Example of radioisotope dating
Example of radioisotope dating - Reallife cam videos
The zircon formation may have occurred tens to hundreds of thousands of years before the eruption and deposition.
If these crystals were pure, they would contain just zirconium, silica, and oxygen; however, uranium happens to have a similar arrangement of outer electrons to zirconium, and so as zircons form, "mistakes" are sometimes made, and uranium is substituted for zirconium.
To see how it works, we'll start at the beginning, using uranium as an example: At left, a zircon crystal in a thin section cut from granite. Crystal structure image adapted fromadapted from Materialscientist CC Attribution-Share Alike 3.0 Unported Tens to hundreds of thousands of years before a major volcanic eruption, magma builds up beneath the surface of the Earth.
In the magma, crystals of zirconium silicate (called zircons), as well as other crystals, form.
For example, over time, uranium atoms lose alpha particles (each made up of two protons and two neutrons) and decay, via a chain of unstable daughters, into stable lead.
Although it is impossible to predict when a particular unstable atom will decay, the decay rate is predictable for a very large number of atoms.
Slightly different dating techniques are used with different radioactive elements, but the same basic logic of estimating backwards based on radioactive decay remains the same.
The geology behind radioisotopic dating Though the basic logic behind radioisotopic dating relies on nuclear physics and quantum theory, many geologic processes also factor into our ability to date a particular rock. How do they know that the rock isn't contaminated with elements that would throw off the dating?
Zircons are nearly perfect clocks because we can be relatively certain that when the crystal formed, no lead was present and that means that when we discover ancient zircons in rocks today, we can be relatively confident that any lead present is the result of radioactive decay.
Geologists extract the appropriate minerals from the rock (in this case, zircon crystals) and use a technique called mass spectrometry to figure out the relative amounts of uranium and lead in the zircon.
How can the formation of a rock be correlated with a particular ancient event?
The answers to all of these questions lie in our understanding of the geologic processes that affect the deposition of radioactive elements.
Thus, when a geologist dates a rock using uranium-lead dating, he or she is actually getting an estimate on the age of its zircon crystals, which formed "shortly" before the volcanic eruption.