COMPRES 2006 Snowbird, UtahDavid Walker, Lamont-Doherty Earth Observatory, Columbia U.

Why ever would the Earth’s core leak?

Why ever would the Earth’s core leak?

With Simon Clark, Martin Kunz, Mike Walter and a With Simon Clark, Martin Kunz, Mike Walter and a COMPRES-supported cast of thousandsCOMPRES-supported cast of thousands

With Simon Clark, Martin Kunz, Mike Walter and a With Simon Clark, Martin Kunz, Mike Walter and a COMPRES-supported cast of thousandsCOMPRES-supported cast of thousands

(NSF CSEDI+2 progress report)

Chondritic Evolution

Evolution of OC

187Os/

188 Os

0.100 0.120 0.140

0.119820

0.119830

0.119840

0.119850

0.119860

0.119870

Mix

ing

186

Os

/188

Os

Mauna Loa Loihi Koolau Mauna Kea Kilauea Hualalai Kohala Siberia Gorgona

solidsolidmantlemantle

InnerInnercorecore

LiquidLiquid metal metalouter coreouter core

Core-Core-flavoredflavoredplumeplume

atmosphereatmosphere

A.Brandon, R.J.Walker et al. (2003)

Some plume basalts show correlated Os anomalies.

OsPtPt

DescendingDescendingslabslab

Sr, O, Nd recycling signal

187Re-driven187Re-driven19

01

90 P

t-dr

iven

Pt-

driv

en1

90

19

0 Pt-

driv

enP

t-dr

iven

Maybe Re?

Manghnani and Yagi

Is the core really leaking?Is the core really leaking?

Yes, perhaps: Os isotopesHawaiian plume Fe/Mn & Ni

Perhaps not: radiogenic Sr/Os correlation

What could drive it?What could drive it?What could drive it?What could drive it?

Cooling drives changes in solubility

Reorient for buoyant slag floating on the core

FeO solution reaction

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 100 200 300 400

P kilobars

DV

cc/

mo

leDAClimit

O2 fromDaresbury

O’Neill et al.Rubie et al.Multi-anvil

DVsolution = LiquidVFeO – CrystalVFeO

What determines oxygen solubility(P)?

Solubility Solubility extremely extremely

limitedlimited

Solubility Solubility extremely extremely

limitedlimited

Manghnani and Yagi

Thermal exsolution of a floating ‘slag’(We know the Earth is cooling)

(A year in the lab can save you an hour in the library!)(A year in the lab can save you an hour in the library!)

But we still need to measureOxygen solubility in Fe liquid at high P,T

But we still need to measureOxygen solubility in Fe liquid at high P,T

Does it reach 2% or 20%?

Fe FeO

100 microns

X-ray absorptiontransmission

imaging in situ

X-ray beamX-ray beam

How to measure Oxygen solubility in molten Fe

at a megabar?

[Underway withCOMPRES support

for the ALS 12.2.2 team]

Lasermelting

http://xraysweb.lbl.gov/bl1222/home.htm

Experiments at ALS/LBL With Mike Walter*, Simon

Clark, Martin Kunz, and many others

*

X-rays in

LBL ALS Station 12.2.2

Remote and/orautomated pneumatic

P ramping

Remote and/orautomated pneumatic

P ramping

Double-sidedLaser heatingDouble-sidedLaser heating

X-rays in

LBL ALS Station 12.2.2

Double-sided pyrometryDouble-sided pyrometry

High-resolution imaging

Laser

FeO crystals in 100 hole

DAC gasket image

In situ DAC X-Radiographic Imaging (XRI)

Gasket

Fe

FeO

X-ray density for chemical analysis!

Thin CdS phosphor

CCD and optics

FeFeO

Liq

Itrans

Fe

FeO

Liquid %O2

Single in situ property (Itrans)needed to characterize

chemistry along abinary join.

Absorption(ع) &/or emission

Itrans

Fe

FeO

Liquid

%O2

Peritecticpossible

to recognizewhen reactants

are spatiallyresolved.

FeFeO

Does this work?

FeS

Fe

50 kilobars

Melting shows erosionStation 12.2.2 ALS

Melting shows erosion

50 kilobars

FeS

Fe

What about Fe-FeO?

Fe-FeS after first melting

at ~50 kbar

48000

50000

52000

54000

56000

58000

60000

0 10 20 30 40 50 60

Position (Pixels = ~1.5 microns)

6 K

V X

-ray

co

un

ts

Expected liquidUsselman, 1975

First Liquid

Fe

FeS

Topography convolved with chemistry

-and-resolution limited by

phosphor sharpness and sample preparation

It seems to work!

550 kilobars550 kilobars

FeO

Fe

No erosion on melting!

Consistent with the DAC results of Takafuji et al. (2005) <6%Consistent with the DAC results of Takafuji et al. (2005) <6%

XRI @ 120 kbar

Are there other solutions to the problem?

Oxygen solubility does not appear to be high enough to be interesting.

Lumpy D′′ probably not

exsolved,floating slagon molten Fe of the outer

core

Glatzmaier & Roberts 1995

Earth’s dynamomagnetic field

mantlecore

low [Fe]

Toroidal magnetic field in the outer core generates local anodic

and cathodic areas at the CMB ~ 1 V

Could this drive any electrochemicaltransfers across the CMB?

(See Abby Kavner’s forthcoming paper in EPSL)(See Abby Kavner’s forthcoming paper in EPSL)

What does the presence of life do for us?What does the presence of life do for us?

Oxidative corrosion of coremantle

Core signal generated by recycled oxidized crust.Contaminated plume source

D” includesCMB magma

chambers

N2 + O2 Oxidized crust

Iron meets oxygen!

When oxygen does not dissolve in iron.

rustysurface rustysurface Bright inner coreBright inner core

solidsolidmantlemantle

InnerInnercorecore

Liquid metalLiquid metalouter coreouter core

Core-Core-flavoredflavoredplumeplume

N2 + O2

DD" with magmatic" with magmatictitration chamberstitration chambers

Most effective and quick if oxygen solubility low

Revenge of the plants!

OxidizedOxidizedslabslabOs-Sr-Nd-O signal of

recycled crust not ashow stopper. It is the

key to the deliverymechanism for the corrosive reaction.

Test: when does the Os signal start?[>2.8 Gy ago (Puchtel et al.)]

Test: when does the Os signal start?[>2.8 Gy ago (Puchtel et al.)]

Why not electrochemistry?Why not electrochemistry?

Remaining questions:

Does the biosphere-core feedbackdeserve to be taken seriously?