How is the absolute age of a rock expressed?

The absolute age of a rock is expressed in years, providing a specific time frame for when the rock was formed. This is typically determined using radiometric dating techniques, which measure the decay of radioactive isotopes within the rock. By calculating the ratio of parent isotopes to daughter isotopes, scientists can estimate the time elapsed since the rock solidified. This method allows for precise dating compared to relative age dating, which only determines the sequence of events.