# Presentation: 249908

## Preservation of Organic Biomarkers on Earth:

**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,

## Topics

- 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

## 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

## 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)

## Biogenic organic materials

- Patterns in spatial arrangements of C-atoms
- stereochemistry

## Biogenic organic materials

- Patterned structures

- Patterning is preserved in the fossilized remains of chlorophyll

## Biogenic organic materials

- Patterning is a generic ‘biomarker’

**low 11,12,13, 14**

**low**
**16-19**

**low 21-24**

## Organic Rich Rocks (1)

- 	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)

## Organic Rich Rocks (2)

**OM concentration mechanisms vary in time and space**
**Predictable with knowledge of local sedimentary geology**

## Organics on Early Earth

-  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

## Finding authentic biomarkers in Archean sediments is difficult -

- similar analytical challenges to finding organics on Mars

- Organics on Early Earth

## Strelley Pool Formation

## Aromatic hydrocarbons from Hydropyrolysis

- Marshall et al., Precambrian Research 2007

## Murchison (hydro)pyrolysate

**Mark Sephton, Cheng-Gong Sun, Gordon Love and Colin Snape GCA**

## Martian PAH

- 5

- 10

- 15

- 20

- 25

- 30

- 35

- 40

- 45

- retention time (min)

- 0

- solvent extracted Nakhla

- procedural blank

- C2

- CN

- OH

- -22.0

- -21.6

- -22.1

- -18.0

- 13C:

- 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, 711-716. **

## PAH proposed to be 

- 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

## Agouron Griqualand

- Drilling Project

**Transvaal Supergroup**
**ca. 2.67 – 2.46 Ga**

**Sumner & Beukes *****SAJG***** 2006**

## 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

## Composition of Core Samples

***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.

## Diasteranes/

**Diasteranes/**
**Regular Steranes**

**27**

**27**

- GKF Bitumen II

## To what degree are they ultimately dependent on O2-photosynthesis ???

**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 O2-photosynthesis ???
- (Spear et al., PNAS 2005)

## Water chemistry similar to Octopus Spring, pH c. 8, silica pptn

**“****Bison Pool”**

- Silicious streamers & biofilms in outflow
- Aquificales dominate silica sediments and streamers

- Meyer-Dombard et al., 2005, Geobiology & DRMD, Raymond and Shock work in progress

## “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
- H2 + O2 for energy
- CO2 or formate for C
- Crenarchaeal taxa
- typically  heterotrophic

- Meyer-Dombard et al., Geochim.Cosmochim. Acta 71 Supp, A661 & work in progress

## Bison Pool ‘chemosynthetic’ silicious biofilm community dependent on O2 from photosynthesisAbundant 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  

## Marine hydrothermal microbial community independent of sunlight; preservable in ophiolite ? 

- Marine hydrothermal microbial community independent of sunlight; preservable in ophiolite ?

- Atlantis Massif

## Serpentinization: source of H2 and alkalinity

*Serpentinization*: source of H2 and alkalinity

- Kelly et al., 2005

## Lost City Hydrothermal Field

- Towers
- CaCO3 and Mg(OH)2
- 0.05% 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**

## 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**

## Lost City Methanosarcinales are methanogens

**Bradley et al., GCA 2008 In Press**

## Who are they & what are they doing??

## Slide 31

## Depth profiles of IPLs in marine sediments.

## Crenarchaeal biomass correlates with TOC 

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

## 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

**Notes:**
Extracted biomarkers are highly mature, consistent with regional geology and maximum thermal exposure 2.2-2.5 billion years ago.
There is no evidence for significant biodegradation.
Hydrocarbon distributions vary within a 10 m scale and some lithofacies specific variations are observed.These observations are inconsistent with petroleum contamination from drill rigs or naturally migrated sources which would have stained the each core more uniformly.
Regional geology (i.e. faults, intrusions) constrains the likelihood of hydrocarbons migrating from younger rocks of adjacent basins. 
Hydrocarbon migration from older rock units below these formations is possible. However, there exists no good source rocks capable of producing oils that would have contaminates all 3 cores spread across the Hamersely Basin.
	 In order to account for the most biomarkers observed, all 3 cores, drilled >200 km apart and separate by 
	    numerous faults and intrusions would have to have been contaminated. 
 Pyrolysis products are consistent with extracted hydrocarbons in structure. Preliminary isotopic data suggests isotopic consistency as well. 
All of the microbial sources of the observed biomarkers are consistent with molecular phylogenetic and molecular clock studies published to date.