Carbon 14's half-life is not nearly long enough to measure dates in the geological past.

For that elements with a half life of many millions of years are required.

Here are the half-lives of some other radioactive elements: These are said to be used in dating techniques of gas formation light emission called thermoluminescence).

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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.

Of course C-14 would never be of any use for dating dinosaur bearing deposits, unless you want everything to date to around 40,000 years!

Radio-Carbon dating can be used for dates up to ~80,000 years ago.

Even in the case of very long half-lives, modern scientific instruments are now accurate enough to give very fine readings.

We usually hear of Carbon 14 dating, which is very important in archaeology.

Any further back than that and your standard deviations go way up.

Also, C-14 years do not correlate with actual calendar years, since the amount of C-14 isotopes in the atmosphere has fluctuated in the past, and the dating method assumes it was constant.

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.

Fortunately, we are able to date older fossils using the radiometric breakdown of other elements (Potassium-Argon dating, Argon-Argon dating, and Rubidium dating [I'm writing this without any refs - so this last one might be wrong]).