The age of the oldest white dwarf stars. The age of the Universe can also be estimated from a cosmological model based on the Hubble carbon dating the universe and the densities of matter and dark energy. The actual age measurements are consistent with the model-based age which increases our confidence in the Big Bang model. The Age of the Elements The age of the chemical elements can be estimated using radioactive decay to determine how old a given mixture of atoms is.
The most definite ages that can be determined this way are ages since the solidification of rock samples. When a rock solidifies, the chemical elements often get separated into different crystalline grains in the rock.
For example, sodium and calcium are both common elements, but their chemical behaviours are quite different, so one usually finds sodium and calcium in different grains in a differentiated rock.
Using the known rate of change in radio-active elements (radiometric dating), some Earth rocks have been shown to be billions of years old.