What is absolute age?

Absolute age is the age of a geologic formation in years. Unlike relative age, which determines whether a formation is older or younger than its surrounding formations, absolute age provides geologists with the actual age of a formation.

The absolute age is determined by a number of dating techniques:

• Radiometric dating examines the radioactive isotopes in an object, which decay at a constant rate. By examining them, geologists can calculate its age.
• Luminescence dating establishes an object's age by determining when it was last heated. When objects absorb radiation, the radiation frees electrons within it. These electrons become trapped, but can be released and measured to determine the object's age.
• Amino acid dating is used to calculate the age of organic compounds. Amino acids alter at a steady rate after organisms die. Scientists measuring the ratio of healthy amino acids to decayed acids, can determine its age.