Radioactive dating is used to determine the age of fossils, and radioactive dating requires the use of a decay curve. Given these facts, what is used to determine the age of fossils among the following options:
- Calcium carbonate
 - dinosaurs
 - a barometer
 - electron microscope
 - a thermometer
 - a decay curve
 - chemical equations
 - Physical weathering


 

      a decay curve   