic Organic Materials Ideal reference point is OM in meteorites Predominantly macromolecular OM – kerogen • Pyrolysis to convert to small, identifiable molecules Simple organic acids, diacids, amino acids, hydroxy acids, alcohols, amines n- and branched hydrocarbons incl. methane Aromatic hydrocarbons (PAH) Message: Characterized by simple ‘random’ chemical structures

4. Biogenic organic materials Macromolecular material – kerogen Pyrolysis to convert to small, identifiable molecules Complex structures with very specific patterns DNA, proteins, cellulose, membrane lipids Made from simpler building blocks 4 bases for DNA 20 amino acids 2 lipid precursors (2-C acetate and 5C isoprene)

5. Biogenic organic materials Amino acids ‘L’a-helix in proteins 28 stereoisomers possible for cholesterol‘Biology’ makes only one Patterns in spatial arrangements of C-atoms stereochemistry

6. Biogenic organic materials • Patterns in the way C-atoms are linked together • Patterned structures Patterning is preserved in the fossilized remains of chlorophyll

7. Biogenic organic materials • Patterning is a generic ‘biomarker’ low 11,12,13, 14 low 16-19 low 21-24

8. Organic Rich Rocks (1) • Microbial organic matter can be ‘ephemeral’ • Often eaten (ecology), oxidized, > 99% recycled on short timescales • Often at low concentration where it is being formed: • most plankton communities ‘dilute’ • often thin biofilms on solid substrates (mineral surfaces) • layered accumulations (mats) an exception • Can be massively concentrated by surface processes: • exported as fecal pellets & adsorbed on mineral surfaces • focussed by aqueous transport processes • Best preserved when: • its isolated (from biology, O2 or other oxidants, radiation) • concentrated (old productivity vs preservation argument!) • it has a ‘tight’ association with minerals (clays, carbonates, evaporites)

9. Organic Rich Rocks (2) OM concentrated in depocentres (eg lakes) sediments: predictable by cyclostratigraphy OM concentrated & preserved in fine gained (clay) sediments: predictable by sequence stratigraphy OM concentration mechanisms vary in time and space Predictable with knowledge of local sedimentary geology

10. Organics on Early Earth • Poor preservation of the rocks is the biggest obstacle to finding and interpreting early Earth organics • Destructive processes include: • Geology deep burial  metamorphism  C and CH4 • uplift  weathering  oxidation  recycling • Ionising radiation  alteration to ‘pyrobitumen’ • Little unambiguous record > 3 Ga • 3.45 Ga Strelley Pool Fm (Allwood,2006; Marshall, 2007) • 2.7-2.3 Ga Transvaal (Fischer, 2008; Waldbauer, 2008) • 600 Ma-present: Age of petroleum and other fossil organics ubiquitous and abundant

11. Organics on Early Earth • Finding authentic biomarkers in Archean sediments is difficult - • similar analytical challenges to finding organics on Mars

12. Strelley Pool Formation

13. Py P Urapunga 4 1.5Ga MePy MeP MeBiPh * + % * MeCh FlA + C2-Py B(e)Py B(ghi)Per 2MeN + + Co 2 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00 75.00 80.00 04 Dec 01 05 Py SPC 120803-5 3.45 Ga % MePy P FlA MeBiPh MeP 2MeN * + MeCh C2-Py + * B(e)Py + B(ghi)Per + Co 11 Time 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00 75.00 80.00 Aromatic hydrocarbons from Hydropyrolysis Marshall et al., Precambrian Research 2007

14. methyl pyrene methyl chrysene TIC pyrene chrysene S coronene benzo[ghi] perylene phenanthrene response retention time Pyrolysis products • HMW, 3 to 7-ring aromatics • pyrenes, chrysenes • volatiles lost Previous work • Hayatsu et al. 1977 - chemical degradation, 2 to 4 ring • Kovalenko et al. 1992 - lazer desorption ionisation, 2 to 7 ring Murchison (hydro)pyrolysate Mark Sephton, Cheng-Gong Sun, Gordon Love and Colin Snape GCA

15. Martian PAH procedural blank d13C: -22.0 -21.6 -22.1 -18.0 solvent extracted Nakhla • Martian meteorites (e.g. Nakhla) • PAH • Contamination less likely for HMW OM • pyrolysis products • Structures and isotopes superficially similar to carbonaceous chodrites • Mars PAH may be abiotic and • originate from meteoritic infall C2 CN OH 0 5 10 15 20 25 30 35 40 45 retention time (min) Sephton et al., 2002 Planet Space Sci 50, 711-716.

16. PAH proposed to be molecular fossils ? ‘ PAH are abundant as fossil molecules in ancient sedimentary rocks ’ No patterns so cannot say if its biogenic or not

17. Agouron Griqualand Drilling Project Transvaal Supergroup ca. 2.67 – 2.46 Ga Sumner & Beukes SAJG 2006

18. Figure 3. Untreated Rinsed Outside flat Outside curve Inside 10 cm Protocols for Archean Hydrocarbons Clean by removing outside surfaces Compare ‘solvent extractable’ vs ‘mineral associated’ hydrocarbons Crush, extract with solvent, add internal stds  Bitumen 1 Demineralize extracted sediment and re-extract residue with solvents  Bitumen-2 Sherman et al., Organic Geochemistry 38, 1987–2000, 2007

19. Cyclic Terpenoids (0.2-1 ppb) Biomarkers Bitumen I Hydrocarbons Steranes (0.07-0.48 ppb) Hopanes (0.05-0.26 ppb) Whole Rock Saturates (2-386 ppb) Silicate Sulfide Oxide (9-99 wt%) Carbonate (1-90 wt%) Aromatics (1-488 ppb) Cheilanthanes (0.05-0.34 ppb) Organic Matter Bitumen I (14-605 ppb) Kerogen (Insoluble, macromolecular; H/C <0.2) Cyclic Terpenoids (0.9-19.5 ppb) Organic Matter (0.4-11.4 wt%) Biomarkers Saturates (14-382 ppb) Hopanes (0.30-11.35 ppb) Steranes (0.36-6.31 ppb) Aromatics (18-300 ppb) Bitumen II (70-506 ppb) Cheilanthanes (0.22-1.88 ppb) Bitumen II Hydrocarbons Composition of Core Samples In these ancient rocks, best preserved biomarkers evidently within crystalline minerals; these H/C accessible after dissolution Waldbauer et al., Precambrian Res. 2008.

20. 29 28 29 28 GKP Bitumen I GKF Bitumen I Diasteranes/ Regular Steranes 27 27 GKF Bitumen II

21. To what degree are they ultimately dependent on O2-photosynthesis ??? (Spear et al., PNAS 2005) High TOC sediments based on photosynthetic communities < 70˚C outflow Low TOC sediments colonized by chemosynthetic communities in vent and > 70˚C outflow

22. “Bison Pool” Water chemistry similar to Octopus Spring, pH c. 8, silica pptn Silicious streamers & biofilms in outflow Aquificales dominate silica sediments and streamers Meyer-Dombard et al., 2005, Geobiology & DRMD, Raymond and Shock work in progress

23. “Bison Pool” 16S rRNA survey Chemosythetic: Zone 1 Pink Streamers Aquifex = water maker H2 + O2 for energy CO2 or formate for C Crenarchaeal taxa typically heterotrophic Geothermobacterium BACTERIA Thermotoga Thermus Aquificales OP11 Desulfurococcales 1 ARCHAEA Uncult. Cren. 2 Uncultured Crenarchaea 1 Desulfuro. 2 Meyer-Dombard et al., Geochim.Cosmochim. Acta 71 Supp, A661 & work in progress

24. Bison Pool ‘chemosynthetic’ silicious biofilm community dependent on O2 from photosynthesisAbundant O2 suggests OM preservation in continental hydrothermal systems problematic‘Fossil’ Yellowstones rare in Earth’s geological record; difficult to evaluate them as potential Mars analogues

25. Marine hydrothermal microbial community independent of sunlight; preservable in ophiolite ? Atlantis Massif

26. Serpentinization: source of H2 and alkalinity olivine + water  serpentine + brucite + magnetite + H2 Kelly et al., 2005

27. Lost City Hydrothermal Field Towers CaCO3 and Mg(OH)2 0.05% and 0.6% TOC δ13C from -27.7‰ to -2.8‰ Vent Fluids Hydrogen – up to 15 mmol/kg Methane – up to 2 mmol/kg Calcium – up to 30 mmol/kg pH – 9 to 11 Kelly et al., 2005; Bradley et al., GCA 2008 In Press

28. Lost City Hydrothermal Field Archaeal biomass dominated by Methanosarcinales (Schrenk, 2004) sn-2 hydroxyarchaeol archaeol Firmicutes prominent in bacterial biomass (Brazelton et al., 2006) Likely acting as sulfate reducers Bradley et al., GCA 2008 In Press

29. Lost City Methanosarcinales are methanogens Bradley et al., GCA 2008 In Press

30. Who are they & what are they doing??

32. Depth profiles of IPLs in marine sediments. JS Lippet al.Nature000, 1-4 (2008) doi:10.1038/nature07174

33. Crenarchaeal biomass correlates with TOC Labeling shows consumption of complex organics only: a predominantly heterotrophic community

34. Concluding Thoughts Organic compounds made by terrestrial organisms have generic structural & isotopic traits. Searching for biosynthetic patterning in extraterrestrial OM is a sound approach to life detection On Earth, organic matter is largely concentrated in sediments deposited in aquatic environments If OM preserved on Mars, expect a tight association with low temperature, sedimentary minerals – clays, evaporites, silica