Modern geologists date minerals called zircons, tiny crystals that form in volcanic eruptions and that are hardy enough to survive for billions of years.
Zircons consist of silica, oxygen and the element zirconium, but are occasionally contaminated with uranium as they form.
Everything on our world eventually is eroded or subsumed back into the crust.
To get a truly precise date for the origin of our planet, scientists have to look beyond it. The asteroids that meteorites come from are some of the most primitive objects in the solar system.
Because of the structure of the crystals, zircons never include lead when they are forged inside the Earth.