The age of rocks is determined by radiometric dating, which looks at the proportion of two different isotopes in a sample. Radioactive isotopes break down in a predictable amount of time, enabling geologists to determine the age of a sample using equipment like this thermal ionization mass spectrometer.

How are the ages of the Earth and universe calculated?

The age of the Earth is measured by studies of radioactive elements. The results consistently indicate an age of about 4.56 billion years for the Earth. The age of the Universe is measured in several ways. One method is based on the rate of expansion of the Universe.