Fact 1: Radioactive dating is used to determine the age of fossils.

Fact 2: Radioactive isotopes are commonly used for dating .

Given the two facts above, answer the question "what is used to determine the age of fossils?" with the following options: 
- Conifers
 - Sediment
 - calcite
 - skull
 - loose soil
 - cracking
 - exoskeleton
 - isotopes


 

        isotopes 