Co‐‐evolution of the atmosphere,
Cop,oceans, and life of Earth
Yasuhito SEKINE
DDept.
t C
Complexity
l it SSci.i & EEngr.
The Universityy of TokyoyHabitable planet workshop. 2009.8.18

Today’s topic: co‐evolution of Earth & life

Figure after TPF HP• Earth is the only known aqua planet so far.
• We
W needd tto kknow h
how ththe ocean, atmosphere,thandd liflife
have evolved and interacted over Earth’s history.

Log ((partial ppressuress) (bar)Evolution of Earth’s atmosphereN20‐11O2‐22CO2‐3‐4CH43.0

2.0
1.0
Ageg ((billion yyears ago)g )0(Holland, 1984; Tajika & Matsui, 1992; Kasting, 1993;
Rye & Holland, 1998; Farquhar et al., 2000; Pavlov et al., 2001; Hoffman & Schrag, 2000; Zahnle et al., 2006)

Log ((partial ppressuress) (bar)Evolution of Earth’s atmosphere
Cyanobacteriab0(O2‐producing‐1b1bacteria)i )‐22‐3CH4
Phytoplankton‐4(Eukaryotes)
3.0

N2O2
Methanogen
Mth(CH4‐producingCO2b t i )bacteria)
2.0
1.0
Ageg ((billion yyears ago)g )0(Holland, 1984; Tajika & Matsui, 1992; Kasting, 1993;
Rye & Holland, 1998; Farquhar et al., 2000; Pavlov et al., 2001; Hoffman & Schrag, 2000; Zahnle et al., 2006)

Log ((partial ppressuress) (bar)Evolutionof Earth’s
Q1. How had
the earlyatmosphere
Earth been
The Great
Oxidation
Event:
seen
from space?
tthee mostost ssignificant
g ca t chemicalc e ca transitiont a stoQ2
Q2.
Wh did th
the O2 levelsl l risei Nat
the titime??
2t th0 Why
Cyanobacteria is considered to have evolved at least 2.7billi years ago (Bbillion(Brocksk ettOal.,l 1999)‐1
12‐22CO2‐3‐4CH4Q3 Why
Q3.
Wh
the2.0iincrease iin
3.0 did th
1.0O2 occur 0sorapidly
p yAgeingeologicaltimescale?
g g((billiongyyears ago)g )(Holland, 1984; Tajika & Matsui, 1992; Kasting, 1993;
Rye & Holland, 1998; Farquhar et al., 2000; Pavlov et al., 2001; Hoffman & Schrag, 2000; Zahnle et al., 2006)

Q1. How had the early Earth been
seen fromfspace??
Key:ey: Titanta (O(Organicga c chemistryc e st y in C
CH4‐richc atmosphere)
at osp e e)

N2CH4HC2H2C4H2HCN

H
Titan atmosphereN2: 95–98%, CH4: 2–5%

Organicaerosols

Q1. How had the early Earth been
seen fromfspace??
Key:
ey: Titanta (O(Organicga c chemistryc e st y in C
CH4‐richc atmosphere)
at osp e e)
Titan aerosol analog (tholin)
Formed from N2/CH4=9/1 gas mixtures

Titan atmosphereN2: 95–98%, CH4: 2–5%

Orange early Earth?
TimeAtmosphericA
h i Oxidizing
composition

O2 N2

CO2N2Aerosol formed from N2/CH4 = 9/1

CH4 + 3O ⇒ CO + 2H2O
CH4/CO2 > 0.5 (Trainer et al., 2007)

PlanetaryRange for aerosol
N2mass24⇒ Laboratory experiments are key to predict theCO + CH
H2formation
surface environment of Super Earths.

H2Aerosol formed from H2/CH4 = 10/1

CH4

CH4/H2 > 0.05? (Khare et al., 1984)

H2 He + CH4 + NH3

C2H2 + 6H ⇒ 2CH4

Black Super Earths?

Reducing

Q2. Why 2.5–2.2 billion years ago?
Key: Ocean composition (A decline in Ni abundance inthe oceans from 2.5 billion yyears ago)g ) ((Konhauser et al.,, 2009))

Molar Ni/Fe

Cooling Earth’s mantle and a decrease ineruption deposits of Ni‐Ni‐rich volcanic rocks.

Highg Ni abundancein the oceans
Oceanic Ni
depletion
Ancient marine sediments(Banded iron formations)
Age (billion years ago)

Q2. Why 2.5–2.2 billion years ago?
Key: Ocean composition (A decline in Ni abundance inthe oceans from 2.5 billion yyears ago)g ) ((Konhauser et al.,, 2009))

Molar Ni/Fe

Ni is an bioessential element formethanogen

Ni+Highg Ni abundancein the oceans
An enzyme of methanogen
Oceanic
Ni
depletion

Thermal evolution & a decline in Ni in the oceans⇒ a methanogen
hf i & an increase
famineiini O2.
Age (billion years ago)

Q3. Why did O2 increase so rapidly?
Key: Climate change (A decline in CH4⇒ severe ice age)
Log (partial presssures) (bbar)

The Great Oxidation Event0
‐1

N2‐2

Glaciations O2((Huroniani glaciation)l i i )

‐3
3

CO2

CH4
How were3.0
the severe 2.0
glaciations 1.0
related with the0increase in O2 Agelevels?
⇒yearsTiming(billionago)is everything!
‐44

Osmium (Os) isotopic compositions inancienti t oceans (Sekine et al., under review)
・Point 1: Continental crusts have high concentrations of 187Os
decayed from 187Re contained in continents.
192Os

190Os

β decayy ((λ=1.66X10-11)
187Os

189Os
188Os

187Re

・Point 2: Os is a redox‐sensitive element, soluble and mobile
in hydrological cycle only under oxidizing atmospheres
Oxidizing
Reducing

Os(immobile)

HOsO5‐(mobile)

Osmium (Os) isotopic compositions inancienti t oceans (Sekine et al., under review)
O idi i atmospheres
Oxidizingth⇒ seawatert 187Os/O /188Os
O > 0.120 12
Reducing atmospheres ⇒ seawater 187Os/188Os ~ 0.120 12
Continental (radiogenic) Os

No input

187Os/188Os 〜1.4 (high)Oxidative
Current seawater Osweathering
187Os/188Os 〜1.06
Hydrothermal
activities

Mantle‐derived Os

187Os/188Os 〜0.12 (low)(Peucker Ehrenbrink & Ravizza,(Peucker‐EhrenbrinkRavizza 2000)

Huronian Supergroup (Canada)
2.22 billion years ago
Climatic cycles
Interglacial
Gowgandafm

Glaciation
Interglacial

Bruce fmGlaciation
Interglacialcarbonate

Ramseylake fm

Gl i tiGlaciation

glacial diamictite
sandstone
mudstone
volcanic rock2.45 billion years ago

Variation in initial 187Os/188Os (age =2.3±0.2 Ga)
Sandstone‐siltstone interval (greenhouse)

Recordingg a climatic recoveryy

Glacial diamictite ((ice house))
Mantle‐derived
value at 2.3 Ga

Variation in initial 187Os/188Os (age =2.3±0.2 Ga)
Increasingg
radiogenic Os⇒An increase in
the input of
The synchronicity of anradiogenic
episode of increasingcontinental
O2 tit lO
Osand deglaciation.

Climatic recovery acted to accelerate
the inputriseO2⇒ No
p in of(by providing
continental nutrients (phosphate) for
Mantle‐derived
radiogenic Os
value at 2.3 Ga
cyanobacteria?) (Kirschvink et al., 2000; Sekine et al., under review).

Relationship between climate & O2
Gl i tiGlaciation

Cyanobacteria
blooming

O2 increase

Mitigating thegreenhouse effect

CH4 decline

Atmospheric reactions

Log (partial ppressuress) (bar)N20
A positive feedback: A driving force for the rapid &Glaciationstransition to the oxidizing
world‐11irreversibleO2‐22‐3CH4CO2‐43.0

2.0
1.0
Age (billion years ago)0

In the aftermath of the rise in O2…

・ Enhancements of other redox‐sensitive
redox sensitive metals Mo,Mo Zn,
Zn & V inoceans, bioessential element for Eukaryotes (Anbar & Knoll, 2002; Knollet al., 2006; Dupont et al., 2006) ⇒ leading to prosperity of Eukaryotes
Log (partial ppressuress) (bar)

Eukaryote
0

Bacteria & Achaea‐1
1N2Animals

O2‐22‐3CH4CO2‐43.0

2.0
1.0
Age (billion years ago)0

Summaryy・ In Earth’s history, the evolutions of the atmosphere, ocean,Log (partial ppressuress) (bar)and climate have been closely related with that of life.
0

Change in volcanic rocks (Ni(Ni‐‐poor rocks)
N

2

Methanogen famine & decline in CH4‐1
1O2

Climatic change: Glaciation
Glaciation––interglaciation
‐2
2‐3‐4

Supply of nutrients for cyanobacteria & the rise in O2
CHCO2
4
The prosperity of Eukaryotes (including us)

3.0

2.0
1.0
Age (billion years ago)0

Summaryy・ Earth is, probably, not the only aqua planet.
2010’s: Sizes & densities of Earths Kepler mission (NASA)
How many Earths are in our galaxy?

Darwin mission (ESA)2020’s:2020
s: Atmospheres of Earths Terrestrial Planet Finder (NASA)

How many Earths have oxidizing atmospheres?
How many reducing atmospheres?
Or, something else?