It is based on the fossils found in rocks of different ages and on radiometric dating of the rocks. To get an age in years, we use radiometric dating of the rocks. Not every rock can be dated this way, but volcanic ash deposits are among those that can be dated.

Can volcanic ash be carbon dated?

Radioactive elements are common only in rocks with a volcanic origin, so the only fossil-bearing rocks that can be dated radiometrically are volcanic ash layers. Carbon dating uses the decay of carbon-14 to estimate the age of organic materials, such as wood and leather.

Is limestone older than mudstone?

Thus, we can deduce that the mudstone and shale are older than the rhyolite dike. Thus we know that the fault is younger than the limestone and shale, but older than the basalt above.