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Neogene: the story on HearLore | HearLore
Neogene
The word Neogene was coined in 1853 by an Austrian palaeontologist named Moritz Hörnes, yet the period it describes spans 20.45 million years of Earth history. Before this term was established, geologists used the label Tertiary Period to define the span of time now covered by both the Paleogene and Neogene, a classification that persists in informal conversation despite losing its formal status. Hörnes, who lived from 1815 to 1868, introduced a new vocabulary to describe the rocks deposited during this era, creating a framework that would eventually be refined by the International Commission on Stratigraphy. The Neogene serves as the second period of the Cenozoic Era and the eleventh period of the Phanerozoic, marking a time when the Earth began to look strikingly similar to the world we inhabit today. This period bridges the gap between the ancient past and the modern age, ending at the boundary of the Quaternary Period 2.58 million years ago. The debate over where to draw the line between the Neogene and the Quaternary has sparked decades of disagreement among geologists, particularly regarding whether the ongoing geological time should be included within the Neogene or treated as a distinct period. Marine geologists often argue for inclusion, while terrestrial geologists insist on separation, creating a confusing terminology that reflects the fine divisibility of time units as they approach the present. The compromise reached in 2009 by the ICS finally set the base of the Quaternary at 2.58 million years ago, effectively ending the Neogene at that precise moment.
Shifting Continents
The most significant geological event of the Neogene was the formation of the Isthmus of Panama, which connected North and South America late in the Pliocene epoch. This massive land bridge did more than just join two continents; it fundamentally altered global ocean circulation by cutting off warm ocean currents from the Pacific Ocean to the Atlantic Ocean. With this connection established, only the Gulf Stream remained to transfer heat to the Arctic Ocean, a change that would have profound consequences for global climate. Simultaneously, the Indian subcontinent continued its relentless collision with Asia, pushing up the Himalayas and reshaping the topography of the Eurasian landmass. Sea levels fell during this period, creating land bridges between Africa and Eurasia and between Eurasia and North America, allowing species to migrate across previously separated regions. These continental movements were not merely background events but active drivers of evolutionary change, forcing species to adapt to new environments or face extinction. The shifting geography created a dynamic stage upon which the drama of life would unfold, setting the scene for the diversification of mammals and the eventual rise of humans. The Neogene continents were very close to their current positions, yet the subtle shifts in their arrangement triggered a cascade of environmental changes that rippled through the biosphere.
Who coined the word Neogene and when was it created?
The word Neogene was coined in 1853 by the Austrian palaeontologist Moritz Hörnes. Hörnes lived from 1815 to 1868 and introduced this new vocabulary to describe rocks deposited during the era. The term eventually replaced the older label Tertiary Period in formal geological classification.
When did the Neogene period end and what event marked its conclusion?
The Neogene period ended 2.58 million years ago at the boundary of the Quaternary Period. The International Commission on Stratigraphy reached a compromise in 2009 to set this base date, effectively ending the Neogene at that precise moment. This decision resolved decades of disagreement between marine and terrestrial geologists regarding the timeline.
What geological event formed the Isthmus of Panama during the Neogene?
The formation of the Isthmus of Panama connected North and South America late in the Pliocene epoch. This massive land bridge fundamentally altered global ocean circulation by cutting off warm currents from the Pacific Ocean to the Atlantic Ocean. The event also caused sea levels to fall and created land bridges between Africa and Eurasia as well as Eurasia and North America.
How did the climate change during the Middle Miocene and Late Miocene periods?
The Middle Miocene brought a warm phase known as the Middle Miocene Climatic Optimum driven by the emplacement of the Columbia River Basalt Group. Around 11 million years ago this warm interval gave way to the much cooler Late Miocene, marking the beginning of a long-term cooling trend. Between 7 and 5.3 million years ago a decrease in global temperatures termed the Late Miocene Cooling ensued due to decreases in carbon dioxide concentrations.
Which marine predators dominated the oceans during the Neogene period?
The oceans of the Neogene were dominated by large carnivores like megalodons and livyatans. About 19 million years ago approximately 70% of all pelagic shark species disappeared in a catastrophic event that reshaped the marine ecosystem. Despite these losses marine and continental flora and fauna developed a modern appearance signaling a transition toward the ecosystems we recognize today.
When did the first hominins appear and where did they emerge during the Neogene?
The first hominins appeared near the end of the Neogene period in Africa. Homo habilis emerged as the period drew to a close while ice age mammals like the mammoths and woolly rhinoceros were common in the Pliocene. This appearance occurred in Africa where the first humans emerged as the period drew to a close.
The global climate of the Neogene became increasingly seasonal and followed an overall drying and cooling trend that had begun during the Paleogene. The Early Miocene was relatively cool, with mid-latitude seawater and continental thermal gradients already resembling those of the present day. However, the Middle Miocene brought a warm phase known as the Middle Miocene Climatic Optimum, driven by the emplacement of the Columbia River Basalt Group. Around 11 million years ago, this warm interval gave way to the much cooler Late Miocene, marking the beginning of a long-term cooling trend. Between 7 and 5.3 million years ago, a decrease in global temperatures termed the Late Miocene Cooling ensued, driven by decreases in carbon dioxide concentrations. The ice caps on both poles began to grow and thicken, a process enhanced by positive feedbacks from the increased formation of sea ice. During the Pliocene, from about 5.3 to 2.7 million years ago, another warm interval occurred, known as the Pliocene Warm Interval, which interrupted the longer-term cooling trend. The Pliocene Thermal Maximum happened between 3.3 and 3.0 million years ago, featuring atmospheric carbon dioxide levels similar to contemporary times. This period is often seen as an analogous climate to the projected climate of the near future as a result of anthropogenic global warming. Towards the end of the Pliocene, decreased heat transport towards the Antarctic resulting from a weakening of the Indonesian Throughflow cooled the Earth, a process that exacerbated itself in a positive feedback as sea levels dropped and the ITF diminished. By the end of the period, the first of a series of glaciations of the current Ice Age began, setting the stage for the Quaternary Period.
Sharks and Giants
The oceans of the Neogene were dominated by large carnivores like megalodons and livyatans, apex predators that ruled the seas with terrifying efficiency. About 19 million years ago, approximately 70% of all pelagic shark species disappeared, a catastrophic event that nearly drove sharks to extinction. This mass extinction event, occurring almost 20 million years ago, reshaped the marine ecosystem and allowed other groups of life to rise to dominance. The reptile group Choristodera went extinct in the early part of the period, while the amphibians known as Allocaudata disappeared at the end of it. Neogene also marked the end of the reptilian genera Langstonia and Barinasuchus, terrestrial predators that were the last surviving members of Sebecosuchia, a group related to crocodiles. Despite these losses, marine and continental flora and fauna developed a modern appearance, signaling a transition toward the ecosystems we recognize today. The oceans were a theater of evolution where large carnivores thrived, yet the disappearance of so many shark species suggests a fragile balance that could be easily disrupted. This period of ecological upheaval set the stage for the diversification of mammals and birds, which continued to evolve into modern forms while other groups of life remained relatively unchanged. The Neogene was a time of both destruction and renewal, where the extinction of some groups paved the way for the rise of others.
Grasslands Rise
In response to the cooler, seasonal climate, tropical plant species gave way to deciduous ones, and grasslands replaced many forests across the globe. Grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses, antelope, and bison. About 20 million years ago, gymnosperms in the form of some conifer and cycad groups started to diversify and produce more species due to the changing conditions. DNA duplication linked to the origin and evolution of pine trees and their relatives played a crucial role in this transformation. With lower levels of carbon dioxide in the atmosphere, plants expanded and reached ecological dominance in grasslands during the last 10 million years. Also, Asteraceae, the daisy family, went through a significant adaptive radiation, becoming a dominant force in the plant kingdom. Eucalyptus fossil leaves occur in the Miocene of New Zealand, where the genus is not native today, but have been introduced from Australia, hinting at the complex history of plant migration. Ungulates in North America became noticeably more cursorial and increased their stride lengths across the Oligocene-Miocene boundary, likely in response to the increased habitat openness during the Miocene. This shift in vegetation and animal adaptation created a new world where speed and endurance became key survival traits. The rise of grasslands transformed the landscape, forcing animals to adapt to open environments and driving the evolution of the grazing mammals that would eventually dominate the planet.
First Humans
The first hominins, the ancestors of humans, appeared near the end of the Neogene period, marking a pivotal moment in the history of life on Earth. This appearance occurred in Africa, where the first humans, Homo habilis, emerged as the period drew to a close. While mammals and birds continued to be the dominant terrestrial vertebrates, the emergence of hominins signaled the beginning of a new chapter in evolution. An explosive radiation of ursids took place at the Miocene-Pliocene boundary, showcasing the diversity of life that thrived during this time. Ice age mammals like the mammoths and woolly rhinoceros were common in the Pliocene, coexisting with the early hominins in a world that was rapidly changing. The appearance of the first humans was not an isolated event but part of a broader pattern of adaptation and diversification that characterized the Neogene. The climate changes and the rise of grasslands created new challenges and opportunities for early hominins, driving the evolution of traits that would eventually lead to the development of modern humans. This period was a crucible for human evolution, where the first steps toward our species were taken in the vast landscapes of Africa. The Neogene was a time of transition, where the world was becoming more familiar to us, yet the emergence of our ancestors added a new layer of complexity to the story of life.
Green Sahara
During the Pliocene, Green Sahara phases of wet conditions in North Africa were frequent and occurred about every 21,000 years, being especially intense when Earth's orbit's eccentricity was high. These periods of wetness transformed the arid Sahara into a savanna-like environment, supporting a diverse array of flora and fauna that thrived in the lush conditions. The Pliocene Warm Interval had similar levels of atmospheric carbon dioxide to contemporary times, making it a valuable analog for understanding the potential impacts of current global warming. The Green Sahara phases were not merely temporary fluctuations but significant climatic events that shaped the evolution of species in North Africa and beyond. These wet periods created corridors for migration and allowed species to expand their ranges, influencing the distribution of life across the continent. The cyclical nature of these Green Sahara phases, driven by Earth's orbital eccentricity, highlights the intricate relationship between planetary cycles and climate. The Pliocene was a time of dynamic change, where the Sahara oscillated between arid and lush conditions, creating a complex tapestry of environments that supported a wide variety of life. These Green Sahara phases were a testament to the resilience and adaptability of life, as species thrived in the face of changing climates and environmental pressures.