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Deep Time

Intro | Precambrian Eon | Paleozoic Era | Mesozoic Era | Cenozoic Era

Cenozoic Era: (248 mya-present)

Paleocene | Eocene | Oligocene | Miocene | Pliocene | Pleistocene | Holocene



Pleistocene Epoch (1.8-0.01 mya)

During the Pleistocene, glaciers repeatedly advance from the Arctic north over Europe and North America, then retreat. The first major glacial flow occurs about 1.6 mya. Ice, up to a mile thick in places, spreads from Greenland over the Arctic Sea into northern Europe and Canada. As the ice advances, temperatures ahead of the flow drop significantly.

The temperature change has a profound impact on life. Mammoths, rhinos, bison, reindeer, and musk oxen all evolve to have warm, woolly coats to protect them from frigid conditions. These new mammals feed on the small bushes and hardy grasses that tolerate cold as they follow the moving line of glaciers. Glacial retreats allow for the temporary return of warm-weather plants such as oak and beech trees, lush grasses, and flowers. During these "interglacial" periods, species that sought shelter in the warmer south return to their old habitats.

The hominid line continues to evolve during the Pleistocene. About 100,000 years ago, anatomically modern humans first appear. Many scientists think early humans impact other mammal species through hunting, as human populations expand and disperse into new habitats. By the end of the Pleistocene, nearly all large mammals are extinct, including woolly mammoths, giant wolves, saber-toothed cats, giant ground sloths, and massive wombats.

0.6 mya: Early humans

Homo heidelbergensis displays physical characteristics of modern humans: increased brain capacity, smaller teeth, and a face that slopes less than that of other hominid ancestors. A fossil jaw found in Mauer, Germany, dates these early humans to approximately 600,000 years ago.

0.1 mya: Modern humans

Modern humans (Homo sapiens) disperse throughout Africa, the Middle East, and Europe. They have larger brain cases than most, if not all other, hominids and higher foreheads than their immediate ancestors. Early European H. sapiens, called Cro-Magnons, have lean builds. Cave paintings suggest they have brains capable of sophisticated behavior.

Late Pleistocene extinction


0.01 mya




More than 200 genera of very large herbivores (2 tons or more) go extinct, including 95 percent in North America


Human intervention (over-hunting), climate change


The late Pleistocene extinction is uncharacteristic of other mass extinction events. Extinction takes place at different times on different continents, but always targeting a specific kind of animal. What's more, climate change alone probably did not cause it. Over about 40,000 years, 200 or more groups of large herbivores are wiped out. With their prey absent from the food chain, many carnivores and scavengers also die off. Temperature fluctuates throughout the last ice ages, but the fossil record does not indicate an unusual concentration of death among smaller animals, plants, or marine creatures, at least some of which would likely have been affected by climate change. Instead, the loss of very large fauna almost always coincides with the arrival of humans to a continent. This suggests the possibility of over-hunting by early human settlers.


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A smoking gun? (0.01 mya)

The pattern of large mammal extinction toward the end of the Pleistocene suggests that humans, as they spread across the planet, hunt these animals out of existence. There is little evidence of extinction among smaller animals, plants, or marine life at this time.

From their roots in Africa and southeast Asia, humans spread first to Australia about 55,000 years ago. Shortly after their arrival, giant marsupials, large reptiles, and 450-pound flightless birds begin dying en masse. This trend continues throughout Eurasia and the Americas.

By 11,000 years ago -- only 1,000 years since humans are known to have arrived in North America -- mammoths, mastodons, horses, camels, and ground sloths go extinct, followed closely by their predators, which include lions, giant wolves, great bears, and saber-toothed cats. Interestingly, moose, caribou, and grizzly bears, which had earlier crossed over from Eurasia, survive, perhaps having been better conditioned to avoid humans.


-> Go to the Holocene Epoch

Intro | Precambrian Eon | Paleozoic Era | Mesozoic Era | Cenozoic Era

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