Radioactive dating methods beyond 60000 years
With the discovery of radiometric dating, it became possible for the first time to attempt precise figures.
Radiometric dating works on the principle that certain atoms and isotopes are unstable.
These unstable atoms tend to "decay" into stable ones; they do this by emitting a particle or particles. The time it takes for half of a given amount of a radioactive element to decay into a stable one is what is known as the "half-life".
By matching the proportion of original unstable isotope to stable decay product, and knowing the half-life of that element, one can thus deduce the age of the rock, as shown in the following diagram.
For example, Uranium (U-235 or U-238) runs into the Thorium series then breakdowns into Radium and Radon, and finally, into Lead (the stable isotope).
Volcanic tuft containing U-235 also contains (stable) Lead associated directly with it.
The Christian Creationists have criticized it on the grounds that it is inaccurate.
Also, it is of little use in anything more recent than 5,000 years ago.
The radioactive isotope Carbon 14 has a half-life of 5,730 years.