Dating rocks using 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.However, rocks and other objects in nature do not give off such obvious clues about how long they have been around.Carbon-14 is a method used for young (less than 50,000 year old) sedimentary rocks.This method relies on the uptake of a naturally occurring radioactive isotope of carbon, carbon-14 by all living things.By anyone's standards, 50 billion years is a long time.In fact, this form of dating has been used to date the age of rocks brought back to Earth from the moon.A commonly used radiometric dating technique relies on the breakdown of potassium (Ar in an igneous rock can tell us the amount of time that has passed since the rock crystallized.
So, if you know the radioactive isotope found in a substance and the isotope's half-life, you can calculate the age of the substance. Well, a simple explanation is that it is the time required for a quantity to fall to half of its starting value.
It works because we know the fixed radioactive decay rates of uranium-238, which decays to lead-206, and for uranium-235, which decays to lead-207.