Radiometric dating is a very useful tool, but it does have limits: The material being dated must have measurable amounts of the parent and/or the daughter isotopes. Radiometric dating can be done on only some materials. It is not useful for determining the age of sedimentary rocks.

## What are some limitations in the use of 14c for radioactive dating?

Despite its usefulness, radiocarbon dating has a number of limitations. First, the older the object, the less carbon-14 there is to measure. Radiocarbon dating is therefore limited to objects that are younger than 50,000 to 60,000 years or so.

## Why is U-238 used to date the Earth instead of I 131?

Uranium 238 has a half life of 4.5 billion years. Uranium can be used to date the age of the earth. If 50% of pure uranium is left in a sample the sample is assumed to be 4.5 billion years old. So no fossils can be dated directly using U 238.