Uranium-lead dating uses four different isotopes to find the age of the rock.The four isotopes are uranium-235, uranium-238, lead-207, and lead-206.The energies involved are so large, and the nucleus is so small that physical conditions in the Earth (i.e. The rate of decay or rate of change of the number N of particles is proportional to the number present at any time, i.e.
A secondary electron microscopy image of a zircon from volcanic ash, about four thousandths of an inch (100 microns) across.
Thus, if we start out with 1 gram of the parent isotope, after the passage of 1 half-life there will be 0.5 gram of the parent isotope left.
After the passage of two half-lives only 0.25 gram will remain, and after 3 half lives only 0.125 will remain etc.
This commonly occurs if the system has been heated or otherwise disturbed, causing a loss of some of the lead daughter atoms.
Because Pb are chemically identical, they are usually lost in the same proportions. Wetherill has shown that the two points on the Concordia curve intersected by this straight line will represent the time of initial crystallization and the time of the subsequent lead loss.