# Radioisotopes in radioactive dating

Because plants use carbon dioxide for photosynthesis, this isotope ends up inside the plant, and because animals eat plants, they get some as well.

When a plant or an animal dies, it stops taking in carbon-14.

With radiocarbon dating, the amount of the radioactive isotope carbon-14 is measured.

Compared to some of the other radioactive isotopes we have discussed, carbon-14's half-life of 5,730 years is considerably shorter, as it decays into nitrogen-14.

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.

So, you might say that the 'full-life' of a radioactive isotope ends when it has given off all of its radiation and reaches a point of being non-radioactive.

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.

For example, with potassium-argon dating, we can tell the age of materials that contain potassium because we know that potassium-40 decays into argon-40 with a half-life of 1.3 billion years.

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

The uranium-235 to lead-207 decay series is marked by a half-life of 704 million years.

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.