* Fossil Succession: Fossils appear in a specific order within the rock layers. Older fossils are found in deeper, older layers, while newer fossils are found in shallower, younger layers. This principle, known as the law of superposition, helps us determine the relative age of fossils.

* Index Fossils: Some fossils, called index fossils, are very distinctive and existed for a relatively short period of time. If an index fossil is found with another fossil, it helps scientists estimate the age of that fossil.

* Radiometric Dating: Although fossil records provide a relative dating framework, radiometric dating techniques like carbon dating and uranium-lead dating can provide absolute ages for rocks and fossils. This allows us to estimate the exact age of fossils in years.

In summary, fossil records help us understand the relative age of fossils, while radiometric dating provides absolute ages. Together, these methods allow us to build a comprehensive timeline of life on Earth.