What is the half-life of uranium-238 in billions of years?

The half-life of uranium-238 is 4.468 billion years.

A radioactive isotope’s half-life is the time required for half the atoms in a sample to decay. It does not mean that every atom decays on the same schedule: each individual decay is random, while a large population follows a highly predictable statistical pattern. Uranium-238 decays primarily by alpha emission, beginning a chain that ultimately ends at stable lead-206.

Uranium-238 is the most abundant naturally occurring uranium isotope, making up roughly 99.27% of natural uranium. Its exceptionally long half-life means that it remains present in rocks formed billions of years ago, while still producing measurable radioactivity and radiogenic heat inside Earth.

The isotope is especially important in uranium–lead dating. By comparing uranium-238 with its lead-206 decay products in suitable minerals such as zircon, geologists can estimate the ages of ancient rocks and meteorites. Uranium-235 is a different isotope with a much shorter half-life of about 704 million years, so the two should not be confused.