Pleistocene The lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: "Discoaster pentaradiatus" and "Discoaster surculus". The Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age. The revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. The modern continents were essentially at their
Plio-Pleistocene because the greater Plio-Pleistocene period covers the gradual but prolonged long-term cooling of the earth's atmosphere from the generally warmer temperatures of the late Oligocene / early Neogene times to and continuing through the Late Pleistocene—and indeed continuing through current times, if the present interglacial warming is considered as merely superimposed on the longer trend of cooling. Beginning about 3 mya, the late Pliocene saw the start of glaciation in the Northern Hemisphere, and many authors may informally use the term "Plio-Pleistocene" as a synonym for the period during which the Northern Hemisphere has been glaciated. Plio-Pleistocene The term Plio-Pleistocene