Age of fossils in the past was generally determined by radio-carbon method and other methods involving radioactive elements found in the rocks. More precise methods, which were used recently and led to the revision of the evolutionary period for different groups of organisms, includes

• A. study of carbohydrates/proteins in fossils
• B. study of the conditions of fossilization
• C. Electron Spin Resonance (ESR) and fossil DNA
• D. study of carbohydrates/proteins in rocks