Roger SummonsDepartment of Earth, Atmospheric and

Planetary SciencesMIT

Preservation of Organic Biomarkers on Earth:

Generic Biosignatures, Petroleum Source Rocks,

Early Earth Organic Record, OM & Hydrothermal Ecosystems

OM & Deep Biosphere,

What is a biomarker? Criteria for discriminating biogenic vs non-biogenic organic compounds on Earth & Mars

Petroleum Source RocksPotentially useful analogues for understanding organic matter concentration & preservation on Earth

OM in Ancient Sediments

OM & Hydrothermal Ecosystems

OM & Deep Biosphere

Topics

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 – kerogenPyrolysis to convert to small, identifiable molecules

Complex structures with very specific patternsDNA, proteins, cellulose, membrane lipids

Made from simpler building blocks4 bases for DNA

20 amino acids

2 lipid precursors (2-C acetate and 5C isoprene)

Biogenic organic materials

Patterns in spatial arrangements of C-atomsstereochemistry

HO

310 8

13

14

17

20

H H

9

28 stereoisomers possible for cholesterol

‘Biology’ makes only one

CCH3

H

COOH

CH3C

H

HOOC

H2N NH2

L-alanine D-alanine

CCH3

H

COOH

CH3C

H

HOOC

H2N NH2

L-alanine D-alanine

Amino acids ‘L’-helix in proteins

• Patterns in the way C-atoms are linked together– Patterned structures

Biogenic organic materials

Patterning is preserved in the fossilized remains of chlorophyll

Biogenic organic materials• Patterning is a generic ‘biomarker’

Patterns of C-number- example of a leaf wax

Patterning is a consequence of universal biochemical pathwaysmin10 20 30 40 50 60 70 min10 20 30 40 50 60 70 min10 20 30 40 50 60 70

C15

‘cluster’

C20

‘cluster’isoprenoids

‘odd over even’C29-C33 ‘cluster’ of

n-alkanes

low 11,12,13, 14

low16-19

low 21-24

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)

Organic Rich Rocks (1)

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

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 Ga3.45 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

Organics on Early Earth

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

04 Dec 01 05

SPC 120803-5 3.45 Ga

Time15.00 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

%

11

P MePy

Py

2MeNFlA

C2-Py MeChB(e)Py

B(ghi)Per Co

MePMeBiPh

**

++

++

Marshall et al., Precambrian Research 2007

Urapunga 4 1.5Ga

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

%

2

Py

P

MePy

2MeNC2-Py

MeChB(e)Py B(ghi)Per

Co

MePMeBiPh**

FlA++

++

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. 1977 - chemical degradation, 2 to 4 ring• Kovalenko et al. 1992- lazer desorption ionisation, 2 to 7 ring

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 -18.013C:

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 andoriginate from meteoritic infall

Sephton et al., 2002 Planet Space Sci 50, 711-716.

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 Supergroupca. 2.67 – 2.46 Ga

Sumner & Beukes SAJG 2006

Outside flat

Untreated

Rinsed

InsideOutside 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

Organic Matter (0.4-11.4 wt%)

SilicateSulfideOxide

(9-99 wt%)

Carbonate(1-90 wt%)

Whole Rock

Bitumen I(14-605 ppb)

Bitumen II(70-506 ppb)

OrganicMatter

Kerogen(Insoluble, macromolecular; H/C <0.2)

S

S

O

HN

S

S

O S

NHO

O

S

O

Aromatics(1-488 ppb)

Saturates(2-386 ppb)

CyclicTerpenoids

(0.2-1 ppb) Steranes(0.07-0.48 ppb)

Hopanes(0.05-0.26 ppb)

Cheilanthanes(0.05-0.34 ppb)

Bitumen IHydrocarbons

Biomarkers

Aromatics(18-300 ppb)

Saturates(14-382 ppb)

CyclicTerpenoids(0.9-19.5 ppb)

Bitumen IIHydrocarbons

Steranes(0.36-6.31 ppb)

Hopanes(0.30-11.35 ppb)

Cheilanthanes(0.22-1.88 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. 2008.

C27

0.0 0.5 1.0 1.5

GKF Bitumen IGKP Bitumen IDwyka (GKF)Dwyka (GKP)GKF Bitumen II

C28

0.0 0.5 1.0 1.5 2.0

C29

0.0 0.5 1.0 1.5GKF

DepthGKPDepth

L

KN

R

N

K

D

M

V

B

167.3178.5192.3230.0268.4

314.7

450.1

705.3

895.5

966.2

1309.81326.3

1424.71435.0

173.4228.5239.5316.4

332.5

418.7

636.9

678.2

960.0980.1

1051.2

1248.9

HH

H

H

H

H

HH

H

H

H

H

Diasteranes/Regular Steranes

27

27

28

28

29

29

GKF Bitumen I

GKP Bitumen I

GKF Bitumen II

Low TOC sediments Low TOC sediments colonized by chemosyntheticcolonized by chemosynthetic

communities in ventcommunities in ventand > 70and > 70˚̊C outflowC outflow

High TOC sediments based on High TOC sediments based on photosynthetic communitiesphotosynthetic communities

< 70< 70˚̊C outflowC outflow

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

(Spear et al., PNAS 2005)

“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

“Bison Pool” 16S rRNA survey

Aquificales

Thermotoga

Geothermobacterium

Thermus

OP11

Desulfurococcales 1

UnculturedCrenarchaea 1

BACTERIA

Desulfuro. 2

Uncult. Cren. 2ARCHAEA

Chemosythetic: Zone 1Pink Streamers

Aquifex = water maker

H2 + O2 for energy

CO2 or formate for C

Crenarchaeal taxatypically 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 ?

Atlantis Massif

olivine + water serpentine + brucite + magnetite + H2

Serpentinization: source of H2 and alkalinity

Kelly et al., 2005

Lost City Hydrothermal FieldTowers

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 11Kelly et al., 2005; Bradley et al., GCA 2008 In Press

Lost City Hydrothermal FieldArchaeal biomass dominated by

Methanosarcinales (Schrenk, 2004)

O

OH

O

O

OH

O

OH

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

-140

-120

-100

-80

-60

-40

-20

0

20

13

, ‰

methane archaeal diethers

Lost CityMethanotrophs

AOM communitiesMethanogens

Cultures

H2/CO2 Acetate TMAHMMV HR ERB NW BS

Location Substrate

Lost City Methanosarcinales are methanogensBradley et al., GCA 2008 In Press

Who are they & what are they doing??

JS Lipp et al. Nature 000, 1-4 (2008) doi:10.1038/nature07174

Depth profiles of IPLs in marine sediments.

Crenarchaeal biomass correlates with TOC

Labeling shows consumption of complex organics only:a predominantly heterotrophic community

Concluding ThoughtsOrganic 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