Determination of Age of Fossils: The age of fossils can be determined by following methods-
1. Relative Dating Methods: In early days, mechanism of absolute dating was not present and as a result relative dating technique were used to determine the age of rock and fossils. In this technique, the position and erosin rate of rock in particular environment. Older rocks are situated in deeper had ancient fossils and superficial rocks had fossils of recent fossils.

2. Absolute Dating Methods: These methods are using spontaneous decay of unstable radioactive nuclei into stable radioactive nuclei at a constant and known rate. Absolute dating technique uses radioactive nuclei in three different techniques:

(i) Uranium-Lead Technique: This technique was introduced by Baltwood in 1907. Rocks contains uranium (U238) in the form of mineral zircon. Uranium decay spontaneously to Lead as per the given scheme (Scheme 6.1). It has a half life of 4.5 billion years which means it will take 4,500,000,000 years to decay 50% uranium. So determination of content of uranium and lead in a rock or fossil can be used to determine the age of rock or fossil.