Traditionally, either a sub‐era of the Cenozoic era of geologic time that began 1.806 Ma ago and continues to the present day; it is sometimes known as the Pleistogene period and includes the Pleistocene and Holocene epochs, during which there have been numerous ice‐sheet advances in the northern hemisphere. However, the boundary between the Quaternary and the preceding Tertiary was never clearly defined and the International Commission on Stratigraphy proposed abandoning both terms, Tertiary and Quaternary, as formal names. Quaternary researchers objected strongly, so that name (but not Tertiary) has been retained, commencing either 2.588 Ma ago at the start of the Gelasian stage (2.588–1.806 Ma ago) or about 3.6 Ma ago at the start of the preceding Piacenzian stage (3.6–2588 Ma ago).