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.

So, in our example , after the second life is over (that's 10 years since each half life is 5 years), there will be $$\frac 1 2$$ of $$50\%$$ of the substance left, which, of course is $$25 \%$$.

And the pattern continues, every 5 years another half life reduces the substance by $$\frac 1 2$$, so after the the third life is over ( the 15 year mark), there will be $$\frac 1 2$$ of $$25\%$$ of the substance left , which is $$12.5 \%$$.

In this first chart, we have a radioactive substance with a half life of 5 years.

As you can see, the substance initially has 100% of its atoms, but after its first half life (5 years) only 50% of the radioactive atoms are left. Literally, half of the substance is gone every five years (the half life of this particular substance).

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.

By the end of the 8th grade, students should know that all matter is made up of atoms, which are far too small to see directly through a microscope.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.The thing that makes this decay process so valuable for determining the age of an object is that each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life.This lesson is the third in a three-part series about the nucleus, isotopes, and radioactive decay.The first lesson, Isotopes of Pennies, deals with isotopes and atomic mass.

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