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GIFTGIFT 20052005 TheHistoryofTheHistoryof theEarththeEarth

EGU,EGU, ViennaVienna 26-2726-27thth AprilApril 2005 2005 Issues

™ How are Earth-like planets built?

™ How did silicate and metal reservoirs form?

™ How did Earth acquire its volatile elements? Why isotope geochemistry ?

Why isotope geochemistry ?

Three main kinds of information:

™ Rates and timing ™ Tracing ™ Past and present conditions Rates and timing Some significant radio-nuclides in the early solar system Nuclide Half-life (Myrs) Daughter

41Ca 0.1 41K 26Al 0.73 26Mg 60Fe 1.5 60Ni 53Mn 3.7 53Cr 107Pd 6.5 107Ag 182Hf 8.9 182W 247Cm 12 235U 205Pb 15 205Tl 129I16129Xe 92Nb 36 92Zr 244Pu 80 136Xe 146Sm 103 142Nd 235U704 207Pb 238U 4468 206Pb 87Rb 48800 87Sr Tracing

(Hillson, 1986) Tracing

0.722

e. canine1 Sr 0.721 86 d. canine1 teeth

Sr/ canine2, 87 0.720 1st, 2nd premolar (enamel) intestine 0.719 bone cortical 0.718 trabecular

0.717 0 1020304050 age [years] Past and present conditions

Stable isotopes

18O 18O 16 sample − 16 std . δ 18O = O O x1000 18O std . 16O MultipleMultiple collectorcollector inductively inductively coupled coupled plasmaplasma source source massmass spectrometryspectrometry

Opens the periodic table for isotopic research IA VIIIA Most of the world pre-1995 1 H II IIIA IVA VA VIA VIIA He 2 Li Be B C N O F Ne 3 Na Mg IIIB IVB VB VIB VIIB --- VIIIB --- IB IIB Al Si P S Cl Ar 4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 6 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 7 Fr Ra Ac Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Unstable and Atmophile Lithophile Siderophile Chalcophile uncharacterised IA VIIIA Oxford developing… 1 H II IIIA IVA VA VIA VIIA He 2 Li Be B C N O F Ne 3 Na Mg IIIB IVB VB VIB VIIB --- VIIIB --- IB IIB Al Si P S Cl Ar 4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 6 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 7 Fr Ra Ac Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Unstable and Atmophile Lithophile Siderophile Chalcophile uncharacterised Oxford developing… 1 H He 2 Li B C N O Ne 3 Mg Si S Cl Ar 4 K Ca Ti V Cr Fe Ni Cu Zn Ga Ge Se Br Kr 5 Rb Sr Zr Mo Ru Pd Ag Cd In Sn Sb Te Xe 6 Ba La Hf Ta W Re Os Ir Pt Hg Tl Pb Rn 7 Ra Ce Nd Sm Eu Gd Dy Er Yb Lu Th Pa U

Atmophile Lithophile Siderophile Chalcophile ToTo taketake advantageadvantage ofof MCMC--ICPMSICPMS youyou needneed

PhysicistsPhysicists whowho cancan designdesign andand buildbuild newnew kindskinds ofof MCMC--ICPMSICPMS instrumentsinstruments ToTo taketake advantageadvantage ofof MCMC--ICPMSICPMS youyou needneed

ExpertsExperts inin laserlaser technologytechnology Issues

™ How are Earth-like planets built?

™ How did silicate and metal reservoirs form?

™ How did Earth acquire its volatile elements? Planet formation

Disk theory Star formation

Astronomers can see stars like our Sun forming in the Orion Nebula

Many of the new stars are embedded in a disk of dust and gas Dusty disks can also be detected around slightly older stars with interferometry.

HR4796A is ~ 8 million years old Time-scales Saturn About 100 times bigger than the Earth

Must have formed fast to trap nebular gases How did the Earth and Moon form? Ni others 4% 2% O30% Fe32% “Earth Pie” “Earth S3% Mg 14% Si15% Models for accreting the Earth

™ Solar mass nebula (Cameron 1978) ™ Minimum mass solar nebula (e.g. Hayashi 1978) ™ Late stage collisions with no nebula (e.g. Wetherill 1986)

The Moon probably formed from debris produced in a giant impact between the proto-Earth (~90% Earth mass) and another planet called "Theia" (~10% Earth mass).

dust and rock debris... clumped together...... and formed the Moon Model Time-scales for Accreting the Earth (>95%)

™ Solar mass nebula < 106 yrs (Cameron 1978) ™ Minimum mass solar nebula ~ 5 ×106 yrs (e.g. Hayashi 1978) ™ Late stage collisions with no nebula 107 -108 yrs (e.g. Wetherill 1986) George Wetherill, 1986 Isotopes and time-scales

100 nucleosynthesis in stars

% abundance remaining % abundance 0 0 collapse of solar nebula end of planetary growth start of planetary growth

start of galaxy → time → present Isotopes and time-scales

100 nucleosynthesis in stars stable

% abundance remaining % abundance 0 0 collapse of solar nebula end of planetary growth start of planetary growth

start of galaxy → time → present Isotopes and time-scales

100 nucleosynthesis in stars stable

long-lived

% abundance remaining % abundance 0 0 collapse of solar nebula end of planetary growth start of planetary growth

start of galaxy → time → present Some significant radio-nuclides in the early solar system Nuclide Half-life (Myrs) Daughter

41Ca 0.1 41K 26Al 0.73 26Mg 60Fe 1.5 60Ni 53Mn 3.7 53Cr 107Pd 6.5 107Ag 182Hf 8.9 182W 247Cm 12 235U 205Pb 15 205Tl 129I 16 129Xe 92Nb 36 92Zr 244Pu 80 136Xe 146Sm 103 142Nd 235U 704 207Pb 238U 4468 206Pb 87Rb 48800 87Sr

238238U/U/204204PbPb inin thethe earthearth

238 204 238 204 U/ Pbtotal earth = 5 × U/ Pbsolar system 238 204 U/ Pbtotal earth = 0.7

SilicateSilicate earthearth

238 204 corecore U/ Pbsilicate earth ~ 8 Pb-richPb-rich 238 204 U-poorU-poor U/ Pbcore = 0 U-rich,U-rich, Pb-poorPb-poor Clair Patterson 1956 Isotopes and time-scales

100 nucleosynthesis in stars stable

long-lived

% abundance remaining % abundance 0 0 collapse of solar nebula end of planetary growth start of planetary growth

start of galaxy → time → present Isotopes and time-scales

100 nucleosynthesis in stars stable

long-lived

short-lived (extinct) % abundance remaining % abundance 0 0 collapse of solar nebula end of planetary growth start of planetary growth

start of galaxy → time → present supernova remnant Cassiopeia A real stardust Some significant radio-nuclides in the early solar system Nuclide Half-life (Myrs) Daughter

41Ca 0.1 41K 26Al 0.73 26Mg 60Fe 1.5 60Ni 53Mn 3.7 53Cr 107Pd 6.5 107Ag 182Hf 8.9 182W 247Cm 12 235U 205Pb 15 205Tl 129I 16 129Xe 92Nb 36 92Zr 244Pu 80 136Xe 146Sm 103 142Nd 235U 704 207Pb 238U 4468 206Pb 87Rb 48800 87Sr

Isotopes of hafnium and tungsten 40 Hafnium (Hf) 30

20

10

0 40

30

% Abundance 20

10 Tungsten (W) 0 174 176 178 180 182 184 186 Mass (amu) Isotopes of hafnium and tungsten 40 Hafnium (Hf) 30 182Hf ×1000 20 (extinct)

10 6 T½= 9 × 10 yrs 0 40

30

% Abundance 20

10 Tungsten (W) 0 174 176 178 180 182 184 186 Mass (amu) Isotopes of hafnium and tungsten 40 Hafnium (Hf) 30 182Hf ×1000 20 (extinct)

10 6 T½= 9 × 10 yrs 0 40

30 182W produced

% Abundance 20 by decay ×1000 10 Tungsten (W) 0 174 176 178 180 182 184 186 Mass (amu) Hf/W in the Earth

Hf/Wtotal Earth = Hf/Wsolar system = 1

SilicateSilicate EarthEarth

corecore Hf/Wsilicate Earth = 15 W-richW-rich Hf-poorHf-poor Hf/Wcore = 0 Hf-rich,Hf-rich, W-poorW-poor NBNB SilicateSilicate EarthEarth == Earth'sEarth's PrimitivePrimitive MantleMantle

Asteroid 4 Vesta - the source of eucrites? EucritesEucrites relative relative toto bulkbulk silicatesilicate EarthEarth

Eucrites have a large Bouvante excess in 182W Millbillillie relative to BS Earth... Stannern

Bereba BSE Juvinas Pasamonte Jonzac Serra de Mage Angra dos Reis

-10 0 +10 +20 +30 +40 +50 ε182W (BSE) CarbonaceousCarbonaceous chondrites...chondrites...

...represent...represent bulkbulk solarsolar systemsystem EucritesEucrites relative relative toto bulkbulk solarsolar systemsystem

Bulk solar system is Bouvante 182 Millbillillie slightly lower in W ……thereforetherefore than BS Earth (Kleine Stannern and others 2002) AsteroidAsteroid 44 VestaVesta Bereba accretedaccreted andand BSE differentiateddifferentiated Juvinas BSS Pasamonte overover aa shortershorter Jonzac timetime frameframe thanthan EarthEarth Serra de Mage Angra dos Reis

-10 0 +10 +20 +30 +40 +50 ε182W (BSE) Some eucrites thought to come from Asteroid 4 Vesta

Earliest formed objects -calcium aluminum refractory inclusions

0 20 40 60 Time after start of solar system (millions of years) EucritesEucrites relative relative toto bulkbulk solarsolar systemsystem

Bulk solar system is Bouvante slightly lower in 182W Millbillillie than BS Earth (Kleine Stannern and others 2002) …what…what doesdoes Bereba thisthis meanmean forfor BSE Juvinas the time-scale BSS the time-scale Pasamonte ofof EarthEarth Jonzac accretion?accretion? Serra de Mage Angra dos Reis

-10 0 +10 +20 +30 +40 +50 ε182W (BSE) George Wetherill, 1986 Accretion of the Earth

1.0 τ = 10

0.8 13 17

25 0.6 50 100 0.4

0.2 Wetherill 1986 Mass fraction of earth τ = accretionary mean life (Myrs) 0 0 20 40 60 80 100 Time (Myrs) Continuous core formation

ÎÎ

Gradual accretion, mixing, isotopic equilibration and metal segregation

The ~ 2 εW excess of the silicate Earth relative to average solar system is consistent with ~63% accretion in 11 Myrs τ Earth

Some eucrites thought to come from Asteroid 4 Vesta

Earliest formed objects -calcium aluminum refractory inclusions

0 20 40 60 Time after start of solar system (millions of years) Model Time-scales for Accreting the Earth (>95%)

™ Solar mass nebula < 106 yrs (Cameron 1978) ™ Minimum mass solar nebula ~ 5 ×106 yrs (e.g. Hayashi 1978) ™ Late stage collisions with no nebula 107 -108 yrs (e.g. Wetherill 1986) 9 Mars - rates and timing Martian meteorites Martian meteorites MartianMartian Martian meteorites meteoritesmeteorites ALH84001 (1) ALH77005 (1) Shergotty (1) Zagami (1) 182 EETA79001 (1) Have high ε W EETA79001 (2) but low Hf/W in Lafayette (1) Nakhla (1) martian mantle Chassigny (1) DAG 476 (2) SAU 051 (2)

(Lee and Halliday 1997, Kleine et al. 2004) -3 -2 -1 0 1 2 3 4

ε182W 4 180 184 180 184 λt Hf/ W = ( Hf/ W)BSS.e

3 Nakhla MartianMartian

0.3 0.07 meteorites 2 meteorites W 1 λ=0.5 0.1 0.05 182 Tungsten data ε Zagami 0 calibrated with a model of -1 exponential core formation -2 0.1 1.0 10.0 100.0 Longevity of W depletion by metal segregation (Myrs)

SomeSome sourcessources developeddeveloped withinwithin aboutabout 11 millionmillion yearsyears τ Earth

Some eucrites thought to come from Asteroid 4 Vesta

Earliest formed objects -calcium aluminum refractory inclusions

0 20 40 60 Time after start of solar system (millions of years) τ Earth

Latest core formation on Mars

Some eucrites thought to come from Asteroid 4 Vesta

Early reservoirs on Mars Earliest formed objects -calcium aluminum refractory inclusions

0 20 40 60 Time after start of solar system (millions of years) Issues

™ How are Earth-like planets built?

™ How did silicate and metal reservoirs form?

™ How did Earth acquire its volatile elements?

Accretion would have left the Earth really HOT...

…with oceans of MOLTEN ROCK CoreCore formationformation

The standard model

DenseDense metallicmetallic ironiron liquidsliquids descenddescend throughthrough thethe silicatesilicate EarthEarth Continuous core formation

ÎÎ

Gradual accretion, mixing, isotopic equilibration and metal segregation

The ~ 2 εW excess of the silicate Earth relative to average solar system is consistent with ~63% accretion in 11 Myrs

τ Earth

Latest core formation on Mars

Some eucrites thought to come from Asteroid 4 Vesta

Early reservoirs on Mars Earliest formed objects -calcium aluminum refractory inclusions

0 20 40 60 Time after start of solar system (millions of years) τ Earth

Earth's Moon

Latest core formation on Mars

Some eucrites thought to come from Asteroid 4 Vesta

Early reservoirs on Mars Earliest formed objects -calcium aluminum refractory inclusions

0 20 40 60 Time after start of solar system (millions of years) 80 (Myrs) 60 accrete τ

40

20

Mean life of accretion 0 0 20 40 60 80 100 120 140 160 180 200

Hf-W age of Earth Model Time of Giant Impact tGI (Myrs) (Yin et al. 2002) 80 (Myrs) 60 accrete

τ Possible effect of isotopic disequilibrium 40 during accretion

20

Mean life of accretion 0 0 20 40 60 80 100 120 140 160 180 200

Hf-W age of Earth Model Time of Giant Impact tGI (Myrs) (Yin et al. 2002) Hf-W age of Moon (Halliday 2004) Clair Patterson 1956

Bulk Silicate Earth 15.8

Geochron Pb 204 15.3 Pb/ 207

Estimates of the BSE

14.8 17.0 17.5 18.0 18.5 19.0 206Pb/204Pb 15.8 GG91 KC99 A88 L91 ZH88 Geochron D84 AL89

Pb MKC03

204 K89 DZ79 15.3 Pb/

207 KT97 Estimates of the BSE

14.8 17.0 17.5 18.0 18.5 19.0 206Pb/204Pb 80 (Myrs) 60 accrete

τ Possible effect of isotopic disequilibrium 40 during accretion

20

Mean life of accretion 0 0 20 40 60 80 100 120 140 160 180 200

Hf-W age of Earth Model Time of Giant Impact tGI (Myrs) (Yin et al. 2002) Hf-W age of Moon (Halliday 2004) 80

(Myrs) Possible effect of late loss of 60 lead from the silicate Earth accrete

τ Possible effect of isotopic disequilibrium 40 during accretion U-Pb age of Earth (Halliday 2004) 20

Mean life of accretion 0 0 20 40 60 80 100 120 140 160 180 200

Hf-W age of Earth Model Time of Giant Impact tGI (Myrs) (Yin et al. 2002) Hf-W age of Moon (Halliday 2004) Issues

™ How are Earth-like planets built?

™ How did silicate and metal reservoirs form?

™ How did Earth acquire its volatile elements? 350 M 300 δ Xe (‰)

250

200

150 The Earth’s 100 atmosphere 50 Earth Atmospheric Xe is fractionated 0 relative to the -50 Solar Wind Xe -100 solar wind -150 or U-Xe -200 U-Xe

-250 Mass M (amu) -300 124 126 128 129 130 131 132 134 136 Isotopes provide clues about the origin of planet Theia

The Earth and Moon are very different today, but isotopes show they formed from the same "stuff "... Oxygen isotope tests of provenance from Wetherill (1994) Oxygen Isotopes in Primitive Meteorites 15 ) ? la M u b A e n C lar C e o lin s 1 the - f e o ordinary p 10 o en l yg s x chondrites o ve iti m ri CI p on ( ati on cti fra ial tr ine 5 res l ter (‰) carbonaceous chondrites

O CI CI clasts 17 CM CM δ 0 CV3 CO CK CR CV3 CH -5 enstatite chondrites CK ordinary chondrites CO CCAM - carbonaceous chondrite anhydrous mineral line

data from R. Clayton -10 -5 0 5 10 15 20 25 δ18O(‰) OxygenOxygen isotopesisotopes forfor thethe Moon,Moon, MarsMars andand VestaVesta

4.0 HED Mars (SNC) unpubl. 3.5 Moon, Wiechert et al. 2001

)

‰ ( 3.0

W

O 2.5

M

S 2.0 TFL

O

7

1 δ 1.5

1.0 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 δ18OSMOW(‰) Apollo Missions lunar meteorites (Clayton and Mayeda 1996) this study (Clayton and Mayeda 1975) Terrestrial O*OO rcinto Line Fractionation 18 δλ−δ=Δ 17

17

Δ

O ( ‰ )

1 7 OriginOriginOrigin ofofof EarthEarthEarth’s’’ss waterwaterwater ??? Isotopic analysis of oxygen in zircons with an ion probe provides evidence of the existence of low temperature water since 4.3 billion years ago

U-Pb + trace elements oxygen U-Pb The major portion of Earth’s water may come from water-rich planetesimals

Comets have a different D/H The Sr isotopic composition of the Moon provides time-integrated Rb/Sr for Theia 0.6992

Moon Sr 0.6990 APB 86 CEPB Lunar highlands samples Sr/

87 BSSI Time-integrated Rb/Sr THEIA = 0.07±0.02 0.6988

Rb/Sr MOON = 0.006 Rb/Sr MARS = 0.07 The inner solar system may have been dominated by volatile-rich Mars-like proto-planets

Lark and deGoursac [2001] ™ The Earth accreted with a mean life of >15 Myrs and over time-scales of 107 to 108 yr ™ This is consistent with accretion with little nebular gas ™ The Moon-forming Giant Impact occurred at ~ 45 Myrs ™ Discrepant time-scales are consistent with incomplete mixing of metal and silicate during accretion ™ There was also late of loss of volatiles from the Earth ™ Theia had a chemistry similar to that of Mars but formed at a heliocentric distance similar to Earth ™ The inner solar system may have been dominated by Mars-like objects ™ Water was added by 4.3 Ga