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Roger Summons Department of Earth, Atmospheric and Planetary Sciences MIT Preservation of Organic Biomarkers on Earth: Generic Biosignatures, Petroleum.

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Presentation on theme: "Roger Summons Department of Earth, Atmospheric and Planetary Sciences MIT Preservation of Organic Biomarkers on Earth: Generic Biosignatures, Petroleum."— Presentation transcript:

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

2 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 Topics

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 Patterns in spatial arrangements of C-atoms stereochemistry 2 8 stereoisomers possible for cholesterol ‘Biology’ makes only one Amino acids ‘L’  -helix in proteins

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

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

8 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, O 2 or other oxidants, radiation) concentrated (old productivity vs preservation argument!) it has a ‘tight’ association with minerals (clays, carbonates, evaporites) Organic Rich Rocks (1)

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

10 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 CH 4 uplift  weathering  oxidation  recycling Ionising radiation  alteration to ‘pyrobitumen’ Little unambiguous record > 3 Ga 3.45 Ga Strelley Pool Fm (Allwood,2006; Marshall, 2007) Ga Transvaal (Fischer, 2008; Waldbauer, 2008) 600 Ma-present: Age of petroleum and other fossil organics ubiquitous and abundant Organics on Early Earth

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

12 Strelley Pool Formation

13 Aromatic hydrocarbons from Hydropyrolysis 04 Dec SPC Ga Time % 11 P MePy Py 2MeN FlA C2-Py MeCh B(e)Py B(ghi)Per Co MeP MeBiPh * * Marshall et al., Precambrian Research 2007 Urapunga 4 1.5Ga % 2 Py P MePy 2MeN C2-Py MeCh B(e)Py B(ghi)Per Co MeP MeBiPh * * FlA

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

15 Martian PAH retention time (min) 0 solvent extracted Nakhla procedural blank C2C2 CN OH  13 C: 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 Sephton et al., 2002 Planet Space Sci 50,

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 – 2.46 Ga Sumner & Beukes SAJG 2006

18 Outside flat Untreated Rinsed Inside Outside curve 10 cm Figure 3. 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 Protocols for Archean Hydrocarbons Sherman et al., Organic Geochemistry 38, 1987–2000, 2007

19 Organic Matter ( wt%) Silicate Sulfide Oxide (9-99 wt%) Carbonate (1-90 wt%) Whole Rock Bitumen I ( ppb) Bitumen II ( ppb) Organic Matter Kerogen (Insoluble, macromolecular; H/C <0.2) Aromatics (1-488 ppb) Saturates (2-386 ppb) Cyclic Terpenoids (0.2-1 ppb) Steranes ( ppb) Hopanes ( ppb) Cheilanthanes ( ppb) Bitumen I Hydrocarbons Biomarkers Aromatics ( ppb) Saturates ( ppb) Cyclic Terpenoids ( ppb) Bitumen II Hydrocarbons Steranes ( ppb) Hopanes ( ppb) Cheilanthanes ( ppb) Biomarkers 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

20 Diasteranes/ Regular Steranes GKF Bitumen I GKP Bitumen I GKF Bitumen II

21 Low TOC sediments colonized by chemosynthetic communities in vent and > 70˚C outflow High TOC sediments based on photosynthetic communities < 70 ˚ C outflow To what degree are they ultimately dependent on O 2 -photosynthesis ??? (Spear et al., PNAS 2005)

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 Aquificales Thermotoga Geothermobacterium Thermus OP11 Desulfurococcales 1 Uncultured Crenarchaea 1 BACTERIA Desulfuro. 2 Uncult. Cren. 2 ARCHAEA Chemosythetic: Zone 1 Pink Streamers Aquifex = water maker H 2 + O 2 for energy CO 2 or formate for C Crenarchaeal taxa typically heterotrophic Meyer-Dombard et al., Geochim.Cosmochim. Acta 71 Supp, A661 & work in progress

24 Bison Pool ‘chemosynthetic’ silicious biofilm community dependent on O 2 from photosynthesis Abundant O 2 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 olivine + water  serpentine + brucite + magnetite + H 2 Serpentinization: source of H 2 and alkalinity Kelly et al., 2005

27 Lost City Hydrothermal Field Towers CaCO 3 and Mg(OH) % and 0.6% TOC δ 13 C 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) archaeol sn-2 hydroxyarchaeol 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??

31

32 JS Lipp et al. Nature 000, 1-4 (2008) doi: /nature07174 Depth profiles of IPLs in marine sediments.

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


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