Download Hadean-Archean habitability

Hadean - Early Archean:
4.4 to ~ 3.5 Ga
How to build a habitable planet?
Jack Hills in Australia meta-conglomerat with the oldest minerals on Earth 4.4 Ga
Geological time scale
1 : Hadean
Quasi no rock record
2 : Archean
Rock record
First cooling of magma ocean
Alteration of basalt to produce serpentinite
crust ~ as today on seafloor
146Sm
→ 142 Nd (T1/2= 103 Ma) silicate/silicate fractionation before total decay
of 146Sm < 150 Ma, done early Hadean
Acasta (Canada)
oldest rocks on Earth, end of Hadean, 4.01 Ga
Acasta (Canada)
oldest rocks on Earth, end of Hadean, 4.01 Ga
Acasta (Canada)
oldest rocks on Earth, end of Hadean, 4.01 Ga
Zircon
ages
Jack Hills (Australia) meta-conglomerat
Archean in age but contains very old zircons
Jack Hills (Australia) meta-conglomerat
Archean in age but contains very old zircons
Jack Hills (Australia) meta-conglomerat
Archean in age but contains very old zircons
ZrSiO4
1 mm
U-Pb age at 4.4 Ga
Part of the grain crystalized
shortly after end of magma
ocean
Age distribution of zircons
Different dates on
different zircon layers
Several age populations
Oldest
Quartz, micas and plagioclase
∂18O in zircons = 5 to 7.4 ‰
Original magma’s = ∂18O ~ 8.5 to 9.5‰
(La/Lu)N zircons (La/Lu)N of magma~ 200 = TTG magma
4.4 Gyr zircons not so different from actual zircons
Granitic inclusions present in zircons
Quartz, micas and plagioclase
∂18O in zircons = 5 to 7.4 ‰
Original magma’s = ∂18O ~ 8.5 to 9.5‰
(La/Lu)N zircons (La/Lu)N of magma~ 200 = TTG magma
4.4 Gyr zircons not so different from actual zircons
Continental crust & oceans in Hadean
Granitic inclusions, quartz, micas, plagioclase
La/Lu data same as Archean crust
Stable continental crust at 4.4 Ga
∂18O indicates that magma interacted with relatively
cold water (~ 70 ºC)
Liquid water is present
Ocean present at 4.4 Ga
Looks like Hadean already was habitable
“cool early earth”
(but was it inhabited?)
Implications for the origin of life
Early Hadaen (4.568-4.40
Ga) Magma Ocean
Late Hadaen (4.40- 4.00
Ga) Continental crust + liquid water
ocean
Late heavy bombardment
Archean (4.00 – 2.50 Ga)
Continents, oceans, plate tectonic,
etc.
No life possible
Conditions favorable
for life
Sterilization ??
Life is present
Between 4.0 and 3.8 Ga
Late heavy bombardment
Between 4.0 and 3.8 Ga
Collisions - impacts all over solar system
Hubble ST
Fragment G
impact
Asteroid Eros
1994 Shoemaker-Levy 9 on Jupiter
NASA deep impact
33x13x13 km
1 km
Surface comet Tempel 1
140 km crater on Europa’s ice
Mare
Orientale
on the
Moon ~ 930
km
multi-ring
crater
Collisions - impacts all over solar system
Hubble ST
Fragment G
impact
Asteroid Eros
1994 Shoemaker-Levy 9 on Jupiter
NASA deep impact
33x13x13 km
1 km
Surface comet Tempel 1
140 km crater on Europa’s ice
Mare
Orientale
on the
Moon ~ 930
km
multi-ring
crater
Collisions - impacts all over solar system
Hubble ST
Fragment G
impact
Asteroid Eros
1994 Shoemaker-Levy 9 on Jupiter
NASA deep impact
33x13x13 km
1 km
Surface comet Tempel 1
140 km crater on Europa’s ice
Mare
Orientale
on the
Moon ~ 930
km
multi-ring
crater
Cratering event on solid surface
Cratering event on solid surface
Cratering event on solid surface
Cratering event on solid surface
Suevite
Cratering event on solid surface
Suevite
Melt-rock
Cratering event on solid surface
Suevite
Fractured breccia
Melt-rock
Cratering event on solid surface
Shocked
minerals
100 µm
Suevite
Fractured breccia
Melt-rock
Cratering event on solid surface
Tektites
1 cm
Shocked
minerals
100 µm
Suevite
Fractured breccia
Melt-rock
Comparative
stratigraphy of
Early Earth and
Moon
3.4
3.5
3.6
Mare Lavas
Orientale
Schrödinger
Cluster of Lunar
craters around
4.0 to 3.8 Ga
Imbrium
Sereniatis
& Crisium
3.7
Early
Imbrian
Nulliak Quartzite
3.8
Amitsôq Gneiss
LH B
Isua Gneiss
3.9
Nectaris
4.0
Oldest
impact melt
Acasta Gneiss
4.1
4.2
4.3
Oldest
Anorthosite
crust
4.4
Origin of
Moon
4.5
Jack Hill Zircon
Origin of
Earth
Late heavy bombardment
2 hypotheses
Slow decline
Rapid decline but short peak
Cool early earth
Another ? Archean rate
Hadean
Archean
Arguments for the LHB
~ 3.9 Ga max. age of Lunar impact melt and = shock degassing
ages of Lunar and Martian meteorites
How to preserve ancient Lunar crust (4.4 Ga old anorthosites) if
elevated bombardment in Hadean ?
No elevated PGE in Lunar crust contrary to what expect if
bombardment constant over 500 Myr (based on available samples)
LHB = mass added to the Moon = 2x1013 g/an if extrapolated
over whole Hadean > Lunar mass or Moon formed at ~4.1 Ga
Terrestrial zircons do not show shock features and formed on a
rather cool Earth
Traces of LHB on Earth ?
No impact marker in Isua (shocked qz, PGE)
LHB missed Earth ?
Chronology problem: LHB terminated before Isua
Traces erased by sedimentation and erosion
Search for it on other planets
Extrapolate Moon data to Earth
Moon: 1700 craters > 20 km, 15 > 300 -1200 km, multiple ring
basins
Earth: > 10 000 craters > 20 km, 200 > 1000 km,
1 crater 20 km every 104 years
Possible consequences
Vaporize all of part of oceans, ejection of atmosphere
Large basins are formed
Volcanism, fracture of oceanic crust
Contribution of OM, and noble gases
Impact rate and Hadean environments
Hadean impact rate is elevated no life possible (hyp. 1)
Cool early Earth hypothesis and effect of LHB
Low impact rater : life originates in Hadean (hypothesis)
Complete extinction during LHB, second start in Archean
Major Hadean diversification but mass extinction during LHB,
only hyperthermophiles survive on deep ocean floor,
and radiate in Archean
Major Hadean diversification but mass extinction during LHB,
bottleneck effect, new radiation during Archean
Origin and cause of LHB
Models show that 0.350 to 1.2 Ga after formation of solar
system, gas planets migrate towards their current orbits
(Jupiter and Saturn inward, Neptune and Uranus outward)
Destabilize orbits of asteroids and comets
Objects come flying towards inner solar system
Impact craters (basins) as a craddle for life ?
hypothesis of origin in hydrothermal vents handicaped by high vent Tº > 350 ºC
destroys all organic molecules
Melt-rock generates hydrothermal circulation
Important extension of hydrothermal environments in the crater, life > 106 year, enough to
concentrate complex organic molecules
Ries (25 km), Manson (35 km) and Puchezh-Katunki (80 km) mineralogy show temperature
gradients 400 to < 100°C.
Crater contains highly fractured and brechiated rocks, inducing active circulation and microenvironments with exposed mineral surfaces to favorable help catalyze pre-biotic
chemistry
Complex organic molecules delivered by the projectile
Yellowstone Geyser system, complex biosphere
Stromatolites first form to recolonize Ries crater lake
Do complex organic molecules survive an impact ?
Complex organic molecules are destroyed by the high temperatures generated by impact (Chyba et al.,
1990)
Still valid for asteroidal projectile at ~ 20 km/s
Computer model : amino acids survive a cometary impact in the ocean
Comet volatile and ice-rich, easily vaporized but the high energy cloud cools rather quickly
The lower the impact angle, the lower temperature in the cloud, the higher the survival rate of
Text
organic molecules
Oblique (angle < 15°) impact of a comet in the ocean could spread (> 10%) of its amino acid
content
Such impacts are rare, but considering impact rate in the Hadean or during LHB, they could have
contributed to the concentration/reaction of amino acids in the oceans
Association amino acids and altered clay particles (spherules) offer surface for pre-biotic
chemistry ?
Archean impact rate ?
Ejecta layer
Location
Age (Ga)
Thickness cm
Acraman
Australia
0.59
40
Sudbury
Ontario
1.86
25 to 70
Ketilidian
Greenland
~ 2.0
100
Dales Gorges
Australia
2.48
30
Wittenoom
Australia
2.54
100
Revilio
Australia
2.56
20
Carawine
Australia - S. Africa
2.63
2470
S4 (Barberton)
South Africa
3.24
15
S3 (Barberton)
South Africa
3.24
200
S2 (Barberton)
South Africa
3.26
310
S1 (Barberton)
South Africa
3.47
35
KT
World
0.065
few cm (to 1 m)
Archean and Proterozoic impact layers
1 cm
0.5 mm
Impact ejecta layer Wittenoom, Australia
Comparison
Cretaceous-Tertiary layer
10 km impact 65 Ma ago
Archean and Proterozoic impacts
Ejecta layers thick and with large impact spherules, PGE anomaly
but rare shocked grains
Spherule composition originally basaltic, associated with tsunami
deposition
Large size impacts: > KT boundary, projectiles 20 to 50 km?
Oceanic impacts ?
Detection coincidence ? impact rate > today, peak in
bombardments ?
How did life cope with elevated rate ?
Geological time scale
1 : Hadean
2 : Archean
Quasi no rock record
Rock record
Archean continental crust: a long record
Isua gneiss, sedimentary rocks, Greenland dated at 3.865 Ga
Deposited as turbidite
Amitsôq gneiss, plutonic rocks, Greenland dated at 3.82 Ga
Magmatic origin
Current distribution of Archean terranes
Gneiss of Shaw (Australia) at 3.45 Ga
Swaziland gneiss complex at 3.644 Ga
Greenstone belts
Banded Iron formation
Gopping Gap, Pilbara,
Australia
3.5 Ga
Barberton, komatiite,
South Africa
3.445 Ga
Chert, Barberton,
3.445 Ga
Pilbara, Australia 3.5 GA
Shark bay Australia
today
Are these equivalent to stromatolites ?
Films of Cyanobacteria
trapping sedimentary grains
in shallow water
environments
Greenstone belts
Tholeitic basalt
Kuhmo, Finland
2.65 Ga
Grauwackes
Kuhmo, Finland
2.65 Ga
Late Plutonic rocks
Granodiorite of Arola, Finland 2.65 Ga
Proportion of Archean terranes
Kuhmo, Finland 2.7 Ga
Gurur, India 3.1 Ga
Arola, Finland 2.7 Ga
Komatiites: evidence for a warmer Archean Earth
Magmatic rock that does
not exist after end of
Archean
1 cm
1 cm
Komatiites = equivalent to ridge basalts ?
Komatiites = ultra basic lava’s SiO2 = 45%, MgO = 25%
High density
Elevated proportion of mantle fusion
Formation Tº are very high ~ 1650 ºC
Originated from deep within the mantle, contain diamonds
Only present in the Archean
Warmer mantle need, now too cold to generate komatiites
Archean continental crust
Rocks
Tdh = Trondhjemite
To = Tonalite
TTG
Gd = Granodiorite
Archean crust versus today’s crust
Archean TTG
Calco-alcaline crust of today
Fundamental differences in magmatic processes between
Archean and today
H2O released
lowers melting point
Subduction today
a cold plate sinks below another
wet melting generates magma
Hot plate melts
Archean subduction of a hot plate
that melts quickly and dry
Higher mantle fusion & different plate tectonic
Very long angle subduction
Buoyancy of both plates is almost same
4.0 Ga ago the Earth internal heat
production was 4 x higher than today
To avoid melting, the heat must be
evacuated:
- Faster mantle convection
- Longer ridge length
Intense magmatism
and
hydrothermalism
Black smoker
Size of Earth is constant, consequently longer ridge length
implies much smaller plates
Current
average plate size = >>1000 km
Archean
average plate size = ~ 100 km
Pilbara craton Australia
Dome and basin structures evidence for vertical tectonic
Vertical tectonic, soft cheese principle
Heavy lithologies
sink in the softer
underlying rocks
Summary Archean plate tectonic
Mini-plates
Rapid plates
Low angle subduction
Very long oceanic ridges
Intense hydrothermalism
Dry melting of hot plate in subduction
No major mountain belts, soft cheese principle
Emerged continents ?
Continents above water in Archean
At 3.86 Ga in Isua presence of detritic sediments most likely
eroded from continent located above water
Conglomerat in Barberton,
difficult to form under water
Fossil dessication
cracks from Barberton
Dessication cracks
At 3.4 Ga Barberton lithologies contain garnet recording
pressure 15kbar (~ 45 km depth in crust today)
Some kind of mountains existed, how high ?
Growth of crustal material
Wilson cycle-like?
First traces of life
Earth Moon
2.5 Ga
Window origin of life
3.8 Ga
Metamorphism
renders
microfossil and C
isotopic evidence
ambiguous
> 2.7 Ga
The tracers:
1) Morphological fossils: microfabrics, stromatolites
A) Endolithic
coccoids in a
crack of an 3.8
Ga Isua BIF
samples
(Westfall & Folk,
2003)
C)
Abiologic
microstructure
produced in the
laboratory (GarciaRuiz et al., 2003).
B) Carbonaceous microstructure in Apex chert (3.4 Ga) either microfossil
“ballerina” or a pure metamorphic process of mineral mimicking biology
(Brasier et al. 2002)
2) Molecular fossils: derived from cellular macromolecules, ex. lipids, steranes, hopanes
but : very small quantities preserved with major risk of contamination (Brocks et al. 2003) there
is not clear record < 2.7 Ga because of metamorphism
3) Isotope ratios: ex. ∂13C or ∂34S : ∂13C = ([(13C/12C)sample/(13C/12C)std]-1)*1000
Carbonates ∂13C = 0‰ and remains of biological material = ~ -25 0‰
Consequently low ∂13C values in Archean sediments could indicate life
but: graphite forming abiologically during metamorphism also has low ∂13C !
There is nothing conclusive before 2.7 Ga
The tracers:
1) Morphological fossils: microfabrics, stromatolites
A) Endolithic
coccoids in a
crack of an 3.8
Ga Isua BIF
samples
(Westfall & Folk,
2003)
Controversial
C)
Abiologic
microstructure
produced in the
laboratory (GarciaRuiz et al., 2003).
B) Carbonaceous microstructure in Apex chert (3.4 Ga) either microfossil
“ballerina” or a pure metamorphic process of mineral mimicking biology
(Brasier et al. 2002)
2) Molecular fossils: derived from cellular macromolecules, ex. lipids, steranes, hopanes
but : very small quantities preserved with major risk of contamination (Brocks et al. 2003) there
is not clear record < 2.7 Ga because of metamorphism
3) Isotope ratios: ex. ∂13C or ∂34S : ∂13C = ([(13C/12C)sample/(13C/12C)std]-1)*1000
Carbonates ∂13C = 0‰ and remains of biological material = ~ -25 0‰
Consequently low ∂13C values in Archean sediments could indicate life
but: graphite forming abiologically during metamorphism also has low ∂13C !
There is nothing conclusive before 2.7 Ga
After 2.5 Ga explosion of evidence for life forms
5 µm
1 µm
Bacterial filament in
Gunflint Chert 2.5 Ga
Modern Leptothrix Febacteria
Modern Eoentophysalis
Eoentophysalis
cyanobacteria in Early
Proterozoic cherts
Along with isotopic evidence of advanced metabolism
reduced chemical species: CH4, H2, S, H2S, Fe2+, chemoautotrophic,
followed soon after by photosynthesis
Diversification of metabolism
a possible scenario ?
The rise of O2 between ~ 2.4 to 2.0 Ga
The great oxidation event
Lots of debates currently on exact timing and consequences
O2 producers could have originated earlier but rise in O2 was delayed by various processes:
tectonic, burial Corg., unstable climate etc.
Fractionation of S isotope is mass independent under UV photolysis when no O3 layer and for
O2 < 10-5 PAL
After 2.3 Ga when O2 present in atmosphere normal mass dependent fractionation of S
Oxidized paleosols, red beds are present
Decrease in BIF that form in anoxic oceans, no more precipitation of Fe
Evaporite deposits, and carbonates increase significantly
Consequences for organisms
O2 poisoning, extinction or refuge in anoxic environments, less methanogenesis
Radiation of photosynthetic organisms, replacement, new metabolism, new possibilities
Stromatolites become very abundant (but perhaps already present around 2.8 Ga?)
Consequences for climate
1st : faint young sun paradox: between 4.0 Ga and today sun’s increased it luminosity by 37%
Sun
If the Earth had same atmosphere as today it
would have been frozen until ~ 2.0 Ga.
However no (or very few) traces of glaciations
(diamictite, isotopic signals) in the Archean
Evolution of luminosity of 3 stellar masses
through time
Lots of greenhouse gas would keep Earth warm
CO2 but also CH4, in absence of O2, methanogenesis (considered a early metabolism)
occurring in anoxic conditions would be highly efficient capable to sustain warm climate:
If Archean atm = today’s (without O2) the CO2 + CH4 PAL leads to average Tº < -10 ºC, CH4
must rise to 10 PAL = T 0ºC, 100 PAL = T 5ºC and 1000 PAL = T 15ºC average
Consequences for climate
Rise of O2 would affect production of the main greenhouse gas CH4 by restricting
progressively anoxic environments
Less and less CH4 in atmosphere, CO2 cannot compensate, most likely also decreases
Glaciations results: Clear evidence first phase at 2.9 Ga (Pongola glaciation), then Huronian
glaciations 3 events between 2.45 and 2.32 Ga, matches rising of O2
At 2.2 Ga evidence for low latitude Makganyene glaciations = First Snowball Earth ?
What is a snowball Earth ?
Glaciations extending down to equator runaway ice albedo feedback drops Tº to -50ºC for a
few 1000 y, then Tº stabilizes around -10ºC after million of years of ice cover the lack of
silicate weathering + volcanic emissions lead to CO2 greenhouse effect in atmosphere and
melting of ice, it is followed by global tropical conditions (see Hoffman et al. 1998).