Neogene

The Neogene is a major geological period that shaped our modern world. It spans 20.45 million years of Earth's history. This period began when the Paleogene Period ended. It serves as the second period of the Cenozoic Era. The Neogene is also the eleventh period of the Phanerozoic Eon. Geologists use this time to study how our current continents and climates formed. Some scientists even debate where the Neogene ends and the Quaternary Period begins. This discussion exists because the most recent geological records are very detailed.

The Neogene is divided into two distinct epochs. The first is the Miocene epoch, which is the earlier part. The second is the Pliocene epoch, which is the later part. Within the Miocene, there are six specific ages. These are the Aquitanian, Burdigalian, Langhian, Serravallian, Tortonian, and Messinian ages. The Pliocene is divided into two ages: the Zanclean and the Piacenzian. These divisions help scientists organize the complex changes occurring in the Earth's crust and atmosphere.

Large-scale movements of the Earth's surface defined this era. The continents moved into positions very close to where they are today. One of the most significant events was the formation of the Isthmus of Panama. This land bridge connected North and South America late in the Pliocene. This connection acted as a barrier in the ocean. It cut off warm ocean currents from moving between the Pacific and Atlantic Oceans. This change left only the Gulf Stream to move heat toward the Arctic Ocean.

The climate during the Neogene underwent a long-term cooling trend. The early Miocene was relatively cool for the planet. However, the Middle Miocene Climatic Optimum (MMCO) brought a warm phase. This warmth was driven by the emplacement of the Columbia River Basalt Group. Around 11 million years ago, the world entered the much cooler Late Miocene. During this time, ice caps at both poles began to grow and thicken. This process was helped by the increased formation of sea ice.

Temperature shifts continued through the Pliocene epoch. Between 7 and 5.3 million years ago, the Late Miocene Cooling (LMC) occurred. This cooling was driven by a decrease in carbon dioxide concentrations. Later, the Pliocene Warm Interval (PWI) occurred from 5.3 to 2.7 million years ago. This interval had carbon dioxide levels similar to our current atmosphere. During the Pliocene, North Africa also experienced "Green Sahara" phases. These wet conditions occurred roughly every 21,000 years.

Life on land and in the sea changed significantly. Mammals and birds evolved into many modern forms. As the climate became drier and more seasonal, forests were replaced by grasslands. This allowed grazing animals like horses, antelope, and bison to thrive. In the oceans, massive predators like megalodons and livyatans dominated. About 19 million years ago, 70% of all pelagic shark species disappeared. Toward the end of the Pliocene, the first humans, Homo habilis, appeared in Africa.

History shows how we came to name this period. The term "Neogene" was coined in 1853 by Moritz Hörnes. He was an Austrian palaeontologist. Before this, many used the term "Tertiary Period." While "Tertiary" is no longer a formal term, it is still used informally. Geologists have worked hard to define the exact end of the Neogene. In 2009, the International Commission on Stratigraphy decided on a clear boundary. They set the end of the Neogene at 2.58 million years ago. This marks the beginning of the Quaternary Period.