Earth Science

Earth History

Radiometric Dating

Study Tip
Calculating half-lives is a concept you might have learned in math. Combining the calculations with this study guide might help you understand the concept better.

Radiometric Dating

Radiometric dating is the process of using the concentrations of radioactive substances to estimate the age of a material.

Radiocarbon Dating

  • Radiocarbon dating can determine the age of once-living organisms aged 100-50,000 years old using young carbon-based materials. It can also use older isotopes to determine the age of older rocks and minerals.
Study Tip
Calculating half-lives is a concept you might have learned in math. Combining the calculations with this study guide might help you understand the concept better.
  • The atmosphere has 3 isotopes of carbon: carbon-12, carbon-13, and carbon-14.
  • Only carbon-14 is radioactive, and it has a half-life of 5,730 years.
  • After organism’s death, the carbon-14 decays to stable nitrogen-14.

Potassium-Argon Dating

  • Potassium-Argon dating can determine the age of rocks that range 100,000-1 billion years old. It is mostly used on young geological materials and deposits in the bones of human ancestors.
  • Potassium-40 decays to argon-40, with half-life of 1.26 billion years. The potassium-40 : argon-40 ratio in a crystal can help estimate the crystal’s age.

Uranium-Lead Dating

  • Uranium-lead dating can determine the age of igneous rocks from 1 million-4.6 billion years old.
  • The two types of uranium isotopes used for dating are:
  • Uranium-238; it decays into lead-206, with a half-life 4.47 billion years.
  • Uranium-235; it decays into lead-207, with a half-life of 704 million years.

Limitations

  • The material being dated must have measurable amounts of the parent/daughter isotopes.
  • Different radiometric techniques should be used to date the same sample. If calculated ages agree, they are thought to be accurate.
  • It is not very useful for determining the age of sedimentary rocks. For sedimentary rocks, scientists use nearby igneous rocks that can be dated to get a general time frame.
Concept Check
  • What are the three types of radiometric dating? What materials do they use?
  • What are some limitations of radiometric dating?