[11][12] The Miocene boundaries are not marked by distinct global events but by regionally defined transitions from the warmer Oligocene to the cooler Pliocene Epoch.

The Miocene is of particular interest to geologists and palaeoclimatologists because major phases of the geology of the Himalaya occurred during that epoch, affecting monsoonal patterns in Asia, which were interlinked with glacial periods in the northern hemisphere.

[15] The Miocene faunal stages from youngest to oldest are typically named according to the International Commission on Stratigraphy:[16] Regionally, other systems are used, based on characteristic land mammals; some of them overlap with the preceding Oligocene and following Pliocene Epochs: Continents continued to drift toward their present positions.

[21] The Tian Shan experienced significant uplift in the Late Miocene, blocking westerlies from coming into the Tarim Basin and drying it as a result.

[32] During the Oligocene and Early Miocene, the coast of northern Brazil,[33] Colombia, south-central Peru, central Chile and large swathes of inland Patagonia were subject to a marine transgression.

[34] The transgressions in the west coast of South America are thought to be caused by a regional phenomenon while the steadily rising central segment of the Andes represents an exception.

[35][37] The Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene, forming the Chile Triple Junction.

At first the Antarctic Plate subducted only in the southernmost tip of Patagonia, meaning that the Chile Triple Junction lay near the Strait of Magellan.

[38] The asthenospheric window associated to the triple junction disturbed previous patterns of mantle convection beneath Patagonia inducing an uplift of ca.

[37][39] As the southern Andes rose in the Middle Miocene (14–12 million years ago) the resulting rain shadow originated the Patagonian Desert to the east.

Although northern Australia is often believed to have been much wetter during the Miocene, this interpretation may be an artefact of preservation bias of riparian and lacustrine plants;[41] this finding has itself been challenged by other papers.

[48] This cool event occurred immediately after the Oligocene-Miocene Transition (OMT) during a major expansion of Antarctica's ice sheets,[49] but was not associated with a significant drop in atmospheric carbon dioxide levels.

[51] Global cooling caused the East Asian Summer Monsoon (EASM) to begin to take on its modern form during the Early Miocene.

[55] MMCO warmth was driven by the activity of the Columbia River Basalts[56][57][58] and enhanced by decreased albedo from the reduction of deserts and expansion of forests.

[61] The July ITCZ, the zone of maximal monsoonal rainfall, moved to the north, increasing precipitation over southern China whilst simultaneously decreasing it over Indochina during the EASM.

[64] The MMCO ended around 14 million years ago,[48] when global temperatures fell in the Middle Miocene Climate Transition (MMCT).

[77] Greenland may have begun to have large glaciers as early as 8 to 7 Ma,[78][79] although the climate for the most part remained warm enough to support forests there well into the Pliocene.

[81] In the Great Rift Valley of Kenya, there was a gradual and progressive trend of increasing aridification, though it was not unidirectional, and wet humid episodes continued to occur.

[95] The coevolution of gritty, fibrous, fire-tolerant grasses and long-legged gregarious ungulates with high-crowned teeth, led to a major expansion of grass-grazer ecosystems[citation needed].

Herds of large, swift grazers were hunted by predators across broad sweeps of open grasslands, displacing desert, woodland, and browsers[citation needed].

[100] One study, however, has attributed the expansion of grasslands not to a CO2 drop but to the increasing seasonality and aridity, coupled with a monsoon climate, which made wildfires highly prevalent compared to before.

[107] Mustelids diversified into their largest forms as terrestrial predators like Ekorus, Eomellivora, and Megalictis and bunodont otters like Enhydriodon and Sivaonyx appeared.

[114] Approximately 100 species of apes lived during this time[citation needed], ranging throughout Africa, Asia and Europe and varying widely in size, diet, and anatomy.

[115] The first hominins (bipedal apes of the human lineage) appeared in Africa at the very end of the Miocene, including Sahelanthropus, Orrorin, and an early form of Ardipithecus (A. kadabba).

[121] In the oceans, brown algae, called kelp, proliferated, supporting new species of sea life, including otters, fish and various invertebrates.

[127] The youngest members of Sebecidae, a clade of large terrestrial predatory crocodyliformes distantly related to modern crocodilians, from which they likely diverged over 180 million years ago, are known from the Miocene of South America.

The early Miocene Saint Bathans Fauna is the only Cenozoic terrestrial fossil record of the landmass, showcasing a wide variety of not only bird species, including early representatives of clades such as moa, kiwi and adzebills, but also a diverse herpetofauna of sphenodontians, crocodiles and turtles as well as a rich terrestrial mammal fauna composed of various species of bats and the enigmatic Saint Bathans Mammal.

The change resulted from fracture reactivation during the Pyrenean-Alpine orogeny, enabling sulphate-reducing microbes to permeate into the Fennoscandian Shield via descending surficial waters.

[131] There is evidence from oxygen isotopes at Deep Sea Drilling Program sites that ice began to build up in Antarctica about 36 Ma during the Eocene.

Oceans cooled partly due to the formation of the Antarctic Circumpolar Current, and about 15 million years ago the ice cap in the southern hemisphere started to grow to its present form.