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

Fact 2: Extinct organisms represented only by fossils.

Given the two facts above, answer the question "What is used to determine the age of extinct organisms?" with the following options: 
- viruses
 - an electron microscope
 - Echinoderm.
 - fossils of Panthera leo
 - genetic material
 - the Sun
 - tectonic plates coliding
 - radioactive dating


 

        radioactive dating 