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Why did some geologists question whether the Quaternary should be a formal period?

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Quaternary paleogeography — Quaternary Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the Quaternary Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

Some geologists questioned the status of the Quaternary as a formal period because they favored a different organizational structure for the Cenozoic Era. Specifically, a growing number of experts preferred to divide the Cenozoic into two distinct periods: the Paleogene and the Neogene.12

This preference led to debates regarding the utility of the traditional "Tertiary" and "Quaternary" labels, which were based on an antiquated 19th-century classification system. While these terms remained useful for specific climatic and continent-based studies, the push to replace them with the Paleogene and Neogene periods caused the formal status of the Quaternary to be challenged for many years.12

The International Commission on Stratigraphy (ICS) even recommended in 2005 that the Quaternary be relegated to an informal sub-era. However, this was ultimately resolved in 2008 when the ICS abandoned the sub-era structure and formally designated the Quaternary as the uppermost period of the Cenozoic Era, a decision officially ratified by the International Union of Geological Sciences in 2009.12