Quaternary Period is the latest of the major geologic time periods used to divide Earth’s history. The Quaternary Period began about 2.6 million years ago and extends to the present. The term quaternary, meaning fourth, comes from an outdated classification system in which Earth’s history was divided into four periods.
The Quaternary Period consists of two shorter times called epochs. The Pleistocene Epoch ended about 11,500 years ago. The Holocene Epoch extends from that time to the present. Some scientists have proposed a third epoch, the Anthropocene Epoch, to describe the interval in which the effects of human activity on the environment have become as significant as natural effects. Scholars may date the beginning of such a period to the development of agriculture , more than 10,000 years ago, or to the Industrial Revolution , beginning in the late 1700’s. The term Anthropocene Epoch has not achieved official acceptance.
The Quaternary Period is best known for its ice ages. An ice age is a period in Earth’s history when ice sheets cover vast regions of land. Glaciers began to form in Antarctica around 35 million years ago, well before the start of the Quaternary Period. By about 2.6 million years ago, the start of the Quaternary Period, large ice sheets had begun to cover North America and Europe as well. Many areas that are today deserts had higher rainfall and were filled by large lakes . On the other hand, many areas that are now rain forests were grasslands . Following the retreat of the ice, the early Holocene Epoch had a warmer climate than the present. A number of warm and cool periods have occurred since then. The last cooling event, called the Little Ice Age, lasted several hundred years and ended in the 1800’s. Since the Little Ice Age, the climate has been warming due to natural causes and human activities. Human activities—particularly the burning of such fossil fuels as coal , oil, and natural gas —release large amounts of carbon dioxide and other greenhouse gases into the atmosphere. Such gases warm the atmosphere by trapping heat close to the planet.
The first human beings appeared during the Quaternary Period. Several human species once existed at the same time. These humans had spread widely out of Africa by 1 million years ago. Modern humans appeared around 200,000 years ago and replaced the more ancient species. Also, many large animals, such as mammoths and saber-toothed cats , went extinct at the end of the Pleistocene Epoch. Some scientists think early humans may have played a role in their extinction , for example through overhunting.
