Dating uranium 235
This means that any lead found in zircon minerals was made by radioactive decay, after the formation of the mineral. Zircon also concentrates Uranium (You) and (although less so) Thorium (Th) and excludes lead (Pb), which means it has a very high You/Pb ratio.The two decay chains used on zircon dating are the uranium series and the actinium series.The half-life of the uranium series is 4.47 billion years, and the half-life of the actinium series is 710 million years.
This makes the zircons go straight back to the starting point on the Concordia graph, off of their original line. As long as no other geological event occurs, the whole Discordia line moves along the Concordia line, pointing to the age of the geological event that caused the disturbance.
When a grain of mineral forms, the clock starts at zero.
Uranium decay traps lead atoms in the crystal; these atoms get more concentrated over time.
Scientists use this method to date rocks that formed from between 1 million to 4.5 billion years ago, and they estimate the Earth is 4.543 billion years old.
The oldest and most reliable method they use is called Uranium-lead (U-Pb) dating.
It is usually found in the form of tiny grains, making up usually less than 10% of a given sample, spread out through the rock.