Determining Primordial Abundances

Helium:

• Created during BBN, but also created inside stars and expelled during late stages of stellar evolution. Helium abundance should rise with metallicity.
• Measure using Helium abundances in HII regions in low metallicity dwarf galaxies.

Deuterium:

• Created during BBN, essentially nowhere else. Destroyed inside stars. Deuterium measurements should be lower limits on primordial abundances.
• Measure using quasar absorption line spectra.
  

Image courtesy Neil Crighton, Swinburne U

Lithium:

• ⁷Li created during BBN, inside stars, and during cosmic ray collisions ("spallation").
• ⁶Li only created during cosmic ray spallation.
• Measure lithium in halo dwarf stars with T>6000K so that lithium in atmosphere is not burned during convective cycling.