However, rocks and other objects in nature do not give off such obvious clues about how long they have been around.
So, we rely on radiometric dating to calculate their ages.
These two uranium isotopes decay at different rates. The half-life of the uranium-238 to lead-206 is 4.47 billion years.
The uranium-235 to lead-207 decay series is marked by a half-life of 704 million years.
Uranium is not the only isotope that can be used to date rocks; we do see additional methods of radiometric dating based on the decay of different isotopes.