Answer: Ancient Relative of a living organism
Explanation: Ancient Relative because by using the index fossil, you are also using the law of superposition. This law does not give you an accurate/specific date but instead the order they are in (i.e me saying i am older than my siblings compared to me saying i am 2 years older than them). By using an ancient relative of a living thing then we can see its phylogenic tree and measure around how old it is. Fossils also hold carbon and chemicals in there bones which allows us to use carbon dating. Carbon dating is an accurate way of measuring age.
