If we know the number of radioactive parent atoms present when a rock formed and the number present now, we can calculate the age of the rock using the decay constant.The number of parent atoms originally present is simply the number present now plus the number of daughter atoms formed by the decay, both of which are quantities that can be measured.These radioactive elements constitute independent clocks that allow geologists to determine the age of the rocks in which they occur.The radioactive parent elements used to date rocks and minerals are: Radiometric dating using the naturally-occurring radioactive elements is simple in concept even though technically complex. This age has been determined with the radioactive dating technique.
Measuring two long-lived radioactive elements in meteorites, uranium-238 and thorium-232, has placed the age of the Milky Way at in the same time frame.
The principal evidence for the antiquity of Earth and its cosmic surroundings is: Spontaneous breakdown or decay of atomic nuclei, termed radioactive decay, is the basis for all radiometric dating methods.
Radioactivity was discovered in 1896 by French physicist Henri Becquerel.
The United States Geological Survey(USGS) website has a lot of indepth material about how the age of the Solar System was determined.
The basics of it are that all material radioactively decays into a stable isotope.
The oldest meteorites ever dated in the Solar System are 4,56 billion years old, the oldest minerals on Earth are 4,4 billion years old, and the oldest rocks on Earth are 4 billion years old.