Cenozoic

The Cenozoic Era represents the most recent 66 million years of Earth’s geological history and marks a period of profound biological and environmental transformation. Beginning immediately after the Cretaceous–Palaeogene extinction event, it is characterised by the rapid rise and diversification of mammals, birds, insects, and flowering plants. As the final era of the Phanerozoic Eon, it follows the Mesozoic and Palaeozoic Eras and encompasses the geological interval during which the continents assumed their modern positions, global climates fluctuated dramatically, and human beings evolved and came to dominate planetary systems.

Nomenclature and Definition

The term Cenozoic derives from Ancient Greek roots meaning “new life.” It was introduced in 1840 by the British geologist John Phillips, who originally spelled it “Kainozoic.” Subsequent refinements in usage led to the now-standard spelling, though alternative forms such as Caenozoic and Cainozoic still appear in historical literature. The name corresponds to the major eras of the Phanerozoic, complementing the Mesozoic (“middle life”) and Paleozoic (“old life”) Eras, and aligns conceptually with the Proterozoic Eon (“earlier life”).
The Cenozoic is divided into three periods—Paleogene, Neogene, and Quaternary—which are further subdivided into seven epochs: Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. The International Commission on Stratigraphy formally recognised the Quaternary Period in 2009, replacing the older Tertiary concept with the Paleogene and Neogene.

Paleogene Period

Spanning 66 to 23.03 million years ago, the Paleogene includes the Paleocene, Eocene, and Oligocene epochs and encompasses the early recovery from the extinction that ended the age of dinosaurs.
Paleocene (66–56 Ma)The first epoch witnessed the emergence of modern placental mammals. With large reptiles removed from ecosystems, surviving lineages diversified rapidly. Dense but species-poor forests spread across much of the globe, and climatic warming allowed tropical conditions to extend towards the poles. Continental masses remained widely separated, with the Tethys Sea dividing Afro-Eurasia and the Americas separated by the open strait where the Isthmus of Panama would later form.
Eocene (56–33.9 Ma)Warm conditions peaked during the early Eocene, characterised by elevated atmospheric carbon dioxide and minimal polar temperature gradients. Early primates, whales, horses, and numerous archaic mammalian groups flourished. Large predatory birds occupied apex roles. Mid-Eocene tectonic rearrangements, notably the initiation of the Antarctic Circumpolar Current, triggered significant climatic cooling and retraction of tropical forests. Giant marine mammals evolved during this period. By the late Eocene, renewed seasonality encouraged the expansion of grasslands, and the epoch ended with the Eocene–Oligocene extinction event, marked most clearly in Europe by the Grande Coupure.
Oligocene (33.9–23.03 Ma)This epoch saw the continued global cooling and a shift towards more open habitats. Grasslands spread widely, promoting the diversification of grazing mammals and giving rise to early elephants, cats, dogs, and marsupials now familiar in modern ecosystems. New plant lineages appeared, and seasonal rainfall patterns intensified. The continued cooling of the climate set the stage for even more profound changes in the Neogene.

Neogene Period

Extending from 23.03 to 2.58 million years ago, the Neogene comprises the Miocene and Pliocene epochs, which were dominated by climatic shifts, faunal evolution, and tectonic reorganisation.
Miocene (23.03–5.333 Ma)Grasses expanded across the continents, altering terrestrial food chains and encouraging evolutionary radiations among herbivorous mammals. Kelp forests emerged along coastlines, enabling new marine ecosystems to develop. Perissodactyls diversified significantly, and apes proliferated into numerous species. The final closure of the Tethys Sea through the uplift of the Arabian Peninsula increased regional aridity. By the epoch’s end, the majority of modern seed plant families were established.
Pliocene (5.333–2.58 Ma)The Pliocene experienced more variable climates, influencing the evolution of contemporary flora and fauna. The Mediterranean temporarily desiccated during the Messinian salinity crisis, when lowered global sea levels restricted inflow from the Atlantic. In Africa, early hominins such as Australopithecus appeared. The formation of the Isthmus of Panama allowed intercontinental migration during the Great American Interchange, dramatically reshaping ecosystems. The spread of savannas accelerated, while monsoon systems and major deserts such as the Sahara became more defined.

Quaternary Period

The Quaternary, from 2.58 million years ago to the present, is dominated by climatic oscillations, the rise of humans, and the extinction of many megafauna species. It includes the Pleistocene and Holocene epochs.
Pleistocene (2.58 Ma–11,700 years ago)Repeated glaciations defined the Pleistocene, with ice sheets advancing into mid-latitudes. Africa’s progressive aridification gave rise to deserts including the Sahara, Namib, and Kalahari. Mammoths, woolly rhinos, giant ground sloths, sabre-toothed cats, and early humans inhabited varied habitats. Human populations expanded following the end of major drought cycles. The epoch concluded with widespread megafaunal extinctions affecting most continents, though Africa retained many of its large mammals.
Holocene (11,700 years ago–present)The Holocene encompasses all recorded human history. Its relatively stable climate facilitated the development of agriculture, complex societies, and technological civilisations. Human activity has accelerated extinctions, with many species lost since the Industrial Revolution, an ongoing crisis sometimes referred to as the Sixth Extinction. Anthropogenic impacts on climate, ecosystems, and geology have become increasingly prominent.

Tectonic Evolution

Throughout the Cenozoic, continental drift shaped modern geography. Australia migrated northwards after separating from Antarctica and collided with Southeast Asia. Antarctica settled over the South Pole and developed a permanent ice sheet. The Atlantic Ocean widened while the narrowing of the Tethys Sea led to the formation of the Mediterranean and other basins. Around 28 million years ago, the land bridge between North and South America formed, altering ocean circulation and climate. India’s collision with Eurasia uplifted the Himalayas, dramatically influencing global weather patterns.