Radioisotopic dating method currently used
Radioisotopic dating is a key tool for studying the timing of both Earth's and life's history.
This suite of techniques allows scientists to figure out the dates that ancient rock strata were laid down and hence, provides information about geologic processes, as well as evolutionary processes that acted upon the organisms preserved as fossils in interleaved strata.
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.
Because lead (the stable daughter of uranium) has a very different arrangement of electrons, it does not make its way into the crystal as it is forming.
The formation of crystals in the magma marks the moment that the radio-isotopic clock starts ticking.
Radioactive decay Radioisotopic dating relies on the process of radioactive decay, in which the nuclei of radioactive atoms emit particles.
This releases energy (in the form of radiation) and often transforms one element into another.
That means that in 704 million years, one gram of uranium will be reduced to ½ gram of uranium.
These zircon crystals are tiny just a tenth of a millimeter long but they are the key to uranium-lead dating.