slide1 l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Origin and Early Evolution of the Earth: a volatile elements perspective PowerPoint Presentation
Download Presentation
Origin and Early Evolution of the Earth: a volatile elements perspective

Loading in 2 Seconds...

play fullscreen
1 / 45

Origin and Early Evolution of the Earth: a volatile elements perspective - PowerPoint PPT Presentation


  • 123 Views
  • Uploaded on

Origin and Early Evolution of the Earth: a volatile elements perspective. Cider 2010 Bill McDonough Geology, University of Maryland. Support from:. A volatile rich planet?. Time Line. 1 st order Structure of Earth Rock surrounding metal. 1897. Emil Wiechert. 1915. CORE-MANTLE. 1925.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Origin and Early Evolution of the Earth: a volatile elements perspective' - ishmael


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Origin and Early Evolution of the Earth:

a volatile elements perspective

Cider 2010

Bill McDonough

Geology, University of Maryland

Support from:

slide3

Time Line

1st order Structure of Earth

Rock surrounding metal

1897

Emil Wiechert

1915

CORE-MANTLE

1925

UPPER-LOWER MANTLE

INNER-OUTER CORE

1935

PLATE TECTONICS

1970

1995

slide4

5 Big Questions:

  • What is the Planetary K/U ratio?
  • Is the mantle in-gassing or de-gassing?
  • Distribution of volatiles in mantle?
  • Volatiles in the core?
  • Volatiles at Core-Mantle Boundary?

planetary volatility curve

secular changes

whole vs layered convection

Light element in the core

hidden reservoirs

slide5

Role of Giant Impacts: volatiles

  • Earth’s volatile budget was likely shaped by Mars-sized impacted events.
  • Did the late veneer introduce HSE and volatiles?
  • Differences in the volatile budget of the Earth and Moon?
slide6

More volatile questions

  • What are the volatile elements?
  • What are their abundances in the Earth?
  • When did we inherit them?
  • How did we inherited?
  • Is there a secular variation in the volatile elements abundances of the Earth?
slide7

Volatiles: defined

  • - H2O, CO2, N2, CH4, (i.e., H, C, N, O)
  • Noble gases (group 18 elements)
  • - elements with half-mass condensation T <1250 K
  • - elements readily degassed (e.g., Re, Cd, Pb…)
  • - chalcogens (group 16: i.e., O, S, Se and Te)
  • - halides (group 17: i.e., F, Cl, Br, I)?
  • alkali metals (group 1: Cs, Rb, K…)?
slide8

What are the moderately volatile elements?

Refractory >1400 K

“Si, Mg, Fe, Ni… 1350 to 1250 K

Moderately volatile 1250 to 650 K

Volatile <650 K

classified affinity where

Siderophile iron core

Lithophile oxide mantle

Chalcophile sulfur mostly core

Redox conditions in the Solar System…..

slide10

What is the composition of the Earth?

and where did this stuff come from?

Nebula

Meteorite

Heterogeneous mixtures of components with different formation temperatures and conditions

Planet:

mix of metal, silicate, volatiles

slide11

Volatiles: distribution

  • Atmosphere (N2 78%, O2 21%, Ar 1%, other)
  • Mantle volatiles: H2O, C(C, CO2, CO, CH4),
  • sulfides, etc
  • Core volatiles: FeC, FeN, FeO, FeS, FeH
slide12

Rings aroundbPictoris

Okamoto et al

(2004, Nature)

63 light yrs away

Astro-mineralogy -- determine size, crystal structure and chemistry of dust grains in space, often around protostars (observations usually at mid-infrared wavelengths (2–30 mm)).

0.1 μm- and 1.5 μm-sized olivine, pyroxene and quartz.

slide13

What’s in the ISM (interstellar medium)

Mid-infrared spectroscopy (IRS) Spitzer

X-ray absorption fine structure (XAFS) Chandra

<2.2% crystallinity in silicate exist indiffuse ISM.

In the Galactic ISM Si exists in the form of silicates, whereas a significant fraction of S exists in the gas phase.

ISM/solar O/Si 0:63 ± 0:17

Mg/Si 1:14 ± 0:13

S/Si 1:03 ± 0:12

Fe/Si 0:97 ± 0:31

The ratio of Mg to Fe in olivine is >1.2 and 15%–37% of the total O atoms in the ISM must be contained in silicate grains.

slide14

Star (~1 Myr) with a clearing disk

low-mass pre–main-sequence star

Spitzer Space Telescope Infrared Spectrograph

Glassy olivine

Cleared out

D’Alessio et al (2005) ApJ

slide15

Astro-Mineralogy

Von Boekel et al (2004; Nature)

HD142527 inner disk

Olivine

Pyroxene

hydrosilicate

ISM

slide16

“Standard” Planetary Model

  • Chondrites, primitive meteorites, are key
  • So too, the composition of the solar photosphere
  • Refractory elements (RE) in chondritic proportions
  • Absolute abundances of RE – model dependent
  • Mg, Fe & Si are non-refractory elements
  • Chemical gradient in solar system
  • Non-refractory elements: model dependent
  • U & Th are RE, whereas K is moderately volatile
slide17

H

O

C

N

Solar photosphere

(atoms Si = 1E6)

B

Li

C1 carbonaceous chondrite

(atoms Si = 1E6)

slide18

Inner nebular regions of dust to be highly crystallized,

Outer region of one star has

- equal amounts of pyroxene and olivine

- while the inner regions are dominated by olivine.

Boekel et al (2004; Nature)

Olivine-rich

Ol & Pyx

slide19

Mg/Si variation in the SS

Forsterite

-high temperature

-early crystallization

-high Mg/Si

-fewer volatile elements

Enstatite

-lower temperature

-later crystallization

-low Mg/Si

-more volatile elements

slide20

Olivine

Potential temperature gradient

Pyroxene

slide21

EARTH

CO

CV

CI

CM

H

LL

L

EL

EH

slide22

Earth @ 1 AU

Mars @ 2.5 AU

Olivine-rich

EARTH

CO

CV

CI

CM

H

LL

L

MARS

SS Gradients

EL

-thermal

-compositional

-redox

EH

Pyroxene-rich

slide23

Planetary Compositional Models - Earth

Mg/Si -- unknown needs to be fixed

Hidden reservoirs -- maybe?

142Nd Early Earth Reservoir -- unlikely

“Chondritic Earth” -- yes, (RLE)! but…

5) Future research -- geoneutrinos

-KamLAND, Borexnio, SNO+, etc

slide24

Earth is “like” an Enstatite Chondrite!

Mg/Si -- is very different

shared isotopic Xi -- O, Cr, Mo,Ru, Nd,

shared origins -- unlikely

core composition -- no K, U in core.. S+

“Chondritic Earth” -- lost meaning…

6) Javoy’s model? -- needs to be modified

slide25

Ca, Al, REE, K, Th & U

Lithophile

elements

Atmophilie elements

Core

Mantle

Fe, Ni,

P, Os

Siderophile

elements

slide28

Si

Fe

Mg

weight % elements

slide29

Th & U

Volatility trend

@ 1AU from Sun

slide30

Silicate Earth

REFRACTORY ELEMENTS

VOLATILE ELEMENTS

Allegre et al (1995), McD & Sun (’95)

Palme & O’Neill (2003)

?

Lyubetskaya & Korenaga (2007)

Normalized concentration

Potassium

in the core

Half-mass Condensation Temperature

slide31

Core elements remaining in the Silicate Earth

Siderophile*and Chalcophile*

*dominant chemical characteristic, but not an exclusive definition

slide34

4 most abundant elements in the Earth:

Fe, O, Si and Mg

6 most abundance elements in the Primitive Mantle:

- O, Si, Mg, and – Fe, Al, Ca

This result and 1st order physical data for the core yield a precise estimate for the planet’s Fe/Al ratio : 20 ± 2

slide35

What’s in the core?

What would you like?

Constraints: density profile, magnetic field, abundances of the elements,

Insights from: cosmochemistry, geochemistry, thermodynamics, mineral physics, petrology, Hf-W isotopes (formation age)

How well do we know some elements?

slide38

Core compositional models

Model 1

Model 2

others

slide40

Earth’s D/H ratio

  • Do we really know comets
  • D/H ratio of the oceans
  • What do chondrites tell us?
  • Source of water and other volatiles vs the sources of noble gases?

Ref: Owen and Bar-Nun, in R. M. Canup

and K. Righter, eds., Origin of the Earth

and Moon (2000), p. 463

slide41

Last CIDER report on volatiles in the Earth - Saal et al 2009

Progress Report Conclusions:

Approximate concentrations

Depleted Mantle H2O 50 ppm; CO2 20 ppm; Cl 1 ppm; F 7 ppm

Enriched Mantle H2O 500 ppm; CO2 420 ppm; Cl 10 ppm; F 18 ppm

Total Mantle H2O 366 ppm; CO2 301 ppm; Cl 7 ppm; F 15 ppm

  • Earth: 61024 kg Oceans: 1.41021 kg
  • Ordinary chondritic planet -- 4 oceans
  • Carbonaceous chondritic planet -- 600 oceans
  • Enstatite chondritic planet -- ~2-4 oceans
slide42

Volatile Budget!

H/C ratio of the bulk silicate Earth is superchondritic, owing chiefly to the high H/C ratio of the exosphere.

H/C ratio of the mantle is lower than that of the exosphere, requiring significant H/C fractionation during ingassing or outgassing at some point in Earth history.

Hirschmann and Dasgupta (2009)

slide43

Earth’s volatiles from chondrites?

Let’s hear from what Sujoy has to say!…

slide44

When it comes to volatiles…. remember, always, the words of

Francis Birch (1952)

Unwary “readers” should take warning that ordinary language undergoes modification to a high-pressure form when applied to the interior of the Earth. A few examples of equivalents follow:

High-pressure form Ordinary meaning

certain dubious

undoubtedly perhaps

positive proof vague suggestion

unanswerable argument trivial objection

pure iron uncertain mixture of all the elements