Neogene

The Neogene is a time in Earth's history. It lasted for 20.45 million years, from the end of the Paleogene Period 23.04 million years ago to the start of the present Quaternary Period 2.58 million years ago. It is part of the Cenozoic and the Phanerozoic. The Neogene has two parts: the earlier Miocene and the later Pliocene.

During this time, mammals and birds changed and evolved into the forms we see today. The first humans, Homo habilis, appeared in Africa near the end of this period. There were also changes in where the continents were. One big event was when North America and South America connected at the Isthmus of Panama late in the Pliocene. This changed ocean currents and affected the climate.

The world's climate became cooler during the Neogene. This cooling led to large periods of ice covering much of the land later on. The word "Neogene" was first used in 1853 by a scientist named Moritz Hörnes.

Divisions

The Neogene has two main parts called epochs. The earlier part is the Miocene and the later part is the Pliocene.

The Pliocene Epoch has two ages: the Piacenzian Age and the Zanclean Age. The Miocene Epoch has six ages: the Messinian Age, Tortonian Age, Serravallian Age, Langhian Age, Burdigalian Age, and Aquitanian Age. Some places may use other names for these ages.

Paleogeography

During the Neogene, the continents were almost in the same places as they are today. The land bridge called the Isthmus of Panama formed, connecting North and South America. The Indian subcontinent kept moving into Asia, creating the tall mountains known as the Himalayas. As sea levels dropped, new paths called land bridges appeared between Africa and Eurasia, and also between Eurasia and North America.

Climate

The global climate during this time became more seasonal and continued to get drier and cooler. This trend started in an earlier time period called the Paleogene.

In the early part of this period, called the Early Miocene, the world was relatively cool. Later, during the Middle Miocene, Earth experienced a warm period known as the Middle Miocene Climatic Optimum. This warmth was caused by large volcanic activity in what is now the Columbia River Basalt Group. After this warm time, the climate cooled again in the Late Miocene, and ice began to build up at the poles.

During the Pliocene, the world warmed up once more in a period called the Pliocene Warm Interval. This warm time had carbon dioxide levels similar to today and is studied to understand possible future climate changes. By the end of this period, the Earth began to cool and the first big glaciations of the current Ice Age started.

Flora and fauna

During this time, plants and animals began to look more like they do today. Some ancient reptiles, like the group called Choristodera, disappeared early on. Other reptiles such as Langstonia and Barinasuchus also vanished. The oceans had huge predators like Megalodon and Livyatan, and many shark species disappeared about 19 million years ago.

Mammals and birds were the main land animals, evolving in many shapes and sizes. In North America, hoofed animals like ungulates started moving faster, probably because the land became more open. The first early humans, known as hominins, appeared near the end of this period.

Plants also changed a lot. About 20 million years ago, some conifer and cycad trees grew more kinds. As the climate cooled, tropical plants were replaced by trees that lose their leaves in winter, and grasslands spread out. This helped grasses grow more, and animals like horses, antelope, and bison evolved to eat them. During the cooler time called the Pliocene, big ice age animals like mammoths and woolly rhinoceros lived. With less CO₂ in the air, a special kind of plant called C₄ plants became common in grasslands. Flowers like Asteraceae (which include daisies) also spread a lot. Fossils of Eucalyptus trees have been found from the Miocene in New Zealand, even though these trees are not native there today.

Disagreements

Scientists have sometimes disagreed about when the Neogene Period ended. Traditionally, it ended at the close of the Pliocene Epoch.

Some scientists wanted to include recent time—the Quaternary—within the Neogene. Others thought the Quaternary should be separate. After discussions, they agreed to make the Quaternary its own period beginning 2.58 million years ago. This means the Neogene Period ends at that same point.