Radioactive dating uranium
If half of the uranium-238 has turned into lead-206 the rock will be 4500 million years old.Radioactive elements were incorporated into the Earth when the Solar System formed.
When living things die, they stop taking in carbon-14, and the radioactive clock is "set"!
All rocks and minerals contain tiny amounts of these radioactive elements.
Radioactive elements are unstable; they breakdown spontaneously into more stable atoms over time, a process known as radioactive decay.
Prior to 1905 the best and most accepted age of the Earth was that proposed by Lord Kelvin based on the amount of time necessary for the Earth to cool to its present temperature from a completely liquid state.
Although we now recognize lots of problems with that calculation, the age of 25 my was accepted by most physicists, but considered too short by most geologists. Recognition that radioactive decay of atoms occurs in the Earth was important in two respects: Principles of Radiometric Dating Radioactive decay is described in terms of the probability that a constituent particle of the nucleus of an atom will escape through the potential (Energy) barrier which bonds them to the nucleus.