<human>:  What methods do scientists use to determine the age of a fossil?
<bot>: Scientists use several different methods to determine the age of a fossil, such as carbon dating, thermoluminescence dating, and potassium argon dating. By measuring the amount of certain isotopes found in the fossil, scientists can calculate its age. Other techniques include comparing the fossil to those of known species and looking for similarities and differences. Additionally, scientists may look at the surrounding sediment layers and use index fossils to estimate the age of the fossil.