  Using asteroseismic data from the Kepler satellite, we explore the systematic
uncertainties arising from changes in the input physics used when constructing
evolution models of solar-type stars. We assess the impact of including atomic
diffusion and of varying the metallicity mixture on the determination of global
stellar parameters (i.e., radius, mass, and age). We find significant
systematic uncertainties on global stellar parameters when diffusion is
included in stellar grids. Furthermore, we find the systematic uncertainties on
the global stellar parameters to be comparable to the statistical uncertainties
when a different metallicity mixture is employed in stellar grids.
