We present the results of new theoretical work on surface ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ evolution in the oldest halo stars along with a new and refined analysis of the predicted primordial lithium abundance resulting from big-bang nucleosynthesis. This allows us to determine the constraints which can be imposed upon cosmology using primordial lithium and both standard big-bang and stellar-evolution models. This leads to a constraint on the baryon density today of $0.0044<\mathrm{}{\Omega }_b{h}^2<0.025\mathrm{}$ (where the Hubble constant is $100h$ km ${\sec }^{-1\mathrm{}}$ ${\mathrm{Mpc}}^{-1\mathrm{}}$), and impose limitations on alternative nucleosynthesis scenarios.

• Received 31 January 1989

DOI:https://doi.org/10.1103/PhysRevLett.62.1583