Epoch· The columns of time

Miocene

23 Ma → 5.3 Ma

The longest epoch of the Neogene, in which a plateau rises and a monsoon strengthens with it, apes are many and various, and the Mediterranean dries out at the very end.

What the evidence shows

India had driven into Asia and pushed up a plateau the size of western Europe to five kilometres above the sea, and by the Miocene that surface is doing what mountains do to weather: in summer it heats far faster than the ocean beside it, and the air rising off it draws wet ocean air inland behind it. The monsoon strengthens as the plateau rises further, enough to leave its signature in the sediments of the surrounding seas. In Africa, between 7 and 6 million years ago, a crushed skull from Chad carries the hole where the spine enters set forward, as in us and not in a chimpanzee: the oldest candidate for our own branch. The epoch ends on a spectacle. Between 5.96 and 5.33 million years the Mediterranean loses its link to the Atlantic and largely evaporates, leaving salt flats a kilometre below sea level and up to two kilometres of salt on its floor, until the Atlantic breaks back through at Gibraltar.

Bounds and conventions

Golden spikes hold both ends. The plateau rose and the monsoon strengthened over the same stretch of time, which does not prove that one made the other: the link is read from that coincidence, and the data are still too thin to settle it. The Chadian skull is contested on two counts: its date rests on faunal comparison rather than radiometry, and the reading of its posture has been challenged since publication, though a thigh bone described in 2022 was offered in support. How fast the Atlantic refilled the Mediterranean is reconstructed from the shape of the channel it cut, not observed, and the estimates are dramatic enough to be worth treating as estimates.

Sources

1. Cohen, K. M., Finney, S. C., Gibbard, P. L., Fan, J.-X. (2013). The ICS International Chronostratigraphic Chart. Episodes 36(3), 199–204, mise à jour continue, voir Cohen et al. (2025), Episodes.
2. Edwards et al. (2010), Science · The origins of C4 grasslands: integrating evolutionary and ecosystem science
3. García-Castellanos et al. (2009), Nature · Catastrophic flood of the Mediterranean after the Messinian salinity crisis
4. Brunet et al. (2002), Nature · A new hominid from the Upper Miocene of Chad, Central Africa
5. Tada et al. (2016), Progress in Earth and Planetary Science · Evolution and variability of the Asian monsoon and its potential linkage with uplift of the Himalaya and Tibetan Plateau