Lectures 1-5: the chemical composition of Earth

1. Introductions
   1. Who am I?
   2. Who are you?
2. Course structure
3. Making the Earth
   1. Chemical composition of the solar system
   2. Refractory and volatile elements
   3. Lithophile and Siderophile
4. Primitive Mantle
   1. Melting Olivine
   2. Pyrolite model

We acknowledge and respect the lək̓ʷəŋən peoples on whose traditional territory the university stands and the Songhees, Esquimalt and W̱SÁNEĆ peoples whose historical relationships with the land continue to this day.

Who am I?

• Blake Dyer (he/him/his)
  • I prefer Blake over Dr. Dyer or Professor Dyer

• Undergraduate at Rice University 2006-2010

• PhD at Princeton University 2010-2015

• Postdoc at LDEO (Columbia University) 2016-2019

• Started in SEOS at UVic in Nov 2019

• Fifth time teaching EOS 240
  • Also teach Advanced Sed/Strat, Marine Geology, and The Dynamic Earth

Research interests: the geologic history of climate and life

Research interests: the geologic history of climate and life

Who are you?

Some optional prompts:

• Name
• Why are you here?
  • What program are you in and/or why?
  • What do you hope to learn in EOS 240?
  • What challenges do you anticipate?

Geochemistry: a toolset for investigating Earth systems

1. How and when did the Earth form?

2. What about the continents?

3. When did life on Earth begin?

4. How has climate changed in the past?

5. Where should we look for habitable planets?

Schematic of Earth.

What is the chemical composition of Earth?

What is the black rock? What are the green bits?

The hot disk begins to emit radiation to space, rapidly cools, and a temperature gradient develops.

What are the major rock forming elements on Earth?

Earth $\approx$ MgO + CaO + SiO$_2$ + Al$_2$O$_3$ + FeO

Should the Sun and Earth have the same chemistry? How could we check?

Planetary Formation

Condensation sequence calculations

Condensation sequence calculations

Practice Problem: Condensation of Corundum from the Solar Nebula

Q1: Calculate the temperature that Corundum (Al$_2$O$_3$) begins condensing from the solar nebula using the following values (assume no other reactions):

$$ \mathrm{2Al + 3O \leftrightarrow Al_2O_3} $$

• Solar abundance (atoms) of Al: 8.51 x 10$^4$
• Solar abundance (atoms) of O: 2.36 x 10$^7$
• Solar abundance (atoms) of H: 2.6 x 10$^{10}$
• Pressure in the nebula: 10$^{-3}$ atm
• Gas constant (R): 8.314 J/mol K
• $\Delta$G$^\circ$ (standard free energy of reaction) for condensation of Al$_2$O$_3$: -1.23 x 10$^6$ J/mol

Q2: At what temperature will this reaction finish condensing all of the Aluminum in the nebula?

Recall: Earth $\approx$ MgO + CaO + SiO$_2$ + Al$_2$O$_3$ + FeO

from IPython.display import HTML

HTML(
    """
<center>
<div align="middle;height:10vh;">
<video width="60%" controls>
      <source src="videos/planet_formation.mp4" type="video/webm">
</video></div></center>"""
)

Define Goldschmidt classification.

Define Goldschmidt classification.

Define Primitive Mantle. What do we know about the modern mantle?

Olivine Solid Solution Phase Diagram.

Melting trends.

Pyrolite Model: Ringwood, A.E., 1962. A model for the upper mantle. Journal of Geophysical Research.

Chondrites

Chondrules: molten 'droplets' of nebular dust

AOAs: Ameboidal Olivine Aggregates ~100% olivine

CAIs: Calcium Aluminum Inclusions are the first condensates

Mineralogy of Chondrite phases

Chondrites have variable composition

Practice problem

The observed chondritic mass abundances for Calcium and Aluminum are:

Element	wt % in Chondrite	Atomic Mass
Ca	0.92	40.1
Al	0.85	27

The average wt % of CaO and Al$_2$O$_3$ in Basalt and Harzburgite:

Oxide	wt % in Basalt	wt % in Harzburgite
CaO	11.3	6.1
Al$_2$O$_3$	15.1	5.1

What ratio do you need to mix basalt and harzburgite back together to get the composition of the mantle before melt was removed? Assumptions:

• Pyrolite is a combination of melt (basalt) and melted mantle (harzburgites)
• Earth has the same Refractory Lithophile Elemental (RLE) abundances as Chondrites

Solution.

Solution.