Evidence About Earth’s Past (Book)
ABSOLUTE AGES OF ROCKS
- Other Radioactive Isotopes
The isotopes in Table below are used to date igneous rocks. These isotopes have much longer half-lives than carbon-14. Because they decay more slowly, they can be used to date much older specimens. Which of these isotopes could be used to date a rock that formed half a million years ago?
|Unstable Isotope||Decays to||At a Half-Life of (years)||Dates Rocks Aged (years old)|
|Potassium-40||Argon-40||1.3 billion||100 thousand – 1 billion|
|Uranium-235||Lead-207||700 million||1 million – 4.5 billion|
|Uranium-238||Lead-206||4.5 billion||1 million – 4.5 billion|