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Quaternary Period—2.58 MYA to Today

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fossil bone bed and murals of mammoths
Pleistocene age bone bed excavation at Waco Mammoth National Monument, Texas.

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Introduction

The Quaternary Period is the third and last of the three periods of the Cenozoic Era. You and I are living in this period, which began only 2.58 million years ago. This is less than 0.1% of all of geologic time! A thin layer of sediments deposited during the Quaternary covers much of the Earth’s land surface. In the future, only a small part of this cover will become preserved as rocks, just as what we see for every other period represents only a small part of what was originally deposited. The Quaternary Period is famous for the many cycles of glacial growth and retreat, the extinction of many species of large mammals and birds, and the spread of humans. The Quaternary Period is divided into two epochs, from youngest to oldest: the Holocene and Pleistocene. We are living in the Holocene.

Holocene Epoch

The Holocene Epoch is the most recent span of geologic time. Marked climatic warming and the disappearance of the continental glaciers mark the transition between the Pleistocene and Holocene. The extinction of megafauna (large animals) such as mammoths, mastodons, giant ground sloths, saber-toothed cats, and short-faced bears also denotes the end of the Pleistocene and beginning of the Holocene. Because the interglacial (warm) periods of the Pleistocene were of longer duration than the time elapsed since the end of the Pleistocene, the present Holocene Epoch may be another interglacial stage, with large-scale glaciers returning at some future time. However, this natural pattern may be perturbed by the activities of humans, which have caused CO2 to increase in the atmosphere, steadily warming since the Industrial Revolution. This warming impacting natural systems in many national parks.

Pleistocene Epoch

3 people working on a fossil excavation with bones exposed
Excavation of a Pleistocene pygmy mammoth at Channel Islands National Park, California.

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Popularly known as the “Ice Age”, geologists pinpoint the beginning of the Pleistocene Epoch when the climate cooled and ice sheets began covering Earth’s landmasses. During the Pleistocene the accumulation of snow and ice into continental-scale glaciers resulted in tremendous drops in sea level. This lowering of marine waters exposed dry land in what is now the Bering Strait between Alaska and Siberia. The resultant land bridge permitted animals to move between the two continents, including the dispersal of the first humans into the Americas.

Among the better known animals of the Pleistocene are the extinct relatives of elephants—mammoths and mastodons—along with giant ground sloths and large predators such as the saber-toothed cat and short-faced bear. Investigators have found the remains of dwarf mammoths from the Pleistocene on San Miguel, Santa Rosa, and Santa Cruz islands in Channel Islands National Park off the coast of California. Researchers have found the remains of other Pleistocene animals such as the Shasta ground sloth, the extinct Harrington’s mountain goat, and an extinct vampire bat in caves in Carlsbad Caverns, Guadalupe Mountains, Mammoth Cave, and Grand Canyon national parks.

Significant Quaternary events

The most distinctive physical features were land bridges, which affected the migration of organisms during the Neogene. Climates cooled somewhat over the duration of this period culminating in continental glaciations during the Pleistocene Epoch. At the end of the Pleistocene a catastrophe destroyed two-thirds of the large mammals in North America and South America. The reason for the late-Pleistocene extinction is unresolved but climate change and over-hunting may have been factors.

Learn more about events in the Quaternary Period

Modern forms of Homo sapiens first appeared about 195,000 years ago. Modern humans have an average brain size of about 82 cubic inches (1,350 cc). The forehead rises sharply, eyebrow ridges are very small or more usually absent, the chin is prominent, and the skeleton is very slight. About 40,000 years ago, with the appearance of the Cro-Magnon culture, tool kits started becoming markedly more sophisticated, using a wider variety of raw materials such as bone and antler, and containing new implements for making clothing, engraving, and sculpting. Fine artwork, in the form of decorated tools, beads, ivory carvings of humans and animals, clay figurines, musical instruments, and spectacular cave paintings appeared over the next 20,000 years (Leakey 1994).
About 2.7 million years ago, a land bridge formed: the Isthmus of Panama connected North America and South America. Until then South America had been an island continent, similar to Australia today, and hosted a diversity of marsupials and giant flightless birds. The land connection allowed migrations in both directions, and several South American mammals successfully migrated northward, for example opossum, armadillo, and porcupine. North American mammals that migrated into South America included cats, dogs, bears, tapirs, and camels. South America would have no jaguars or llamas if it had not been connected to North America.

During the Pleistocene Epoch, vast continental glaciers covered much of northern North America and Eurasia. In some places, ice sheets were two miles (3 km) thick. With so much water locked up in the form of ice, sea level dropped to about 430 feet (130 m) below current levels. When sea level was lowered, North America and Eurasia became connected by the Bering “land bridge.” [Note: There was intermittent contact between Asia and North America before the Pleistocene, which allowed proboscideans to arrive during the Miocene.] During the Pleistocene, mammoths arrived in North America and mastodons, which evolved in America, appear to have spread into Eurasia.
Many of the large mammals and some of the large birds of North America, South America, and Australia became extinct at the end of the Pleistocene Epoch. This was a rather modest extinction compared to the other “mass extinctions” discussed throughout this knowledge center. Nevertheless, this extinction was distinctive in that most of its victims were large, land-dwelling mammals weighing more than 90 pounds (40 kg). In North America 33 of 45 large genera (73%) died out. In South America 46 of 58 genera (80%) went extinct. In Australia 15 of its 16 large genera (94%) were lost. By contrast, Europe lost 7 of 23 large genera (30%), and only 2 of 44 (4%) died in Africa south of the Sahara. Clearly, extinctions were much more severe in the Americas and Australia.

The cause of the extinction; the reason it was restricted mostly to large, land-dwelling mammals; and why it took place primarily in the Americas and Australia have been the subjects of heated scientific debate. According to one hypothesis, these animals died out because they could not adapt to rapid climatic changes at the end of the Pleistocene. A competing hypothesis, known as “prehistoric overkill,” holds that human hunters killed off these large animals. Further study may show that the extinction resulted from a combination of many different factors. Populations that were already under stress from climatic changes were perhaps more vulnerable to hunting when humans began to occupy new areas (Wicander and Monroe 2000).

Visit—Quaternary Parks

Every park contains some slice of geologic time. Here we highlight a few parks associated with Quaternary Period. This is not to say that a particular park has only rocks from the specified period. Rather, rocks in selected parks exemplify a certain event or preserve fossils or rocks from a certain geologic age.

More about the Cenozoic

yellow background with test cenozoic era 66 MILLION TO 11,700 YEARS AGO

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Tags: fossils paleontology geology geologic time

Last updated: November 23, 2020