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Last edited 17 Jun 2025

Measures of significant periods of time

Terms describing periods of time are often used in architectural history to describe certain timespans between significant cultural events and longer timespans between global events. There can be some confusion between terms for example era can be correctly used to describe a English architectural stylistic periods between two signifiant events, such as the Edwardian era, Victorian era and so on, the term is also used to refer to much longer periods in a geological scale.

Another term that might be be used in reference to the built environment, in particular in terms or ancient history might be Age, such as Iron age and Stone age dwellings. Finally in terms of sustainability or circular economic perspective is the term epoch might be used to describe the time frame which has been coined by the human age or the Anthropocene epoch or period. This is 'a proposed new geological epoch resulting from significant human-driven changes to the structure and functioning of the Earth System, including the climate system.’ Climate Change 2021, The Physical Science Basis, published by the Intergovernmental Panel on Climate Change in 2021.

Below is a list of the various categories of geological time frames.

Eon: The largest unit of geologic time.
Era: A subdivision of an eon, lasting hundreds of millions of years. (also used more generally)
Period: A subdivision of an era, lasting millions of years to tens of millions of years. (also used more generally)
Epoch: A subdivision of a period, hundreds of thousands of years to tens of millions of years.
Sub-epoc: Thousands of years to millions of years
Age: Thousands of years to millions of years.