A major chunk of the current time span on our planet, i.e., the Cenozoic Era, began after the catastrophic Cretaceous-Paleogene Mass Extinction, eradicating most of the ruling dinosaur and other reptile species. This provided mammals a chance to evolve and dominate.
The Dominance of Life
Life on our planet developed millions of years ago, but if large life-forms are taken into consideration, then intelligent organisms like the Homo sapiens have never dominated any specific era or even a period. The Cenozoic Era can be known as the arrival and dominance of intelligent life-forms like modern human beings, which changed the world scenario permanently.
The term ‘Cenozoic’ has been derived from the Greek words: kainos meaning ‘new’ and zoe meaning ‘life’. It is the shortest era of the Earth, spanning from about 66 million years ago to the present. After the sudden K-T boundary mass extinction, mammals got a chance to evolve extensively in this era, and hence, it is also called ‘The Age of The Mammals’. The climate of our planet stabilized and atmospheric oxygen slowly increases with a simultaneous decrease in carbon dioxide and other toxic gaseous elements.
Earlier, the Cenozoic comprised two periods: Tertiary and Quaternary, the former being divided into Paleogene and Neogene, but now the term Tertiary is slowly phased out. Instead, the era is now divided into three periods: Paleogene, Neogene, and Quaternary, ranging from the oldest to the youngest. They are again subdivided into a number of stages/epochs. Apart from mammals, the Aves class of Chordates, i.e., the birds also evolved a lot, and several of them were larger than the average height of a human.
Interesting Facts and Major Events of the Cenozoic Era
Cenozoic Era Timeline and Periods
Based on different factors like the geological and tectonic environment, the Cenozoic Era is divided into three periods. Other aspects like climatic factors, arrival of humans, floral and faunal evolution, etc., are also taken in consideration while marking the boundaries between two periods and their epochs.
The Cenozoic Era consists of the following time spans or periods: Paleogene, Neogene, and Quaternary. Paleogene and Neogene were earlier clubbed together as Tertiary, and are still sometimes referred by this name. Paleogene is divided into three epochs – Paleocene, Eocene, Oligocene. Neogene consists of two epochs: Miocene and Pliocene, whereas Quaternary is divided into Pleistocene and Holocene (the current epoch).
Cenozoic Era Geology and Tectonics
After the K-Tr boundary mass extinction, the geology of our planet changed considerably as the supercontinent called Pangaea split into separate individual continental landmasses. These land portions started drifting and became the present day continents. The Australian portion had already split apart in the early Cretaceous Period, and it shifted towards the north, merging with the Southeast Asian regions. The tectonic plate of Antarctica moved towards the current South polar region, and South America shifted north to merge with the North American tectonic plate by a narrow isthmus. Lastly, the Indian plate separated from Africa and collided with the Eurasian Plate to form the youngest mountain chain in the world, the Himalayas, around 50 million years ago.
Research indicates that Pangaea actually split into two larger continental land masses called Laurasia and Gondwanaland. North America, Europe and Russia arose from the Laurasian landmass, while portions of the subcontinents of Africa, India, and South America were formed from Gondwanaland. Before the formation of the Indian subcontinent, the enormous Tethys Ocean was present in the area, but after the collision of Arabian tectonic plate with Eurasia, this ocean disappeared after the formation of Mediterranean Sea. In the current epoch, i.e., Holocene, the continents are still drifting slowly in varying directions as they did millions of years before.
Regarding mountain orogenies, apart from the Himalayas, the Alpine orogeny also took place, wherein the Alps and the Carpathian mountains were formed. In North America, the lithology got uplifted, leading to the formation of the Rocky Mountains in the western areas. Various kinds of rocks belonging to this era are found all over the planet, though the stratigraphy is dominated by sedimentary deposits (like Tertiary and Quaternary sediments). Some degree of metamorphism is also seen, especially where subduction took place (for example metabasalts of the ophiolite sequences in northern Himalayas).
Cenozoic Era Climate
After the mass extinction event, our planet experienced a spell of warm climate called the Paleocene-Eocene Thermal Maximum, which occurred around 55 million years ago. After this event of global warming, the Drake Passage was formed, wherein the South American tectonic plate completely detached itself from the Antarctic Plate. Thus, the cold Antarctic Circumpolar Current started affecting the upper land masses, and a trend of global cooling began, extending up to the middle Cenozoic.
In the northern hemisphere, climate became cold due to the effect of Gulf and Humboldt currents, further causing massive Ice Ages across Europe, Siberia, and North America. It is believed that currently we are experiencing an interval of interglacial period (a time span between two glacial periods, which is usually characterized by a climate with high atmospheric temperatures and melting glaciers).
Before the Holocene, Earth experienced several cold climatic conditions, which manifested in the form of Ice Age events, the latest one being the little Ice Age that took place around the 15th century, before the industrial civilization.
Many sedimentary evidences in the form of glacial till deposits and moraines exist, which prove the cyclic warming and cooling trend of our planet’s climate that started way before the Cenozoic Era. Glaciation not only developed in the northern hemisphere, but also took place in the Antarctic region. The best and most convincing evidence of climate fluctuation can be referred from the Dansgaard-Oeschger events, which are a series of climatic changes that occurred at least 25 times dating back to the last glaciation. This research was conducted by analyzing some ice cores that were extracted from Greenland.
Cenozoic Era Flora
The most extensive evolution in terms of flora took place in the form of development of angiosperms or flowering plants. Also, savannahs and alpine grasslands started occupying large spaces on land, which did not happen much in the earlier eras.
The dominance of Gymnosperms got reduced, and different varieties of angiosperms evolved forming deciduous and evergreen forests in temperate, subtropical, and tropical areas. Entire orders of gymnosperms got extinct as they could not withstand the ever-changing climatic conditions and fluctuations.
Cenozoic Era Fauna
The biggest change that happened in this Era was the evolution and dominance of mammals that changed the entire ecosystem on our planet. Mammals developed in all three main conditions or habitats: land, water, and air. As flowering plants were on the rise, numerous new species of insects appeared; the relation being pollination of spores by the insect species. Though reptiles experienced less development since dinosaurs got extinct, many new groups like that of the snakes, crocodiles, turtles, etc., thrived a lot. Crocodiles are rather said to be living fossils as research indicates their existence even during the time of dinosaurs.
Large mammals like the Sabre-toothed Tiger, Woolly Mammoth, Duck-billed Platypus, Glyptodonts, Eurohippus horse, Paraceratherium, Phorusrhacus (a flightless bird), Macrauchenia patachonica, etc., thrived on the continental portions of Earth. Other examples like Doedicurus clavicaudatus, and Megatherium americanum are also quite famous. The Sabre-toothed tiger was a tertiary ancestor of modern-day tigers and others related large cat species. The Mammoth is said to exist during the time of prehistoric humans, and was probably hunted down to extinction. It was an ancestor of currently existing elephants. The Paraceratherium was a large genus of rhinoceros, which did not have any horns, while Megatherium Americanum is said to be a species of giant sloths, from which the present-day sloth bears have evolved.
In the oceans, Megalodon sharks, Ammonites, and Corals (polyps) started thriving due to increase in nutrient flow after the continents separated. Today’s animals like camels, horses, bears, etc., evolved only at the boundary between Pleistocene and Holocene. Before getting extinct in the last millennium, modern humans knew much about other famous Quaternary animals like the Irish Elk, Stellar Sea Cow, Tasmanian Tiger, Caspian Tiger, Woolly Rhinoceros, and Quagga.
Human activities and associated industrial revolution had such extensive and profound effects on the Earth in terms of all parameters, that no other event, not even an earlier mass extinction matched the changes done in an artificial manner to the environment! Thus, several scientists have put forth a proposal to use the term ‘Anthropocene’, which supposedly marks the beginning of domination of humans since they appeared about a million years ago.