  Using the values of the cosmological parameters obtained from Wilkinson
Microwave Anisotropy Probe (WMAP) and the cosmological chemical clock observed
by high-redshift quasars, it is shown that star formation should have started
by the redshift $z_F > 9.5$, and that $z_F$ is sensitive only to $\omegamz h^2$
in flat $\Lambda$CDM cosmology.
