The rate of isotope decay is very consistent, and is not effected by environmental changes like heat, temperature, and pressure. This makes radiometric dating quite reliable. Because carbon-14 decays relatively rapidly compared to other isotopes, it can only be used to date things that are less than 60,000 years old.

Why is radioactive dating useful and reliable?

The unswerving regularity of this decay allows scientists to determine the age of extremely old organic materials—such as remains of Paleolithic campfires—with a fair degree of precision. The decay of uranium-238, which has a half-life of nearly 4.5 billion years, enabled geologists to determine the age of the Earth.

Why is radiometric dating unreliable?

For example, after extensive testing over many years, it was concluded that uranium-helium dating is highly unreliable because the small helium atom diffuses easily out of minerals over geologic time. As a result, this method is not used except in rare and highly specialized applications.