The Pliocene Period, the sprouting of the human branch

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Article 33: During the Pliocene, large polar ice caps start to develop. Some apes come down from the trees and start to exist on the plains in Africa. Australopithecus afarensis, like Lucy, lives in East-Africa.

The Pliocene Period of the Earth’s history lasts 2,5 million years, beginning 5 and ending 2,5 million years ago.

The global average temperature in the mid-Pliocene (3,3–3 mya) is 2–3 °C higher than today. The global sea level is 25 m higher and the Northern Hemisphere ice sheet is ephemeral before the onset of extensive glaciation over Greenland, that occurs in the late Pliocene, around 3 Mya.

Pliocene temperatures

During the Pliocene, global temperatures, particularly at high latitudes, are believed to have been significantly warmer than today. Credit to NASA Goddard Institute for Space Studies

Nevertheless, the Pliocene is a time of global cooling after the warmer Miocene.

The Pliocene seas are alive with sea cows, seals and sea lions. Alligators and crocodiles die out in Europe as the climate cools. The cooling and drying of the global environment may contribute to the enormous spread of grasslands and savannas during this period.

The next picture shows a modern herd of zebra grazing on an African savanna. Grazing mammals, such as the perissodactyls and artiodactyls, diversify in the Miocene and Pliocene as grasslands and savanna spread across most continents.

Change in vegetation
This change in vegetation undoubtedly is a major factor in the rise of long-legged grazers, who come to live in these areas at the expense of browsers such as goats. The Mediterranean Sea dries up completely and remains plains and grasslands for the next several million years.

Continents continue to drift, moving from positions possibly as far as 250 km from their present locations, to positions only 70 km from their current locations. Africa’s collision with Europe forms the Mediterranean Sea, cutting off the remnants of the Tethys Ocean. The Panamanian land-bridge between North and South America appears during the Pliocene, allowing migrations of plants and animals into new habitats. During the Pliocene the tectonic plates of India and Asia also collide, which forms the Himalayas.

Of even greater impact is the accumulation of ice at the poles, which will lead to the extinction of most species living there, as well as to the advance of the glaciers and ice ages of the Late Pliocene and the following Pleistocene. During the Pliocene, large polar ice caps start to develop and Antarctica becomes the frozen continent that it is today. It is uncertain what causes this climate cooling during the Pliocene. Changes in the amount of heat transported by oceans may be a possible explanation.

It is also possible that the raising of the Himalayas, caused by plate collisions between India and Asia, accelerates the cooling process.

It is also during this time that some apes come down from trees and start to exist on the plains in Africa. In fact, it is generally believed that one of the first recognizable hominins, Australopithecus, evolves in the late Pliocene.

Australopithecus aforensis
Australopithecus afarensis, Skeleton of Lucy, 3,2 million years B.P.

Australopithecus afarensis is one of the longest-lived and best-known early human species. Paleo-anthropologists have uncovered remains from more than 300 individuals!

Found between 3,85 and 2,95 million years ago in Eastern Africa (Ethiopia, Kenya, Tanzania), this species survived for more than 900.000 years, which is over four times as long as our own species has been around.

It is best known from the sites of Hadar, Ethiopia (‘Lucy’), Dikika, Ethiopia and Laetoli, Tanzania. Similar to chimpanzees, Australopithecus afarensis children grew rapidly after birth and reached adulthood earlier than modern humans. This meant Australopithecus afarensis had a shorter period of growing up than modern humans have today, leaving them less time for parental guidance and socialization during childhood.

Ape and human

Australopithecus afarensis has both ape and human characteristics: members of this species have apelike face proportions (a flat nose, a strongly projecting lower jaw) and brainpan (with a small brain, usually less than 500 cubic centimeters – about 1/3 the size of a modern human brain), and long, strong arms with curved fingers adapted for climbing trees. They also have small canine teeth like all other early humans, and a body that stands on two legs and regularly walks upright. Their adaptations for living both in the trees and on the ground helps them survive for almost a million years, as climate and environments changes.

Thanks to the University of California, Berkeley, Museum of Paleontology, and to the Smithsonian National Museum of Natural History

ShantiShanti is a regular contributor
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