Lesson Topics

1 | Radioisotopes

2 | Radioactive Decay

3 | Using Radioisotopes for Absolute Dating

4 | Radiocarbon Dating

5 | Potassium-Argon Dating

6 | Summary

Lesson Summary

• Radioisotopes (radioactive isotopes) are unstable variants of chemical elements that undergo spontaneous radioactive decay.

• Radioactive decay involves the release of radiation and the formation of a stable isotope.

• The rate at which a particular radioisotope decays is constant.

• It is measured in half-lives which correspond to the time required for one half of all atoms to undergo radioactive decay.

• Radiometric dating uses the predictable rates of radioactive decay of radioisotopes to determine the absolute age of objects by measuring the relative amounts of naturally occurring radioisotopes contained within them.

• Geochronology refers to the use of absolute dating methods, such as radiometric dating, for determining the ages of rocks, sediments and fossils.

• Radiometric dating methods used in geochronology include radiocarbon dating and potassium-argon dating.

• Radiocarbon dating (carbon-14 dating) is used for determining the age of biological materials up to about 60,000 years old.

• When organisms die, they no longer absorb carbon, so the amount of carbon-14 contained within them slowly decreases due to radioactive decay.

• Hence, the proportion of carbon-14 atoms in a biological sample can be used to determine how long ago an organism died.

• Potassium-argon dating is used for determining the age of rocks and mineralised fossils older than about 100,000 years.

• When molten rock crystallises, argon-40 gas that is produced through the radioactive decay of potassium-40 accumulates within the rock.

• Hence, the proportion of argon-40 to potassium-40 can be used to determine how long ago a rock formed.

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(Header image: Elena, Adobe Stock)