Definition of radioisotope dating valerie ward popular online dating guide
For example, as shown at left below, uranium-235 has a half-life of 704 million years.
That means that in 704 million years, one gram of uranium will be reduced to ½ gram of uranium.
Scientists usually express this as an age range (e.g., one billion years plus or minus half a million years), meaning that they are very confident that the true date falls somewhere within that range.
With modern techniques, these ranges have gotten narrower and narrower, and consequently, even very ancient rocks can be dated quite precisely.
These zircon crystals are tiny just a tenth of a millimeter long but they are the key to uranium-lead dating.
The answers to all of these questions lie in our understanding of the geologic processes that affect the deposition of radioactive elements.
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.
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.
Of course, in this case "shortly" is meant in terms of geologic timescales.