There are two ways of finding the age of the fossil.
1. Relative dating
2. Radioactive dating.
Relative dating: In this method, we can only compare the ages of the fossil but cannot precisely find it. In relative dating, we dig the earth and look for the presence of fossils, and it is reasonable that the fossil discovered closer to the surface of the earth is most recent one and the fossil discovered in the deeper layers is the older one. So here we talk about the age of fossil in relative terms.
Radioactive dating: All organic matter on the earth is made up of various elements. Some elements exist in different isotopic forms such as C-12 and C-14. C-14 is radioactive isotope, it is unstable and decays over time at a steady rate. This steady rate is known as half life of the respective isotope. We can calculate the ratio of observed abundance of that radioactive isotope and its decay product in the fossil or rock we are studying. This is the principle of radioactive dating.
The sun gets its energy from the process of nuclear fusion. This process occurs in the sun's core or interior, where temperature and pressure are extremely high. During most of the sun's life, energy comes from the fusion of hydrogen nuclei
