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

Fact 2: Radioactive dating requires the use of a decay curve.

Given the two facts above, answer the question "What is used to determine the age of fossils?" with the following options: 
- Calcium carbonate
 - dinosaurs
 - a barometer
 - electron microscope
 - a thermometer
 - a decay curve
 - chemical equations
 - Physical weathering


 

      a decay curve   