Martian biology speculations from biodegraded petroleum reservoirs Steve Larter, Ian Head

1
Martian biology - speculations from biodegraded
petroleum reservoirsSteve Larter, Ian Head Tom
Curtis CEGS, University of Newcastle, UK PRG,
Petroleum Reservoir Group, University of Calgary,
Canada

• While much of Mars is very ancient, with a
  surface consisting of very old cratered volcanic
  terrains where life is unlikely to be found
  (1,2), any life that does exist on Mars is most
  likely to be found in the subsurface in areas
  where sedimentary processes have accumulated
  sediments and preserved them at depths where free
  liquid water exists today! To date no significant
  samples of the Martian subsurface are available
  for study but it is reasonable to conclude that
  any Martian biosphere will have similar genesis
  and survival issues to organisms in Earths deep
  biosphere. Petroleum reservoirs provide a unique
  access portal to the Earths subsurface biosphere
  and recent advances in understanding subsurface
  petroleum biodegradation provide some hints to
  what type of life, if any, we might expect in
  Mars. We discuss Martian biology from the
  speculative perspective of the petroleum geology/
  geochemistry of biodegraded oil reservoirs in
  Earth.

Zengler et al, 1999 Head et al, 2003
refs
DeltaG

-
1596kJ
4C16 H34
30H20
49CH4 15CO2
from mineral hydrolysis

H2
from kerogen maturation


From oil aromatisation
Biomass CH4 CO2
refs
K
NH4
PO4 ---
Co, Ni,
nutrients and trace elements from mineral
diagenesis
5. Biodegradation-oil plus water makes life plus
gas
9. The limits of prokaryotic diversity at all
scales-Curtis et al, 2002.
8. Curtis et al 2002- biodiversity theory. The
area under the individuals curve is NT the total
number of individualsNmax number of individuals
in most abundant species
rates and times
NT
ST
NT/Nmax
sample
Ratio ref.
Comparisons of observed degradation rates in
oilfields with the maintenance energy
requirements of microorganisms in the range
10-11 to 10-14 micrograms carbon per cell per
second allows us to make a broad assessment of
the maximum biomass size and suggests that the
degradation flux of hydrocarbons in reservoirs
could be consumed slowly by the maintenance
energy requirements of, on the order, of as
little as 109 microorganisms per square meter of
reservoir area or a few thousand organisms/ cm³
operating near the oil water contact (6). This is
in the range reported for cell counts in
sediments extrapolated to ca 2km depth (7) and
is not unreasonable as many degraded oils fields
we have seen have residual oil columns near the
oil water contact where we have had the best
results in isolating microbial nucleic acid
signatures and where we speculate much
degradation occurs. While we cannot confirm the
size nor the metabolic rate of the biomass with
this geological approach we conjecture from these
results that the deep biosphere in degrading
oilfields is possibly operating at very low
levels of metabolic activity perhaps near
maintenance states (a largobiosphere) though we
cannot eliminate the possibility that it is more
active but much smaller. On balance, it appears
that while the deep biosphere is undoubtedly hot
and exciting it is in oilfields, and probably
elsewhere, including any remnant biosphere in
Mars very slow and malnourished!
(per ml or g)
(per ml or g)
Giovanonni
4
sea
106
163
2. Surface ages of inner planets (NASA)
1. Age of Martian surface (NASA)
4
lake
106
163
Miskin Head
Milner Curtis
Map showing the distribution of Martian craters
15 km in diameter within 65O latitude. All
craters shown here superpose the surface on which
they appear (no buried craters are included). The
large volcanoes in the Tharsis and Elysium
regions and the Hellas and Argyre impact basins
are included for reference.
activated
1.5
109
72
sewage
10
dry soil 1
109
6380
McCaig et al
wet soil 2
109
30,000
100
Dykhuizen
background
Largobiosphere Oil reservoir

1.5
103
10. Estimates of diversity at small scales
Examination of compositional gradients in
biodegrading oilfields (3) has allowed us to
tentatively establish the rates of biodegradation
active at the base of oil columns and to indicate
that the rates of destruction of oil and the
charging rates of oilfields are quite similar in
many cases (Larter et al, 2003). It appears that
that reservoirs buried to 80oC or higher are
effectively sterilized with regard to hydrocarbon
degraders and are not recolonized with near
surface organisms during uplift (4) indicating
the deep biosphere results not from continued
invasion of organisms into deep
synthesis

• If we extrapolate these finding to Mars, where
  near surface life is unlikely to have survived
  then what does this tell us about any existing
  deep Martian biosphere inherited originally from
  evolution of near surface Martian microorganisms.
  This assumes, as in Earth, any Martian deep
  biosphere is derived from the surface. In the
  deep Martian crust where free water will exist,
  anaerobic conditions similar in many respects to
  deep oil reservoirs will exist. Similar mineral
  nitrogen and phosphorus nutrient limitations can
  be expected as in Earth (Head et al, 2003).
  Surface derived electron donor supply in the form
  of any reactive fossil carbon is unlikely to have
  persisted to the present day as on Earth as much
  of the Martian crust is very ancient (109years)
  and thus with Earth oil reservoir carbon
  consumption rates much of the reactive fossil
  carbon in more permeable parts of the crust will
  have likely been consumed by heterotrophic
  organisms within in the first billion years or
  the subsurface will represent once deeply buried
  and thus sterile uplifted crust. Heterotrophs are
  unlikely to be found on Mars! It is thus likely
  that much of Mars is either dead or that any
  persisting Martin life in the deep subsurface
  will consist of organisms either deriving energy
  from reduction of carbon dioxide with hydrogen or
  from anaerobic oxidation of methane all three
  compounds being likely still being charged from
  the Martian deep crust and mantle to this day. We
  conclude that while much of Mars is probably dead
  any existing Martians surviving today will be in
  deep porous rocks and will be low diversity
  Archaea and associated symbiotic bacteria
  associated with methane cycling.

Martian sedimentary basins are believe to be very
old (109a). Oligotrophic subsurface OM
consumption rates would have eaten all the OM
long ago so any surviving subsurface Martians
would have to be Hydrogenotrophic Methanogens-CO2
from mantle H2 from mineral hydrolysis.
3. Compositional gradients provide degradation
rates
sediments from the present surface but is a
stable isolated biosphere derived from long
period evolution of surface derived organisms
during burial (Wilhelms et al, 2001). Recent
field studies suggesting that the actual fluxes
of hydrocarbons being destroyed in oilfields
around 40-70oC are around 10-4kg/m2/year of oil
water contact area and in excess of 50 of oil
may be destroyed in reservoir at advanced levels
of biodegradation with methane the common
terminal end product produced dominantly from
carbon dioxide reduction(5- Head et al, 2003).
These rates are comparable with the total
subsurface respiration seen in ocean margin
sediments (Dhont et al, 2002).
7. Bacterial counts subsurface marine sediments
Parkes et al, Nature 1994
6. A biodegradation model run on a Chinese
reservoir
bibliography
Current reservoir temperature and reservoir
vitrinite reflectance (Ro), for reservoirs in
the uplifted Barents Sea basins (no degraded
oils) and the subsiding N.Sea basins (degraded
oils). The horizontal shaded bar indicates
reflectance levels equivalent to
paleotemperatures of 80-90 degrees centigrade,
the vertical shaded bar the current 80-90 degrees
centigrade region.
Biodegradation in deep reservoirs proceeds
slowly under anaerobic and oligotrophic
conditions, typical timescales of biodegradation
being around 10 million years with large
fractions of oil being mineralized with methane
as a common terminal product (Head et al, 2003).
It is nutrients, principally mineral derived
phosphorus and nitrogen, not electron acceptors
or donors that are limiting in Earth, but on
Mars, electron donor supply must often be
limiting with the electron donors related not to
burial of surface derived organic matter as on
earth but to supply of either hydrogen or methane
from below! Recent advances in biodiversity
theory (Curtis et al, 2002 - 8) relate NT and
Nmax (8) to different types of environments. We
suggest speciation is driven by chemical
gradients which relate to the relative rates of
metabolism and mass transport processes
homogenizing the environment. While diffusively
mixed, the low rates of metabolism of petroleum
reservoir largobiospheres suggests the biosphere
will be well mixed even though diffusion is the
predominant mixing mechanism and we suggest that
the petroleum largobiosphere will thus have low
total individual numbers (ca 103 cells/cc) and
also have a low diversity (indeed will have comparable diversity to other
well mixed/connected environments such as sewage
treatment plants, non-stratified advecting marine
and lacustrine water columns (10).

• Curtis, T.P., Sloan, T. and Scannell, J.W. 2002.
  Estimating procaryotic diversity and its limit.
  PNAS, 99, 16, 10494-10499.
• Dhont, S., Rutherford, S. and Spivack, A.
  Subsurface life in deep sea sediments. Science,
  295, 2067-2070.
• Head, I. M., D. M. Jones, and S. R. Larter. 2003.
  Biological activity in the deep subsurface and
  the origin of heavy oil. Nature 426
  (6964)344-352.
• Larter, S. R., A. Wilhelms, I. Head, M. Koopmans,
  A. Aplin, R. Di Primio, C. Zwach, M. Erdmann, and
  N. Telnaes. 2003. The controls on the composition
  of biodegraded oils in the deep subsurface (Part
  1) Biodegradation rates in petroleum reservoirs.
  Org. Geochem. 34601-613.
• Parkes, R.J. et al, The deep biopshere, 1994,
  Nature, 371, 410-413.
• Wilhelms, A., S. R. Larter, I. Head, P.
  Farrimond, R. di-Primio, and C. Zwach. 2001.
  Biodegradation of oil in uplifted basins
  prevented by deep-burial sterilisation. Nature
  4111034-1037.

4. Uplifted sterilised reservoirs not biodegraded