This period is divided into the following epochs:
(Formerly part of the Quaternary)
|This is the Modern Age of Man, and though its 12,000 years is but a blink of an eye in the age of the Earth, human impact has been profound, spreading across the globe, inhabiting and dominating and profoundly affecting the environment and climate.|
(Formerly part of the Quaternary)
|1.5 (MYA) to
|This is the Epoch of Ice for it was during this time that the Earth was buried (as much as 1/3) by the Pleistocene Ice Age. Homo erectus and Homo sapiens appear in the fossil records while woolly mammoths and sabre-toothed tigers roamed the grasslands. Land bridges between continents are revealed by falling sea levels, a consequence of intense glaciation. Some important land bridges including the Bering bridge joining Alaska to Siberia and the North Sea bridge between Britain and Europe.|
|Pliocene||5 to 1.5||Many of the grassland mammals went extinct as climate and the environment undergo change, inexorably marching towards the Ice Age of the Pleistocene. The isthmus of Panama formed to join South America and North America, forever changing the fauna species and distribution as well as global climate.|
|Miocene||23 to 5||Most of the modern birds had appeared by the end of the Miocene. In response to a cooling climate, prairies spread across the landscape populated by newly-arrived grasses. In turn, grazing animals rapidly diversify to adapt to the dietary requirements of the new landscape as well as the necessity for survival in an environment that afforded little protection from predators. Giant megalodon sharks prowl the oceans while elephants take on a more modern physiology. A major expansion and diversification of apes occurs towards the end of the Miocene.|
There is much debate regarding the actual boundaries of the Neogene and whether or not the Cenozoic Era should include a third period entitled the Quaternary to which would belong the Pleistocene and Holocene Epochs. This author has chosen to adopt a more simplistic approach but there are many books out there that use both the Quaternary and Tertiary designations and it can become confusing. Please see the Timeline for more information on the Quaternary and Tertiary divisions. The length of time assigned to each epoch is also a subject of debate. I have chosen to follow D. R. Prothero.2
One of the significant attributes of the Neogene was the occurrence of geological events that shape our modern world. Many of the world’s great mountain ranges arose as the continents and tectonic plates continued in their relentless movement. Where once the continents were separate islands, many continents began to be joined by land bridges (North and South America) or by smaller land masses (Africa joining to Asia via the Arabian Peninsula).
The joining of the continents greatly impacted the flow of the ocean currents, thereby changing the global climate. While the Miocene experienced a temporary temperature spike, the Pliocene presented decidedly cooler temperatures as polar ice caps appear and the climate became drier. In response to the changing climate, the forests begin to disappear and grasslands develop with their tough sod and drier conditions. During the Miocene the first modern grasses appear and by this time nearly all the seed plants in our modern world had made their appearance.
The Miocene was the golden age of mammals. Establishing themselves in every continent and every ecosystem, they radiated into a multitude of shapes, sizes and characteristics. There was more variety of mammals during this time than at any other time before or since and nearly fifty percent of modern-day mammals came from the Miocene.
The Pleistocene is well known for its glacial conditions and woolly creatures. The Pleistocene is referred to as the Great Ice Age not because the glaciation was more severe than any previous era, but because it’s an epoch of which we know more and is closest to us in time. Indeed the strata from the Pleistocene and Holocene is the best preserved because it is the most recent. All over the world scientists can easily investigate the many different climates and conditions from this period.
Despite the cooler conditions during the Pleistocene, the variety and number of creatures is astounding. Woolly mammoths, mastodons and elephants were extant in different parts of the world, while giant beavers, dire wolves, sabre-toothed tigers and giant kangaroos inhabited the grasslands and forests.
At the end of the Pleistocene most of the large animals disappeared and the cause of this extinction is hotly debated. Was it overhunting by humans or was it an impact by a comet in North America that caused such a selective destruction? No one theory seems to answer all questions.
Many of the modern-era animals are recognizable in the Neogene species. From elephants to horses, giraffes to felines, dogs to bears and so on. The early hominids join the throng as Homo habilis and Homo erectus join the other mammals of the grasslands. The list is endless. But the more these animals increased the greater the pressure of competition and as land bridges appeared or continents were joined, massive migrations ensued, spurring on even greater pressure to be successful or face extermination. And thus it was that as these migrations increased, so did the extinction rate for those species that either could not survive in their new home or those who could not compete against the newcomers. Whichever case held sway this is also a time of extinction for many mammal species by the end of the period.
The Holocene, the era of humans beginning approximately 12,000 years ago, is important for it is our history: the rise of civilization, the rule of laws and governments (or lack thereof) and our impact on the world around us. One thing is known: as we progress through the Holocene, the extinction rate of many species is climbing and many of these can be directly related to human impact on the environment.
1. MYA = Millions of Years Ago
2. Prothero, Evolution of the Earth, p. 459.