Radioactive Dating

Contributor: Hannah Brooks. Lesson ID: 12493

Most people have a birth certificate or other identification to show how old they are. Most rocks don't have certificates, so scientists use the half-life to measure the life of long-dead organisms!



learning style
personality style
Grade Level
High School (9-12)
Lesson Type
Dig Deeper

Lesson Plan - Get It!


Can you guess the time period using clues from the clothing in the above image? How old do you think this picture might be?

If you skipped or need to review the four previous Radioactivity Related Lessons, find them in the right-hand sidebar.

Photographs can often be dated based on the clothing the subjects are wearing. When you are older, it will be a lot of fun to look back at your childhood images and think, "Wow, I really wore that!" Unfortunately, objects in creation are a lot harder to date.

  • Have you ever seen a rock that wears clothing?

We can use a process called radioactive dating to figure out the age of materials in creation.

Radioactive dating relies on the idea that radioactive elements' nuclei degrade over time. Remember that the half-life of an element gives us a measurement of how quickly the nuclear breakdown occurs.

Carbon, one of the most abundant elements on Earth, has a radioactive isotope called Carbon-14. Carbon-14 has six protons, six electrons, and eight neutrons. It is heavier than the more common Carbon-12. Carbon-14 is absorbed by plants and consumed by animals while they are alive. When these living organisms die, they are unable to exchange carbon with the environment, so the Carbon-14 isotope begins to degrade. Carbon-14 has a half-life of 5,730 years. That means that every 5,730 years, the amount of Carbon-14 decreases by half. Scientists use this value to measure the amount of Carbon-14 found in an organic sample to date the sample. This is the process that scientists use to date bones from a woolly mammoth.

Carbon dating can only be used for materials that were living. Nonliving substances, like rocks and soil, can be dated using radioactive isotopes of the elements potassium and argon. Potassium has many isotopes; potassium-40 is a radioactive isotope with a half-life over one million years! Scientists count the number of atoms for each type of element to determine how old the rock is.

  • What is the difference between dating organic and inorganic substances?
  • How accurate do you think radioactive dating is? Why?

Respond to this question on a sheet of paper.

Radioactive dating relies on the amount of radioactive isotopes found in a sample. If the material was once living, scientists can use Carbon-14 to determine how old the sample is. For nonliving materials, scientists can compare the number of potassium and argon atoms to determine the age. These calculations provide information about how objects are related in the environment. When bones and ancient tools are discovered, these dating processes give historical context.

In the Got It? section, you will learn more about radiometric dating in the context of creationism.

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