The Ingredients in our Solar System Soup
If we compare the atmosphere of the Sun with a random meteorite, the composition matches nearly perfectly. This explains what our Universe is made of.
Two Places to get Data from
The Solar Photosphere
The Sun contains most of the mass of our solar system (99.86%). We can measure the elements in the Sun via Spectroscopy that analyses the light coming from the Photosphere. The absorption lines show exactly which elements are present.
CI Carbonaceous Chondrites
CI stands for Carbonaceous (rich in carbon/volatiles) Ivuna type (named after the Ivuna meteorite)
Chondrites (primitive meteorites) containing tiny distinct spheres called chondrules (frozen droplets of solar dust). Carbonaceous means it's rich in carbon and water. These CI Chondrites are the most primitive, chemically unaltered rocks we have. They never melted, never differentiated, and never heated up enough to lose their volatile elements. They are essentially fossilized solar dust.
The great Correlation
If we compare the abundance of elements between the Photosphere and the Chondrites, we find that the ratio is 1 for nearly all non-volatile elements. This shows that the Sun and the other solid material formed from the same soup of materials, and the CI Chondrites can be used as a Standard Reference to normalize geochemical data.
Deviations (where the Correlation is not so great anymore)
There are two major groups of exceptions, which tell us about the physical processes in the early solar system.
The Volatile Depletion (Gas vs Rock)
Gases like:
- Hydrogen
- Helium
- Carbon
- Nitrogen
- Oxygen
- Noble Gases
fall way off the line. The Sun has these in big amounts, but there are little of them in CI Chondrites. The reason for this is that these gases can not be easily be trapped inside of rock unless it bonds chemically.
The Lithium Anomaly (Nuclear Burning)
There is one specific element where the Meteorites have more than the Sun: Lithium.
The Meteorites show the correct original abundance, but the sun is depleted its Lithium by a factor of 100. The reason for this is a nuclear effect, the Sun consumes lithium in its nuclear reaction.
Normalization
Because CI Chondrites can be used as a baseline, we can compare the composition of other things in relation to them.
- Value = 1: The rock is primitive (solar-like)
- Value > 1 (Enriched): The element has been concentrated here (e.g., in the Crust)
- Value < 1 (Depleted): The element has been removed (e.g., in the Mantle)
This can smooth out the plot caused by the Oddo-Harkins Rule.
Question and Answers
What two reservoirs are compared to determine the bulk composition of the Solar System?::The Solar Photosphere and CI Carbonaceous Chondrites.
What percentage of the Solar System's mass does the Sun contain?::Approximately
What does the acronym "CI" stand for in meteorite classification?
?
C = Carbonaceous (rich in carbon/volatiles).
I = Ivuna type (named after the Ivuna meteorite).
Why are CI Chondrites used as the standard reference for solar system composition?
?
They are the most primitive, undifferentiated meteorites. They have never melted, meaning they preserve the original chemical mix of the solid dust in the solar nebula.
In a plot of Solar Photosphere vs. CI Chondrite abundances, what is the relationship for Lithophile and Siderophile elements?::They show a 1:1 linear correlation (slope = 1).
Which group of elements shows a massive depletion in CI Chondrites compared to the Sun?::The Volatile elements (Atmophiles: H, He, C, N, Noble Gases).
Why is Lithium (
What is the purpose of "Chondrite Normalization" in geochemistry graphs?
?
To smooth out the natural "zigzag" abundance of elements (Oddo-Harkins effect) and to easily see if a rock is "enriched" or "depleted" relative to the solar system baseline.
If a rock has a Chondrite-normalized value of 10 for a specific element, what does that mean?::The rock has 10 times the concentration of that element compared to the primitive solar system average (Enriched).