this paper we use the ages of the oldest stellar populations between $z=0$ and $z=1.5$ to derive new and independent constraints on two key cosmological parameters, $w$ and $H_0$. Both parameters are relatively poorly constrained by CMB data alone. For example, in order to get accurate constraints on $w$, @SpergelWMAP03 combined the [*WMAP*]{} data with six external data sets: two additional CMB data sets [CBI and ACBAR; @Pearson+02; @Kuo+02], large scale structure measurements from the 2dF galaxy redshift survey [2dFGRS; @Percival+01; @Verde+2dF02], measurements of the Lyman $\alpha$ forest power spectrum [@Croft+02; @Gnedin+02], the luminosity distance–redshift relation from Type Ia supernovae measurements [@Garnavich+98; @Riess+01], and $H_0$ from the [*Hubble Space Telescope*]{} ([*HST*]{}) Key Project [@Freedman+01]. Therefore it is particularly important to obtain accurate and independent measurements of cosmological parameters relying on different physics.

In Section 2 we focus on $w$, summarizing the basis of our method and deriving tight constraints on the equation of state using the ages of globular clusters in combination with the location of the first acoustic peak in the CMB power spectrum. Then, in Section 3, we determine stellar ages for a sample of early-type galaxies between $z=0$ and $z=1.5$ and use the age–redshift relationship defined by 