The Neogene built the grasslands, the Himalayas and, at the very end, us
Between about 23 and 2.6 million years ago, the planet slowly turned into the one we recognise. Continents settled near their present spots, the Americas joined at Panama, forests gave way to grass, horses and bison evolved to graze it, and the first humans appeared in Africa as the ice ages began.
Geologists define the Neogene as the period running from 23.04 to 2.58 million years ago, a span of 20.45 million years split into the Miocene and the later Pliocene. It is the second period of the Cenozoic. The Austrian palaeontologist Moritz Hörnes coined the name in 1853. Together with the Paleogene it covers what used to be called the Tertiary, a label that no longer has formal standing but still turns up in casual use.
The continental map shifted only modestly, but the changes mattered. India kept ramming into Asia and pushing up the Himalayas, falling seas opened land bridges between Africa, Eurasia and North America, and late in the Pliocene the Isthmus of Panama joined the two Americas. That closure blocked warm Pacific water from flowing into the Atlantic, leaving the Gulf Stream as the main carrier of heat toward the Arctic. The long-term trend was cooler, drier and more seasonal, interrupted by warm spells such as the Middle Miocene Climatic Optimum and the Pliocene Warm Interval, whose carbon dioxide levels resembled today's and which is often used as a preview of a warming future.
Life responded dramatically. Tropical forests retreated before deciduous trees and open grassland, grasses diversified, and grazing mammals such as horses, antelope and bison evolved alongside them. C4 plants came to dominate grasslands over the last 10 million years. In the oceans giant predators like Megalodon and Livyatan ruled, although around 19 million years ago about 70 percent of open-ocean shark species vanished. Bears diversified explosively near the Miocene–Pliocene boundary, mammoths and woolly rhinos were common in the Pliocene, and Homo habilis emerged in Africa near the close.
Even the period's end was argued over. Marine geologists wanted the Neogene to continue into the present, while land-based colleagues insisted the Quaternary stood apart. After years of proposals and counterproposals, and talks at the 2008 International Geological Congress in Oslo, the International Commission on Stratigraphy ruled in May 2009 that the Quaternary begins at 2.58 million years ago, closing the Neogene there.
Source: Neogene
