All these methods point to Earth being very, very old -- several billions of years old.
I found several good sources, but none that seemed both complete enough to stand alone and simple enough for a What is radiometric dating?
To explain those rules, I'll need to talk about some basic atomic physics. Hydrogen-1's nucleus consists of only a single proton.
Protons and neutrons together are called nucleons, meaning particles that can appear in the atomic nucleus.
A is a substance that can be used to follow the pathway of that substance through some structure.
For instance, leaks in underground water pipes can be discovered by running some tritium-containing water through the pipes and then using a Geiger counter to locate any radioactive tritium subsequently present in the ground around the pipes.