When granite rock hardens, it freezes radioactive elements in place.
The most common radioactive element in granite is Uranium-238.
As you learned in the previous page, carbon dating uses the half-life of Carbon-14 to find the approximate age of certain objects that are 40,000 years old or younger.
In the following section we are going to go more in-depth about carbon dating in order to help you get a better understanding of how it works.
Since Nitrogen gas makes up about 78 percent of the Earth's air, by volume, a considerable amount of Carbon-14 is produced. Carbon-14 dating can be used on objects ranging from a few hundred years old to 50,000 years old. Libby and others (University of Chicago) devised a method of estimating the age of organic material based on the decay rate of carbon-14.The ratio of carbon-12 to carbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced.The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample.Anything that dies after the 1940s, when Nuclear bombs, nuclear reactors and open-air nuclear tests started changing things, will be harder to date precisely.