The geological time scale relates stratigraphy (layers of rock) to periods of time. The time scale is used by geologists, palaeontologists and many other Earth scientists to date certain historical events on Earth.
As we have already seen in other pages in this section, the Earth is approximately 4.6 billion years old. This age is estimated by radiometric dating. Earth's past has been split into different sections based on events that happened during this time. An example is the boundary between the Cretaceous period and the Palaeogene period (formerly the Tertiary period) which are separated by an extinction event, where the dinosaurs and many other species went extinct.
The scale is split into different units; An Eon is a period of time greater than half a billion years. Eons are split into smaller units called Eras which last several hundreds of millions of years. Eras are split into smaller again units known as Periods which are again split into smaller units called Epochs.
The Geological Timescale
Geological time scale, source: The International Commission on Stratigraphy
There is also a simplified bilingual version of the time scale available to download.
Ireland's geological history spans from the Proterozoic to the Quaternary. Rocks from the Carboniferous period cover the largest area of Ireland (as can be seen on the geological maps of Ireland), below is a more detailed time scale of the Carboniferous.
The Timescale of the Carboniferous Period
Carboniferous time scale source: Sub commission on Carboniferous Stratigraphy