What is the half-life of uranium-238?

The half-life of uranium-238 is 4.468 billion years. In other words, after that length of time, half the uranium-238 atoms in a sample will have decayed into other elements.

Uranium-238 is the most abundant naturally occurring uranium isotope, making up more than 99% of natural uranium. It decays by emitting an alpha particle, beginning a long chain that eventually ends in stable lead-206. Because its half-life is so immense, a uranium sample remains radioactive for billions of years, although its activity is relatively low compared with short-lived isotopes.

This isotope is especially important in uranium–lead radiometric dating, which scientists use to estimate the ages of ancient rocks and minerals. Its decay chain also contributes significantly to Earth’s internal radioactive heat. A common mix-up is uranium-238’s half-life versus uranium-235’s, which is about 704 million years—far shorter.