Absolute dating fossils
The sediment of this area was laid down after ammonite A appeared 199 million years ago, and before ammonite B became extinct 195 million years ago.
This narrows the date of the delta beds to the four million years between these dates.
The Age of Dinosaurs was so many millions of years ago that it is very difficult to date exactly.
The best radioactive element to use to date human fossils is Carbon-14.Index fossils are fossils that can be used to date the rock in which they are found.