The Sun's Composition and Element Abundance

The Sun's Composition

• Studying electromagnetic radiation absorbed by different chemical elements in the Sun's atmosphere allows astronomers to determine the composition of distant stars and galaxies.
• The amount of light absorbed is proportional to the amount of an element present.
• Abundance is measured relative to a standard (e.g., silicon).

Relative Abundance of Elements in the Sun

• Graph displays relative abundance against atomic number.
• Hydrogen (H) and Helium (He) are the most abundant.
• Other elements like oxygen (O), Iron (Fe), and Silicon (Si) present in significant amounts.
• Rare earth elements (REE) are also present but at much lower concentrations.

Abundance of Iron and Lead on Earth

• Iron is significantly more abundant than lead in the Earth's crust.
• Iron is concentrated more in the Earth's mantle and core, whereas lead is concentrated in the crust.
• This difference is due to different geochemical properties, leading to different behaviors during planetary processes since accretion.

Elemental Condensation from the Solar Nebula

• The solar nebula cooled from a hot state, causing elements to condense at different temperatures.
• Elements with higher boiling points condense at higher temperatures than those with lower boiling points.
• Vaporization temperatures of elements differ under varying pressures.

Solar Nebula Condensation Sequence

• Figure 1.16 displays the condensation sequence of the solar nebula at a pressure of ~10 N m⁻².
• Elements & compounds condense at specific temperatures.
• At low pressures, materials condense directly from gases to solids without an intervening liquid phase.

Dominant Components of Early Condensation

• Early condensate (refractory materials) makes up ~5% of the total.
• Metals make up ~20%.
• Silicates make up ~40%.
• Volatiles and ices (remainder).

Mechanisms for Different Planetary Types

• Volatile elements and ices condense at temperatures below 300 K.
• These conditions would only have occurred beyond Mars's orbit during the formation of the solar system.

Meteorites as a Source of Information

• Meteorites contain material representative of the early solar nebula.
• They are derived from the asteroid belt or possibly planetary embryos.
• Gravitational disturbances, particularly from Jupiter, cause collisions, fragmentation, and prevent accretion of asteroids.

Meteorite Classification

• Meteorites are categorized as stony, iron, or stony-iron.
• Stony meteorites are dominated by silicate minerals.
• Iron meteorites are primarily metallic iron.
• Stony-iron meteorites are a hybrid of the other two.

Differentiation of Meteorites

• Iron and stony-iron meteorites have undergone chemical changes (differentiation).
• This involves enrichment of iron and nickel through removal of silicate minerals.
• Stony meteorites comprise chondrites and achondrites, differentiated by the presence of chondrules.

Chondrite Classification

• Chondrites are categorized based on mineralogy:
  • Ordinary chondrites (most abundant)
  • Enstatite chondrites (rich in enstatite)
  • Carbonaceous chondrites (rich in carbon compounds)
• Ordinary chondrites are further subdivided by varying ratios of iron and their state of oxidation.

Overall Meteorite Differentiation

• The primary process driving meteorite differentiation is the separation of metallic phases from silicate minerals.

This quiz explores the composition of the Sun, focusing on the relative abundance of elements like hydrogen, helium, and iron. It also compares the abundance of iron and lead in the Earth's crust and deeper layers, discussing their geochemical properties. Test your knowledge on astronomical and geological element distributions!