Radiocarbon dating age of earth
Therefore, their ages indicate when they were formed.
Because all parts of the solar system are thought to have formed at the same time (based on the solar nebula theory), the Earth must be the same age as the moon and meteorites--that is, about 4.6 billion years old.
Another line of evidence is based on the present-day abundances of the various isotopes of lead found in the Earth's crust. Three of these isotopes (lead 206, 207, 208) result from radioactive decay of isotopes of thorium and uranium.
The fourth, lead 204, is not the result of radioactive decay.
Decay curve of a radioactive element with a half-life equal to one time unit.
This means that all of the lead 204 on the Earth has been around since the formation of the Earth.
Based on extensive sampling of the Earth's crust, scientists determined the present-day abundances of the four isotopes of lead relative to each other and to the parent isotopes that produced three of them.
One line of evidence involves rocks from outside the Earth--meteorites and moon rocks.
Radiometric dating shows that almost all meteorites are between 4.5 and 4.7 billion years old.