The earth has been determined by radiometric dating to be dating velox paper
There are many radiometric clocks and when applied to appropriate materials, the dating can be very accurate.
The oldest crystals on Earth that were formed on Earth are zircon crystals, and are approximately 4.1 billion years old.
For example, a problem I have worked on involving the eruption of a volcano at what is now Naples, Italy, occurred 38500 years ago with a plus or minus of 300 years.
So, when the materials are appropriate and one carefully avoids contamination and re setting radiometric clocks can be VERY ACCURATE.
We call the original, unstable isotope (Uranium) the "parent", and the product of decay (Lead) the "daughter".
From careful physics and chemistry experiments, we know that parents turn into daughters at a very consistent, predictable rate.
The decay constants for most of these systems have been confirmed in other ways, adding strength to our argument for the age of the earth., so there is one zirconium (Zi) for one silicon (Si) for four oxygen (O).