So, we start out with two isotopes of uranium that are unstable and radioactive.They release radiation until they eventually become stable isotopes of lead.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.

For example, uranium-lead dating can be used to find the age of a uranium-containing mineral.

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.

Radiocarbon dating, also known as carbon-14 dating or simply carbon dating, is a method used to determine the age of organic material by measuring the radioactivity of its carbon content.

So, radiocarbon dating can be used to find the age of things that were once alive, like the Iceman.

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. 1979, 1986 © Harper Collins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Cite This Source (rā'dē-ō-mět'rĭk) A method for determining the age of an object based on the concentration of a particular radioactive isotope contained within it.

For inorganic materials, such as rocks containing the radioactive isotope rubidium, the amount of the isotope in the object is compared to the amount of the isotope's decay products (in this case strontium).

With rubidium-strontium dating, we see that rubidium-87 decays into strontium-87 with a half-life of 50 billion years.

By anyone's standards, 50 billion years is a long time.

These differing rates of decay help make uranium-lead dating one of the most reliable methods of radiometric dating because they provide two different decay clocks.

This provides a built-in cross-check to more accurately determine the age of the sample.

These two uranium isotopes decay at different rates. The half-life of the uranium-238 to lead-206 is 4.47 billion years.