L’origine de la vie: ASTROBIOLOGY
Frances Westall
CBM- Orléans
Origin, evolution, distribution and fate of life in the Universe
August 1996
Carl Sagan
August 1996
David S. McKay
Meteorite ALH84001
Found on the ice in Antarctica in 1984
Identified as a meteorite from Mars in
1994
(on basis of O isotope analysis, Mittlefeld, 1994, Meteoritics
Planet. Sci. 29:214-221)
ALH84001 fractured
Zoned carbonate (siderite, magnesite)
globules in fractures
Evidence of life in the ALH84001 meteorite?
1. Polycyclic aromatic hydrocarbons,
PAHs (organic material) are Martian and
characteristic of degraded organic
matter.
2. A mineral assemblage in the
carbonate globules is characteristic of
biologic influence.
3. Sub-micron magnetite grains in the
carbonate globules have properties
indistinguishable from, and unique to,
those formed by some Earth bacteria.
Therefore, they are biogenic.
 Magnetotactic
bacteria on Earth
live at the interface
between
oxic/anoxic waters
 They use the
Earth’s magnetic
field for orientation
Evidence of life in the ALH84001 meteorite?
1. Polycyclic aromatic hydrocarbons,
PAHs (organic material) are Martian and
characteristic of degraded organic
matter.
2. A mineral assemblage in the
carbonate globules is characteristic of
biologic influence.
3. Sub-micron magnetite grains in the
carbonate globules have properties
indistinguishable from, and unique to,
those formed by some Earth bacteria.
Therefore, they are biogenic.
4. Rock surfaces of and near the
carbonate globules are decorated with
bacteria-shaped objects. These objects
are inferred to be mineralized remains of
bacteria.
If this discovery is confirmed, it will surely
be one of the most stunning insights into
Press
NASA, Aug. 7, 1996
our universe that science
has conference,
ever
uncovered. Its implications
are as farWesley Huntress
David McKay
reaching and awe-inspiring
as can
be
NASA assoc.
director
imagined. Even as it promises answers to
some of our oldest questions, it poses still
others even more fundamental.
The History of Martian Rock ALH 84001
Formed
on billion
Mars about
4,1 billion
Mars
4.1
years
ago
4.0 penetrates
billion years
ago
Water
the fractures
and deposits carbonates 3.9 Ga
Rock ejected from Mars by a
16 million years ago
huge impact 16 million years ago
Rock
circulates
in space
for
16 million
years
in space
nearly 16 My
years ago, fractured by impacts
Ejected from Mars
~3.8-3.5
Ga years
Mars dries
up
3.9
billion
agoCarbonates Formed
Meteorite lands in Antarctica
Earth 13,000 years ago
about 13,000 years ago
Resided in Antarctica
Mars Timeline - Meteorite Samples
4.09 Ga
3.9 Ga
 (Carbonates)
Noachian
Hesperian
 1.3 Ga
 165 my
600-700 my
Amazonian
After: Bishop et al., 2009 LPSC XL
Evidence of life in the ALH84001 meteorite?
Huge controversy:
1. Polycyclic aromatic hydrocarbons, PAHs
(organic material) are Martian and
characteristic of degraded organic matter
AND extraterrestrial carbon!
2. A mineral assemblage in the carbonate
globules is characteristic of biologic influence
BUT also may be formed by abiological
processes!
3. Sub-micron magnetite grains in the
carbonate globules have properties
indistinguishable from, and unique to, those
formed by some Earth bacteria. Therefore,
they are biogenic ???????
4. Rock surfaces of and near the carbonate
globules are decorated with bacteria-shaped
objects. These objects are inferred to be
mineralized remains of bacteria BUT are
more likely to be corroded mineral artefacts!
ALH84001 Magnetite
MV-1 Magnetite
0.48nm
MV-1 Biogenic Magnetite has
a unique TruncatedHexaoctahedron Shape
0.48 nm
Magnetotactic bacterium
Scale bars = 20 nm
Problem:
 Magnetotactic
bacteria on Earth
live at the interface
between
oxic/anoxic waters
 They use the
Earth’s magnetic
field for orientation
 But Early Mars is
supposed to have
been ANOXIC (like
the early Earth)
 And at 3,9 Ga ago,
Mars may no longer
have had a
magnetic field
Fundamental questions!
1.
2.
3.
4.
What is life?
How/where did life originate (habitability conditions)?
Life on Earth/other planets?
Other forms of life (weird life)?
ASTROBIOLOGY
Origin, evolution, distribution and fate of life in the Univers
Fundamental questions!
1.
2.
3.
4.
What is life?
How/where did life originate (habitability conditions)?
Life on Earth/other planets?
Other forms of life (weird life)?
1. Origin of life
Origin of the
universe
-13.7 Ga
atoms
Formation of the Earth
molecules
Stars
Planets etc
Origin of life
- 4.5 Ga
organisms
Today
0
1. Origin of life
What is life ?
 A system that is capable of making more of itself, by itself,
and of evolving (A. Brack)
 An autonomous chemical system that undergoes evolution
(NASA)
 Chemical entity that consists of bounded
microenvironments in chemical disequilibrium with their
environment, capable of maintaining a low entropy state by
energy and environment transformation, and capable of
information encoding and transfer (Schultz-Makuch & Irwin,
2004)
1. Origin of life
What is life ?
 Bounded microenvironments and chemical disequilibria
Low energy
High
entropy
UNORGANISED
STATE
Low energy
Low entropy
CRYSTAL
High
energy
Low
entropy
LIVING CELL
 Living systems are able to establish order in a chaotic environment as long as
there is enough energy to resist the natural tendancy to high entropy
 Bounded microenvironments
 Examples of abiotic compartments: pores in hydrothermal
vents, pores in 3D clay structures
What is life ?
1. Origin of life
 Transformation of energy and environment to maintain a low
entropy state (i.e. an ordered state in a chaotic environment)
Low energy
High
entropy
Low energy
Low entropy
High
energy
Low
entropy
UNORGANISED
CRYSTAL
LIVING CELL
STATE
 Transformation of energy from external sources to maintain/increase order at
local (microscopic) levels
Consquences:
Creation and maintenance of a level of complexity that supports emergent
functions that exeed the sum of the parts of the system
What is life ?
1. Origin of life
 Information encoding and transmission
Low energy
High
entropy
Low energy
Low entropy
UNORGANISED
CRYSTAL
STATE
Permanancy/succession
 (mistakes in information coding and transmission
(mutation) essential for evolution)
 Examples of abiotic information transfer:
computer programmes, mineral growth
High
energy
Low
entropy
LIVING CELL
Chlorite
What is life ?
1. Origin of life
 Implications for the origin of life (1)
1. Construction and maintenance of a boundary (membrane) to separate it from
the environment
2. Transformation of energy into energy-yielding reactions to sustain itself
(metabolism)
3. Replicate and transmit genetic information (replication)
What is life ?
1. Origin of life
 Implications for the origin of life (2)
1. Size : small, high volume to surface ratio to ensure good diffusion of nutrients
in and metabolites out BUT large enough to host essential molecular
machinery (quelques centaines de nm?)
2. Liquid medium – dissolves charged ion species, enables chemical reactions
on a reasonable time scale
3. Environmental conditions: temperature, ionic strength, pH, trace element
composition (similar to that of seawater)
1. Origin of life
What is life made of (on Earth)?
Carbon molecules
75-90% water
Essential elements (nutrients, HNOPS, transition metals)
Minimal requirements of life?
- carbon
- liquid water
- nutrients
- energy
Other components/media?
 weird life ?
Abundance
Distribution of elements in the Universe (especially CHON)
Atomic number
1. Origin of life
Prebiotic chemistry  life?
Need association of all the ingredients (membrane, mechanism for
transforming energy, replication molecules) in the right physico-chemical
conditions
 chemical reactor: inflow of ingredients, concentration, assembly
Kinetics of assembly > degradation
Need gentle agitation to get molecules to « bump into » each other and
stick to form the prebiotic building bricks of life
But stable conditions for final assembly of the building bricks first cells
Origin of life
ingredients
Stimulate the
process
Information
preservation
and transfer
protocell
Cell with:
CHONS
catalysers  ARN
RNA


+Life
is
in
chemical
continuity
with
the
abiotic/prebiotic
world
H2O
Virus?
Proteins
energy
Membranes
 Life as a cosmic imperative (C. De Duve, 1974)?
Viruses, are they living entities?
Biological entity
Needs a host to multiply
Can be intracellular or
extracellular
Nucleic acids and proteins
(enzymes) + capside
Possible important role in
évolution (inventor of DNA? (P.
Forterre)
Virus-host organism?
DNA or RNA
Capside
Enzymes
The ingredients of life and habitability
Liquid water
Carbon
Essential elements (HNOPS)
Nutrients (transition metals)
Energy (chemical, heat,
UV, light)
INGREDIENTS OF LIFE
Planetary habitability
4.56 Ga Consolidation of the planet
4.5 Ga Moon-forming impact
 magma ocean
4.4 Ga Water
Uninhabitable planet
Habitable planet
Liquid water
Carbon
Nutients
Energy
Habitable planet
Habitability
SOURCES (for terrestrial planets)
Liquid water
– exogenous (LHB materials,
micrometeorites, comets)
Carbon
- exogenous (LHB materials,
micrometeorites, comets)
- endogenous (Fischer Tropsch synthesis
in the crust)
Energy
- UV, hydrothermal, chemical, light
Nutrients
- rocks
The terrestrial planets were habitable as soon as there were
stable bodies of liquid water at temperatures =/< 80°C voir
30°C
Water on the Early Earth
• Water by 4.3 Ga – evidence from zircons
(Wilde et al. 2001)
• Evidence of low temperature hydrothermal
activity from 4.3 Ga-old zircons (δ18O) and
ancient rocks 3.8-3.3 Ga
Wilde et al 2001. Nature, 409, 175-178
Early Earth – an ocean planet
1. Origin of life
Synthesis of organic molecules
Extraterrestrial origin
Terrestrial origin
Space
Hydrothermal vents
Atmosphere
Semoy, le 24 aout 2012
Synthesis of organic molecules: in hydrothermal systems
CHNOPS
Hydrocarbon from 16 to 29
C, CH3SH, CH3COOH,
thioesters
Fisher –Tropsch reactions
n CO + 2n+1 H2 -> CnH2n+2 + n H2O
1. Origin of life
Synthesis of organic molecules: in a reducing atmosphere
1930 : Oparin, Haldane prebiotic
chemistry
1953 : Urey and Miller experiment
Reacting CH4, NH3, H2, H2O
Activation : electrical discharge
Products dissolve in water 
Synthesis of 4 acides aminés + HCN +
HCHO (cyanide and formaldehyde)
Strecker reaction
HCHO + HCN + NH3 -> NH2-CH2-CN + H2O
NH2-CH2-CN + 2 H2O -> NH2-CH2-COOH + NH3
1. Origin of life
Synthesis of organic molecules: in space
Formation of organic molecules at
at the surface of silicate/ice grains
> 150 chemical species known
(formaldehyde, formic acid, alcohols,
amino acid precurses, …)
But how do these molecules get to the Earth ?
Semoy, le 24 aout 2012
1. Origin of life
Synthesis of organic molecules: incorporporation in..
Meteorites, micrometeorites
Comets
IDPs (interplanetary dust
particles)
Present flux, 20 000 tons/y
(100 tons/y org matter)
 During Hadean flux 1000 x
Organic molecules in the meteorites (+HCN, HCHO, PAH, POM, kerogens,
fullerenes / amino acids, nucleobases, fatty acids, amines, amides,
alcohols…) (Cronin, 1997, Pizzarello, Deamer, 1985); Slight chirality of the amino
acids : Aib (Maurette, Matraj)
Minerals : sulfides, oxides, clays ……
Synthesis of organic matter
Space conditions
Atmospheric entry
Exogenous origin of
organic matter
Impact on Earth
Semoy, le 24 aout 2012
Transition metals:
From rocks, minerals
Nutrients
Energy on the early Earth
 Heat
 Chemical (redox reactions)
 Light (Sun)
Habitable conditions on the early Earth
(global scale)
3.5 Ga
today
 Temperature
 pH
 Atmosphere
 Radiation (UV)
> 50°C ?
~5
<0.2% O2
~54W/m2
15°C
7.2-7.4
21% O2
1W/m2
 Volcanism
 Impacts
much
much
little
+/- nothing
(DNA weighted)*
(late heavy bombardment
~4.0 – 3.85 Ga)
Westall and Southam, 2006
* Cockell and Raven 2004
(1000)
Habitable conditions on the early Earth
(global scale)
3.5 Ga
today
 Temperature
 pH
 Atmosphere
 Radiation (UV)
± 50°C ?
~6-7
<0.2% O2
~54W/m2
15°C
7.2-7.4
21% O2
1W/m2
 Volcanism
 Impacts
much
much
little
+/- nothing
(DNA weighted)*
(late heavy bombardment
~4.0 – 3.85 Ga)
Westall and Southam, 2006
* Cockell and Raven 2004
(1000)
The environment of early Earth
Extreme
Extremely normal for all other planets!!
1. Origin of life: WHERE?
Hydrothermal vents ?
Rocks, minerals, reactive elements
Organic molecules
Energy (heat, redox reactions at the
surfaces of minerals, serpentinisation)
Temperature less than 80°C (30°C)!
Sub-sea vent – protection from radiation
1. Origin of life: WHERE?
Water and pyrite
- Chemical
reactions
at the and
surfaces
of vents
Organic
molecules
beehive
minerals, e.g. pyrite, produce energy
- Holes in minerals and rocks can be sites
of organic molecule concentration and
favorise interactions between molecules
Organic molecules and feldspar
Organic molecules and beehive
vents
1. Origin of life: WHERE?
Deep sea vent biogeochemical cycle diagram
1. Origin of life: WHERE?
Beach area
1. Origin of life: WHERE?
Streams on dry land?
PANSPERMIA
PANSPERMIA
BIOPAN: spores can survive space conditions
But spores formed in evolved organisms!
Complete sterilisation of the Earth?
Late Heavy Bombardment
Late heavy bombardment
Un filtre hydrothermal pour l’évolution de la vie
~3.9 Ga
primitive?
Complete sterilisation of the Earth? NO!
Evidence of the origin of life on the early
Earth ?
None !!
1. Origin of life
I-The Hadean Epoch
3.9-3.85 Ga :
Late heavy
bombardment?
4.4 Ga :
physico-chemical and
geological conditions
for life
-4.56 Ga
4.527 Ga :
Giant Moonforming
impact
Volatilisation
of the light
elements and
a part of the
mantle
Hadean
4.4 Ga:
Zircons
First evidence of
liquid water
Input from
meteorites,
micrometeorites
andd comets
0.5 µm
Oldest
preserved
cellular life
~3.5 Ga
Appearance
Of life
Plate tectonic recycling of the Earth’s crust
MARS
Early Mars
Early Earth
Land-locked planet
Ocean planet
Characteristics of a habitable planet
Liquid water
Carbon
Nutients
Energy
Environmental conditions on the early Earth/Mars
Earth
3.5 Ga
Mars
4.0 Ga
Ocean T°C
~55 (> 100)
~0- >50
Atmosphere
CO2, greenhouse
gases, < 0.2% PAL O2
CO2, greenhouse
gases, < 0.2% PAL O2
pH
Slightly acidic (< 7)
Slightly acidic - neutral
Radiation
54 W/m2 (1000)*
54 W/m2 (1000)*
Hydrothermalism
Extremely active
Extremely active
Volcanism
Extremely active
Extremely active
Impacts
Frequent
Frequent
*Cockell, Raven, 2004
Microbial requirements
Microbial growth depends on its:
- material needs (nutrients)
- on the source of energy and nature of the electron donor
- carbon source
-
Energy and electron donors
Oxidising/reducing reactions that oxidise the nutritive substance (organic,
inorganic; solid/liquid/gas) that the organism lives on
Energy types:
- Chemical energy i.e. the energy contained in the covalent bonds
between atoms (chemotrophs)
- Organic matter (organotrophs)
- Inorganic matter (e.g. minerals) (lithotrophs)
Light energy (photons) – phototrophs
HABITABILITY:
Microbial scales
Scales of habitability
2
Time scale for origin of life from Miller, Lazcano, 1994
Early Mars – a land-locked planet
Habitability scales Time
Space
Origin of life
105-106 y?
101-103 km
Extant life
Day-weeks
102-103 µm
Survival
10-1–106 y?
102-103 µm
 Early Mars was habitable
(on a microbial scale)
MICROBIAL HABITABILITY ON MARS
Origin
of life on Mars?
CONCLUSIONS
Life could possibly have emerged (abiogenesis) at different
times and different places on Mars
 Conditions for continuous evolution did not exist  limited
evolution of life
Very primitive, small life forms
62
HABITABILITY: Examples of primitive, chemotrophic
microorganisms
Pyrococcus jannashii, anaerobic,
hyperthermophilic, chemoorganotroph
Thiothrix, filamentous S-oxidising
chemolithotroph
Hyperthermophilic
virus TV1
63
Measurement type ExoMars mission
Outcrop
Panoramic camera,
microscope,
High resolution camera.
MSL and Curiosity
Instruments on in
situ space missions
are very small, have
very little power and
have reduced
resolution
NavCams, Mast Cam,
microscope
Texture
Panoramic camera,
microscope.
Mast Cam, microscope
Structure
Panoramic camera,
microscope.
Mast Cam, microscope
Optical microscopy, HR
microscope
camera
Mineralogy
ExoMars 2018 and
the Pasteur rover
Mars Science
Laboratory
Elemental
Composition
Traces of Life
Raman
IR spectrometer
XRD spectrometer
CheMin (XRD)
XRF
CheMin( XRF)
CheCam (LIBS)
APXS
LD- MS
SAM (with QMS; GC
and TLS)
VENUS
Maat Mons
volcano
Corona structure
Early VENUS ??
Europe, une lune de Jupiter couverte de glace
Eventuellement la vie ??
La surface glacée d’Europe
Salts (Mg sulphates) on the ice surface
Europa exploration
Titan
Saturn system
TITAN
Atmosphère N2, NH3, CH4
Temperature 94K
(- 179°C)
No life on Titan (today)
Enceladus - cryovolcanism
Enceladus - cryovolcanism
Schultze Makuch et al 2011
Life outside the Solar System?
EXOPLANETS
1st detected in 1995 (Mayor, Dulquez, Nature, 378, 355)
900 known, 2000 candidates; planets, moons
Most about size of Jupiter (hot Jupiters) or Neptune (easier to identify)
Habitable zone (definition?)
~40% stars will have planets smaller than Jupiter, Earth-like planets
(ELP)
 ELP more likely to be around stars with low Li and wide range of
metallicity (heavier elements, not necessary Fe)





 E.g. Earth-like planets around brown dwarfs
- Could have photosynthesis but at different wavelengths than on E
400-700 nm as opposed to 70-1100 nm on Earth
- Detection – O2 (if oxygenic)
- detection of pigments (IR edge rather than red edge)
Raven and Donnelly 2013
Artist's impression of Gliese 581 d, which is one of a few
potential habitable exoplanets confirmed so far
Artist's impression
of Kepler-22b, a
"Super-Earth" within
its star's habitable
zone
WASP-12b is
slowly being
consumed by its
host star.
Another 10
million years or
so, and it will be
gone
Space
Exploration
Pictures.
Image courtesy
NASA/ESA/G.
Bacon
Life in the univers
Carbon-based life
 Carbon, liquid water, nutrients (HNOPS, transition metals),
energy (N.B. C, H, O, among the most common elements in
the universe)
 Organic molecules+ high energy prebiotic molecules
(building bricks of life)  Cell components (molecules for
membrane, catalyst, information coding
 Origin of life – reducing environment: hydrothermal, beach,
(land?)
 Protocell evolution (O2; plate tectonics; co-evolution of life
and Earth)
 Life in extreme environments
 Early Earth: fossils of primitive forms of life (chemotrophs)
BUT, difficult to study!
Life in the universe
Habitability
 Carbon, liquid water, nutrients (HNOPS, transition metals),
energy
 Microbial spatial/temporal scales: origin of life, flourishing life,
dormant life
 Punctuated habitability on Mars
 implications for the evolution of life on Mars
 implications for life detection missions
 Venus, Europa*, Enceladus*…were/are potentially habitable
* outside the « habitable zone »  surface water zone
 Exoplanets ?
 Other kinds of life?
Si, silane, silicon, silicate (zeolite?), B, N, P, S
Si, P – uncommon in universe
4.5
Prebiotic
Billion years
3.5
Oldest
preserved
Origin
of life ? traces of life
2.5
1.5 0.5
Eukaryotes?
0.1
Multicellular life
Diversification of lifee
Geological time scale
Evolution of life
20 µm
1 µm
10 cm
50 cm
PHOTOSYNTHESIS
2. Oxygenic photosynthesis: Synthesis of ATP with O2
6H2O + 6CO2 ----------> C6H12O6+ 6O2
L’oxygène,
la bouffée
Oxygen,a breath
of freshd’air!
air
Rise of oxygen
Early Earth atmosphere < 0.2% present atmospheric level O2
 photochemical degradation of H2O vapour in the upper atmosphere
 eruption of boiling hydrothermal water at the surface
Causes of rise in O2
 Appearance of oxygenic photosynthesis
 Burial of reduced carbon/CO2 in the mantle through plate tectonics
 Increase of CH4 in atmosphere (microbial)
 Increase of SO4 in atmosphere (volcanic)
Small cells - fossilised viruses
TV1
TV1 (75d)
Orange, Westall et al.
Biogeosciences, 8, 1465–1475, 2011
Fine volcanic sand (3.5 Ga-old rock)
1 µm
Early Mars
Ice-covered basins?
Europa
Origin of life on Earth?
Example of chemolithotrphs (E from oxidation of inorganic compounds)
Occur in volcanic sediments 3.5 Ga old from Australia
Environment – beach sands
Oldest sedimentary terranes
Nuvvuagittuq
Isua
~3.8
Ga
Pilbara
<3.5 Ga.
Barberton
<3.5 Ga
Problem of preservation of the Earth’s crust!
Early life on Earth
What kind of life forms?
 Primitive
 Small
 Using organic/inorganic materials as sources of energy and
carbon
 Chemotrophs
- chemorganotroph (energy from oxidation of
organic compounds)
- chemolithotroph (energy from inorganic
compounds)
Early life on Earth
Example of chemolithotrphs (E from oxidation of inorganic compounds)
Occur in volcanic sediments 3.5 Ga old from Australia
Environment – beach sands
Modern analogue: Black sandy/muddy tidal flats on Iceland
beach
Fine volcanic sand
Example – layers of volcanic sediments from a beach environment
Pilbara, 3.5 Ga
Westall et al., 2006; de Vries et al., 2008
Volcanic particles
200 µm
200µm
Westall et al., 2006, 2011
Kitty’s Gap Chert, Pilbara (3.5 Ga)
Microbial corrosion tunnels
Qtz
VP
EPS
EPS
Foucher et al., 2010, Icarus
Westall et al., 2011, PSS
Carbon-coated volcanic particles (Kitty’s Gap Chert, Pilbara, 3.5 Ga)
Mapping Raman spectroscopy of
the thin section of rock
Carbon
 Highly degraded (mature)
carbon
Foucher et al., 2010, Icarus
Colony of coccoids on volcanic particle surface
Altered volcanic
grain
Chert
matrix
(Kitty’s Gap Chert, Pilbara, 3.45 Ga)
Westall et al., 2006, 2011
Silicified microbial colony
Colony of coccoids on volcanic particle surface
volc
coccoids
2 µm
Westall et al., 2006, 2011
Chemolithotrophic microorganisms from 3.5 Ga
0.5 µm
Small!
Two species (0.8, 0.4 µm)
0.5 µm
Westall et al., Geol. Soc. Amer. Spec Pub. 405, 105
Westall et al., 2011. Planet. Space Sci. 59:1093
Early life on Earth
What kind of life forms?
Primitive
Small
Using organic/inorganic materials as sources of energy
and carbon (chemotrophs)
Photosynthesis: sunlight as energy source
N.B. Photosynthesis is a later invention
6CO2 + 12H2S + Sunlight → C6H12O6 + 6H2O + 12S
(carbon chains)
 Produces more energy  more organic molecules  faster growth
 i.e. photosynthetic organisms are more efficient
Early life on Earth
Example of photosynthesisers (E from sunlight)
Volcanic sediments 3.3 Ga old from South Africa
Environment – beach sands
Littoral environment
photic zone
beach
hydrothermal
spring
evaporites
lagoon
beach
hydrothermal
veins
hydrothermal
springs
Modern analogue: biolaminated sediments on a tidal flat
Gerdes, G. et al., 1993. Facies, 29, 61-74
Gerdes, G. et al., 1985. J. Sediment. Petrol., 55, 265-278
Josefsdal Chert, Barberton ~3.3 Ga
Tidalites and
biolaminites
(photosynthetic
microbial mats)
Westall et al., 2006, 2011
Josefsdal Chert, Barberton ~3.3 Ga
Microbial mat
EPS
Filaments
2 µm
50 µm
Pilabara
~ 3.45 Ga
stromatolites
Plan view
Cross section
North Pole, Pilbara, 3.345 Ga
Habitable environments on the early Earth
Habitats
Energy (E) and Carbon Organism types
(C) sources
Water column??
C/E from organic
sources,
E from sunlight
Phototrophs/
organotrophs
Strange carbonaceous structures from the Pilbara, 3,45 Ga
Sugitani et al., 2010, Astrobiology, 10, 899
Early life on Earth
 Anaerobic microbial cells forming colonies, biofilms, microbial mats,
stromatolites
 Colonised all habitable
environments
 Diversified life forms
 Far from the origin of life and
LUCA
LUCA
The origin of life (on Earth)
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Earth habitable (microbial scale) from ~4.4 Ga
Late heavy Bombardment – would not extinguish life
Oldest traces of life preserved ~3.5 Ga
Already diversified biota including:
- chemotrophs (C, energy from organic/inorganic sources)
- phototrophs (energy from sunlight)
 Occuring in all habitable environments
- volcanic/hydrothermal
- beach/shallow/deep sea sediments
- open ocean?
 Anaerobic
BUT No traces of the origin of life, early evolution?
 LOOK ON MARS!