Radiometric dating decay curves
They break down and change into a completely different type of atom. The radioactivity of an object is measured by the number of nuclear decays it emits each second – the more it emits, the more radioactive it is.It is not possible to predict when an individual atom might decay. For example, it might take 10 years for the count rate to drop from 80 Bq to 40 Bq; another 10 years to drop from 40 B to 20 Bq; another 10 years to drop from 20 Bq to 10 Bq and so on. The half-life of a particular isotope is always the same.
There are also trace amounts of the unstable radioisotope carbon-14 (14C) on Earth.
Carbon dating can be used to date things up to about 60 000 years old. Many people think that plants grow by taking food from the soil through their roots but this is not true. Animals eat plants (or other animals that eat plants) so animals are also mostly rearranged carbon dioxide.
All green plants make their own food in their leaves. A tiny fraction of carbon atoms are the radioactive isotope carbon-14.
principle sources: Australian Museum https://au/the-geological-time-scale Wikipedia https://en.wikipedia.org/wiki/Radiometric_dating Carleton University numerical (or "absolute") age is a specific number of years, like 150 million years ago.
A relative age simply states whether one rock formation is older or younger than another formation.