Geological Time

Geological time is vast.

Consider that our lineage Homo first appeared on Earth a little over two million years ago. The history of life in Aotearoa New Zealand extends back to just over 500 million years, and the history of life on planet Earth goes back to over 3700 million years or 3.7 billion years. To help us navigate across this vastness of time the history of the Earth is conveniently divided into segments with different names that are tied to major events.  Further, these segments are nested within one another to help us talk about events in Earth history at different scales.

For example, the lineages of mammals that we are familiar with today (bats, rodents, whales etc.) all have their origins within the Cenozoic, an era of geological time that spans the last 66 million years. Focussing in on whales, the origin of these marine mammals occurred during the Paleogene, a period of geological time that spanned 66.0 to 23.03 million years ago. Narrowing down further, many of the ancient whale species discovered in Aotearoa, including several that we include in this eBook (see: Archaic dolphin connects oceans of Zealandia to endangered river resident), are from rocks that were once the ancient sea floor during the Duntroonian Stage 27.3 to 25.2 million years ago. These nested divisions of geological time help to contextualise the events that have shaped the tree of life, from the grand to the fleeting.

Geological time is often represented as a time scale diagram like the one below. In our time scale diagram we show the last 541 million years out of the 4.6 billion year history of Earth. The time segments here include eras, which are divided into periods, then into epochs, then into series, and finally into stages. This geological time scale diagram is based on the New Zealand Timescale produced by GNS Science Te Pū Ao and features the local series and stages used in New Zealand.

A diagram representing the previous 541 million years of geological time. This time scale diagram was created new for this eBook and has been adapted from the New Zealand Geological Time Scale published by GNS Science Te Pū Ao, which has the citation Raine JI, Beu AG, Boyes AF, Campbell HJ, Cooper RA, Crampton JS, Crundwell MP, Hollis CJ, Morgans HEG. 2015. Revised calibration of the New Zealand Geological Timescale: NZGT2015/1. GNS Science Report 2012/39.

Geological time scale diagrams can be challenging to read. If you would like to see the same information presented in a key word searchable table then head across to the supplementary chapter Geological Time (table).