When we age date a planet, we are actually just dating the age of the surface, not the whole planet. From Wikipedia, radioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom element of one type, called the parent nuclide transforming to an atom of a different type another element or another isotope of the same elementnamed the daughter nuclide.
When there is a scientific discussion about the age of, say a meteorite or the Earth, the media just talks about the large radioactive datings results and not about the dating technique e. On the other hand, when the media talk about "more recent events," ages that are more comprehendible, such as when early Man built a fire or even how old a painting is or some ancient parchmentthen we bring up the dating technique in order to better validate the findings.
So, you can use the radioactive elements to measure the age of rocks and minerals.
Radioactive dating can also be applied to the dating of rocks as old as the Earth, for example) reveal the amount by which the carbon 14 results need to be. Background radiocarbon activity is measured, and the values obtained are deducted from the sample's radiocarbon dating results. Background samples.