Epoch· The columns of time
Miocene
23 Ma → 5.3 Ma
The Miocene, from 23 to 5.3 million years ago, is the longest epoch of the Neogene: the Tibetan plateau rose and the monsoon strengthened, apes diversified, and the Mediterranean dried out at the end.
Longest epoch of the Neogene, marked by the uplift of the Tibetan plateau and the strengthening of the monsoon, by the diversity of apes, and closed by the drying of the Mediterranean.
What the evidence shows
India had driven into Asia and raised a plateau the size of western Europe five kilometres above sea level, and in the Miocene that surface produces the climatic effect proper to relief of that extent: in summer it warms far faster than the neighbouring ocean, and the air rising from it draws moist oceanic air inland. The monsoon strengthens as the plateau rises further, enough to leave a signature in the sediments of the surrounding seas. In Africa, between 7 and 6 million years, a distorted cranium from Chad has a forward-placed foramen magnum, as in humans and not in chimpanzees: the oldest candidate for the human lineage. The epoch ends with the Messinian salinity crisis: between 5.96 and 5.33 million years, the Mediterranean loses its connection with the Atlantic and largely evaporates, leaving salt flats a kilometre below sea level and up to two kilometres of evaporites on its floor, before the Atlantic forces the passage at Gibraltar once more.
Bounds and conventions
Golden spikes bound both ends. The uplift of the plateau and the strengthening of the monsoon occur within the same interval, which does not establish a causal relation: the link rests on that concurrence, and the data remain insufficient to demonstrate it. The Chadian cranium is contested on two points: its date proceeds from faunal comparison rather than radiometric measurement, and the interpretation of its posture has been debated since publication, a femur described in 2022 supporting it. The rate at which the Mediterranean refilled is reconstructed from the morphology of the channel cut and not observed.