Nucleosynthetic processes:

Fusion:•Hydrogen•Helium•Carbon•Oxygen

After Fe, neutron addition takes place (rapid and slow processes)

Summary – Solar abundances of the elements:

• H and He are the most abundant elements• Elements with higher atomic numbers decrease in

abundance exponentially• Peak at Fe, unusually low abundances for Li, Be, B• Isotopes with even atomic numbers and mass numbers

more abundant than those with odd atomic numbers• Sun is H-burning to form He, solar system contains

elements formed in older, more massive stars

Meteorites – extraterrestrial rocks that enter the Earth’s atmosphere and strike the Earth’s surface

Basic Classification:• Stony (silicates)

– Chondrites– Achondrites

• Stony-iron (mixed silicate and metal)• Iron (metal)

Falls are witnessed falling through the atmosphere (meteors), finds are found. Most finds are irons.

http://meteorites.asu.edu/

The nebular hypothesis

The solar nebula (gas) contracted, cooled and condensed into dust sized particles that accreted (stuck together as the result of collisions) into protoplanets (asteroid sized bodies) and then larger planets

http://meteorites.asu.edu/

Evidence that chondrites are representative of early solar system materials:

• 1:1 ratio of non-volatile elements to those in the sun• “sedimentary”, non-equilibrated texture - formed by

accretion of condensed particles with little subsequent heating or alteration

• presence of minerals predicted to be formed by condensation of solar nebula, such as corundum, Fe metal, troilite, etc.

Also inferred: achondrites, iron and stony-meteorites represent fragments of accreted planetesimals that had heated internally, melted and differentiated

The nebular hypothesis

The solar nebula (gas) contracted, cooled and condensed into dust sized particles that accreted (stuck together as the result of collisions) into protoplanets (asteroid sized bodies) and then larger planets

Measured quantity =Heat of vaporization

Hypotheses for the formation of Earth (other planets and moons)

• Heterogeneous accretion • Homogeneous accretion• Chondrite mixing

Chondrite minerals:

•Ca-Al inclusions (CAI’s) (corundum, perovskite, melilite, anorthite)•Silicates in chondrules: enstatite, diopside, olivine, anorthite•Metal: Fe, Ni•Troilite (FeS)•Serpentine•Carbonaceous material