Absolute dating volcanic ash layers
Once the rocks are placed in order from to oldest and youngest, we also know the relative ages of the fossils that we collect from them.Relative age dating tells us which fossils are older and which fossils are younger. To get an age in years, we use radiometric dating of the rocks.
This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.The geological time scale is used by geologists and paleontologists to measure the history of the Earth and life.It is based on the fossils found in rocks of different ages and on radiometric dating of the rocks.It is possible to calculate the age of a sample by measuring the uranium content and the density of the fission tracks.The age of volcanic rocks and ash can be determined by measuring the proportions of argon (in the form of argon-40) and radioactive potassium within them.When volcanic rocks and minerals are formed, they do not contain fission tracks.
The number of tracks increases over time at a rate that depends on the uranium content.
These include radiometric dating of volcanic layers above or below the fossils or by comparisons to similar rocks and fossils of known ages.
Knowing when a dinosaur or other animal lived is important because it helps us place them on the evolutionary family tree.
The volcanic ash layer is dated as 507 million years old.
The fossil species below the ash must be slightly older than 507 million years, and the species above the ash must be slightly younger.
We cannot be sure if the rock layers with the same fossils are identical in age.