The two cascades are different—235U becomes 207Pb and 238U becomes 206Pb.
What makes this fact useful is that they occur at different rates, as expressed in their half-lives (the time it takes for half the atoms to decay).
Uranium comes in two common isotopes with atomic weights of 235 and 238 (we'll call them 235U and 238U).
The 235U–207Pb cascade has a half-life of 704 million years and the 238U–206Pb cascade is considerably slower, with a half-life of 4.47 billion years.
So when a mineral grain forms (specifically, when it first cools below its trapping temperature), it effectively sets the uranium-lead "clock" to zero.
Of all the isotopic dating methods in use today, the uranium-lead method is the oldest and, when done carefully, the most reliable.
Unlike any other method, uranium-lead has a natural cross-check built into it that shows when nature has tampered with the evidence.
Free 5-day trial Radiometric dating is used to estimate the age of rocks and other objects based on the fixed decay rate of radioactive isotopes.
Learn about half-life and how it is used in different dating methods, such as uranium-lead dating and radiocarbon dating, in this video lesson. As we age, our hair turns gray, our skin wrinkles and our gait slows.THANK YOU SOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO MUCH!!!!!!! I FINALLY UNDERSTOOD THIS BECAUSE OF THIS WEBSITE!!!THANKS AGAIN AND I HOPE THE DEVELOPERS MAKE MORE WEBSITES ABOUT SCIENCE TO HELP ME OUT!!Lead atoms created by uranium decay are trapped in the crystal and build up in concentration with time.If nothing disturbs the grain to release any of this radiogenic lead, dating it is straightforward in concept.The methods work because radioactive elements are unstable, and they are always trying to move to a more stable state. This process by which an unstable atomic nucleus loses energy by releasing radiation is called radioactive decay.