Part 3- The Earth and its Reservoirs

Question 0

How are relative abundances of elements in the Sun measured?

Answer 0

Measuring the intensity of certain wavelengths of light emitted by elements in the photosphere and by looking at meteorites

Question 1

How much of the mass of the solar system does the sun account for?

Answer 1

> 99%

Question 2

What name is given to the group of meteorites that have relative elemental abundances almost identical to the photosphere?

Answer 2

Carbonaceous Chondrites

Particularly the most primitive- CI carbonaceous chondrites

Question 3

What are CI carbonaceous chondrites used for?

Answer 3

To define the average composition of the solar system.

Question 4

What abundance of O, Fe, Si and Mg does the earth have?

Answer 4

Chondritic relative abundances

Question 5

Where does most of the Fe occur on earth?

Answer 5

In the core (in reduced form)

Question 6

Where does most of the O, Si and Mg occur?

Answer 6

In the silicate mantle

Question 7

What group of elements is the silicate portion of the earth highly depleted in?

Answer 7

Volatile elements

Question 8

What does the volatile and refractory classification scheme describe?

Answer 8

At which temperatures elements condense to form dust grains at the conditions of the solar nebular.

Question 9

What temperatures do refractory elements condense at?

Answer 9

Very high (>1400K)

Question 10

Give an example of a common refractory element.

Answer 10

Fe, Mg, Si

Question 11

What condensation temperatures do moderately volatile elements have?

Answer 11

1250 to 650 K

Question 12

What condensation temperatures do highly volatile elements have?

Answer 12

<650K

Question 13

Give an example of a volatile element.

Answer 13

Na, Zn, Ar, Ne

Question 14

Why are the terrestrial planets of the inner solar system strongly depleted in volatile elements?

Answer 14

Too hot at time of formation.

Question 15

What are the Earth’s 3 major geochemical reservoirs?

Answer 15

The core (1/3 of the mass of the earth), the mantle and the continental crust.

Question 16

What does the Bulk Silicate Earth (BSE) describe?

Answer 16

BSE = Mantle + Continental Crust

Question 17

What is the composition of the BSE identical to?

Answer 17

The primitive mantle (Earth’s mantle before the formation of the CC).

Question 18

What is ~95% of the Earth’s core formed of? What is the other ~5%?

Answer 18

Iron and Nickel.

Unidentified light elements- probably O, Si, S or C.

Question 19

Why does the composition of the BSE differ form the Solar System average?

Answer 19

• Volatile depletion in the solar nebular.

* Depletion of siderophile elements in the silicate Earth by core formation

Question 20

Which groups have the largest depletions in the BSE?

Answer 20

Most volatile and most siderophile.

Question 21

Which groups are enriched in the BSE?

Why?

Answer 21

Refractory and lithophile.

As a consequence of mass balance- depletion of others.

Question 22

How does the continental crust differ from the mantle (2)?

Answer 22

CC is low in Mg.
CC is high in Ca, Al, Na and K.
Mantle is opposite.

Question 23

Where else are the elements Ca, Al, Na and K enriched?

Why?

Answer 23

In basalts.

They partition preferentially into mantle melts.

Question 24

What can the depleted (current) mantle be regarded as?

Answer 24

A residue of partial melting.

Question 25

What rock does the CC have an average composition akin to?

Answer 25

Andesites

Question 26

How do scientists know about the composition of the mantle (2)?

Answer 26

• Direct samples form the upper mantle- alpine peridotite massifs and xenoliths.
• Velocities of seismic waves through the mantle.

Question 27

What is the relative composition of the mantle?

Answer 27

Relatively homogeneous ultramafic composition.

Question 28

What is the structure of the mantle?

Answer 28

Exclusively solid with slow convection.

Whole mantle convection is accepted as opposed to layered convection.