Radiometric dating instruments
These elements have much longer half-lives than Carbon, and in some cases can be cross-referenced if more than one of these elements is present in a volcanic tuft.
There are other methods for dating fossils, such as thermoluminescence.
By comparing the proportion of the two, one can work out how old the deposit is.
If the sample is 75% U-235 and 15% Lead (and 10% other), then the sample is approximately 300 mya.
The radioactive isotope Carbon 14 has a half-life of 5,730 years.
This has made it useful for measuring prehistory and events occurring within the past 35 to 50 thousand years.
For that elements with a half life of many millions of years are required.Any further back than that and your standard deviations go way up.