As Earth went from the Oligocene through the Miocene and into the Pliocene, the climate slowly cooled towards a series of ice ages. The Miocene boundaries are not marked by a single distinct global event but consist rather of regionally defined boundaries between the warmer Oligocene and the cooler Pliocene Epoch.
During the Early Miocene, the Arabian Peninsula collided with Eurasia, severing the connection between the Mediterranean and Indian Ocean, and allowing a faunal interchange to occur between Eurasia and Africa, including the dispersal of proboscideans into Eurasia. During the late Miocene, the connections between the Atlantic and Mediterranean closed, causing the Mediterranean Sea to nearly completely evaporate, in an event called the Messinian salinity crisis. The Strait of Gibraltar opened and the Mediterranean refilled at the Miocene–Pliocene boundary, in an event called the Zanclean flood.
The apes first evolved, arose, and diversified during the early Miocene (Aquitanian and Burdigalian Stages), becoming widespread in the Old World. By the end of this epoch and the start of the following one, the ancestors of humans had split away from the ancestors of the chimpanzees to follow their own evolutionary path during the final Messinian Stage (7.5–5.3 Ma) of the Miocene. As in the Oligocene before it, grasslands continued to expand and forests to dwindle in extent. In the seas of the Miocene, kelp forests made their first appearance and soon became one of Earth's most productive ecosystems.
The plants and animals of the Miocene were recognizably modern. Mammals and birds were well-established. Whales, pinnipeds, and kelp spread.
The Miocene is of particular interest to geologists and palaeoclimatologists as major phases of the geology of the Himalaya occurred during the Miocene, affecting monsoonal patterns in Asia, which were interlinked with glacial periods in the northern hemisphere.
^Krijgsman, W.; Garcés, M.; Langereis, C. G.; Daams, R.; Van Dam, J.; Van Der Meulen, A. J.; Agustí, J.; Cabrera, L. (1996). "A new chronology for the middle to late Miocene continental record in Spain". Earth and Planetary Science Letters. 142 (3–4): 367–380. Bibcode:1996E&PSL.142..367K. doi:10.1016/0012-821X(96)00109-4.
Lyell, Charles (1833). Principles of Geology, …. Vol. 3. London, England: John Murray. p. 54. From p. 54: "The next antecedent tertiary epoch we shall name Miocene, from μειων, minor, and χαινος, recens, a minority only of fossil shells imbedded in the formations of this period, being of recent species."
^Gibson, M. E.; McCoy, J.; O’Keefe, J. M. K.; Otaño, N. B. Nuñez; Warny, S.; Pound, M. J. (2022). "Reconstructing Terrestrial Paleoclimates: A Comparison of the Co-Existence Approach, Bayesian and Probability Reconstruction Techniques Using the UK Neogene". Paleoceanography and Paleoclimatology. 37 (2): e2021PA004358. Bibcode:2022PaPa...37.4358G. doi:10.1029/2021PA004358. S2CID245937316.
^Steinthorsdottir, M.; Coxall, H. K.; Boer, A. M. de; Huber, M.; Barbolini, N.; Bradshaw, C. D.; Burls, N. J.; Feakins, S. J.; Gasson, E.; Henderiks, J.; Holbourn, A. E.; Kiel, S.; Kohn, M. J.; Knorr, G.; Kürschner, W. M.; Lear, C. H.; Liebrand, D.; Lunt, D. J.; Mörs, T.; Pearson, P. N.; Pound, M. J.; Stoll, H.; Strömberg, C. a. E. (2021). "The Miocene: The Future of the Past". Paleoceanography and Paleoclimatology. 36 (4): e2020PA004037. Bibcode:2021PaPa...36.4037S. doi:10.1029/2020PA004037. S2CID234434792.