Aruandeperioodi

Aruandeperioodi, also known as the *Aruan Cycle* or *Aruan Epoch*, refers to a proposed geological time scale segment within the broader framework of Earth's history. The term originates from Finnish geological literature and is used to describe a hypothetical or less formally recognized period in Earth's stratigraphic record. Unlike the widely accepted International Chronostratigraphic Chart, which divides Earth's history into eons, eras, periods, epochs, and ages, the Aruandeperioodi is not part of the official global stratigraphic framework.

The concept appears to be rooted in Finnish geological studies, particularly those examining the Precambrian era, which spans from the formation of Earth approximately 4.6 billion years ago until the beginning of the Cambrian Period around 541 million years ago. The Aruandeperioodi is sometimes loosely associated with the late Precambrian, particularly the Ediacaran Period (635–541 million years ago), a time marked by the appearance of early multicellular life forms and significant environmental changes. However, its precise boundaries and significance remain debated and are not universally accepted.

In Finnish geological literature, the term may be used informally to describe a transitional phase within the Ediacaran or adjacent periods, reflecting local stratigraphic observations. Some researchers suggest it could correspond to a period of intense glacial activity, known as "snowball Earth" events, or other climatic shifts that influenced the development of early ecosystems. Despite its occasional mention in regional studies, the Aruandeperioodi lacks formal recognition in international geological circles, where such divisions are typically standardized through the International Commission on Stratigraphy.

For most scientific purposes, Earth's geological time scale relies on the established International Chronostratigraphic Chart, which provides a globally consistent framework for understanding Earth's history. The Aruandeperioodi, therefore, remains a niche or localized concept rather than a standardized division in global stratigraphy.