The Neogene Period spanned approximately 20.45 million years, beginning about 23.03 million years ago and concluding 2.58 million years ago. It represents the second period of the Cenozoic Era, often called the “Age of Mammals.” During the Neogene, the planet underwent profound transformations in its geology, climate, and biological ecosystems, laying the groundwork for the world we recognize today. The period is defined by a consistent trend of global cooling and the near-final configuration of the continents, which spurred the evolution of modern life forms.
Defining the Neogene Timeframe
The Neogene Period is formally bounded by specific shifts in the fossil record and rock layers. Its starting point, 23.03 million years ago, marks the transition from the preceding Paleogene Period (Oligocene Epoch) to the Miocene Epoch. The end date, 2.58 million years ago, is set by the beginning of the Quaternary Period (Pleistocene Epoch), chosen due to a significant change in Earth’s climate and magnetic record. The Neogene is chronologically situated between the Paleogene and the Quaternary, which continues to the present day.
The Neogene Period is divided into two major epochs, each with distinct geological and biological characteristics. The earlier and longer is the Miocene Epoch, which lasted from 23.03 million years ago to 5.33 million years ago. Following this is the shorter Pliocene Epoch, lasting from 5.33 million years ago to 2.58 million years ago. The boundary between the Miocene and Pliocene is marked by the Messinian Salinity Crisis, a major global event where the Mediterranean Sea nearly dried up.
The International Commission on Stratigraphy defines these boundaries based on changes in deep-sea sediment cores and the appearance or disappearance of microfossils. The transition into the Quaternary is tied to the onset of major Northern Hemisphere glaciation and a shift in Earth’s magnetic polarity, known as the Gauss-Matuyama boundary. This dating allows geologists and paleontologists to correlate events across the globe.
Major Global Geological Transformations
The Neogene Period featured immense tectonic plate activity, sculpting the continents into nearly their modern arrangements. Plate movements continued the convergence of landmasses that began earlier in the Cenozoic Era. This movement led to intense orogeny, or mountain-building processes, as continental plates collided.
A profound geological event was the continued collision of the Indian subcontinent with the Asian plate, causing the final uplift of the Himalayan mountain range. The northward push of the African plate into the Eurasian plate resulted in the formation and elevation of the European Alps and the Pyrenees. In the Americas, the subduction of oceanic crust beneath the continental plates contributed to the rise and extension of the Andes Mountains along the western edge of South America.
Continental activity also had profound effects on ocean circulation and global geography. In the late Pliocene, the closing of the gap between North and South America led to the formation of the Isthmus of Panama, a land bridge that connected the two continents. This event permanently altered global ocean currents by cutting off the direct flow of warm equatorial water between the Pacific and Atlantic oceans, which significantly impacted global climate patterns. The formation of these extensive mountain ranges and the Isthmus of Panama marked the near completion of the modern continental configuration.
Climate Change and Global Cooling
The Neogene was characterized by a long-term trend toward global cooling and increased aridity, departing from the warmer conditions of the Paleogene. The uplift of mountain ranges, particularly the Himalayas, changed atmospheric circulation patterns, driving this climatic shift. This process gradually transformed a world dominated by forests into one featuring more open, temperate landscapes.
A significant development was the stabilization and thickening of the Antarctic ice sheet, which formed during the preceding Oligocene Epoch. The expansion of this southern ice mass profoundly influenced global climate by increasing the planet’s albedo, meaning more solar radiation was reflected back into space, thereby reinforcing the cooling. The cooling trend was punctuated by warmer intervals, such as the Middle Miocene Climatic Optimum (17 to 15 million years ago).
As the Neogene progressed into the late Pliocene, cooling intensified, culminating in the initiation of major Northern Hemisphere glaciation around 3.3 to 2.58 million years ago. This marked the transition into the ‘icehouse’ world of the Quaternary Period, with ice sheets expanding across North America and Eurasia. The global drop in sea levels, caused by water locked up in continental ice sheets, exposed vast areas of continental shelf and created land bridges, facilitating species migration.
The Rise of Modern Ecosystems
The Neogene’s geological and climatic changes drove the evolution of modern terrestrial ecosystems. The combination of global cooling, increased aridity, and declining atmospheric carbon dioxide levels favored the expansion of open habitats over dense forests. The most visible biological consequence was the global spread of C4 grasslands, particularly during the Late Miocene, around 10 million years ago.
C4 grasses possess a distinct photosynthetic pathway, providing an advantage in warmer, drier conditions and lower carbon dioxide concentrations compared to ancestral C3 plants. The dominance of these grasslands spurred the diversification of herbivorous mammals specializing in grazing. This led to the evolution and radiation of modern groups, including horses (adapted for grinding grass), camels, and bovids like antelope and bison.
The emergence of these new biomes in Africa was significant for the evolution of primates. The shift from continuous forests to mosaics of woodland and savanna is linked to the appearance of early hominids, such as Australopithecus, during the Pliocene Epoch. These ancestors of modern humans evolved adaptations for bipedalism, which provided an advantage for movement and survival across the open African landscape.