Over the last few posts, we’ve covered everything from the diversification of life in the Cambrian Explosion, to the worst mass extinction in Earth’s history, the Great Dying, and the age of the dinosaurs. Today, though, I’ll be talking about one of the least discussed eras on the entire Geologic Timescale: the Cenozoic. While you might not recognize the name, it’s actually the era we’re in right now. Often called the age of mammals, the Cenozoic includes everything after the K-T extinction event that killed all the non-avian dinosaurs.

 

Beginning 65 million years ago, the Cenozoic’s first of 7 (or possibly 8) epochs was the Paleocene (66-56 Ma). According to the USGS, this 10 million year-long epoch was the time of the diversification of small mammals.  As most of the dinosaurs were extinct, new ecological niches opened for the first rodents, primitive primates, and mammalian carnivores. The climate during the Paleocene was already warmer than today, but around 56 Ma, a sudden global warming event signaled the beginning of a new Epoch, the Eocene (56-34 Ma).

 

Much of the Eocene’s dramatic changes can be explained by plate tectonics. At the beginning of this epoch, India first began colliding with Asia to form the Himalayas, while Australia later broke away from Antartica to form the Circum-Antarctic current. During the Eocene, the first massive mammals appeared, including whales and primitive elephants and horse-like animals. For most of this epoch, temperatures were so warm that palm trees and alligators could survive in the Arctic circle. When the Circum-Antarctic current opened, however, a rapid period of global cooling brought an end to the Eocene.

 

During the Oligocene (34-23 Ma), the climate cooled greatly, creating widespread savannahs and temperate forests while Antarctica became covered in glaciers. The presence of grasslands allowed mammals to continue growing and the largest ever land mammal evolved: Paraceratherium. According to a Largest.org list of the largest land mammals, Paraceratherium was a 15-20 ton (33,000-44,000 lb) species of hornless rhinoceros that lived from 35-20 Ma in Eurasia. This giant was 40 feet tall and over twice the size of an African Bush Elephant, the largest land mammal alive today. (To learn more about Paraceratherium, check out this PBS Eons video.) During this time, early dogs, cats, monkeys, pigs, camels, and horses also evolved. However, the dramatic change in temperature from the Eocene meant that many species could not adapt and went extinct.

 

The Miocene Epoch (23-5 Ma) was yet another time dominated by plate tectonics and the climate changes they can produce. During the Miocene, the Himalayas and Appalachians were further uplifted, and land bridges connected Africa and Asia and North America and Siberia. This greatly affected ocean currents, and the climate began to cool further, causing prairies to expand. Hoofed mammals like horses began to flourish, elephants migrated to North America, and the first anthropoid, or human-like apes evolved.

 

The global temperature continued to fall into the Pliocene Epoch (5-2.6 Ma), and ice continued to grow in both the Arctic and Antartica, eventually leading to a series of ice ages. Also during this epoch, the first early hominids evolved in Africa. According to a Smithsonian article, Australopithecus, one of the longest lived and well-known hominid species lived between 3.85-2.95 Ma in Eastern Africa. Although they had brains only about 1/3 the size of our own, these early hominids survived for 900,000 years, four times as long as humans have walked the Earth. If you’d like to learn more about early hominids, check out this interactive human evolution timeline.

 

The Pliocene ice ages continued into the Pleistocene (2.6 million – 10,000 years ago), and during an ice age maximum, the northern quarter of the globe was covered in ice up to 13,000 feet thick (2.46 mi). This cold climate gave rise to large, ice age mammals like the wooly mammoths and saber-toothed cats, which went extinct due to climate fluctuations and being hunted by humans.

 

According to ThoughtCo., the final epoch in the Geologic Timescale, the Holocene (10,000 years ago – present) comprises all of modern human history. However, some scientists argue that the Holocene has ended and the Anthropocene, the age of “new man”, has begun. According to the Subcommission on Quaternary Stratigraphy, the Anthropocene is “the present geological time interval, in which many conditions and processes on Earth are profoundly altered by human impact”. This proposed epoch is marked by human-caused changes to the carbon cycle, erosion and sediment transport, sea level rise and acidification, habitat loss, and the proliferation of new “minerals” and “rocks” like concrete and plastics. The human impact on the Earth is undeniable, and we might just get our own segment of the Geologic Timescale because of it.

 

That’s it for my major overview of the geologic timescale, but I hope to add more posts about related topics in the future. Thanks for traveling through time with me, and I hope you know more about the Earth now than you did when you first clicked on my blog!