Shale itself doesn't have a specific age. It's a type of sedimentary rock formed from the accumulation of mud and silt. The age of a particular shale formation depends on when the mud and silt were deposited and lithified (turned into rock).

Here's why:

* Sedimentary rocks are formed by layers: Shale, like other sedimentary rocks, is formed in layers. The oldest layers are at the bottom, and the youngest are at the top.

* Dating methods: Geologists use various methods to date sedimentary rocks, including:

* Radiometric dating: This technique uses the decay of radioactive isotopes to determine the age of specific minerals within the rock.

* Fossils: The fossils found in a shale layer can be used to determine the age of the rock based on the known ages of the organisms.

Therefore, the age of a shale formation can range from a few thousand years old to billions of years old. It all depends on when the sediment was deposited and what methods are used to date it.