Early on, before we had more precise means to date fossils, geologists and paleontologists relied on relative dating methods. They looked at the position of sedimentary rocks to determine order.
When was the first fossil dated?
The oldest fossils are around 3.48 billion years old to 4.1 billion years old. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils.
What significance is it that fossil can be dated?
Dating of the fossils contributes to a clearer timeline of evolutionary history. Older methods of dating were more subjective, often an educated hypothesis based on the evidence available.