Common lead dating
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.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.Separating out the zircons is, therefore, a very meticulous process.That way, scientists know the exact composition of that tiny sample.A single grain of zircon may contain different compositions and ages. It is a difficult concept to wrap our heads around, and yet through a lot of very detailed work both in the field and in the laboratory, geologists have found a way to go back in time and see how the world was millions and even billions of years ago.The graph will show not only the age of the rocks but also when important geological events occurred in the past.So how do scientists get the zircon and figure out its age? Geologists go out looking for certain types of rock that they know to be older than others.
Every 710 million years the 235U of the actinium series would be at its half-life, so there would be the same amount of uranium and lead atoms.
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.
The zircons are studied with an electron microprobe; they hit the zircons with an electron beam to see the cathodoluminescent light that results after it.
All of the atoms in the sample give off X-rays with different wavelengths after being hit with the electron beam, according to their atomic makeup.